Compare regions, not four loose numbers

`PixelRegion` derives `PartialEq`, `Clone` and `Copy`, so `assert_corners!`
compares one against another instead of flattening both to a tuple whose
order there was nothing to check. A failure now prints two regions.

Cargo.lock

@@ -567,9 +567,9 @@ dependencies = [
 
 [[package]]
 name = "dlib"
-version = "0.5.3"
+version = "0.5.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ab8ecd87370524b461f8557c119c405552c396ed91fc0a8eec68679eab26f94a"
+checksum = "330c60081dcc4c72131f8eb70510f1ac07223e5d4163db481a04a0befcffa412"
 dependencies = [
  "libloading",
 ]
@@ -2158,9 +2158,9 @@ checksum = "a993555f31e5a609f617c12db6250dedcac1b0a85076912c436e6fc9b2c8e6a3"
 
 [[package]]
 name = "quick-xml"
-version = "0.41.0"
+version = "0.38.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e660451e55124f798a69a5af3f49ccfbefbd41910eefd25caf2393e1f3473ec1"
+checksum = "b66c2058c55a409d601666cffe35f04333cf1013010882cec174a7467cd4e21c"
 dependencies = [
  "memchr",
 ]
@@ -2353,15 +2353,6 @@ version = "0.8.52"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0c6a884d2998352bb4daf0183589aec883f16a6da1f4dde84d8e2e9a5409a1ce"
 
-[[package]]
-name = "rig-input"
-version = "0.1.0"
-dependencies = [
- "iris",
- "wayland-client",
- "wayland-protocols-wlr",
-]
-
 [[package]]
 name = "roxmltree"
 version = "0.21.1"
@@ -2918,9 +2909,9 @@ dependencies = [
 
 [[package]]
 name = "wayland-backend"
-version = "0.3.17"
+version = "0.3.12"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "38a91b4eaddff87b1cd1074985e3713da4af2c49742d1b356b2c01670a67a078"
+checksum = "fee64194ccd96bf648f42a65a7e589547096dfa702f7cadef84347b66ad164f9"
 dependencies = [
  "cc",
  "downcast-rs",
@@ -2932,9 +2923,9 @@ dependencies = [
 
 [[package]]
 name = "wayland-client"
-version = "0.31.15"
+version = "0.31.12"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e3c36a0f861ad76d0901f2800b46321410d9f73f2ea88aac0650d86c32688073"
+checksum = "b8e6faa537fbb6c186cb9f1d41f2f811a4120d1b57ec61f50da451a0c5122bec"
 dependencies = [
  "bitflags 2.10.0",
  "rustix 1.1.3",
@@ -2966,9 +2957,9 @@ dependencies = [
 
 [[package]]
 name = "wayland-protocols"
-version = "0.32.13"
+version = "0.32.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "23d0c813de3daa2ed6520af85a3bd49b0e722a3078506899aa9686fea58dc4b6"
+checksum = "baeda9ffbcfc8cd6ddaade385eaf2393bd2115a69523c735f12242353c3df4f3"
 dependencies = [
  "bitflags 2.10.0",
  "wayland-backend",
@@ -2991,9 +2982,9 @@ dependencies = [
 
 [[package]]
 name = "wayland-protocols-wlr"
-version = "0.3.12"
+version = "0.3.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "eb04e52f7836d7c7976c78ca0250d61e33873c34156a2a1fc9474828ec268234"
+checksum = "e9597cdf02cf0c34cd5823786dce6b5ae8598f05c2daf5621b6e178d4f7345f3"
 dependencies = [
  "bitflags 2.10.0",
  "wayland-backend",
@@ -3004,9 +2995,9 @@ dependencies = [
 
 [[package]]
 name = "wayland-scanner"
-version = "0.31.11"
+version = "0.31.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "338e30461b3a2b67d70eb30a6d89f8e0c93a833e07d2ae89085cd070c4a00ac0"
+checksum = "5423e94b6a63e68e439803a3e153a9252d5ead12fd853334e2ad33997e3889e3"
 dependencies = [
  "proc-macro2",
  "quick-xml",
@@ -3015,9 +3006,9 @@ dependencies = [
 
 [[package]]
 name = "wayland-sys"
-version = "0.31.11"
+version = "0.31.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d8eab23fefc9e41f8e841df4a9c707e8a8c4ed26e944ef69297184de2785e3be"
+checksum = "1e6dbfc3ac5ef974c92a2235805cc0114033018ae1290a72e474aa8b28cbbdfd"
 dependencies = [
  "dlib",
  "log",

Cargo.toml

@@ -3,9 +3,6 @@ name = "iris"
 version.workspace = true
 edition.workspace = true
 
-[features]
-layout-diagnostics = ["iris-core/layout-diagnostics"]
-
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
@@ -23,7 +20,7 @@ tokio = { workspace = true, features = ["sync", "rt", "rt-multi-thread"] }
 tokio = { workspace = true, features = ["sync", "rt", "rt-multi-thread", "time"] }
 
 [workspace]
-members = ["core", "macro", "rig-input"]
+members = ["core", "macro"]
 
 [workspace.package]
 version = "0.1.0"
@@ -43,5 +40,3 @@ arboard = "3.6.1"
 iris-core = { path = "core" }
 iris-macro = { path = "macro" }
 tokio = "1.49.0"
-wayland-client = "0.31.15"
-wayland-protocols-wlr = { version = "0.3.12", features = ["client"] }

core/Cargo.toml

@@ -3,9 +3,6 @@ name = "iris-core"
 version.workspace = true
 edition.workspace = true
 
-[features]
-layout-diagnostics = []
-
 [dependencies]
 wgpu = { workspace = true }
 bytemuck ={ workspace = true }

core/src/event/manager.rs

@@ -79,7 +79,6 @@ type EventData<Rsc, E> = (E, Rc<dyn for<'a> EventFn<Rsc, <E as Event>::Data<'a>>
 pub struct TypeEventManager<Rsc: HasEvents, E: Event> {
     // TODO: reduce visiblity!!
     pub active: HashMap<LayerId, HashMap<WidgetId, E::State>>,
-    pub global: E::Global,
     map: HashMap<WidgetId, Vec<EventData<Rsc, E>>>,
 }
 
@@ -108,7 +107,6 @@ impl<Rsc: HasEvents, E: Event> Default for TypeEventManager<Rsc, E> {
     fn default() -> Self {
         Self {
             active: Default::default(),
-            global: Default::default(),
             map: Default::default(),
         }
     }
@@ -140,13 +138,11 @@ impl<Rsc: HasEvents + 'static, E: Event> TypeEventManager<Rsc, E> {
     pub fn run_fn<'a>(
         &mut self,
         id: impl IdLike,
-    ) -> impl for<'b> FnOnce(EventCtx<'_, Rsc, E::Data<'b>>, &mut Rsc) -> bool + 'a {
+    ) -> impl for<'b> FnOnce(EventCtx<'_, Rsc, E::Data<'b>>, &mut Rsc) + 'a {
         let fs = self.map.get(&id.id()).cloned().unwrap_or_default();
         move |ctx, rsc| {
-            let mut consumed = false;
             for (e, f) in fs {
                 if let Some(data) = e.should_run(&ctx.data) {
-                    consumed |= e.consumes(&data);
                     f(
                         EventCtx {
                             state: ctx.state,
@@ -156,7 +152,6 @@ impl<Rsc: HasEvents + 'static, E: Event> TypeEventManager<Rsc, E> {
                     )
                 }
             }
-            consumed
         }
     }
 }

core/src/event/mod.rs

@@ -9,19 +9,10 @@ pub use rsc::*;
 pub trait Event: Sized + 'static + Clone {
     type Data<'a>: Clone = ();
     type State: Default = ();
-    /// State the whole event type keeps, rather than one copy per widget.
-    type Global: Default = ();
     #[allow(unused_variables)]
     fn should_run<'a>(&self, data: &Self::Data<'a>) -> Option<Self::Data<'a>> {
         Some(data.clone())
     }
-
-    /// Whether having run on this data uses up whatever triggered it, so
-    /// nothing further should see it.
-    #[allow(unused_variables)]
-    fn consumes(&self, data: &Self::Data<'_>) -> bool {
-        false
-    }
 }
 
 pub trait EventLike {

core/src/event/rsc.rs

@@ -21,13 +21,12 @@ pub trait HasEvents: Sized + UiRsc + HasState {
 }
 
 pub trait RunEvents: HasEvents {
-    /// Whether anything that ran used up what triggered it.
     fn run_event<E: EventLike>(
         &mut self,
         id: impl IdLike,
         data: <E::Event as Event>::Data<'_>,
         state: &mut Self::State,
-    ) -> bool {
+    ) {
         let f = self.events_mut().get_type::<E>().run_fn(id);
         f(EventCtx { state, data }, self)
     }

core/src/layout_diagnostics.rs

@@ -1,482 +0,0 @@
-//! Opt-in counters and coarse timers for explaining CPU layout cost.
-//!
-//! Enable the `layout-diagnostics` feature. With it disabled, none of the
-//! instrumentation is compiled into Iris. The retained rig in
-//! `tests/layout_diagnostics.rs` is the ordinary entry point.
-//!
-//! Timers are inclusive: `update total` contains `full layout` or
-//! `incremental layout`, and `text render` contains shaping and glyph
-//! placement. They locate cost within one instrumented run and must not be
-//! added together. Use an uninstrumented build under `perf` for final CPU
-//! totals; counting every primitive and distinct widget deliberately perturbs
-//! the instrumented run.
-//!
-//! Call [`trace_widget`] before a frame to retain the ordered constraint,
-//! reuse, size, placement, and text events for one suspicious widget. The
-//! selection is a set and survives [`take`] until cleared.
-
-use crate::{Axis, Len, Size, UiRegion, WidgetId, util::Vec2};
-use std::{
-    cell::RefCell,
-    collections::{HashMap, HashSet},
-    fmt::Write,
-    time::Instant,
-};
-
-#[derive(Clone, Copy)]
-pub(crate) enum Counter {
-    Updates,
-    ResizeDependents,
-    DrawRequests,
-    WidgetDraws,
-    PlaceCalls,
-    SizeReads,
-    HintHits,
-    HintMisses,
-    RetainedSizeHits,
-    ReuseAttempts,
-    ReuseExact,
-    ReuseMoved,
-    ReuseDirty,
-    ReuseWrongParent,
-    ReuseUnslotted,
-    ReuseOwnResize,
-    ReuseDescendantResize,
-    ResizeChecks,
-    ResizeCheckChildren,
-    QueuePops,
-    DepthSteps,
-    EagerReaderRedraws,
-    LocalRedraws,
-    SizeChanges,
-    ReaderEdges,
-    PrimitiveWrites,
-    TextRenders,
-    TextShapeHits,
-    TextShapes,
-}
-
-impl Counter {
-    const COUNT: usize = Self::TextShapes as usize + 1;
-
-    const NAMES: [&'static str; Self::COUNT] = [
-        "updates",
-        "resize dependents",
-        "draw requests",
-        "widget draws",
-        "place calls",
-        "draw-result size reads",
-        "hint hits",
-        "hint misses",
-        "retained size hits",
-        "reuse attempts",
-        "reuse exact",
-        "reuse moved",
-        "reuse: dirty",
-        "reuse: wrong parent",
-        "reuse: unslotted",
-        "reuse: own resize",
-        "reuse: descendant resize",
-        "resize checks",
-        "resize children checked",
-        "redraw queue pops",
-        "depth steps",
-        "eager reader redraws",
-        "local redraws",
-        "size changes",
-        "reader edges",
-        "primitive writes",
-        "text renders",
-        "text shape hits",
-        "text shapes",
-    ];
-}
-
-#[derive(Clone, Copy)]
-pub(crate) enum TimerKind {
-    Update,
-    FullLayout,
-    ResizeMarking,
-    IncrementalLayout,
-    TextRender,
-    TextShape,
-    GlyphPlacement,
-}
-
-impl TimerKind {
-    const COUNT: usize = Self::GlyphPlacement as usize + 1;
-
-    const NAMES: [&'static str; Self::COUNT] = [
-        "update total",
-        "full layout",
-        "resize marking",
-        "incremental layout",
-        "text render",
-        "text shape",
-        "glyph placement",
-    ];
-}
-
-#[derive(Clone)]
-pub struct Report {
-    counters: [u64; Counter::COUNT],
-    nanos: [u64; TimerKind::COUNT],
-    distinct_widgets: usize,
-    distinct_text_widgets: usize,
-    hot_widgets: Vec<Callsite>,
-    hot_text: Vec<Callsite>,
-    traces: Vec<TraceEvent>,
-}
-
-impl Default for Report {
-    fn default() -> Self {
-        Self {
-            counters: [0; Counter::COUNT],
-            nanos: [0; TimerKind::COUNT],
-            distinct_widgets: 0,
-            distinct_text_widgets: 0,
-            hot_widgets: Vec::new(),
-            hot_text: Vec::new(),
-            traces: Vec::new(),
-        }
-    }
-}
-
-impl Report {
-    pub fn counters(&self) -> impl Iterator<Item = (&'static str, u64)> + '_ {
-        Counter::NAMES.into_iter().zip(self.counters)
-    }
-
-    /// Inclusive elapsed time accumulated for each targeted operation.
-    pub fn timings_ns(&self) -> impl Iterator<Item = (&'static str, u64)> + '_ {
-        TimerKind::NAMES.into_iter().zip(self.nanos)
-    }
-
-    pub fn distinct_widgets(&self) -> usize {
-        self.distinct_widgets
-    }
-
-    pub fn distinct_text_widgets(&self) -> usize {
-        self.distinct_text_widgets
-    }
-
-    pub fn hot_widgets(&self) -> &[Callsite] {
-        &self.hot_widgets
-    }
-
-    pub fn hot_text(&self) -> &[Callsite] {
-        &self.hot_text
-    }
-
-    /// Ordered layout events for widgets selected with [`trace_widget`].
-    pub fn traces(&self) -> &[TraceEvent] {
-        &self.traces
-    }
-
-    /// Formats nonzero totals divided by `frames`.
-    pub fn per_frame(&self, frames: usize) -> String {
-        let divisor = frames.max(1) as f64;
-        let mut out = String::new();
-        for (name, value) in self.counters() {
-            if value != 0 {
-                let _ = writeln!(out, "  {name:<27} {:>12.2}", value as f64 / divisor);
-            }
-        }
-        if self.distinct_widgets != 0 {
-            let _ = writeln!(
-                out,
-                "  {:<27} {:>12}",
-                "distinct widgets", self.distinct_widgets
-            );
-        }
-        if self.distinct_text_widgets != 0 {
-            let _ = writeln!(
-                out,
-                "  {:<27} {:>12}",
-                "distinct text widgets", self.distinct_text_widgets
-            );
-        }
-        for (name, nanos) in self.timings_ns() {
-            if nanos != 0 {
-                let ms = nanos as f64 / divisor / 1_000_000.0;
-                let _ = writeln!(out, "  {name:<27} {ms:>12.3} ms");
-            }
-        }
-        if !self.hot_widgets.is_empty() {
-            let _ = writeln!(out, "  hottest widget draws:");
-            for callsite in &self.hot_widgets {
-                let calls = callsite.calls as f64 / divisor;
-                let _ = writeln!(
-                    out,
-                    "    {calls:>9.2}  {:?} {}",
-                    callsite.id, callsite.label
-                );
-            }
-        }
-        if !self.hot_text.is_empty() {
-            let _ = writeln!(out, "  hottest text renders:");
-            for callsite in &self.hot_text {
-                let calls = callsite.calls as f64 / divisor;
-                let _ = writeln!(
-                    out,
-                    "    {calls:>9.2}  {:>3} widths  {:?} {}",
-                    callsite.distinct_widths, callsite.id, callsite.label
-                );
-            }
-        }
-        if !self.traces.is_empty() {
-            let _ = writeln!(out, "  targeted layout trace:");
-            for event in &self.traces {
-                let _ = writeln!(out, "    {event:?}");
-            }
-        }
-        out
-    }
-}
-
-#[derive(Clone)]
-pub struct Callsite {
-    pub id: WidgetId,
-    pub label: String,
-    pub calls: u64,
-    pub distinct_widths: usize,
-}
-
-#[derive(Clone, Copy, Debug, PartialEq)]
-pub enum ReuseOutcome {
-    Exact,
-    Moved,
-    Dirty,
-    WrongParent,
-    Unslotted,
-    OwnResize,
-    DescendantResize,
-}
-
-/// One targeted layout event. Events are retained in execution order, making
-/// repeated constraint paths visible without logging every widget globally.
-#[derive(Clone, Copy, Debug, PartialEq)]
-pub enum TraceEvent {
-    DrawRequest {
-        id: WidgetId,
-        parent: Option<WidgetId>,
-        region: UiRegion,
-        pixel_size: Vec2,
-        slotted: bool,
-    },
-    Reuse {
-        id: WidgetId,
-        outcome: ReuseOutcome,
-    },
-    SizeReported {
-        id: WidgetId,
-        size: Size,
-    },
-    Placed {
-        id: WidgetId,
-        parent: WidgetId,
-        region: UiRegion,
-    },
-    SizeRead {
-        id: WidgetId,
-        reader: WidgetId,
-        size: Size,
-    },
-    HintRead {
-        id: WidgetId,
-        reader: WidgetId,
-        axis: Axis,
-        hint: Option<Len>,
-    },
-    TextRendered {
-        id: WidgetId,
-        width: Option<f32>,
-    },
-}
-
-#[derive(Default)]
-struct Calls {
-    label: String,
-    count: u64,
-    widths: HashSet<Option<u32>>,
-}
-
-#[derive(Default)]
-struct Current {
-    report: Report,
-    widgets: HashMap<WidgetId, Calls>,
-    text_widgets: HashMap<WidgetId, Calls>,
-    traced: HashSet<WidgetId>,
-}
-
-thread_local! {
-    static CURRENT: RefCell<Current> = RefCell::new(Current::default());
-}
-
-pub(crate) fn bump(counter: Counter) {
-    CURRENT.with_borrow_mut(|current| current.report.counters[counter as usize] += 1);
-}
-
-pub(crate) fn draw_widget(id: WidgetId, label: &str) {
-    CURRENT.with_borrow_mut(|current| {
-        let calls = current.widgets.entry(id).or_default();
-        if calls.label.is_empty() {
-            calls.label = label.to_owned();
-        }
-        calls.count += 1;
-    });
-}
-
-/// Adds a widget to the targeted trace set. Selection survives [`take`]
-/// until explicitly removed or cleared.
-pub fn trace_widget(id: impl Into<WidgetId>) {
-    CURRENT.with_borrow_mut(|current| {
-        current.traced.insert(id.into());
-    });
-}
-
-pub fn untrace_widget(id: impl Into<WidgetId>) {
-    CURRENT.with_borrow_mut(|current| {
-        current.traced.remove(&id.into());
-    });
-}
-
-pub fn clear_traced_widgets() {
-    CURRENT.with_borrow_mut(|current| current.traced.clear());
-}
-
-fn trace(id: WidgetId, event: TraceEvent) {
-    CURRENT.with_borrow_mut(|current| {
-        if current.traced.contains(&id) {
-            current.report.traces.push(event);
-        }
-    });
-}
-
-pub(crate) fn draw_request(
-    id: WidgetId,
-    parent: Option<WidgetId>,
-    region: UiRegion,
-    pixel_size: Vec2,
-    slotted: bool,
-) {
-    trace(
-        id,
-        TraceEvent::DrawRequest {
-            id,
-            parent,
-            region,
-            pixel_size,
-            slotted,
-        },
-    );
-}
-
-pub(crate) fn reuse(id: WidgetId, outcome: ReuseOutcome) {
-    trace(id, TraceEvent::Reuse { id, outcome });
-}
-
-pub(crate) fn size_reported(id: WidgetId, size: Size) {
-    trace(id, TraceEvent::SizeReported { id, size });
-}
-
-pub(crate) fn placed(id: WidgetId, parent: WidgetId, region: UiRegion) {
-    trace(id, TraceEvent::Placed { id, parent, region });
-}
-
-pub(crate) fn size_read(id: WidgetId, reader: WidgetId, size: Size) {
-    trace(id, TraceEvent::SizeRead { id, reader, size });
-}
-
-pub(crate) fn hint_read(id: WidgetId, reader: WidgetId, axis: Axis, hint: Option<Len>) {
-    trace(
-        id,
-        TraceEvent::HintRead {
-            id,
-            reader,
-            axis,
-            hint,
-        },
-    );
-}
-
-pub(crate) fn render_text(id: WidgetId, label: &str, width: Option<f32>) {
-    CURRENT.with_borrow_mut(|current| {
-        let calls = current.text_widgets.entry(id).or_default();
-        if calls.label.is_empty() {
-            calls.label = label.to_owned();
-        }
-        calls.count += 1;
-        calls.widths.insert(width.map(f32::to_bits));
-        if current.traced.contains(&id) {
-            current
-                .report
-                .traces
-                .push(TraceEvent::TextRendered { id, width });
-        }
-    });
-}
-
-pub(crate) struct Timer {
-    kind: TimerKind,
-    start: Instant,
-}
-
-pub(crate) fn timer(kind: TimerKind) -> Timer {
-    Timer {
-        kind,
-        start: Instant::now(),
-    }
-}
-
-impl Drop for Timer {
-    fn drop(&mut self) {
-        let nanos = self.start.elapsed().as_nanos().min(u64::MAX as u128) as u64;
-        CURRENT.with_borrow_mut(|current| current.report.nanos[self.kind as usize] += nanos);
-    }
-}
-
-/// Takes all diagnostics accumulated on this thread and resets them.
-pub fn take() -> Report {
-    CURRENT.with_borrow_mut(|current| {
-        current.report.distinct_widgets = current.widgets.len();
-        current.report.distinct_text_widgets = current.text_widgets.len();
-        current.report.hot_widgets = hottest(&current.widgets);
-        current.report.hot_text = hottest(&current.text_widgets);
-        let report = std::mem::take(&mut current.report);
-        current.widgets.clear();
-        current.text_widgets.clear();
-        report
-    })
-}
-
-fn hottest(calls: &HashMap<WidgetId, Calls>) -> Vec<Callsite> {
-    let mut calls: Vec<_> = calls
-        .iter()
-        .map(|(&id, calls)| Callsite {
-            id,
-            label: calls.label.clone(),
-            calls: calls.count,
-            distinct_widths: calls.widths.len(),
-        })
-        .collect();
-    calls.sort_by(|a, b| b.calls.cmp(&a.calls).then_with(|| a.label.cmp(&b.label)));
-    calls.truncate(8);
-    calls
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    #[test]
-    fn taking_a_report_resets_its_counters() {
-        let _ = take();
-        bump(Counter::Updates);
-        bump(Counter::Updates);
-
-        let report = take();
-        assert_eq!(report.counters().next(), Some(("updates", 2)));
-        assert!(take().counters().all(|(_, count)| count == 0));
-    }
-}

core/src/lib.rs

@@ -10,9 +10,6 @@
 #![feature(coerce_unsized)]
 #![feature(option_into_flat_iter)]
 
-#[cfg(feature = "layout-diagnostics")]
-pub mod layout_diagnostics;
-
 mod attr;
 mod event;
 mod num;

core/src/orientation/axis.rs

@@ -1,6 +1,6 @@
 use super::*;
 
-#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+#[derive(Copy, Clone, Eq, PartialEq)]
 pub enum Axis {
     X,
     Y,

core/src/orientation/pos.rs

@@ -56,6 +56,13 @@ impl UiVec2 {
         }
     }
 
+    pub const fn outside(&self, region: &UiRegion) -> UiVec2 {
+        UiVec2 {
+            x: self.x.outside(&region.x),
+            y: self.y.outside(&region.y),
+        }
+    }
+
     pub fn axis_mut(&mut self, axis: Axis) -> &mut UiScalar {
         match axis {
             Axis::X => &mut self.x,
@@ -202,6 +209,12 @@ impl UiScalar {
         }
     }
 
+    pub const fn outside(&self, span: &UiSpan) -> Self {
+        let rel = self.rel.lerp_inv(span.start.rel, span.end.rel);
+        let abs = self.abs - rel.lerp(span.start.abs, span.end.abs);
+        Self { rel, abs }
+    }
+
     pub fn within_len(&self, len: UiScalar) -> Self {
         self.within(&UiSpan {
             start: UiScalar::ZERO,
@@ -270,6 +283,13 @@ impl UiSpan {
         }
     }
 
+    pub const fn outside(&self, parent: &Self) -> Self {
+        Self {
+            start: self.start.outside(parent),
+            end: self.end.outside(parent),
+        }
+    }
+
     pub const fn len(&self) -> UiScalar {
         self.end - self.start
     }
@@ -304,7 +324,14 @@ impl UiRegion {
             y: self.y.within(&parent.y),
         }
     }
-    pub const fn axis(&self, axis: Axis) -> &UiSpan {
+    pub const fn outside(&self, parent: &Self) -> Self {
+        Self {
+            x: self.x.outside(&parent.x),
+            y: self.y.outside(&parent.y),
+        }
+    }
+
+    pub const fn axis(&mut self, axis: Axis) -> &UiSpan {
         match axis {
             Axis::X => &self.x,
             Axis::Y => &self.y,

core/src/primitive/text.rs

@@ -1,5 +1,3 @@
-#[cfg(feature = "layout-diagnostics")]
-use crate::layout_diagnostics::{self as diag, Counter, TimerKind};
 use crate::{
     Align, GlyphAtlas, GlyphEntry, GlyphKey, PlacedGlyph, RegionAlign, UiColor, util::Vec2,
 };
@@ -140,14 +138,8 @@ impl TextBuffer {
             max_width: width,
         };
         if self.layout_key.as_ref() == Some(&layout_key) {
-            #[cfg(feature = "layout-diagnostics")]
-            diag::bump(Counter::TextShapeHits);
             return;
         }
-        #[cfg(feature = "layout-diagnostics")]
-        diag::bump(Counter::TextShapes);
-        #[cfg(feature = "layout-diagnostics")]
-        let _shape = diag::timer(TimerKind::TextShape);
         let mut builder = data
             .layout_ctx
             .ranged_builder(&mut data.font_ctx, &self.text, 1.0, true);
@@ -279,16 +271,8 @@ impl TextData {
         attrs: &TextAttrs,
         width: Option<f32>,
     ) -> RenderedText {
-        #[cfg(feature = "layout-diagnostics")]
-        diag::bump(Counter::TextRenders);
-        #[cfg(feature = "layout-diagnostics")]
-        let _render = diag::timer(TimerKind::TextRender);
         buffer.shape(self, attrs, width);
-        let glyphs = {
+        let glyphs = self.place(buffer);
-            #[cfg(feature = "layout-diagnostics")]
-            let _place = diag::timer(TimerKind::GlyphPlacement);
-            self.place(buffer)
-        };
         RenderedText {
             glyphs,
             size: buffer.size(),

core/src/render/data.rs

@@ -1,10 +1,11 @@
-use crate::{UiRegion, util::Id, util::Vec2};
+use crate::{UiRegion, util::Id};
 use wgpu::*;
 
 #[repr(C)]
 #[derive(Copy, Clone, bytemuck::Pod, bytemuck::Zeroable, Default)]
 pub struct WindowUniform {
-    pub dim: Vec2,
+    pub width: f32,
+    pub height: f32,
 }
 
 #[repr(C)]
@@ -12,17 +13,15 @@ pub struct WindowUniform {
 pub struct PrimitiveInstance {
     pub region: UiRegion,
     pub mask_idx: MaskIdx,
-    pub move_idx: MoveIdx,
 }
 
 impl PrimitiveInstance {
-    const ATTRIBS: [VertexAttribute; 6] = vertex_attr_array![
+    const ATTRIBS: [VertexAttribute; 5] = vertex_attr_array![
         0 => Float32x2,
         1 => Float32x2,
         2 => Float32x2,
         3 => Float32x2,
         4 => Uint32,
-        5 => Uint32,
     ];
 
     pub fn desc() -> VertexBufferLayout<'static> {
@@ -44,45 +43,4 @@ impl MaskIdx {
 #[derive(Debug, Copy, Clone, bytemuck::Pod, bytemuck::Zeroable)]
 pub struct Mask {
     pub region: UiRegion,
-    pub move_idx: MoveIdx,
-}
-
-/// Its own type rather than another `Id<u32>`, because it sits beside
-/// `MaskIdx` in an instance and the two must not be swappable.
-#[repr(transparent)]
-#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash, bytemuck::Pod, bytemuck::Zeroable)]
-pub struct MoveIdx(u32);
-
-impl MoveIdx {
-    pub const NONE: Self = Self(u32::MAX);
-
-    pub(crate) fn slot(idx: usize) -> Self {
-        Self(idx as u32)
-    }
-
-    pub(crate) fn idx(self) -> usize {
-        self.0 as usize
-    }
-}
-
-/// One link of the chain a primitive's position is resolved through: the box
-/// its contents are placed within, given in the coordinates of the slot it
-/// names. Moving or resizing a subtree writes its own slot and nothing else.
-///
-/// The identity is `UiRegion::FULL`, not zero: a zeroed entry is a box of no
-/// extent, which collapses everything under it to a point.
-#[repr(C)]
-#[derive(Debug, Copy, Clone)]
-pub struct MoveOffset {
-    pub region: UiRegion,
-    pub parent: MoveIdx,
-}
-
-unsafe impl bytemuck::Pod for MoveOffset {}
-unsafe impl bytemuck::Zeroable for MoveOffset {}
-
-impl MoveOffset {
-    pub fn new(parent: MoveIdx, region: UiRegion) -> Self {
-        Self { region, parent }
-    }
 }

core/src/render/mod.rs

@@ -17,7 +17,7 @@ mod texture;
 mod util;
 
 pub use atlas::*;
-pub use data::{Mask, MaskIdx, MoveIdx, MoveOffset};
+pub use data::{Mask, MaskIdx};
 pub use primitive::*;
 
 const PRELUDE: &str = include_str!("./shader/prelude.wgsl");
@@ -34,7 +34,6 @@ pub struct UiRenderNode {
     active: Vec<usize>,
     window_buffer: Buffer,
     masks: ArrBuf<Mask>,
-    moves: ArrBuf<MoveOffset>,
 }
 
 struct RenderLayer {
@@ -128,35 +127,32 @@ impl UiRenderNode {
         for primitive in &mut self.primitives {
             primitive.render.update(ui);
         }
-        let mut regroup = false;
         if ui.masks.changed {
             ui.masks.changed = false;
-            regroup |= self.masks.update(device, queue, &ui.masks[..]);
+            if self.masks.update(device, queue, &ui.masks[..]) {
-        }
-        if ui_render.moves.changed {
-            ui_render.moves.changed = false;
-            regroup |= self.moves.update(device, queue, ui_render.moves.entries());
-        }
-        if regroup {
                 self.shared_group = Self::shared_group(
                     device,
                     &self.shared_layout,
                     &self.window_buffer,
                     &self.masks,
-                &self.moves,
                 );
             }
         }
+    }
 
     pub fn resize(&mut self, size: impl Into<Vec2>, queue: &Queue) {
         let size = size.into();
-        let slice = &[WindowUniform { dim: size }];
+        let slice = &[WindowUniform {
+            width: size.x,
+            height: size.y,
+        }];
         queue.write_buffer(&self.window_buffer, 0, bytemuck::cast_slice(slice));
     }
 
     pub fn new(device: &Device, config: &SurfaceConfiguration) -> Self {
         let window_uniform = WindowUniform {
-            dim: Vec2::new(config.width as f32, config.height as f32),
+            width: config.width as f32,
+            height: config.height as f32,
         };
         let window_buffer = device.create_buffer_init(&BufferInitDescriptor {
             label: Some("window"),
@@ -170,13 +166,7 @@ impl UiRenderNode {
             BufferUsages::STORAGE | BufferUsages::COPY_DST,
             "ui masks",
         );
-        let moves = ArrBuf::new(
+        let shared_group = Self::shared_group(device, &shared_layout, &window_buffer, &masks);
-            device,
-            BufferUsages::STORAGE | BufferUsages::COPY_DST,
-            "ui move offsets",
-        );
-        let shared_group =
-            Self::shared_group(device, &shared_layout, &window_buffer, &masks, &moves);
 
         Self {
             shared_layout,
@@ -187,7 +177,6 @@ impl UiRenderNode {
             layers: HashMap::default(),
             active: Vec::new(),
             masks,
-            moves,
         }
     }
 
@@ -263,8 +252,7 @@ impl UiRenderNode {
         })
     }
 
-    /// What every draw in the ui is given: the window, the masks and the
+    /// What every draw in the ui is given: the window and the masks.
-    /// move chain every position is resolved through.
     fn shared_layout(device: &Device) -> BindGroupLayout {
         device.create_bind_group_layout(&BindGroupLayoutDescriptor {
             entries: &[
@@ -288,16 +276,6 @@ impl UiRenderNode {
                     },
                     count: None,
                 },
-                BindGroupLayoutEntry {
-                    binding: 2,
-                    visibility: ShaderStages::VERTEX | ShaderStages::FRAGMENT,
-                    ty: BindingType::Buffer {
-                        ty: BufferBindingType::Storage { read_only: true },
-                        has_dynamic_offset: false,
-                        min_binding_size: BufferSize::new(size_of::<MoveOffset>() as u64),
-                    },
-                    count: None,
-                },
             ],
             label: Some("ui shared"),
         })
@@ -308,7 +286,6 @@ impl UiRenderNode {
         layout: &BindGroupLayout,
         window: &Buffer,
         masks: &ArrBuf<Mask>,
-        moves: &ArrBuf<MoveOffset>,
     ) -> BindGroup {
         device.create_bind_group(&BindGroupDescriptor {
             layout,
@@ -321,10 +298,6 @@ impl UiRenderNode {
                     binding: 1,
                     resource: masks.buffer.as_entire_binding(),
                 },
-                BindGroupEntry {
-                    binding: 2,
-                    resource: moves.buffer.as_entire_binding(),
-                },
             ],
             label: Some("ui shared"),
         })

core/src/render/primitive.rs

@@ -3,7 +3,7 @@ use std::{any::TypeId, marker::PhantomData};
 use crate::{
     Color, TextureHandle, UiData, UiRegion, WidgetId,
     render::{
-        data::{MaskIdx, MoveIdx, PrimitiveInstance},
+        data::{MaskIdx, PrimitiveInstance},
         page::GlyphRender,
         texture::ImageRender,
     },
@@ -246,7 +246,6 @@ impl LayerDraws {
             primitive,
             region,
             mask_idx,
-            move_idx,
         }: PrimitiveInst<P>,
     ) -> PrimitiveHandle {
         self.updated = true;
@@ -259,11 +258,7 @@ impl LayerDraws {
             .get_or_insert_with(InstanceList::new::<P>)
             .push(
                 id,
-                PrimitiveInstance {
+                PrimitiveInstance { region, mask_idx },
-                    region,
-                    mask_idx,
-                    move_idx,
-                },
                 bytemuck::bytes_of(&primitive),
             );
         PrimitiveHandle {
@@ -309,7 +304,6 @@ pub struct PrimitiveInst<P> {
     pub primitive: P,
     pub region: UiRegion,
     pub mask_idx: MaskIdx,
-    pub move_idx: MoveIdx,
 }
 
 pub struct PrimitiveChange {
@@ -353,7 +347,7 @@ impl RectPrimitive {
 
 /// `color` is multiplied by the atlas alpha for a mask glyph; a colour glyph
 /// takes the texel unchanged, which `GlyphEntry::IS_COLORED` selects.
-#[repr(C)]
+#[repr(C, align(8))]
 #[derive(Debug, Copy, Clone)]
 pub struct GlyphPrimitive {
     pub uv_min: Vec2,
@@ -364,8 +358,8 @@ pub struct GlyphPrimitive {
     pub flags: u32,
 }
 
-// Manual rather than derived: `Vec2`'s alignment leaves four bytes of padding
+// Manual rather than derived: the align(8) leaves four bytes of padding, which
-// here, which is how WGSL lays the struct out.
+// is how WGSL lays the struct out.
 unsafe impl bytemuck::Pod for GlyphPrimitive {}
 unsafe impl bytemuck::Zeroable for GlyphPrimitive {}
 impl Primitive for GlyphPrimitive {

core/src/render/shader/prelude.wgsl

@@ -7,8 +7,6 @@
 var<uniform> window: WindowUniform;
 @group(0) @binding(1)
 var<storage> masks: array<Mask>;
-@group(0) @binding(2)
-var<storage> move_offsets: array<MoveOffset>;
 
 struct WindowUniform {
     dim: vec2<f32>,
@@ -17,49 +15,6 @@ struct WindowUniform {
 struct Mask {
     x: UiSpan,
     y: UiSpan,
-    move_idx: u32,
-}
-
-struct MoveOffset {
-    x: UiSpan,
-    y: UiSpan,
-    parent: u32,
-}
-
-struct Region {
-    x: UiSpan,
-    y: UiSpan,
-}
-
-const MOVE_NONE: u32 = 4294967295u;
-// Keep in step with `iris_core::CHAIN_LIMIT`. It bounds a malformed cycle
-// rather than any real tree, and the CPU walk uses the same number so both
-// resolve a deep one the same way.
-const CHAIN_LIMIT: u32 = 64u;
-
-fn scalar_within(s: UiScalar, p: UiSpan) -> UiScalar {
-    return UiScalar(
-        mix(p.start.rel, p.end.rel, s.rel),
-        s.abs + mix(p.start.abs, p.end.abs, s.rel),
-    );
-}
-
-fn span_within(s: UiSpan, p: UiSpan) -> UiSpan {
-    return UiSpan(scalar_within(s.start, p), scalar_within(s.end, p));
-}
-
-fn resolve_move(idx: u32, local: Region) -> Region {
-    var r = local;
-    var at = idx;
-    for (var step = 0u; step < CHAIN_LIMIT; step++) {
-        if at == MOVE_NONE {
-            break;
-        }
-        let entry = move_offsets[at];
-        r = Region(span_within(r.x, entry.x), span_within(r.y, entry.y));
-        at = entry.parent;
-    }
-    return r;
 }
 
 struct UiSpan {
@@ -78,7 +33,6 @@ struct InstanceInput {
     @location(2) y_start: vec2<f32>,
     @location(3) y_end: vec2<f32>,
     @location(4) mask_idx: u32,
-    @location(5) move_idx: u32,
 }
 
 struct VertexOutput {
@@ -98,15 +52,10 @@ fn vs_main(
 ) -> VertexOutput {
     var out: VertexOutput;
 
-    let local = Region(
+    let top_left_rel = vec2(in.x_start.x, in.y_start.x);
-        UiSpan(UiScalar(in.x_start.x, in.x_start.y), UiScalar(in.x_end.x, in.x_end.y)),
+    let top_left_abs = vec2(in.x_start.y, in.y_start.y);
-        UiSpan(UiScalar(in.y_start.x, in.y_start.y), UiScalar(in.y_end.x, in.y_end.y)),
+    let bot_right_rel = vec2(in.x_end.x, in.y_end.x);
-    );
+    let bot_right_abs = vec2(in.x_end.y, in.y_end.y);
-    let r = resolve_move(in.move_idx, local);
-    let top_left_rel = vec2(r.x.start.rel, r.y.start.rel);
-    let top_left_abs = vec2(r.x.start.abs, r.y.start.abs);
-    let bot_right_rel = vec2(r.x.end.rel, r.y.end.rel);
-    let bot_right_abs = vec2(r.x.end.abs, r.y.end.abs);
 
     let top_left = floor(top_left_rel * window.dim) + floor(top_left_abs);
     let bot_right = floor(bot_right_rel * window.dim) + floor(bot_right_abs);
@@ -132,13 +81,10 @@ fn masked(in: VertexOutput, color: vec4<f32>) -> vec4<f32> {
         return color;
     }
     let mask = masks[in.mask_idx];
-    // Its own chain, not the drawn primitive's, so a stationary viewport
+    let tl = vec2(mask.x.start.rel, mask.y.start.rel);
-    // clips content that moves inside it.
+    let tl_abs = vec2(mask.x.start.abs, mask.y.start.abs);
-    let m = resolve_move(mask.move_idx, Region(mask.x, mask.y));
+    let br = vec2(mask.x.end.rel, mask.y.end.rel);
-    let tl = vec2(m.x.start.rel, m.y.start.rel);
+    let br_abs = vec2(mask.x.end.abs, mask.y.end.abs);
-    let tl_abs = vec2(m.x.start.abs, m.y.start.abs);
-    let br = vec2(m.x.end.rel, m.y.end.rel);
-    let br_abs = vec2(m.x.end.abs, m.y.end.abs);
 
     let top_left = floor(tl * window.dim) + floor(tl_abs);
     let bot_right = floor(br * window.dim) + floor(br_abs);

core/src/ui/active.rs

@@ -1,39 +1,14 @@
-use crate::{
+use crate::{LayerId, MaskIdx, PrimitiveHandle, TextureHandle, UiRegion, WidgetId};
-    LayerId, MaskIdx, MoveIdx, PrimitiveHandle, Size, TextureHandle, UiRegion, WidgetId, util::Vec2,
-};
 
 /// important non rendering data for retained drawing
 #[derive(Debug)]
 pub struct ActiveData {
     pub id: WidgetId,
     pub region: UiRegion,
-    /// What the widget said it used of `region`, the last time it drew.
-    pub size: Size,
-    /// The pixel size of the box it drew against. `region` alone cannot say:
-    /// it is a fraction of a slot's box, and the same fraction of a box that
-    /// has since changed is a different number of pixels.
-    pub px: Vec2,
     pub parent: Option<WidgetId>,
     pub textures: Vec<TextureHandle>,
     pub primitives: Vec<PrimitiveHandle>,
     pub children: Vec<WidgetId>,
-    /// The children whose size this widget read while drawing.
-    pub size_deps: Vec<WidgetId>,
-    /// Offered pixel axes which flowed into this widget's reported size,
-    /// directly or through a child size it read.
-    pub size_box_inputs: [bool; 2],
-    /// Output axes read while producing `size`, distinct from the widget's
-    /// own box when that box has a fixed pixel length.
-    pub size_output_inputs: [bool; 2],
-    /// The output dimensions against which those dependencies were observed.
-    pub output_px: Vec2,
-    /// Output axes it read directly or while resolving its offered box.
-    pub reads_output: [bool; 2],
-    /// The slot its primitives are positioned through: its own if its parent
-    /// placed it, otherwise the nearest ancestor that has one.
-    pub move_idx: MoveIdx,
-    /// The slot `region` is given in, which is whatever its parent drew in.
-    pub parent_move: MoveIdx,
     pub mask: MaskIdx,
     pub layer: LayerId,
 }

core/src/ui/cache.rs

@@ -0,0 +1,18 @@
+use crate::{BothAxis, Len, UiVec2, WidgetId, util::HashMap};
+
+#[derive(Default)]
+pub struct Cache {
+    pub size: BothAxis<HashMap<WidgetId, (UiVec2, Len)>>,
+}
+
+impl Cache {
+    pub fn remove(&mut self, id: WidgetId) {
+        self.size.x.remove(&id);
+        self.size.y.remove(&id);
+    }
+
+    pub fn clear(&mut self) {
+        self.size.x.clear();
+        self.size.y.clear();
+    }
+}

core/src/ui/mod.rs

@@ -1,21 +1,17 @@
 use crate::{
-    Mask, MoveIdx, MoveOffset, PrimitiveRegistry, TextData, Textures, UiRegion, WeakWidget,
+    Mask, PrimitiveRegistry, TextData, Textures, WeakWidget, WidgetId, Widgets, util::TrackedArena,
-    WidgetId, Widgets,
-    util::{Arena, Id, TrackedArena},
 };
 
-/// How far the shader will walk a move chain. It bounds a malformed cycle
-/// rather than any real tree; `Moves::resolve` uses the same number so the
-/// two agree on what a deep tree resolves to.
-pub const CHAIN_LIMIT: u32 = 64;
-
 mod active;
+mod cache;
 mod painter;
 mod render_state;
+mod size;
 
 pub use active::*;
 pub use painter::{Painter, PrimitiveLike};
 pub use render_state::*;
+pub use size::*;
 
 #[derive(Default)]
 pub struct UiData {
@@ -27,88 +23,6 @@ pub struct UiData {
     pub masks: TrackedArena<Mask, u32>,
 }
 
-/// Where each widget's drawing sits relative to its parent's slot, so moving
-/// a subtree writes one entry rather than every descendant's primitives.
-#[derive(Default)]
-pub struct Moves {
-    arena: Arena<MoveOffset, u32>,
-    pub changed: bool,
-}
-
-impl Moves {
-    pub fn push(&mut self, parent: MoveIdx, region: UiRegion) -> MoveIdx {
-        self.changed = true;
-        MoveIdx::slot(self.arena.push(MoveOffset::new(parent, region)).idx())
-    }
-
-    /// Re-points a slot at a different parent, for a widget drawn somewhere
-    /// else in the tree than it was.
-    pub fn set_parent(&mut self, idx: MoveIdx, parent: MoveIdx) {
-        let entry = self.arena.get_mut(Id::preset(idx.idx() as u32));
-        if entry.parent != parent {
-            entry.parent = parent;
-            self.changed = true;
-        }
-    }
-
-    pub fn remove(&mut self, idx: MoveIdx) {
-        self.changed = true;
-        self.arena.remove(Id::preset(idx.idx() as u32));
-    }
-
-    /// Sets the box a slot's contents are placed within, itself given in the
-    /// coordinates of its parent slot.
-    pub fn set(&mut self, idx: MoveIdx, region: UiRegion) {
-        let entry = self.arena.get_mut(Id::preset(idx.idx() as u32));
-        if entry.region != region {
-            entry.region = region;
-            self.changed = true;
-        }
-    }
-
-    /// Composes a region held in `idx`'s coordinates down the chain, which is
-    /// the same walk the vertex shader does.
-    pub fn resolve(&self, idx: MoveIdx, local: UiRegion) -> UiRegion {
-        let mut region = local;
-        let mut at = idx;
-        for _ in 0..CHAIN_LIMIT {
-            if at == MoveIdx::NONE {
-                return region;
-            }
-            let entry = self.arena[at.idx()];
-            region = region.within(&entry.region);
-            at = entry.parent;
-        }
-        debug_assert!(
-            at == MoveIdx::NONE,
-            "a move chain longer than {CHAIN_LIMIT} resolves to the wrong place, \
-             and the shader stops at the same depth"
-        );
-        region
-    }
-
-    /// How many slots a region in `idx` is composed through, which is what
-    /// the shader's walk costs per primitive.
-    pub fn depth(&self, idx: MoveIdx) -> usize {
-        let mut depth = 0;
-        let mut at = idx;
-        while at != MoveIdx::NONE && depth < CHAIN_LIMIT as usize {
-            at = self.arena[at.idx()].parent;
-            depth += 1;
-        }
-        depth
-    }
-
-    pub fn entries(&self) -> &[MoveOffset] {
-        &self.arena
-    }
-
-    pub fn clear(&mut self) {
-        self.changed = true;
-        self.arena = Arena::default();
-    }
-}
-
 pub trait UiRsc {
     fn ui(&self) -> &UiData;
     fn ui_mut(&mut self) -> &mut UiData;

core/src/ui/painter.rs

@@ -1,11 +1,9 @@
-#[cfg(feature = "layout-diagnostics")]
-use crate::layout_diagnostics::{self as diag, Counter};
 use crate::{
-    Axis, Len, RenderedText, Size, StrongWidget, TextAttrs, TextBuffer, TextData, TextureHandle,
+    Axis, Len, RenderedText, Size, SizeCtx, StrongWidget, TextAttrs, TextBuffer, TextData,
-    UiRegion, UiRenderState, UiRsc, UiScalar, UiVec2, WidgetId,
+    TextureHandle, UiRegion, UiRenderState, UiRsc, UiScalar, UiVec2, Widget, WidgetId,
     render::{
-        GlyphPrimitive, Mask, MaskIdx, MoveIdx, Primitive, PrimitiveHandle, PrimitiveInst,
+        GlyphPrimitive, Mask, MaskIdx, Primitive, PrimitiveHandle, PrimitiveInst, PrimitiveKind,
-        PrimitiveKind, TexturePrimitive,
+        TexturePrimitive,
     },
     util::Vec2,
 };
@@ -15,21 +13,11 @@ pub struct Painter<'a> {
     pub(super) state: &'a mut UiRenderState,
     pub(super) rsc: &'a mut dyn UiRsc,
 
-    /// This widget's box, in the coordinates of `move_idx`.
     pub(super) region: UiRegion,
     pub(super) mask: MaskIdx,
     pub(super) textures: Vec<TextureHandle>,
     pub(super) primitives: Vec<PrimitiveHandle>,
     pub(super) children: Vec<WidgetId>,
-    /// The children whose size this widget read while drawing.
-    pub(super) size_deps: Vec<WidgetId>,
-    /// Offered pixel axes which can affect the size this draw reports.
-    pub(super) size_box_inputs: [bool; 2],
-    pub(super) size_output_inputs: [bool; 2],
-    pub(super) reads_output: [bool; 2],
-    /// The slot this widget's primitives are positioned through: its own if
-    /// its parent placed it, otherwise the nearest ancestor that has one.
-    pub(super) move_idx: MoveIdx,
     pub layer: usize,
     pub(super) id: WidgetId,
 }
@@ -42,8 +30,6 @@ impl<'a> Painter<'a> {
 
     /// Takes the kind, for a caller writing many of one primitive.
     fn write<P: Primitive>(&mut self, kind: PrimitiveKind<P>, primitive: P, region: UiRegion) {
-        #[cfg(feature = "layout-diagnostics")]
-        diag::bump(Counter::PrimitiveWrites);
         let h = self.state.layers.write(
             self.layer,
             PrimitiveInst {
@@ -52,7 +38,6 @@ impl<'a> Painter<'a> {
                 primitive,
                 region,
                 mask_idx: self.mask,
-                move_idx: self.move_idx,
             },
         );
         self.push_primitive(h);
@@ -79,159 +64,31 @@ impl<'a> Painter<'a> {
 
     pub fn set_mask(&mut self, region: UiRegion) {
         assert!(self.mask == MaskIdx::NONE);
-        self.mask = self.rsc.ui_mut().masks.push(Mask {
+        self.mask = self.rsc.ui_mut().masks.push(Mask { region });
-            region,
-            move_idx: self.move_idx,
-        });
     }
 
     /// Draws a widget within this widget's region.
-    pub fn widget<'s, W: ?Sized>(&'s mut self, id: &'s StrongWidget<W>) -> DrawResult<'s, 'a, W> {
+    pub fn widget<W: ?Sized>(&mut self, id: &StrongWidget<W>) {
-        self.widget_at(id, self.region, false)
+        self.widget_at(id, self.region);
     }
 
     /// Draws a widget somewhere within this one.
-    pub fn widget_within<'s, W: ?Sized>(
+    /// Useful for drawing child widgets in select areas.
-        &'s mut self,
+    pub fn widget_within<W: ?Sized>(&mut self, id: &StrongWidget<W>, region: UiRegion) {
-        id: &'s StrongWidget<W>,
+        self.widget_at(id, region.within(&self.region));
-        region: UiRegion,
-    ) -> DrawResult<'s, 'a, W> {
-        let region = region.within(&self.region);
-        self.widget_at(id, region, false)
     }
 
-    /// Draws a child this widget decides the box of, and may decide again
+    fn widget_at<W: ?Sized>(&mut self, id: &StrongWidget<W>, region: UiRegion) {
-    /// once it knows what the child came to. The child gets a slot of its
-    /// own, so placing it a second time writes one entry however much it
-    /// drew -- moved or resized alike, since everything under the slot is
-    /// held as a fraction of its box. A child drawn any other way has no slot
-    /// and can only be given a different box by drawing again.
-    pub fn place<'s, W: ?Sized>(
-        &'s mut self,
-        id: &'s StrongWidget<W>,
-        region: UiRegion,
-    ) -> DrawResult<'s, 'a, W> {
-        #[cfg(feature = "layout-diagnostics")]
-        diag::bump(Counter::PlaceCalls);
-        let region = region.within(&self.region);
-        #[cfg(feature = "layout-diagnostics")]
-        diag::placed(id.id(), self.id, region);
-        self.widget_at(id, region, true)
-    }
-
-    fn widget_at<'s, W: ?Sized>(
-        &'s mut self,
-        id: &'s StrongWidget<W>,
-        region: UiRegion,
-        slotted: bool,
-    ) -> DrawResult<'s, 'a, W> {
-        // A child listed twice would be moved twice.
-        if !self.children.contains(&id.id()) {
         self.children.push(id.id());
-        }
+        self.state.draw_inner(
-        let size = self.state.draw_inner(
             self.layer,
             id.id(),
             region,
             Some(self.id),
-            self.move_idx,
-            slotted,
             self.mask,
             None,
             self.rsc,
         );
-        DrawResult {
-            child: id,
-            painter: self,
-            size,
-        }
-    }
-
-    /// What a child says its length is without being drawn, if it can say.
-    /// Asking counts as reading its size.
-    pub fn size_hint<W: ?Sized>(&mut self, id: &StrongWidget<W>, axis: Axis) -> Option<Len> {
-        let hint = self
-            .rsc
-            .widgets()
-            .get_dyn(id.id())
-            .and_then(|widget| widget.size_hint(axis));
-        #[cfg(feature = "layout-diagnostics")]
-        diag::hint_read(id.id(), self.id, axis, hint);
-        match hint {
-            Some(hint) => {
-                #[cfg(feature = "layout-diagnostics")]
-                diag::bump(Counter::HintHits);
-                self.depend_on_size(id, false);
-                Some(hint)
-            }
-            None => {
-                #[cfg(feature = "layout-diagnostics")]
-                diag::bump(Counter::HintMisses);
-                None
-            }
-        }
-    }
-
-    /// A retained child length valid under the region it is about to be
-    /// offered. Unlike a hint, this is contextual: it is kept only when none
-    /// of the offered pixel axes which produced it changed.
-    pub fn known_len<W: ?Sized>(
-        &mut self,
-        child: &StrongWidget<W>,
-        axis: Axis,
-        region: UiRegion,
-    ) -> Option<Len> {
-        if let Some(hint) = self.size_hint(child, axis) {
-            return Some(hint);
-        }
-        self.retained_size(child, region)
-            .map(|size| size.axis(axis))
-    }
-
-    fn retained_size<W: ?Sized>(
-        &mut self,
-        child: &StrongWidget<W>,
-        region: UiRegion,
-    ) -> Option<Size> {
-        let region = region.within(&self.region);
-        let (size, box_inputs, output_inputs) =
-            self.state
-                .retained_size(child.id(), region, self.move_idx, self.rsc.widgets())?;
-        #[cfg(feature = "layout-diagnostics")]
-        diag::bump(Counter::RetainedSizeHits);
-        self.depend_on_size_inputs(child, box_inputs, output_inputs);
-        Some(size)
-    }
-
-    fn depend_on_size<W: ?Sized>(&mut self, child: &StrongWidget<W>, inherit_inputs: bool) {
-        let (box_inputs, output_inputs) = match inherit_inputs {
-            true => self
-                .state
-                .active
-                .get(&child.id())
-                .map_or(([false; 2], [false; 2]), |active| {
-                    (active.size_box_inputs, active.size_output_inputs)
-                }),
-            false => ([false; 2], [false; 2]),
-        };
-        self.depend_on_size_inputs(child, box_inputs, output_inputs);
-    }
-
-    fn depend_on_size_inputs<W: ?Sized>(
-        &mut self,
-        child: &StrongWidget<W>,
-        box_inputs: [bool; 2],
-        output_inputs: [bool; 2],
-    ) {
-        if !self.size_deps.contains(&child.id()) {
-            self.size_deps.push(child.id());
-        }
-        for (own, child) in self.size_box_inputs.iter_mut().zip(box_inputs) {
-            *own |= child;
-        }
-        for (own, child) in self.size_output_inputs.iter_mut().zip(output_inputs) {
-            *own |= child;
-        }
     }
 
     pub fn render_text(
@@ -240,8 +97,6 @@ impl<'a> Painter<'a> {
         attrs: &TextAttrs,
         width: Option<f32>,
     ) -> RenderedText {
-        #[cfg(feature = "layout-diagnostics")]
-        diag::render_text(self.id, self.rsc.widgets().label(self.id), width);
         let ui = self.rsc.ui_mut();
         ui.text.render(buffer, attrs, width)
     }
@@ -270,48 +125,27 @@ impl<'a> Painter<'a> {
         }
     }
 
-    /// This widget's box, in the coordinates its own primitives are written
-    /// in -- so a region composed `within` it may be drawn directly.
     pub fn region(&self) -> UiRegion {
         self.region
     }
 
-    /// The output's size in pixels. A widget that reads it draws again when
+    pub fn size<W: ?Sized + Widget>(&mut self, id: &StrongWidget<W>) -> Size {
-    /// the output changes, since nothing else can put that right.
+        self.size_ctx().size(id)
-    pub fn output_size(&mut self) -> Vec2 {
+    }
-        self.reads_output = [true; 2];
+
-        self.size_output_inputs = [true; 2];
+    pub fn len_axis<W: ?Sized + Widget>(&mut self, id: &StrongWidget<W>, axis: Axis) -> Len {
+        match axis {
+            Axis::X => self.size_ctx().width(id),
+            Axis::Y => self.size_ctx().height(id),
+        }
+    }
+
+    pub fn output_size(&self) -> Vec2 {
         self.state.output_size
     }
 
-    /// One axis of the output in pixels. Prefer this to [`Self::output_size`]
-    /// when the other axis cannot affect the size this widget reports.
-    pub fn output_len(&mut self, axis: Axis) -> f32 {
-        self.reads_output[axis as usize] = true;
-        self.size_output_inputs[axis as usize] = true;
-        self.state.output_size.axis(axis)
-    }
-
-    /// This widget's box in pixels. Resolved against the output's size and
-    /// the boxes it sits within, so a widget that reads it draws again when
-    /// the output changes.
     pub fn px_size(&mut self) -> Vec2 {
-        self.reads_output = [true; 2];
+        self.region.size().to_abs(self.state.output_size)
-        self.size_box_inputs = [true; 2];
-        let region = self.state.moves.resolve(self.move_idx, self.region);
-        region.size().to_abs(self.state.output_size)
-    }
-
-    /// One axis of this widget's box in pixels. Prefer this to
-    /// [`Self::px_size`] when the other axis cannot affect the reported size.
-    pub fn px_len(&mut self, axis: Axis) -> f32 {
-        self.reads_output[axis as usize] = true;
-        self.size_box_inputs[axis as usize] = true;
-        let region = self.state.moves.resolve(self.move_idx, self.region);
-        region
-            .size()
-            .axis(axis)
-            .to_abs(self.state.output_size.axis(axis))
     }
 
     pub fn text_data(&mut self) -> &mut TextData {
@@ -333,30 +167,9 @@ impl<'a> Painter<'a> {
     pub fn id(&self) -> &WidgetId {
         &self.id
     }
-}
 
-/// A child that has just been drawn. Reading its size records that this
+    pub fn size_ctx(&mut self) -> SizeCtx<'_> {
-/// widget's own size depends on it; dropping it without reading draws the
+        self.state.size_ctx(self.id, self.region.size(), self.rsc)
-/// child and leaves the parent independent of what it came to.
-pub struct DrawResult<'p, 'a, W: ?Sized> {
-    painter: &'p mut Painter<'a>,
-    child: &'p StrongWidget<W>,
-    size: Size,
-}
-
-impl<W: ?Sized> DrawResult<'_, '_, W> {
-    pub fn size(self) -> Size {
-        #[cfg(feature = "layout-diagnostics")]
-        {
-            diag::bump(Counter::SizeReads);
-            diag::size_read(self.child.id(), self.painter.id, self.size);
-        }
-        self.painter.depend_on_size(self.child, true);
-        self.size
-    }
-
-    pub fn len(self, axis: Axis) -> Len {
-        self.size().axis(axis)
     }
 }
 

core/src/ui/render_state.rs

@@ -1,37 +1,19 @@
-#[cfg(feature = "layout-diagnostics")]
-use crate::layout_diagnostics::{self as diag, Counter, ReuseOutcome, TimerKind};
 use crate::{
-    ActiveData, Axis, DrawLayers, IdLike, MaskIdx, MoveIdx, Moves, OnResize, Painter, PixelRegion,
+    ActiveData, Axis, DrawLayers, IdLike, MaskIdx, Painter, PixelRegion, SizeCtx, StrongWidget,
-    Size, StrongWidget, UiRegion, UiRsc, WidgetId, Widgets,
+    UiRegion, UiRsc, UiVec2, WidgetId, Widgets,
-    util::{HashMap, HashSet, Vec2},
+    ui::cache::Cache,
+    util::{HashMap, HashSet, Vec2, forget_ref},
 };
 
-const AXES: [Axis; 2] = [Axis::X, Axis::Y];
-const LAYOUT_EPSILON_PX: f32 = 0.05;
-
-fn pixel_len_changed(old: f32, new: f32) -> bool {
-    (old - new).abs() > LAYOUT_EPSILON_PX
-}
-
 pub struct UiRenderState {
     pub active: HashMap<WidgetId, ActiveData>,
     pub layers: DrawLayers,
     pub(super) output_size: Vec2,
+    pub cache: Cache,
 
     old_root: Option<WidgetId>,
-    resized: [bool; 2],
+    resized: bool,
-    /// Content/state dirtiness whose retained size cannot answer a layout
-    /// question until that widget has drawn again.
-    invalid_sizes: HashSet<WidgetId>,
-    /// Marks introduced only to traverse resize dependency paths. Unlike
-    /// content dirtiness, these may retain an answer whose observed pixel
-    /// axes did not change.
-    resize_marks: HashSet<WidgetId>,
     draw_started: HashSet<WidgetId>,
-    /// A widget's move slot, which outlives any one `ActiveData`: a redraw
-    /// replaces that while its children go on pointing at the slot.
-    slots: HashMap<WidgetId, MoveIdx>,
-    pub moves: Moves,
 }
 
 impl UiRenderState {
@@ -39,23 +21,17 @@ impl UiRenderState {
         Self {
             active: Default::default(),
             layers: Default::default(),
+            cache: Default::default(),
             output_size: Vec2::ZERO,
             old_root: None,
-            resized: [false; 2],
+            resized: false,
-            invalid_sizes: Default::default(),
-            resize_marks: Default::default(),
             draw_started: Default::default(),
-            slots: Default::default(),
-            moves: Default::default(),
         }
     }
 
     pub fn resize(&mut self, size: impl Into<Vec2>) {
-        let size = size.into();
+        self.output_size = size.into();
-        for (axis, resized) in AXES.into_iter().zip(self.resized.iter_mut()) {
+        self.resized = true;
-            *resized |= size.axis(axis) != self.output_size.axis(axis);
-        }
-        self.output_size = size;
     }
 
     pub fn output_size(&self) -> Vec2 {
@@ -63,14 +39,6 @@ impl UiRenderState {
     }
 
     pub fn update<'a>(&mut self, root: impl Into<Option<&'a StrongWidget>>, rsc: &mut dyn UiRsc) {
-        #[cfg(feature = "layout-diagnostics")]
-        diag::bump(Counter::Updates);
-        #[cfg(feature = "layout-diagnostics")]
-        let _update = diag::timer(TimerKind::Update);
-        self.invalid_sizes.clear();
-        self.invalid_sizes
-            .extend(rsc.widgets().needs_redraw.iter().copied());
-        self.resize_marks.clear();
         // safety mechanism for memory leaks; might wanna return a result instead so user can
         // decide whether to panic or not
         if !rsc.widgets().waiting.is_empty() {
@@ -88,75 +56,20 @@ impl UiRenderState {
             );
         }
         let root = root.into();
-        if self.root_changed(root) {
+        if self.needs_full_redraw(root) {
             self.redraw_all(root, rsc);
             self.old_root = root.map(|r| r.id());
-        } else if self.resized.iter().any(|&resized| resized) {
+            self.resized = false;
-            // A region is a fraction of the output plus an offset, resolved
+        } else if rsc.widgets().has_updates() {
-            // against the window in the shader, so a resize moves the whole
-            // drawing on its own. Only a widget that read pixels can be wrong.
-            {
-                #[cfg(feature = "layout-diagnostics")]
-                let _marking = diag::timer(TimerKind::ResizeMarking);
-                let dependents: Vec<_> = self
-                    .active
-                    .iter()
-                    .filter_map(|(&id, active)| {
-                        AXES.into_iter()
-                            .zip(self.resized)
-                            .any(|(axis, changed)| {
-                                changed
-                                    && active.reads_output[axis as usize]
-                                    && pixel_len_changed(
-                                        active.output_px.axis(axis),
-                                        self.output_size.axis(axis),
-                                    )
-                            })
-                            .then_some(id)
-                    })
-                    .collect();
-                for id in dependents {
-                    #[cfg(feature = "layout-diagnostics")]
-                    diag::bump(Counter::ResizeDependents);
-                    rsc.widgets_mut().needs_redraw.insert(id);
-                    if let Some(top) = self.mark_readers(id, rsc) {
-                        rsc.widgets_mut().needs_redraw.insert(top);
-                    }
-                }
-                self.resize_marks.extend(
-                    rsc.widgets()
-                        .needs_redraw
-                        .iter()
-                        .filter(|id| !self.invalid_sizes.contains(id))
-                        .copied(),
-                );
-            }
-        }
-        if rsc.widgets().has_updates() {
             self.redraw_updates(rsc);
         }
-        self.resized = [false; 2];
-        self.invalid_sizes.clear();
-        self.resize_marks.clear();
     }
 
     fn redraw_all(&mut self, root: Option<&StrongWidget>, rsc: &mut dyn UiRsc) {
-        #[cfg(feature = "layout-diagnostics")]
-        let _layout = diag::timer(TimerKind::FullLayout);
         self.clear(rsc);
         // free all resources & cache
         if let Some(id) = root {
-            self.draw_inner(
+            self.draw_inner(0, id.id(), UiRegion::FULL, None, MaskIdx::NONE, None, rsc);
-                0,
-                id.id(),
-                UiRegion::FULL,
-                None,
-                MoveIdx::NONE,
-                false,
-                MaskIdx::NONE,
-                None,
-                rsc,
-            );
         }
     }
 
@@ -168,21 +81,22 @@ impl UiRenderState {
         id: WidgetId,
         region: UiRegion,
         parent: Option<WidgetId>,
-        parent_move: MoveIdx,
-        slotted: bool,
         mask: MaskIdx,
         old_children: Option<Vec<WidgetId>>,
         rsc: &mut dyn UiRsc,
-    ) -> Size {
+    ) {
-        #[cfg(feature = "layout-diagnostics")]
-        {
-            diag::bump(Counter::DrawRequests);
-            diag::draw_request(id, parent, region, self.px_of(parent_move, region), slotted);
-        }
         let mut old_children = old_children.unwrap_or_default();
-        if self.active.contains_key(&id) {
+        if let Some(active) = self.active.get_mut(&id)
-            if let Some(size) = self.try_reuse(id, region, parent_move, rsc) {
+            && !rsc.widgets().needs_redraw.contains(&id)
-                return size;
+        {
+            // check to see if we can skip drawing first
+            if active.region == region {
+                return;
+            } else if active.region.size() == region.size() {
+                // TODO: epsilon?
+                let from = active.region;
+                self.mov(id, from, region);
+                return;
             }
             // if not, then maintain resize and track old children to remove unneeded
             let active = self.remove(id, false, rsc).unwrap();
@@ -190,90 +104,48 @@ impl UiRenderState {
         }
 
         // draw widget
-        let (move_idx, local) = match slotted {
-            // Its box becomes its slot's, so it draws in the slot's own
-            // coordinates and the box it was given is one entry to rewrite.
-            true => (self.move_slot(id, parent_move, region), UiRegion::FULL),
-            false => {
-                self.drop_slot(id);
-                (parent_move, region)
-            }
-        };
-        let px = self.px_of(move_idx, local);
-        rsc.widgets_mut().needs_redraw.remove(&id);
         self.draw_started.insert(id);
 
         let mut painter = Painter {
             state: self,
-            region: local,
+            region,
             mask,
             layer,
             id,
             textures: Vec::new(),
             primitives: Vec::new(),
             children: Vec::new(),
-            size_deps: Vec::new(),
-            size_box_inputs: [false; 2],
-            size_output_inputs: [false; 2],
-            reads_output: [false; 2],
-            move_idx,
             rsc,
         };
 
-        #[cfg(feature = "layout-diagnostics")]
-        {
-            diag::bump(Counter::WidgetDraws);
-            diag::draw_widget(id, painter.rsc.widgets().label(id));
-        }
         let mut widget = painter.rsc.widgets().get_dyn_dynamic(id);
-        let size = widget.draw(&mut painter);
+        widget.draw(&mut painter);
         drop(widget);
-        #[cfg(feature = "layout-diagnostics")]
-        diag::size_reported(id, size);
 
         let Painter {
             state: _,
             rsc: _,
-            region: _,
+            region,
             mask,
             textures,
             primitives,
             children,
-            size_deps,
-            size_box_inputs,
-            size_output_inputs,
-            reads_output,
-            move_idx,
             layer,
             id,
         } = painter;
 
-        debug_assert!(
-            Self::hints_agree(id, size, rsc),
-            "'{}' ({id:?}) drew a size its size_hint disagrees with",
-            rsc.widgets().label(id)
-        );
-
         // add to active
         let active = ActiveData {
             id,
             region,
-            size,
-            px,
             parent,
             textures,
             primitives,
             children,
-            size_deps,
-            size_box_inputs,
-            size_output_inputs,
-            output_px: self.output_size,
-            reads_output,
-            move_idx,
-            parent_move,
             mask,
             layer,
         };
+
         // remove old children that weren't kept
         for c in &old_children {
             if !active.children.contains(c) {
@@ -283,253 +155,20 @@ impl UiRenderState {
 
         rsc.on_draw(&active);
         self.active.insert(id, active);
-        self.invalid_sizes.remove(&id);
-        self.resize_marks.remove(&id);
-        size
     }
 
-    /// The slot a widget's box is held in, made on its first placed draw and
+    fn mov(&mut self, id: WidgetId, from: UiRegion, to: UiRegion) {
-    /// kept until it stops being drawn -- a redraw replaces its `ActiveData`
-    /// while descendants go on naming the slot.
-    fn move_slot(&mut self, id: WidgetId, parent: MoveIdx, region: UiRegion) -> MoveIdx {
-        if let Some(&idx) = self.slots.get(&id) {
-            self.moves.set_parent(idx, parent);
-            self.moves.set(idx, region);
-            return idx;
-        }
-        let idx = self.moves.push(parent, region);
-        self.slots.insert(id, idx);
-        idx
-    }
-
-    /// Gives up a slot a widget no longer needs, because it is drawn somewhere
-    /// that does not place it. Its descendants name it, so this is only
-    /// reached where they are about to be drawn again.
-    fn drop_slot(&mut self, id: WidgetId) {
-        if let Some(idx) = self.slots.remove(&id) {
-            self.moves.remove(idx);
-        }
-    }
-
-    /// The pixel size of a region held in `slot`'s coordinates.
-    fn px_of(&self, slot: MoveIdx, region: UiRegion) -> Vec2 {
-        self.moves
-            .resolve(slot, region)
-            .size()
-            .to_abs(self.output_size)
-    }
-
-    /// A clean widget's retained size, when the offered pixel axes which
-    /// produced that answer are unchanged. This observes the old answer only;
-    /// it does not move or otherwise reuse the widget's drawing.
-    pub(super) fn retained_size(
-        &self,
-        id: WidgetId,
-        region: UiRegion,
-        parent_move: MoveIdx,
-        widgets: &Widgets,
-    ) -> Option<(Size, [bool; 2], [bool; 2])> {
-        if self.size_is_invalid(id, widgets) || self.dirty_size_under(id, widgets) {
-            return None;
-        }
-        let active = self.active.get(&id)?;
-        if active.parent_move != parent_move {
-            return None;
-        }
-        let px = self.px_of(parent_move, region);
-        let valid_box = AXES
-            .into_iter()
-            .zip(active.size_box_inputs)
-            .all(|(axis, depends)| {
-                !depends || !pixel_len_changed(active.px.axis(axis), px.axis(axis))
-            });
-        let valid_output =
-            AXES.into_iter()
-                .zip(active.size_output_inputs)
-                .all(|(axis, depends)| {
-                    !depends
-                        || !pixel_len_changed(
-                            active.output_px.axis(axis),
-                            self.output_size.axis(axis),
-                        )
-                });
-        (valid_box && valid_output).then_some((
-            active.size,
-            active.size_box_inputs,
-            active.size_output_inputs,
-        ))
-    }
-
-    fn size_is_invalid(&self, id: WidgetId, widgets: &Widgets) -> bool {
-        self.invalid_sizes.contains(&id)
-            || (widgets.needs_redraw.contains(&id) && !self.resize_marks.contains(&id))
-    }
-
-    fn dirty_size_under(&self, id: WidgetId, widgets: &Widgets) -> bool {
-        self.active.get(&id).is_some_and(|active| {
-            active.size_deps.iter().any(|child| {
-                self.size_is_invalid(*child, widgets) || self.dirty_size_under(*child, widgets)
-            })
-        })
-    }
-
-    /// The drawing a widget already has, kept for a new box if the box has not
-    /// changed in a way it depends on.
-    fn try_reuse(
-        &mut self,
-        id: WidgetId,
-        region: UiRegion,
-        parent_move: MoveIdx,
-        rsc: &mut dyn UiRsc,
-    ) -> Option<Size> {
-        #[cfg(feature = "layout-diagnostics")]
-        diag::bump(Counter::ReuseAttempts);
-        if rsc.widgets().needs_redraw.contains(&id) {
-            #[cfg(feature = "layout-diagnostics")]
-            {
-                diag::bump(Counter::ReuseDirty);
-                diag::reuse(id, ReuseOutcome::Dirty);
-            }
-            return None;
-        }
-        let active = self.active.get(&id)?;
-        // Drawn somewhere else in the tree: its box is in coordinates it no
-        // longer sits in, and its slot names the wrong parent.
-        if active.parent_move != parent_move {
-            #[cfg(feature = "layout-diagnostics")]
-            {
-                diag::bump(Counter::ReuseWrongParent);
-                diag::reuse(id, ReuseOutcome::WrongParent);
-            }
-            return None;
-        }
-        let (size, old_region, slot, old_px) =
-            (active.size, active.region, active.move_idx, active.px);
-        // In pixels, because `region` is a fraction of a slot's box and that
-        // box may be what changed -- an unchanged fraction of a box half the
-        // size is half the widget.
-        let px = self.px_of(parent_move, region);
-        let mut changed = [false; 2];
-        for (axis, c) in AXES.into_iter().zip(changed.iter_mut()) {
-            *c = pixel_len_changed(old_px.axis(axis), px.axis(axis));
-        }
-        if !changed.iter().any(|&c| c) && old_region == region {
-            #[cfg(feature = "layout-diagnostics")]
-            {
-                diag::bump(Counter::ReuseExact);
-                diag::reuse(id, ReuseOutcome::Exact);
-            }
-            return Some(size);
-        }
-        // Only a placed widget can be given a different box without drawing
-        // again: everything it drew is a fraction of its slot's box, so one
-        // entry says where all of it went.
-        if slot == parent_move {
-            #[cfg(feature = "layout-diagnostics")]
-            {
-                diag::bump(Counter::ReuseUnslotted);
-                diag::reuse(id, ReuseOutcome::Unslotted);
-            }
-            return None;
-        }
-        if changed.iter().any(|&c| c) {
-            let widget = rsc.widgets().get_dyn(id)?;
-            let redraws = AXES
-                .into_iter()
-                .zip(changed)
-                .any(|(axis, c)| c && widget.on_resize(axis) != OnResize::Scale);
-            // Anything under it that has to be drawn again is drawn by drawing
-            // this, because whatever reads that widget's size sits in between
-            // and has to lay out around what it comes to.
-            if redraws {
-                #[cfg(feature = "layout-diagnostics")]
-                {
-                    diag::bump(Counter::ReuseOwnResize);
-                    diag::reuse(id, ReuseOutcome::OwnResize);
-                }
-                return None;
-            }
-            if self.redraws_under(id, changed, rsc) {
-                #[cfg(feature = "layout-diagnostics")]
-                {
-                    diag::bump(Counter::ReuseDescendantResize);
-                    diag::reuse(id, ReuseOutcome::DescendantResize);
-                }
-                return None;
-            }
-        }
-        self.moves.set(slot, region);
         let active = self.active.get_mut(&id).unwrap();
-        active.region = region;
+        for h in &active.primitives {
-        #[cfg(feature = "layout-diagnostics")]
+            let region = self.layers[h.layer].region_mut(h);
-        {
+            *region = region.outside(&from).within(&to);
-            diag::bump(Counter::ReuseMoved);
-            diag::reuse(id, ReuseOutcome::Moved);
         }
-        Some(size)
+        active.region = active.region.outside(&from).within(&to);
+        // SAFETY: children cannot be recursive
+        let children = unsafe { forget_ref(&active.children) };
+        for child in children {
+            self.mov(*child, from, to);
         }
-
-    /// Whether anything under `id` would have to be drawn again for the box
-    /// it is a fraction of changing length, `changed` saying which axes of
-    /// that box did.
-    ///
-    /// A part of a box with no relative extent on an axis is a fixed length,
-    /// held as offsets from that box's start, and composing anything into it
-    /// leaves no relative extent either. So a widget whose own box did not
-    /// change length has no descendant whose box did, and the walk stops
-    /// there -- an 80-wide child of a widened row is not asked at all.
-    fn redraws_under(&self, id: WidgetId, changed: [bool; 2], rsc: &dyn UiRsc) -> bool {
-        #[cfg(feature = "layout-diagnostics")]
-        diag::bump(Counter::ResizeChecks);
-        let Some(active) = self.active.get(&id) else {
-            return false;
-        };
-        let size_deps = &active.size_deps;
-        active.children.iter().any(|&child| {
-            #[cfg(feature = "layout-diagnostics")]
-            diag::bump(Counter::ResizeCheckChildren);
-            let Some(data) = self.active.get(&child) else {
-                return false;
-            };
-            let Some(widget) = rsc.widgets().get_dyn(child) else {
-                return true;
-            };
-            // What it drew to learn this child's size was the child in *this*
-            // box, so a different box is a different answer -- unless the
-            // child gave an exact one without being drawn at all.
-            if size_deps.contains(&child) {
-                let measured = AXES
-                    .into_iter()
-                    .zip(changed)
-                    .any(|(axis, c)| c && widget.size_hint(axis).is_none());
-                if measured {
-                    return true;
-                }
-            }
-            let mut own = changed;
-            for (axis, c) in AXES.into_iter().zip(own.iter_mut()) {
-                *c &= data.region.axis(axis).len().rel != 0.0;
-            }
-            if !own.iter().any(|&c| c) {
-                return false;
-            }
-            let redraws = AXES
-                .into_iter()
-                .zip(own)
-                .any(|(axis, c)| c && widget.on_resize(axis) != OnResize::Scale);
-            redraws || self.redraws_under(child, own, rsc)
-        })
-    }
-
-    fn hints_agree(id: WidgetId, size: Size, rsc: &dyn UiRsc) -> bool {
-        let Some(widget) = rsc.widgets().get_dyn(id) else {
-            return true;
-        };
-        AXES.into_iter().all(|axis| {
-            widget
-                .size_hint(axis)
-                .is_none_or(|hint| hint == size.axis(axis))
-        })
     }
 
     /// NOTE: instance textures are cleared and self.textures freed
@@ -552,16 +191,13 @@ impl UiRenderState {
     }
 
     fn remove_rec(&mut self, id: WidgetId, rsc: &mut dyn UiRsc) -> Option<ActiveData> {
+        self.cache.remove(id);
         let inst = self.remove(id, true, rsc);
         if let Some(inst) = &inst {
             for c in &inst.children {
                 self.remove_rec(*c, rsc);
             }
         }
-        // After the descendants, whose slots name this one as their parent.
-        if let Some(idx) = self.slots.remove(&id) {
-            self.moves.remove(idx);
-        }
         inst
     }
 
@@ -569,61 +205,34 @@ impl UiRenderState {
         for (_, active) in self.active.drain() {
             rsc.on_undraw(&active);
         }
-        self.slots.clear();
+        self.cache.clear();
-        self.moves.clear();
         self.layers.clear();
-        self.invalid_sizes.clear();
-        self.resize_marks.clear();
         rsc.widgets_mut().needs_redraw.clear();
         rsc.free();
     }
 
     pub fn redraw_updates(&mut self, rsc: &mut dyn UiRsc) {
-        #[cfg(feature = "layout-diagnostics")]
+        while let Some(&id) = rsc.widgets().needs_redraw.iter().next() {
-        let _layout = diag::timer(TimerKind::IncrementalLayout);
-        // A reader's answer is only valid after every dirty size it reads has
-        // settled. Equal-depth widgets are independent, so their order does
-        // not matter. Resize dirtiness already marks whole reader chains, so
-        // choosing their shallowest roots coalesces descendants that share a
-        // reader and gives each changing box its final constraints first.
-        while let Some(id) = {
-            let dirty = rsc.widgets().needs_redraw.iter().copied();
-            match self.resized.iter().any(|&resized| resized) {
-                true => dirty.min_by_key(|&id| self.depth(id)),
-                false => dirty.max_by_key(|&id| self.depth(id)),
-            }
-        } {
-            #[cfg(feature = "layout-diagnostics")]
-            diag::bump(Counter::QueuePops);
             self.redraw(id, rsc);
         }
         rsc.free();
     }
 
-    fn depth(&self, id: WidgetId) -> usize {
-        let mut depth = 0;
-        let mut at = Some(id);
-        while let Some(id) = at {
-            #[cfg(feature = "layout-diagnostics")]
-            diag::bump(Counter::DepthSteps);
-            at = self.active.get(&id).and_then(|active| active.parent);
-            depth += 1;
-        }
-        depth
-    }
-
     pub fn root_changed<'a>(&self, root: impl Into<Option<&'a StrongWidget>>) -> bool {
         root.into().map(|r| r.id()) != self.old_root
     }
 
+    // Scheduling and drawing must use the same full-redraw predicate.
+    fn needs_full_redraw<'a>(&self, root: impl Into<Option<&'a StrongWidget>>) -> bool {
+        self.root_changed(root) || self.resized
+    }
+
     pub fn needs_redraw<'a>(
         &self,
         root: impl Into<Option<&'a StrongWidget>>,
         widgets: &Widgets,
     ) -> bool {
-        self.root_changed(root)
+        self.needs_full_redraw(root) || widgets.has_updates()
-            || self.resized.iter().any(|&resized| resized)
-            || widgets.has_updates()
     }
 
     pub fn active_widgets(&self) -> usize {
@@ -649,40 +258,29 @@ impl UiRenderState {
         }
     }
 
-    /// Where a widget is on screen: its box composed through the boxes it
-    /// sits within, which is the walk the vertex shader does.
     pub fn window_region(&self, id: &impl IdLike) -> Option<PixelRegion> {
-        let active = self.active.get(&id.id())?;
+        let region = self.active.get(&id.id())?.region;
-        let region = self.moves.resolve(active.parent_move, active.region);
         Some(region.to_px(self.output_size))
     }
 
     /// redraws a widget that's currently active (drawn)
     pub fn redraw(&mut self, id: WidgetId, rsc: &mut dyn UiRsc) {
+        rsc.widgets_mut().needs_redraw.remove(&id);
         self.draw_started.remove(&id);
-        if rsc.widgets().needs_redraw.contains(&id) && !self.resize_marks.contains(&id) {
+        // check if parent depends on the desired size of this, if so then redraw it first
-            self.invalid_sizes.insert(id);
+        for axis in [Axis::X, Axis::Y] {
-        }
+            if let Some(&(outer, old)) = self.cache.size.axis_dyn(axis).get(&id)
-        // A widget can only answer whether its size changed by drawing in the
+                && let Some(current) = self.active.get(&id)
-        // box its parent chose. If that box changed in pixels, its retained
+                && let Some(pid) = current.parent
-        // placement is stale and the highest size reader must choose the new
-        // box first. Otherwise the widget can draw locally, and its readers
-        // only matter if the returned size actually changed.
-        let box_changed = self.active.get(&id).is_some_and(|active| {
-            let px = self.px_of(active.parent_move, active.region);
-            AXES.into_iter()
-                .any(|axis| pixel_len_changed(active.px.axis(axis), px.axis(axis)))
-        });
-        if (self.resized.iter().any(|&resized| resized) || box_changed)
-            && let Some(top) = self.mark_readers(id, rsc)
             {
-            #[cfg(feature = "layout-diagnostics")]
+                self.cache.size.axis_dyn(axis).remove(&id);
-            diag::bump(Counter::EagerReaderRedraws);
+                let new = self.size_ctx(id, outer, rsc).len_axis(id, axis);
-            self.redraw(top, rsc);
+                self.cache.size.axis_dyn(axis).insert(id, (outer, new));
-            rsc.widgets_mut().needs_redraw.remove(&id);
+                if new != old {
-            return;
+                    self.redraw(pid, rsc);
+                }
+            }
         }
-        rsc.widgets_mut().needs_redraw.remove(&id);
 
         if self.draw_started.contains(&id) {
             return;
@@ -691,58 +289,34 @@ impl UiRenderState {
         let Some(active) = self.remove(id, false, rsc) else {
             return;
         };
-        #[cfg(feature = "layout-diagnostics")]
-        diag::bump(Counter::LocalRedraws);
 
-        let old_size = active.size;
+        self.draw_inner(
-        let size = self.draw_inner(
             active.layer,
             id,
             active.region,
             active.parent,
-            active.parent_move,
-            active.move_idx != active.parent_move,
             active.mask,
             Some(active.children),
             rsc,
         );
-
-        if size != old_size {
-            #[cfg(feature = "layout-diagnostics")]
-            diag::bump(Counter::SizeChanges);
-            if let Some(parent) = self.active.get(&id).and_then(|active| active.parent)
-                && self
-                    .active
-                    .get(&parent)
-                    .is_some_and(|active| active.size_deps.contains(&id))
-            {
-                // Propagate one dependency edge at a time. If drawing the reader
-                // does not change its own size, nothing above it can observe this.
-                rsc.widgets_mut().needs_redraw.insert(parent);
-                self.invalid_sizes.insert(parent);
-                #[cfg(feature = "layout-diagnostics")]
-                diag::bump(Counter::ReaderEdges);
-            }
-        }
     }
 
-    /// The furthest ancestor that read this widget's size, directly or through
+    pub(super) fn size_ctx<'b>(
-    /// widgets that did the same, marking everything below it on the way.
+        &'b mut self,
-    fn mark_readers(&self, id: WidgetId, rsc: &mut dyn UiRsc) -> Option<WidgetId> {
+        source: WidgetId,
-        let mut top = None;
+        outer: UiVec2,
-        let mut at = id;
+        rsc: &'b mut dyn UiRsc,
-        while let Some(active) = self.active.get(&at)
+    ) -> SizeCtx<'b> {
-            && let Some(parent) = active.parent
+        let ui = rsc.ui_mut();
-            && self
+        SizeCtx {
-                .active
+            source,
-                .get(&parent)
+            cache: &mut self.cache,
-                .is_some_and(|p| p.size_deps.contains(&at))
+            text: &mut ui.text,
-        {
+            widgets: &ui.widgets,
-            rsc.widgets_mut().needs_redraw.insert(at);
+            outer,
-            top = Some(parent);
+            output_size: self.output_size,
-            at = parent;
+            id: source,
         }
-        top
     }
 }
 

core/src/ui/size.rs

@@ -0,0 +1,89 @@
+use crate::{
+    Axis, AxisT, IdLike, Len, RenderedText, Size, TextAttrs, TextBuffer, TextData, UiVec2,
+    WidgetAxisFns, WidgetId, Widgets, XAxis, YAxis, ui::cache::Cache, util::Vec2,
+};
+
+pub struct SizeCtx<'a> {
+    pub text: &'a mut TextData,
+    pub(super) source: WidgetId,
+    pub(super) widgets: &'a Widgets,
+    pub(super) cache: &'a mut Cache,
+    /// TODO: should this be pub? rn used for sized
+    pub outer: UiVec2,
+    pub(super) output_size: Vec2,
+    pub(super) id: WidgetId,
+}
+
+impl SizeCtx<'_> {
+    pub fn id(&self) -> &WidgetId {
+        &self.id
+    }
+
+    pub fn source(&self) -> &WidgetId {
+        &self.source
+    }
+
+    pub(super) fn len_inner<A: const AxisT>(&mut self, id: WidgetId) -> Len {
+        if let Some((_, len)) = self.cache.size.axis::<A>().get(&id) {
+            return *len;
+        }
+        let len = self
+            .widgets
+            .get_dyn_dynamic(id)
+            .desired_len::<A>(&mut SizeCtx {
+                text: self.text,
+                source: self.source,
+                widgets: self.widgets,
+                cache: self.cache,
+                outer: self.outer,
+                output_size: self.output_size,
+                id,
+            });
+        self.cache.size.axis::<A>().insert(id, (self.outer, len));
+        len
+    }
+
+    pub fn width(&mut self, id: impl IdLike) -> Len {
+        self.len_inner::<XAxis>(id.id())
+    }
+
+    pub fn height(&mut self, id: impl IdLike) -> Len {
+        self.len_inner::<YAxis>(id.id())
+    }
+
+    pub fn len_axis(&mut self, id: impl IdLike, axis: Axis) -> Len {
+        match axis {
+            Axis::X => self.width(id),
+            Axis::Y => self.height(id),
+        }
+    }
+
+    pub fn size(&mut self, id: impl IdLike) -> Size {
+        let id = id.id();
+        Size {
+            x: self.width(id),
+            y: self.height(id),
+        }
+    }
+
+    pub fn px_size(&mut self) -> Vec2 {
+        self.outer.to_abs(self.output_size)
+    }
+
+    pub fn output_size(&mut self) -> Vec2 {
+        self.output_size
+    }
+
+    pub fn draw_text(
+        &mut self,
+        buffer: &mut TextBuffer,
+        attrs: &TextAttrs,
+        width: Option<f32>,
+    ) -> RenderedText {
+        self.text.render(buffer, attrs, width)
+    }
+
+    pub fn label(&self, id: WidgetId) -> &String {
+        self.widgets.label(id)
+    }
+}

core/src/util/arena.rs

@@ -34,10 +34,6 @@ impl<T, I: IdNum> Arena<T, I> {
         self.tracker.free(id);
         self.data[i]
     }
-
-    pub fn get_mut(&mut self, id: Id<I>) -> &mut T {
-        &mut self.data[id.idx()]
-    }
 }
 
 impl<T, I: IdNum> Default for Arena<T, I> {

core/src/util/math.rs

@@ -1,13 +1,34 @@
+use std::ops::*;
+
 pub const trait LerpUtil {
     fn lerp(self, from: Self, to: Self) -> Self;
+    fn lerp_inv(self, from: Self, to: Self) -> Self;
 }
 
-const impl LerpUtil for f32 {
+pub const trait DivOr {
+    fn div_or(self, rhs: Self, other: Self) -> Self;
+}
+
+const impl DivOr for f32 {
+    fn div_or(self, rhs: Self, other: Self) -> Self {
+        let res = self / rhs;
+        if res.is_nan() { other } else { res }
+    }
+}
+
+const impl<
+    T: const Add<Output = T> + const Sub<Output = T> + const Mul<Output = T> + const DivOr + Copy,
+> LerpUtil for T
+{
     /// linear interpolation
     /// from * (1.0 - self) + to * self
     fn lerp(self, from: Self, to: Self) -> Self {
         from + (to - from) * self
     }
+    /// inverse of lerp
+    fn lerp_inv(self, from: Self, to: Self) -> Self {
+        (self - from).div_or(to - from, from)
+    }
 }
 
 macro_rules! impl_op {

core/src/util/trust.rs

@@ -1,3 +1,8 @@
+#[allow(clippy::missing_safety_doc)]
+pub(crate) unsafe fn forget_ref<'a, T>(x: &T) -> &'a T {
+    unsafe { std::mem::transmute::<&T, &T>(x) }
+}
+
 #[allow(clippy::missing_safety_doc)]
 pub(crate) unsafe fn forget_mut<'a, T>(x: &mut T) -> &'a mut T {
     unsafe { std::mem::transmute::<&mut T, &mut T>(x) }

core/src/util/vec2.rs

@@ -1,11 +1,7 @@
-use crate::util::impl_op;
+use crate::util::{DivOr, impl_op};
 use std::{hash::Hash, ops::*};
 
-/// `align(8)` because that is WGSL's alignment for a `vec2<f32>`, so any GPU
+#[repr(C)]
-/// struct holding one is laid out the way its shader reads it without having
-/// to say so itself. Those structs still need a manual `unsafe impl Pod`,
-/// since the trailing padding this introduces is what `derive(Pod)` refuses.
-#[repr(C, align(8))]
 #[derive(Clone, Copy, PartialEq, Default, bytemuck::Pod, bytemuck::Zeroable)]
 pub struct Vec2 {
     pub x: f32,
@@ -71,6 +67,15 @@ impl_op!(Vec2 Sub sub; x y);
 impl_op!(Vec2 Mul mul; x y);
 impl_op!(Vec2 Div div; x y);
 
+const impl DivOr for Vec2 {
+    fn div_or(self, rhs: Self, other: Self) -> Self {
+        Self {
+            x: self.x.div_or(rhs.x, other.x),
+            y: self.y.div_or(rhs.y, other.y),
+        }
+    }
+}
+
 impl Neg for Vec2 {
     type Output = Self;
 

core/src/widget/mod.rs

@@ -1,4 +1,4 @@
-use crate::{Axis, Len, Painter, Size};
+use crate::{Axis, AxisT, Len, Painter, SizeCtx};
 use std::any::Any;
 
 mod data;
@@ -15,45 +15,32 @@ pub use tag::*;
 pub use view::*;
 pub use widgets::*;
 
-/// What may be done to a widget's drawing when the box it was given changes
-/// on this axis, instead of drawing it again. Asked per axis, because wrapped
-/// text reads the width it is offered and not the height.
-#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
-pub enum OnResize {
-    Scale,
-    Translate,
-    #[default]
-    Redraw,
-}
-
 pub trait Widget: Any {
-    /// Draws the widget, and returns what it used of the box it was given.
+    fn draw(&mut self, painter: &mut Painter);
-    fn draw(&mut self, painter: &mut Painter) -> Size;
+    fn desired_width(&mut self, ctx: &mut SizeCtx) -> Len;
-
+    fn desired_height(&mut self, ctx: &mut SizeCtx) -> Len;
-    /// An exact length the widget can give without a painter or its children.
-    /// Optional, and saves a draw rather than changing one: a hint that
-    /// disagrees with the eventual draw fails a debug assertion.
-    fn size_hint(&self, _axis: Axis) -> Option<Len> {
-        None
 }
 
-    fn on_resize(&self, _axis: Axis) -> OnResize {
+pub trait WidgetAxisFns {
-        OnResize::default()
+    fn desired_len<A: AxisT>(&mut self, ctx: &mut SizeCtx) -> Len;
+}
+
+impl<W: Widget + ?Sized> WidgetAxisFns for W {
+    fn desired_len<A: AxisT>(&mut self, ctx: &mut SizeCtx) -> Len {
+        match A::get() {
+            Axis::X => self.desired_width(ctx),
+            Axis::Y => self.desired_height(ctx),
+        }
     }
 }
 
 impl Widget for () {
-    /// A gap: nothing drawn, at the default length, so a span gives it a share.
+    fn draw(&mut self, _: &mut Painter) {}
-    fn draw(&mut self, _: &mut Painter) -> Size {
+    fn desired_width(&mut self, _: &mut SizeCtx) -> Len {
-        Size::default()
+        Len::ZERO
     }
-
+    fn desired_height(&mut self, _: &mut SizeCtx) -> Len {
-    fn size_hint(&self, _axis: Axis) -> Option<Len> {
+        Len::ZERO
-        Some(Len::default())
-    }
-
-    fn on_resize(&self, _axis: Axis) -> OnResize {
-        OnResize::Scale
     }
 }
 

examples/random.rs

@@ -1,31 +0,0 @@
-//! The seeded random tree `tests/generated.rs` checks, drawn so it can be
-//! looked at. `IRIS_SEED` and `IRIS_DEPTH` choose which one.
-
-use iris::prelude::*;
-use iris::random::Edits;
-
-fn env(name: &str, fallback: u64) -> u64 {
-    std::env::var(name)
-        .ok()
-        .and_then(|v| v.parse().ok())
-        .unwrap_or(fallback)
-}
-
-fn main() {
-    DefaultApp::<State>::run();
-}
-
-#[derive(DefaultUiState)]
-struct State {
-    ui_state: DefaultUiState,
-}
-
-impl DefaultAppState for State {
-    fn new(mut ui_state: DefaultUiState, rsc: &mut DefaultRsc<Self>, _: Proxy<Self>) -> Self {
-        let seed = env("IRIS_SEED", 1);
-        let depth = env("IRIS_DEPTH", 4) as usize;
-        let (root, _) = iris::random::grow(rsc, seed, depth, &Edits::default());
-        ui_state.set_root(root);
-        Self { ui_state }
-    }
-}

examples/text.rs

@@ -1,63 +0,0 @@
-//! Text sizing: wrapped text reads the width it is offered, fixed text does
-//! not, and both report a height their container lays out around.
-
-use iris::prelude::*;
-
-fn main() {
-    DefaultApp::<State>::run();
-}
-
-#[derive(DefaultUiState)]
-struct State {
-    ui_state: DefaultUiState,
-}
-
-const SAMPLE: &str = "Wrapping shapes one source into as many lines as its container \
-    leaves room for, so the height of a paragraph is an answer rather than a setting, and \
-    the same words in a narrower box come back taller. Resize the window and watch the \
-    text below reflow into a different number of lines while nothing about it changes.";
-
-impl DefaultAppState for State {
-    fn new(mut ui_state: DefaultUiState, rsc: &mut DefaultRsc<Self>, _: Proxy<Self>) -> Self {
-        let panel = || rect(Color::WHITE.darker(0.85));
-
-        let wrapped = wtext(SAMPLE)
-            .size(28)
-            .wrap(true)
-            .text_align(Align::LEFT)
-            .pad(16)
-            .background(panel());
-
-        let aligned = (
-            wtext("left").size(24).text_align(Align::LEFT),
-            wtext("centred").size(24).text_align(Align::CENTER),
-            wtext("right").size(24).text_align(Align::RIGHT),
-        )
-            .span(Dir::DOWN)
-            .gap(8)
-            .pad(16)
-            .background(panel());
-
-        // The same words in half the width, which is a different number of
-        // lines and so a different height. A declared width only holds along
-        // a span's own axis, hence the row.
-        let narrow = (
-            wtext(SAMPLE)
-                .size(20)
-                .wrap(true)
-                .pad(16)
-                .background(panel())
-                .align(Align::TOP)
-                .width(rel(0.5)),
-            rect(Color::WHITE.darker(0.95)),
-        )
-            .span(Dir::RIGHT);
-
-        (wrapped, aligned, narrow)
-            .span(Dir::DOWN)
-            .gap(12)
-            .pad(12)
-            .set_root(rsc, &mut ui_state);
-        Self { ui_state }
-    }
-}

rig-input/Cargo.toml

@@ -1,16 +0,0 @@
-[package]
-name = "rig-input"
-version.workspace = true
-edition.workspace = true
-
-# Replays `.touch` recordings through Wayland's virtual-pointer protocol;
-# headless sway has no input devices for coordinate-driving tools to move.
-[[bin]]
-name = "replay-touch"
-path = "src/main.rs"
-
-[dependencies]
-# Share the harness parser so both ways of replaying read a file the same.
-iris = { path = ".." }
-wayland-client = { workspace = true }
-wayland-protocols-wlr = { workspace = true }

rig-input/src/main.rs

@@ -1,141 +0,0 @@
-use iris::harness::{TouchAction, TouchScript};
-use std::time::Duration;
-use wayland_client::protocol::wl_pointer::ButtonState;
-use wayland_client::protocol::{wl_registry, wl_seat};
-use wayland_client::{Connection, Dispatch, QueueHandle, delegate_noop};
-use wayland_protocols_wlr::virtual_pointer::v1::client::{
-    zwlr_virtual_pointer_manager_v1::ZwlrVirtualPointerManagerV1,
-    zwlr_virtual_pointer_v1::ZwlrVirtualPointerV1,
-};
-
-const BTN_LEFT: u32 = 0x110;
-
-const SETTLE: Duration = Duration::from_millis(200);
-
-#[derive(Default)]
-struct Globals {
-    seat: Option<wl_seat::WlSeat>,
-    manager: Option<ZwlrVirtualPointerManagerV1>,
-}
-
-impl Dispatch<wl_registry::WlRegistry, ()> for Globals {
-    fn event(
-        state: &mut Self,
-        registry: &wl_registry::WlRegistry,
-        event: wl_registry::Event,
-        _: &(),
-        _: &Connection,
-        qh: &QueueHandle<Self>,
-    ) {
-        let wl_registry::Event::Global {
-            name,
-            interface,
-            version,
-        } = event
-        else {
-            return;
-        };
-        match interface.as_str() {
-            "wl_seat" => {
-                state.seat = Some(registry.bind(name, version.min(7), qh, ()));
-            }
-            "zwlr_virtual_pointer_manager_v1" => {
-                state.manager = Some(registry.bind(name, version.min(2), qh, ()));
-            }
-            _ => {}
-        }
-    }
-}
-
-delegate_noop!(Globals: ignore wl_seat::WlSeat);
-delegate_noop!(Globals: ZwlrVirtualPointerManagerV1);
-delegate_noop!(Globals: ZwlrVirtualPointerV1);
-
-fn main() {
-    let args: Vec<String> = std::env::args().skip(1).collect();
-    let [width, height, path] = args.as_slice() else {
-        eprintln!("usage: replay-touch WIDTH HEIGHT FILE");
-        std::process::exit(2);
-    };
-    let (width, height) = (parse(width, "WIDTH"), parse(height, "HEIGHT"));
-    let text = std::fs::read_to_string(path)
-        .unwrap_or_else(|e| fail(&format!("could not read {path}: {e}")));
-    let script = TouchScript::parse(&text).unwrap_or_else(|e| fail(&e));
-
-    let conn = Connection::connect_to_env().unwrap_or_else(|e| {
-        fail(&format!(
-            "no wayland display ({e}); is WAYLAND_DISPLAY set?"
-        ))
-    });
-    let mut queue = conn.new_event_queue();
-    let qh = queue.handle();
-    let display = conn.display();
-    display.get_registry(&qh, ());
-    let mut globals = Globals::default();
-    queue
-        .roundtrip(&mut globals)
-        .unwrap_or_else(|e| fail(&format!("wayland roundtrip failed: {e}")));
-
-    let manager = globals.manager.as_ref().unwrap_or_else(|| {
-        fail(
-            "this compositor does not offer zwlr_virtual_pointer_manager_v1, so a pointer cannot \
-             be synthesised; sway and every wlroots compositor do",
-        )
-    });
-    let pointer = manager.create_virtual_pointer(globals.seat.as_ref(), &qh, ());
-
-    // Put the pointer where the gesture starts and let the compositor
-    // settle before anything is pressed. Without this the press is
-    // dropped: sway has just learned about this pointer, and a button
-    // sent in the same breath as the motion that first puts it over a
-    // window arrives before there is a focused surface to send it to --
-    // winit sees `CursorEntered`, the moves and the *release*, never the
-    // press, so the gesture reads as a hover and nothing scrolls. Found
-    // by printing winit's own events; the settle is what fixed it.
-    if let Some(first) = script.samples.first() {
-        pointer.motion_absolute(0, first.pos.x as u32, first.pos.y as u32, width, height);
-        pointer.frame();
-        conn.flush()
-            .unwrap_or_else(|e| fail(&format!("flush: {e}")));
-        std::thread::sleep(SETTLE);
-    }
-
-    let mut previous = 0;
-    for sample in &script.samples {
-        std::thread::sleep(Duration::from_millis(sample.t_ms - previous));
-        previous = sample.t_ms;
-        let t = sample.t_ms as u32;
-        pointer.motion_absolute(t, sample.pos.x as u32, sample.pos.y as u32, width, height);
-        pointer.frame();
-        // The button goes in a frame of its own, *after* the motion has
-        // been committed. Sent in the same frame as the motion that
-        // first puts the pointer over the window, sway drops it: the
-        // client sees `CursorEntered` and the moves but never a
-        // `MouseInput { state: Pressed }`, so the whole gesture reads as
-        // a hover and nothing scrolls. Found exactly that way, by
-        // printing winit's events.
-        let state = match sample.action {
-            TouchAction::Down => Some(ButtonState::Pressed),
-            TouchAction::Up => Some(ButtonState::Released),
-            TouchAction::Move => None,
-        };
-        if let Some(state) = state {
-            pointer.button(t, BTN_LEFT, state);
-            pointer.frame();
-        }
-        conn.flush()
-            .unwrap_or_else(|e| fail(&format!("flush: {e}")));
-    }
-    pointer.destroy();
-    conn.flush().ok();
-}
-
-fn parse(text: &str, what: &str) -> u32 {
-    text.parse()
-        .unwrap_or_else(|_| fail(&format!("{what} is not a whole number: {text:?}")))
-}
-
-fn fail(message: &str) -> ! {
-    eprintln!("replay-touch: {message}");
-    std::process::exit(1);
-}

scripts/headless.conf

@@ -1,14 +0,0 @@
-# The compositor `scripts/run-headless.sh` starts, so that an example has a
-# surface where there is no display. Nothing here is meant to be looked at
-# directly; `grim` is.
-#
-# No Xwayland: winit talks Wayland natively, so an X server is a second thing
-# to go wrong for no gain.
-xwayland disable
-
-# The default output, overridden per run by `--mode`. Larger than the window
-# an example opens, so nothing is scaled or clipped.
-output HEADLESS-1 mode 1920x1200@60Hz
-
-default_border none
-focus_follows_mouse no

scripts/run-headless.sh

@@ -1,182 +0,0 @@
-#!/bin/sh
-# Run an iris example on a machine with no display.
-#
-#   ./scripts/run-headless.sh tabs
-#   ./scripts/run-headless.sh tabs --shot /tmp/tabs.png --seconds 4
-#   ./scripts/run-headless.sh tabs --replay taps.touch --shot /tmp/tabs.png
-#   ./scripts/run-headless.sh app --dir ../elsewhere --mode 1080x2424@120Hz
-#
-# `--dir DIR` names the workspace to build in, defaulting to this one, so a
-# project that depends on iris can be run through the same rig. `--bin` runs a
-# crate binary rather than an example, and takes its own argv from
-# `$RUN_HEADLESS_ARGS`, word-split on purpose.
-#
-# `--mode` sets the output, for running something at a size other than a
-# desktop's -- a phone's, say. Set every run rather than only when it changes:
-# the compositor is reused between runs, so a default-shaped run after a
-# custom one would otherwise inherit the other's output and quietly screenshot
-# the wrong size.
-#
-# `--resize WxH@Hz` changes the output under the app once it is up, then
-# screenshots. A resize is its own case: what it has to match is a cold start
-# at that size, byte for byte, and nothing in `cargo test` can see it.
-#
-# `--replay FILE` drives a `.touch` recording into the window through
-# `replay-touch`, which reads it with the same parser `iris::harness` uses. A
-# recording is `<ms> down|move|up <x> <y>` in the output's own pixels. With
-# `--shot` it also writes `<shot>-before.png` from just before the gesture,
-# since "it moved" is a claim about two pictures.
-#
-# What it supplies is a compositor for winit to open a surface on: a headless
-# sway, and `grim` to screenshot it. Sway gets its own socket and runtime
-# directory rather than joining whatever else is running, because it tiles --
-# adding a window to someone else's compositor resizes theirs.
-set -eu
-
-need() {
-    command -v "$1" >/dev/null 2>&1 || {
-        echo "run-headless: $1 is not installed ($2)" >&2
-        exit 127
-    }
-}
-need sway "the compositor an example opens its window on"
-need swaymsg "sway's control socket"
-
-scripts=$(cd "$(dirname "$0")" && pwd)
-root=$(cd "$scripts/.." && pwd)
-workdir="$root"
-cd "$root"
-run="${XDG_RUNTIME_DIR:-/tmp}/iris-headless"
-seconds=3
-shot=""
-replay=""
-resize=""
-example=""
-kind=example
-mode=1920x1200@60Hz
-
-
-while [ $# -gt 0 ]; do
-    case "$1" in
-        --shot) shot=$2; shift 2 ;;
-        --seconds) seconds=$2; shift 2 ;;
-        --bin) kind=bin; shift ;;
-        --mode) mode=$2; shift 2 ;;
-        --resize) resize=$2; shift 2 ;;
-        --replay) replay=$2; shift 2 ;;
-        --dir) workdir=$(cd "$2" && pwd); shift 2 ;;
-        --) shift; break ;;
-        *) example=$1; shift ;;
-    esac
-done
-[ -n "$example" ] || { echo "usage: $0 NAME [--bin] [--dir DIR] [--mode WxH@Hz] [--resize WxH@Hz] [--replay TOUCH] [--shot PNG] [--seconds N] [-- cargo args]" >&2; exit 2; }
-[ -z "$replay" ] || [ -f "$replay" ] || { echo "run-headless: no touch script at $replay" >&2; exit 2; }
-[ -z "$shot" ] || need grim "the screenshot --shot writes"
-
-mkdir -p "$run"
-export SWAYSOCK="$run/sway.sock"
-
-# Named rather than left to sway's pid-based default, so a second run reuses
-# this compositor instead of starting another beside it.
-if ! swaymsg -t get_version >/dev/null 2>&1; then
-    rm -f "$SWAYSOCK"
-    WLR_BACKENDS=headless WLR_LIBINPUT_NO_DEVICES=1 LIBSEAT_BACKEND=noop \
-        setsid sway -c "$scripts/headless.conf" >"$run/sway.log" 2>&1 &
-    i=0
-    while [ $i -lt 20 ]; do
-        swaymsg -t get_version >/dev/null 2>&1 && break
-        i=$((i + 1)); sleep 0.5
-    done
-    swaymsg -t get_version >/dev/null 2>&1 || {
-        echo "run-headless: compositor did not start; see $run/sway.log" >&2
-        exit 1
-    }
-fi
-
-rm -f "$run/display"
-swaymsg exec -- "sh -c 'printf %s \"\$WAYLAND_DISPLAY\" > $run/display'" >/dev/null
-i=0
-while [ $i -lt 20 ]; do
-    [ -s "$run/display" ] && break
-    i=$((i + 1)); sleep 0.5
-done
-[ -s "$run/display" ] || { echo "run-headless: could not read WAYLAND_DISPLAY" >&2; exit 1; }
-WAYLAND_DISPLAY=$(cat "$run/display")
-export WAYLAND_DISPLAY
-
-echo "run-headless: $WAYLAND_DISPLAY (sway $(swaymsg -t get_version --raw | sed -n 's/.*"human_readable":"\([^"]*\)".*/\1/p'))" >&2
-
-swaymsg output HEADLESS-1 mode "$mode" >/dev/null
-# The extent `replay-touch` positions against, so a script's coordinates
-# are the output's own pixels.
-out_w=${mode%x*}
-out_h=${mode#*x}; out_h=${out_h%@*}
-
-# Built before the app starts, so a compile error is not reported as a
-# window that failed to move.
-[ -z "$replay" ] || (cd "$root" && cargo build --bin replay-touch -p rig-input) >&2
-
-cd "$workdir"
-if [ "$kind" = bin ]; then
-    cargo build --bin "$example" "$@" >&2
-    bin="$workdir/target/debug/$example"
-else
-    cargo build --example "$example" "$@" >&2
-    bin="$workdir/target/debug/examples/$example"
-fi
-
-# Deliberately word-split: this is the binary's own argv, not a single path.
-# shellcheck disable=SC2086
-"$bin" ${RUN_HEADLESS_ARGS:-} >"$run/$example.log" 2>&1 &
-pid=$!
-trap 'kill "$pid" 2>/dev/null || true' EXIT INT TERM
-
-# Wait for the window to be mapped rather than for a number of seconds. A
-# fixed sleep took an all-black screenshot the first time this ran, when sway
-# had started in the same invocation and had not composited its output yet --
-# which is indistinguishable from an app that draws nothing.
-i=0
-while [ $i -lt 40 ]; do
-    kill -0 "$pid" 2>/dev/null || break
-    swaymsg -t get_tree --raw 2>/dev/null | grep -q "\"pid\":$pid," && break
-    i=$((i + 1)); sleep 0.25
-done
-
-i=0
-while [ $i -lt "$((seconds * 2))" ]; do
-    kill -0 "$pid" 2>/dev/null || break
-    i=$((i + 1)); sleep 0.5
-done
-
-if [ -n "$resize" ] && kill -0 "$pid" 2>/dev/null; then
-    swaymsg output HEADLESS-1 mode "$resize" >/dev/null
-    echo "run-headless: resized to $resize" >&2
-    sleep 2
-fi
-
-if [ -n "$replay" ] && kill -0 "$pid" 2>/dev/null; then
-    if [ -n "$shot" ]; then
-        grim "${shot%.png}-before.png"
-        echo "run-headless: wrote ${shot%.png}-before.png (before the gesture)" >&2
-    fi
-    "$root/target/debug/replay-touch" "$out_w" "$out_h" "$replay"
-    # A fling outlives the finger: the gesture's own last sample is not
-    # when the list stops. Long enough for Android's spline to settle
-    # (`FlingCalculator::duration` tops out around a second and a half).
-    sleep 2
-fi
-
-if kill -0 "$pid" 2>/dev/null; then
-    [ -n "$shot" ] && grim "$shot" && echo "run-headless: wrote $shot" >&2
-    kill "$pid" 2>/dev/null || true
-    wait "$pid" 2>/dev/null || true
-    status=0
-else
-    wait "$pid" 2>/dev/null || status=$?
-    echo "run-headless: $example exited early (status ${status:-0})" >&2
-    status=${status:-1}
-fi
-
-echo "--- $example output ---" >&2
-cat "$run/$example.log" >&2
-exit "$status"

src/default/mod.rs

@@ -235,7 +235,8 @@ impl<State: DefaultAppState> AppState for DefaultApp<State> {
             ui_state.focus = None;
         }
         if input_changed {
-            render.run_sensors(rsc, state, cursor_state);
+            let window_size = ui_state.window_size();
+            render.run_sensors(rsc, state, cursor_state, window_size);
         }
         let ui_state = state.default_state_mut();
         if old != ui_state.focus

src/default/sense.rs

@@ -4,14 +4,14 @@ use std::{
     rc::Rc,
 };
 
-#[derive(Debug, Clone, Copy, PartialEq)]
+#[derive(Clone, Copy, PartialEq)]
 pub enum CursorButton {
     Left,
     Right,
     Middle,
 }
 
-#[derive(Debug, Clone, Copy, PartialEq)]
+#[derive(Clone, Copy, PartialEq)]
 pub enum CursorSense {
     PressStart(CursorButton),
     Pressing(CursorButton),
@@ -27,7 +27,7 @@ pub struct CursorSenses(Vec<CursorSense>);
 
 impl Event for CursorSenses {
     type Data<'a> = CursorData<'a>;
-    type Global = Hovered;
+    type State = SensorState;
     fn should_run<'a>(&self, data: &Self::Data<'a>) -> Option<Self::Data<'a>> {
         if let Some(sense) = should_run(self, &data.cursor, data.hover) {
             let mut data = data.clone();
@@ -37,24 +37,6 @@ impl Event for CursorSenses {
             None
         }
     }
-
-    /// A press or a scroll is used up by whatever answered it, so it stops
-    /// there. Hovering is not: a cursor resting somewhere goes on resting.
-    fn consumes(&self, data: &Self::Data<'_>) -> bool {
-        !data.sense.position_only()
-    }
-}
-
-/// Who the cursor was inside, before and after an input. The difference is
-/// whose hover has ended -- including a widget a higher layer has covered,
-/// which the walk stops before reaching.
-///
-/// Two buffers that swap rather than one rebuilt, so an input allocates
-/// nothing once they have grown.
-#[derive(Default)]
-pub struct Hovered {
-    was: Vec<WidgetId>,
-    now: Vec<WidgetId>,
 }
 
 impl CursorSense {
@@ -70,12 +52,6 @@ impl CursorSense {
     pub fn is_dragging(&self) -> bool {
         matches!(self, CursorSense::Pressing(CursorButton::Left))
     }
-
-    /// False if the sense is a button or a scroll, true if it is only about
-    /// where the cursor is.
-    fn position_only(&self) -> bool {
-        matches!(self, Self::HoverStart | Self::Hovering | Self::HoverEnd)
-    }
 }
 
 #[derive(Default, Clone)]
@@ -120,12 +96,6 @@ impl CursorButtons {
 }
 
 impl CursorState {
-    /// True if the cursor is only reporting where it is: no button and no
-    /// scroll this frame.
-    pub fn position_only(&self) -> bool {
-        self.scroll_delta == Vec2::ZERO && self.buttons.iter().all(|(_, state)| state.is_off())
-    }
-
     pub fn end_frame(&mut self) {
         self.buttons.end_frame();
         self.scroll_delta = Vec2::ZERO;
@@ -153,6 +123,11 @@ pub struct Sensor<Ctx: HasEvents, Data> {
 
 pub type SenseShape = UiRegion;
 
+#[derive(Default, Debug)]
+pub struct SensorState {
+    pub hover: ActivationState,
+}
+
 #[derive(Clone)]
 pub struct CursorData<'a> {
     /// where this widget was hit
@@ -172,6 +147,7 @@ pub trait SensorUi {
         rsc: &mut Rsc,
         state: &mut Rsc::State,
         cursor: CursorState,
+        window_size: Vec2,
     );
 }
 
@@ -181,85 +157,46 @@ impl SensorUi for UiRenderState {
         rsc: &mut Rsc,
         state: &mut Rsc::State,
         cursor: CursorState,
+        window_size: Vec2,
     ) {
         // in order to remove this take, need to store active list in UiRenderState somehow
         // this would probably be done through a generic parameter that adds yet another rsc /
         // state like thing, but local to render state, and is passed to UiRsc events so you can
         // update it there?
-        let active = std::mem::take(&mut rsc.events_mut().get_type::<CursorSense>().active);
+        let mut active = std::mem::take(&mut rsc.events_mut().get_type::<CursorSense>().active);
-        let mut hovered = std::mem::take(&mut rsc.events_mut().get_type::<CursorSense>().global);
-        hovered.now.clear();
-        let position_only = cursor.position_only();
-        let region_of = |id| self.window_region(&id);
-
         for layer in self.layers.indices().rev() {
-            let mut consumed = false;
+            let mut sensed = false;
-            for id in active.get(&layer).into_flat_iter().map(|(id, _)| *id) {
+            for (id, sensor) in active.get_mut(&layer).into_flat_iter() {
-                let Some(region) = region_of(id) else {
+                let shape = self.active.get(id).unwrap().region;
-                    continue;
+                let region = shape.to_px(window_size);
-                };
+                let in_shape = cursor.exists && region.contains(cursor.pos);
-                if !cursor.exists || !region.contains(cursor.pos) {
+                sensor.hover.update(in_shape);
+                if sensor.hover == ActivationState::Off {
                     continue;
                 }
-                hovered.now.push(id);
+                sensed = true;
-                let hover = match hovered.was.contains(&id) {
-                    true => ActivationState::On,
-                    false => ActivationState::Start,
-                };
-                // A press or a scroll stops where something answered it, so a
-                // button over a list does not swallow the list's scrolling.
-                consumed |= deliver(self, rsc, state, id, hover, &cursor, region);
-                // A cursor doing neither stops at whatever it is over, so
-                // hovering does not reach through.
-                consumed |= position_only;
-            }
-            // Applied after the layer, never during it: senses on one layer do
-            // not block each other.
-            if consumed {
-                break;
-            }
-        }
 
-        // Whatever the cursor was inside and is not now, whether it left or a
+                let cursor = cursor.clone();
-        // layer above took the input before the walk reached it. A widget that
-        // stopped being drawn has no region to report and is simply dropped.
-        for &id in &hovered.was {
-            if !hovered.now.contains(&id)
-                && let Some(region) = region_of(id)
-            {
-                deliver(self, rsc, state, id, ActivationState::End, &cursor, region);
-            }
-        }
-        std::mem::swap(&mut hovered.was, &mut hovered.now);
 
-        let senses = rsc.events_mut().get_type::<CursorSense>();
-        senses.active = active;
-        senses.global = hovered;
-    }
-}
-
-/// Runs one widget's cursor senses, and says whether they used up the input.
-fn deliver<Rsc: HasEvents>(
-    render: &UiRenderState,
-    rsc: &mut Rsc,
-    state: &mut Rsc::State,
-    id: WidgetId,
-    hover: ActivationState,
-    cursor: &CursorState,
-    region: PixelRegion,
-) -> bool {
                 let data = CursorData {
                     pos: cursor.pos - region.top_left,
                     size: region.bot_right - region.top_left,
                     scroll_delta: cursor.scroll_delta,
-        hover,
+                    hover: sensor.hover,
-        cursor: cursor.clone(),
+                    cursor,
                     // this does not have any meaning;
                     // might wanna set up Event to have a prepare stage
                     sense: CursorSense::Hovering,
-        render,
+                    render: self,
                 };
-    rsc.run_event::<CursorSense>(id, data, state)
+                rsc.run_event::<CursorSense>(*id, data, state);
+            }
+            if sensed {
+                break;
+            }
+        }
+        rsc.events_mut().get_type::<CursorSense>().active = active;
+    }
 }
 
 pub fn should_run(
@@ -268,11 +205,6 @@ pub fn should_run(
     hover: ActivationState,
 ) -> Option<CursorSense> {
     for sense in senses.iter() {
-        // A widget the cursor is no longer inside senses only its position:
-        // the press that ended its hover landed on something else.
-        if !hover.is_on() && !sense.position_only() {
-            continue;
-        }
         if match sense {
             CursorSense::PressStart(button) => cursor.buttons.select(button).is_start(),
             CursorSense::Pressing(button) => cursor.buttons.select(button).is_on(),

src/harness.rs

@@ -37,81 +37,6 @@ macro_rules! assert_corners {
 }
 pub use crate::assert_corners;
 
-/// One replayed pointer sample, cut down to what a window delivers: where the
-/// pointer is, and whether the button changed.
-#[derive(Clone, Copy, Debug, PartialEq, Eq)]
-pub enum TouchAction {
-    Down,
-    Move,
-    Up,
-}
-
-impl TouchAction {
-    fn parse(word: &str) -> Option<Self> {
-        match word {
-            "down" => Some(Self::Down),
-            "move" => Some(Self::Move),
-            "up" => Some(Self::Up),
-            _ => None,
-        }
-    }
-}
-
-#[derive(Clone, Copy, Debug)]
-pub struct TouchSample {
-    pub t_ms: u64,
-    pub action: TouchAction,
-    pub pos: Vec2,
-}
-
-/// A recorded gesture, in the output's own pixels: `<ms> down|move|up <x> <y>`
-/// a line, `#` to end of line ignored.
-///
-/// One parser for both ways of replaying a recording -- into a harness, and
-/// into a real window -- so the two cannot read the same file differently.
-pub struct TouchScript {
-    pub samples: Vec<TouchSample>,
-}
-
-impl TouchScript {
-    pub fn parse(text: &str) -> Result<Self, String> {
-        let mut samples: Vec<TouchSample> = Vec::new();
-        for (i, line) in text.lines().enumerate() {
-            let line = line.split('#').next().unwrap_or("").trim();
-            if line.is_empty() {
-                continue;
-            }
-            let at = |what: &str| format!("touch script line {}: {what}: {line:?}", i + 1);
-            let mut words = line.split_whitespace();
-            let (Some(t), Some(action), Some(x), Some(y), None) = (
-                words.next(),
-                words.next(),
-                words.next(),
-                words.next(),
-                words.next(),
-            ) else {
-                return Err(at("expected `t_ms action x y`"));
-            };
-            let t_ms: u64 = t.parse().map_err(|_| at("t_ms is not a whole number"))?;
-            let action =
-                TouchAction::parse(action).ok_or_else(|| at("action is not down/move/up"))?;
-            let x: f32 = x.parse().map_err(|_| at("x is not a number"))?;
-            let y: f32 = y.parse().map_err(|_| at("y is not a number"))?;
-            if let Some(last) = samples.last()
-                && t_ms < last.t_ms
-            {
-                return Err(at("samples must be in time order"));
-            }
-            samples.push(TouchSample {
-                t_ms,
-                action,
-                pos: Vec2::new(x, y),
-            });
-        }
-        Ok(Self { samples })
-    }
-}
-
 #[derive(Default)]
 pub struct HarnessState {
     pub root: Option<StrongWidget>,
@@ -235,23 +160,6 @@ impl Harness {
         self.release(CursorButton::Left);
     }
 
-    /// Drives a recorded gesture through the harness.
-    pub fn replay(&mut self, script: &TouchScript) {
-        for sample in &script.samples {
-            match sample.action {
-                TouchAction::Down => {
-                    self.move_to(sample.pos);
-                    self.press(CursorButton::Left);
-                }
-                TouchAction::Move => self.move_to(sample.pos),
-                TouchAction::Up => {
-                    self.move_to(sample.pos);
-                    self.release(CursorButton::Left);
-                }
-            }
-        }
-    }
-
     fn button(&mut self, button: CursorButton) -> &mut ActivationState {
         let buttons = &mut self.cursor.buttons;
         match button {
@@ -265,56 +173,9 @@ impl Harness {
     /// window delivers input against too.
     fn sense(&mut self) {
         let cursor = self.cursor.clone();
+        let size = self.render.output_size();
         self.render
-            .run_sensors(&mut self.rsc, &mut self.state, cursor);
+            .run_sensors(&mut self.rsc, &mut self.state, cursor, size);
         self.cursor.end_frame();
     }
 }
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    fn parse(text: &str) -> Result<Vec<(u64, TouchAction, f32, f32)>, String> {
-        Ok(TouchScript::parse(text)?
-            .samples
-            .iter()
-            .map(|s| (s.t_ms, s.action, s.pos.x, s.pos.y))
-            .collect())
-    }
-
-    #[test]
-    fn a_recording_is_time_action_and_a_point() {
-        assert_eq!(
-            parse("0 down 10 20\n16 move 10.5 24\n32 up 10.5 24").unwrap(),
-            [
-                (0, TouchAction::Down, 10.0, 20.0),
-                (16, TouchAction::Move, 10.5, 24.0),
-                (32, TouchAction::Up, 10.5, 24.0),
-            ]
-        );
-    }
-
-    #[test]
-    fn blank_lines_and_comments_are_not_samples() {
-        assert_eq!(
-            parse("# a flick\n\n 0 down 1 2   # the finger lands\n\n").unwrap(),
-            [(0, TouchAction::Down, 1.0, 2.0)]
-        );
-    }
-
-    #[test]
-    fn a_recording_that_goes_backwards_is_rejected() {
-        // Replay waits out the gap between samples, so time running backwards
-        // would silently become no wait at all.
-        let err = parse("16 down 1 2\n0 up 1 2").unwrap_err();
-        assert!(err.contains("time order"), "{err}");
-    }
-
-    #[test]
-    fn a_line_that_is_not_a_sample_says_which_line() {
-        let err = parse("0 down 1 2\n16 wiggle 1 2").unwrap_err();
-        assert!(err.contains("line 2"), "{err}");
-        assert!(err.contains("down/move/up"), "{err}");
-    }
-}

src/lib.rs

@@ -8,7 +8,6 @@
 pub mod default;
 pub mod event;
 pub mod harness;
-pub mod random;
 pub mod widget;
 
 pub use iris_core as core;

src/random.rs

@@ -1,271 +0,0 @@
-//! A seeded random widget tree, for tests and for looking at.
-//!
-//! One seed is one tree, on any machine and after any upgrade, so a test can
-//! grow the same tree twice and a failing seed is reproduced by its number.
-//! `examples/random.rs` draws one; `tests/generated.rs` checks that laying one
-//! out again lands where growing it from scratch would.
-
-use crate::prelude::*;
-use std::collections::HashMap;
-
-/// The declared lengths of one `SetSize`, by axis.
-pub type Lens = [Option<Len>; 2];
-
-/// What a test changes between two trees grown from the same seed, so the
-/// warm one can be mutated and the cold one grown that way to begin with.
-#[derive(Default)]
-pub struct Edits {
-    /// Declared sizes, by the order the `SetSize` wrappers were made.
-    pub sizes: HashMap<usize, Lens>,
-    /// Which children a span has, by the order the spans were made.
-    pub spans: HashMap<usize, SpanEdit>,
-}
-
-#[derive(Default, Clone)]
-pub struct SpanEdit {
-    /// Children to leave out, by index among the ones grown.
-    pub detach: Vec<usize>,
-    /// How many of the span's spares are in it, appended in order.
-    pub attach: usize,
-}
-
-/// xorshift64, written out rather than taken from a crate so that a seed
-/// keeps meaning the same tree.
-pub struct Rng(u64);
-
-impl Rng {
-    pub fn new(seed: u64) -> Self {
-        Self(seed | 1)
-    }
-
-    pub fn bits(&mut self) -> u64 {
-        self.0 ^= self.0 << 13;
-        self.0 ^= self.0 >> 7;
-        self.0 ^= self.0 << 17;
-        self.0
-    }
-
-    pub fn below(&mut self, n: usize) -> usize {
-        (self.bits() % n as u64) as usize
-    }
-
-    pub fn chance(&mut self) -> bool {
-        self.bits() & 1 == 0
-    }
-}
-
-const COLORS: [UiColor; 6] = [
-    UiColor::RED,
-    UiColor::GREEN,
-    UiColor::BLUE,
-    UiColor::YELLOW,
-    UiColor::CYAN,
-    UiColor::MAGENTA,
-];
-
-/// Leaves grown beside every span, for a test to put into it.
-const SPARES: usize = 3;
-
-const WORDS: &str = "Wrapping shapes one source into as many lines as the box \
-    leaves room for, so a paragraph's height is an answer and not a setting.";
-
-/// What growing a tree gives back: every widget in creation order, so two
-/// trees from one seed line up index for index, and the declared sizes, which
-/// are what a test changes to watch the change propagate.
-#[derive(Default)]
-pub struct Tree {
-    pub ids: Vec<WidgetId>,
-    pub sized: Vec<WeakWidget<SetSize>>,
-    pub spans: Vec<Spanned>,
-    pub scrolls: Vec<WeakWidget<Scroll>>,
-    /// Children a `SpanEdit` took out, held so that dropping the last share
-    /// of one does not free its id for the next widget to be given -- which
-    /// would put the two trees' `ids` out of step.
-    pub detached: Vec<StrongWidget>,
-}
-
-pub struct Spanned {
-    pub id: WeakWidget<Span>,
-    /// Leaves grown with the span whether or not they end up in it, so both
-    /// trees make the same widgets in the same order either way. Attaching
-    /// one moves it out of here: a widget belongs to one parent, and one that
-    /// belongs to nobody still has to be held or it reads as a leak.
-    pub spares: Vec<StrongWidget>,
-    /// How many children it was grown with, before any edit.
-    pub grown: usize,
-}
-
-/// Grows the tree `seed` describes, `edits` replacing the declared sizes it
-/// would otherwise have given those wrappers.
-pub fn grow<Rsc: UiRsc + 'static>(
-    rsc: &mut Rsc,
-    seed: u64,
-    depth: usize,
-    edits: &Edits,
-) -> (StrongWidget, Tree) {
-    let mut grow = Grow {
-        rsc,
-        rng: Rng::new(seed),
-        tree: Tree::default(),
-        edits,
-    };
-    let root = grow.node(depth);
-    (root, grow.tree)
-}
-
-struct Grow<'a, Rsc> {
-    rsc: &'a mut Rsc,
-    rng: Rng,
-    tree: Tree,
-    edits: &'a Edits,
-}
-
-impl<Rsc: UiRsc + 'static> Grow<'_, Rsc> {
-    fn leaf(&mut self) -> StrongWidget {
-        let id: StrongWidget = match self.rng.below(4) {
-            // Wrapped and unwrapped, because only one of them reads the width
-            // it is given and so only one has to be drawn again for a new one.
-            0 => wtext(WORDS).size(16).wrap(true).add_strong(self.rsc),
-            1 => wtext("one line, overflowing whatever it is given")
-                .size(16)
-                .wrap(false)
-                .add_strong(self.rsc),
-            _ => {
-                let color = COLORS[self.rng.below(COLORS.len())];
-                let alpha = (self.rng.below(5) * 63) as u8;
-                rect(color.alpha(alpha)).add_strong(self.rsc)
-            }
-        };
-        self.tree.ids.push(id.id());
-        id
-    }
-
-    fn len(&mut self) -> Option<Len> {
-        match self.rng.below(4) {
-            0 => Some(Len::abs(20.0 + self.rng.below(180) as f32)),
-            1 => Some(Len::REST),
-            _ => None,
-        }
-    }
-
-    fn align(&mut self) -> Align {
-        let mut axis = || match self.rng.below(4) {
-            0 => None,
-            1 => Some(AxisAlign::Neg),
-            2 => Some(AxisAlign::Center),
-            _ => Some(AxisAlign::Pos),
-        };
-        let (mut x, y) = (axis(), axis());
-        // Aligning on neither axis is just another transparent wrapper and
-        // would leave this branch unexercised.
-        if x.is_none() && y.is_none() {
-            x = Some(AxisAlign::Center);
-        }
-        Align { x, y }
-    }
-
-    /// A declared size over half the tree, kept where a test can change it.
-    fn sized(&mut self, inner: StrongWidget) -> StrongWidget {
-        if !self.rng.chance() {
-            return inner;
-        }
-        let idx = self.tree.sized.len();
-        let lens = [self.len(), self.len()];
-        let lens = self.edits.sizes.get(&idx).copied().unwrap_or(lens);
-        let id = SetSize {
-            inner,
-            x: lens[0],
-            y: lens[1],
-        }
-        .add(self.rsc);
-        self.tree.sized.push(id);
-        self.tree.ids.push(id.id());
-        id.add_strong(self.rsc)
-    }
-
-    fn node(&mut self, depth: usize) -> StrongWidget {
-        if depth == 0 {
-            return self.leaf();
-        }
-        let positioned = self.rng.below(6);
-        if positioned == 0 {
-            // Scrolling reads the pixel length of its box, which nothing
-            // else here does, and gives its child a box longer than its own.
-            let inner = self.node(depth - 1);
-            let inner = self.sized(inner);
-            let axis = if self.rng.chance() { Axis::X } else { Axis::Y };
-            let id = Scroll::new(inner, axis).add(self.rsc);
-            self.tree.scrolls.push(id);
-            self.tree.ids.push(id.id());
-            return id.add_strong(self.rsc);
-        }
-        if positioned == 1 {
-            let inner = self.node(depth - 1);
-            let inner = self.sized(inner);
-            let id = Aligned {
-                inner,
-                align: self.align(),
-            }
-            .add_strong(self.rsc);
-            self.tree.ids.push(id.id());
-            return id;
-        }
-        if self.rng.below(4) == 0 {
-            let inner = self.node(depth - 1);
-            let inner = self.sized(inner);
-            // Each side its own, since a padding that is the same all round
-            // hides anything that treats one edge differently from another.
-            let mut side = || self.rng.below(24) as f32;
-            let padding = Padding {
-                left: side(),
-                right: side(),
-                top: side(),
-                bottom: side(),
-            };
-            let id = Pad { padding, inner }.add_strong(self.rsc);
-            self.tree.ids.push(id.id());
-            return id;
-        }
-        let grown = 2 + self.rng.below(3);
-        let mut children = Vec::with_capacity(grown);
-        for _ in 0..grown {
-            let child = self.node(depth - 1);
-            children.push(self.sized(child));
-        }
-        if self.rng.chance() {
-            let id = Stack {
-                children,
-                size: StackSize::Child(0),
-            }
-            .add_strong(self.rsc);
-            self.tree.ids.push(id.id());
-            return id;
-        }
-        // Grown either way, so the widget after them has the same id in a
-        // tree that leaves them out as in one that puts them in.
-        let mut spares: Vec<StrongWidget> = (0..SPARES).map(|_| self.leaf()).collect();
-        let idx = self.tree.spans.len();
-        let edit = self.edits.spans.get(&idx).cloned().unwrap_or_default();
-        // Highest first, so an index means the same child however many of its
-        // neighbours are going too.
-        let mut detach = edit.detach.clone();
-        detach.sort_unstable();
-        for j in detach.into_iter().rev() {
-            if j < children.len() {
-                self.tree.detached.push(children.remove(j));
-            }
-        }
-        let attach = edit.attach.min(spares.len());
-        children.extend(spares.drain(..attach));
-        let dir = [Dir::RIGHT, Dir::DOWN, Dir::LEFT, Dir::UP][self.rng.below(4)];
-        let id = Span {
-            children,
-            dir,
-            gap: self.rng.below(3) as f32 * 4.0,
-        }
-        .add(self.rsc);
-        self.tree.ids.push(id.id());
-        self.tree.spans.push(Spanned { id, spares, grown });
-        id.add_strong(self.rsc)
-    }
-}

src/widget/image.rs

@@ -6,17 +6,16 @@ pub struct Image {
 }
 
 impl Widget for Image {
-    fn draw(&mut self, painter: &mut Painter) -> Size {
+    fn draw(&mut self, painter: &mut Painter) {
         painter.primitive(&self.handle);
-        Size::abs(self.handle.size())
     }
 
-    fn size_hint(&self, axis: Axis) -> Option<Len> {
+    fn desired_width(&mut self, _: &mut SizeCtx) -> Len {
-        Some(Len::abs(self.handle.size().axis(axis)))
+        Len::abs(self.handle.size().x)
     }
 
-    fn on_resize(&self, _: Axis) -> OnResize {
+    fn desired_height(&mut self, _: &mut SizeCtx) -> Len {
-        OnResize::Scale
+        Len::abs(self.handle.size().y)
     }
 }
 

src/widget/mask.rs

@@ -5,13 +5,16 @@ pub struct Masked {
 }
 
 impl Widget for Masked {
-    fn draw(&mut self, painter: &mut Painter) -> Size {
+    fn draw(&mut self, painter: &mut Painter) {
         painter.set_mask(painter.region());
-        painter.widget(&self.inner).size()
+        painter.widget(&self.inner);
     }
 
-    /// It clips to the box it was given, not to the part its child used.
+    fn desired_width(&mut self, ctx: &mut SizeCtx) -> Len {
-    fn on_resize(&self, _: Axis) -> OnResize {
+        ctx.width(&self.inner)
-        OnResize::Redraw
+    }
+
+    fn desired_height(&mut self, ctx: &mut SizeCtx) -> Len {
+        ctx.height(&self.inner)
     }
 }

src/widget/position/align.rs

@@ -6,37 +6,30 @@ pub struct Aligned {
 }
 
 impl Widget for Aligned {
-    fn draw(&mut self, painter: &mut Painter) -> Size {
+    fn draw(&mut self, painter: &mut Painter) {
-        let known = match self.align.tuple() {
-            (Some(_), Some(_)) => painter
-                .known_len(&self.inner, Axis::X, UiRegion::FULL)
-                .zip(painter.known_len(&self.inner, Axis::Y, UiRegion::FULL))
-                .map(|(x, y)| Size { x, y }),
-            (Some(_), None) => painter
-                .known_len(&self.inner, Axis::X, UiRegion::FULL)
-                .map(|x| Size { x, y: Len::REST }),
-            (None, Some(_)) => painter
-                .known_len(&self.inner, Axis::Y, UiRegion::FULL)
-                .map(|y| Size { x: Len::REST, y }),
-            (None, None) => Some(Size::REST),
-        };
-        // Drawn where it may be too big only when the aligned axes are not
-        // already known, then given its aligned box once its size is known.
-        let had_size = known.is_some();
-        let size = known.unwrap_or_else(|| painter.place(&self.inner, UiRegion::FULL).size());
         let region = match self.align.tuple() {
-            (Some(x), Some(y)) => size.to_uivec2().align(RegionAlign { x, y }),
+            (Some(x), Some(y)) => painter
-            (Some(x), None) => UiRegion::new(size.x.apply_rest().align(x), UiSpan::FULL),
+                .size(&self.inner)
-            (None, Some(y)) => UiRegion::new(UiSpan::FULL, size.y.apply_rest().align(y)),
+                .to_uivec2()
+                .align(RegionAlign { x, y }),
+            (Some(x), None) => {
+                let x = painter.size_ctx().width(&self.inner).apply_rest().align(x);
+                UiRegion::new(x, UiSpan::FULL)
+            }
+            (None, Some(y)) => {
+                let y = painter.size_ctx().height(&self.inner).apply_rest().align(y);
+                UiRegion::new(UiSpan::FULL, y)
+            }
             (None, None) => UiRegion::FULL,
         };
-        let placed = painter.place(&self.inner, region).size();
+        painter.widget_within(&self.inner, region);
-        if had_size { placed } else { size }
     }
 
-    /// The aligned box is a fraction of its own, so the child keeps its
+    fn desired_width(&mut self, ctx: &mut SizeCtx) -> Len {
-    /// length and stays against the edge it was aligned to.
+        ctx.width(&self.inner)
-    fn on_resize(&self, _: Axis) -> OnResize {
+    }
-        OnResize::Scale
+
+    fn desired_height(&mut self, ctx: &mut SizeCtx) -> Len {
+        ctx.height(&self.inner)
     }
 }

src/widget/position/layer.rs

@@ -6,14 +6,18 @@ pub struct LayerOffset {
 }
 
 impl Widget for LayerOffset {
-    fn draw(&mut self, painter: &mut Painter) -> Size {
+    fn draw(&mut self, painter: &mut Painter) {
         for _ in 0..self.offset {
             painter.next_layer();
         }
-        painter.widget(&self.inner).size()
+        painter.widget(&self.inner);
     }
 
-    fn on_resize(&self, _: Axis) -> OnResize {
+    fn desired_width(&mut self, ctx: &mut SizeCtx) -> Len {
-        OnResize::Scale
+        ctx.width(&self.inner)
+    }
+
+    fn desired_height(&mut self, ctx: &mut SizeCtx) -> Len {
+        ctx.height(&self.inner)
     }
 }

src/widget/position/max_size.rs

@@ -6,20 +6,43 @@ pub struct MaxSize {
     pub y: Option<Len>,
 }
 
-impl Widget for MaxSize {
+impl MaxSize {
-    fn draw(&mut self, painter: &mut Painter) -> Size {
+    fn apply_to_outer(&self, ctx: &mut SizeCtx) {
-        let child = painter.widget(&self.inner).size();
+        if let Some(x) = self.x {
-        let output = painter.output_size();
+            ctx.outer.x.select_len(x.apply_rest());
-        Size {
+        }
-            x: capped(child.x, self.x, output.x),
+        if let Some(y) = self.y {
-            y: capped(child.y, self.y, output.y),
+            ctx.outer.y.select_len(y.apply_rest());
         }
     }
 }
 
-fn capped(len: Len, max: Option<Len>, output: f32) -> Len {
+impl Widget for MaxSize {
-    match max {
+    fn draw(&mut self, painter: &mut Painter) {
-        Some(max) if len.apply_rest().to_abs(output) > max.apply_rest().to_abs(output) => max,
+        painter.widget(&self.inner);
-        _ => len,
+    }
+
+    fn desired_width(&mut self, ctx: &mut SizeCtx) -> Len {
+        self.apply_to_outer(ctx);
+        let width = ctx.width(&self.inner);
+        if let Some(x) = self.x {
+            let width_px = width.apply_rest().to_abs(ctx.output_size().x);
+            let x_px = x.apply_rest().to_abs(ctx.output_size().x);
+            if width_px > x_px { x } else { width }
+        } else {
+            width
+        }
+    }
+
+    fn desired_height(&mut self, ctx: &mut SizeCtx) -> Len {
+        self.apply_to_outer(ctx);
+        let height = ctx.height(&self.inner);
+        if let Some(y) = self.y {
+            let height_px = height.apply_rest().to_abs(ctx.output_size().y);
+            let y_px = y.apply_rest().to_abs(ctx.output_size().y);
+            if height_px > y_px { y } else { height }
+        } else {
+            height
+        }
     }
 }

src/widget/position/offset.rs

@@ -6,12 +6,16 @@ pub struct Offset {
 }
 
 impl Widget for Offset {
-    fn draw(&mut self, painter: &mut Painter) -> Size {
+    fn draw(&mut self, painter: &mut Painter) {
         let region = UiRegion::FULL.offset(self.amt);
-        painter.widget_within(&self.inner, region).size()
+        painter.widget_within(&self.inner, region);
     }
 
-    fn on_resize(&self, _: Axis) -> OnResize {
+    fn desired_width(&mut self, ctx: &mut SizeCtx) -> Len {
-        OnResize::Scale
+        ctx.width(&self.inner)
+    }
+
+    fn desired_height(&mut self, ctx: &mut SizeCtx) -> Len {
+        ctx.height(&self.inner)
     }
 }

src/widget/position/pad.rs

@@ -6,26 +6,28 @@ pub struct Pad {
 }
 
 impl Widget for Pad {
-    fn draw(&mut self, painter: &mut Painter) -> Size {
+    fn draw(&mut self, painter: &mut Painter) {
-        let inner = painter
+        painter.widget_within(&self.inner, self.padding.region());
-            .widget_within(&self.inner, self.padding.region())
-            .size();
-        Size {
-            x: Len {
-                abs: inner.x.abs + self.padding.left + self.padding.right,
-                ..inner.x
-            },
-            y: Len {
-                abs: inner.y.abs + self.padding.top + self.padding.bottom,
-                ..inner.y
-            },
-        }
     }
 
-    /// The padding is an offset from each edge, so a longer box pads the same
+    fn desired_width(&mut self, ctx: &mut SizeCtx) -> Len {
-    /// amount and the child takes the rest.
+        let width = self.padding.left + self.padding.right;
-    fn on_resize(&self, _: Axis) -> OnResize {
+        let height = self.padding.top + self.padding.bottom;
-        OnResize::Scale
+        ctx.outer.x.abs -= width;
+        ctx.outer.y.abs -= height;
+        let mut size = ctx.width(&self.inner);
+        size.abs += width;
+        size
+    }
+
+    fn desired_height(&mut self, ctx: &mut SizeCtx) -> Len {
+        let width = self.padding.left + self.padding.right;
+        let height = self.padding.top + self.padding.bottom;
+        ctx.outer.x.abs -= width;
+        ctx.outer.y.abs -= height;
+        let mut size = ctx.height(&self.inner);
+        size.abs += height;
+        size
     }
 }
 

src/widget/position/scroll.rs

@@ -10,16 +10,11 @@ pub struct Scroll {
 }
 
 impl Widget for Scroll {
-    fn draw(&mut self, painter: &mut Painter) -> Size {
+    fn draw(&mut self, painter: &mut Painter) {
-        let output_len = painter.output_len(self.axis);
+        let output_len = painter.output_size().axis(self.axis);
-        let container_len = UiScalar::abs(painter.px_len(self.axis));
+        let container_len = painter.region().axis(self.axis).len();
-        // Draw in the whole container only when its scrolling-axis length is
+        let content_len = painter
-        // not already known, then place it at the scrolled offset.
+            .len_axis(&self.inner, self.axis)
-        let known_len = painter.known_len(&self.inner, self.axis, UiRegion::FULL);
-        let measured = known_len.is_none();
-        let child = measured.then(|| painter.place(&self.inner, UiRegion::FULL).size());
-        let content_len = known_len
-            .unwrap_or_else(|| child.unwrap().axis(self.axis))
             .apply_rest()
             .within_len(container_len)
             .to_abs(output_len);
@@ -33,8 +28,15 @@ impl Widget for Scroll {
 
         let mut region = UiRegion::FULL.offset(Vec2::from_axis(self.axis, -self.amt, 0.0));
         region.axis_mut(self.axis).end = region.axis(self.axis).start.offset(self.content_len);
-        let placed = painter.place(&self.inner, region).size();
+        painter.widget_within(&self.inner, region);
-        child.unwrap_or(placed)
+    }
+
+    fn desired_width(&mut self, ctx: &mut SizeCtx) -> Len {
+        ctx.width(&self.inner)
+    }
+
+    fn desired_height(&mut self, ctx: &mut SizeCtx) -> Len {
+        ctx.height(&self.inner)
     }
 }
 

src/widget/position/set_size.rs

@@ -6,25 +6,29 @@ pub struct SetSize {
     pub y: Option<Len>,
 }
 
+impl SetSize {
+    fn apply_to_outer(&self, ctx: &mut SizeCtx) {
+        if let Some(x) = self.x {
+            ctx.outer.x.select_len(x.apply_rest());
+        }
+        if let Some(y) = self.y {
+            ctx.outer.y.select_len(y.apply_rest());
+        }
+    }
+}
+
 impl Widget for SetSize {
-    fn draw(&mut self, painter: &mut Painter) -> Size {
+    fn draw(&mut self, painter: &mut Painter) {
-        let child = painter.widget(&self.inner).size();
+        painter.widget(&self.inner);
-        Size {
-            x: self.x.unwrap_or(child.x),
-            y: self.y.unwrap_or(child.y),
-        }
     }
 
-    /// A declared axis is known without looking at the child, which is what
+    fn desired_width(&mut self, ctx: &mut SizeCtx) -> Len {
-    /// lets a span lay out around `.height(rest(1))` without drawing it.
+        self.apply_to_outer(ctx);
-    fn size_hint(&self, axis: Axis) -> Option<Len> {
+        self.x.unwrap_or_else(|| ctx.width(&self.inner))
-        match axis {
-            Axis::X => self.x,
-            Axis::Y => self.y,
-        }
     }
 
-    fn on_resize(&self, _: Axis) -> OnResize {
+    fn desired_height(&mut self, ctx: &mut SizeCtx) -> Len {
-        OnResize::Scale
+        self.apply_to_outer(ctx);
+        self.y.unwrap_or_else(|| ctx.height(&self.inner))
     }
 }

src/widget/position/span.rs

@@ -8,35 +8,13 @@ pub struct Span {
 }
 
 impl Widget for Span {
-    fn draw(&mut self, painter: &mut Painter) -> Size {
+    fn draw(&mut self, painter: &mut Painter) {
-        let axis = self.dir.axis;
+        let total = self.len_sum(&mut painter.size_ctx());
-        // A length for every child before any is placed: from its own hint
-        // where it has one, and from drawing it where it does not.
-        let mut cursor = UiScalar::rel_min();
-        let mut lens = Vec::with_capacity(self.children.len());
-        for child in &self.children {
-            let mut span = UiSpan::new(cursor, UiScalar::rel_max());
-            if self.dir.sign == Sign::Neg {
-                span.flip();
-            }
-            let region = UiRegion::from_axis(axis, span, UiSpan::FULL);
-            let len = match painter.known_len(child, axis, region) {
-                Some(len) => len,
-                None => painter.place(child, region).len(axis),
-            };
-            cursor.abs += len.abs + self.gap;
-            cursor.rel += len.rel;
-            lens.push(len);
-        }
-
-        let gap = self.gap * self.children.len().saturating_sub(1) as f32;
-        let total = lens.iter().fold(Len::abs(gap), |sum, len| sum + *len);
-
         let mut start = UiScalar::rel_min();
-        let mut ortho = Len::ZERO;
+        for child in &self.children {
-        for (child, len) in self.children.iter().zip(&lens) {
             let mut span = UiSpan::FULL;
             span.start = start;
+            let len = painter.len_axis(child, self.dir.axis);
             if len.rest > 0.0 {
                 let offset = UiScalar::new(total.rel, total.abs);
                 let rel_end = UiScalar::rel(len.rest / total.rest);
@@ -46,31 +24,27 @@ impl Widget for Span {
             start.abs += len.abs;
             start.rel += len.rel;
             span.end = start;
-            let mut region = UiRegion::from_axis(axis, span, UiSpan::FULL);
+            let mut child_region = UiRegion::from_axis(self.dir.axis, span, UiSpan::FULL);
             if self.dir.sign == Sign::Neg {
-                region.flip(axis);
+                child_region.flip(self.dir.axis);
-            }
-            let used = painter.place(child, region).size().axis(!axis);
-            // TODO: rel shouldn't do this, but no easy way before actually calculating pixels
-            if used.rel > 0.0 || used.rest > 0.0 {
-                ortho = Len::REST;
-            } else if ortho.rest == 0.0 {
-                ortho.abs = ortho.abs.max(used.abs);
             }
+            painter.widget_within(child, child_region);
             start.abs += self.gap;
         }
-
-        let along = match total.rest == 0.0 && total.rel == 0.0 {
-            true => total,
-            false => Len::default(),
-        };
-        Size::from_axis(axis, along, ortho)
     }
 
-    /// Every child is placed in fractions and offsets of the span's own box,
+    fn desired_width(&mut self, ctx: &mut SizeCtx) -> Len {
-    /// so a longer box holds the same layout and the children follow it.
+        match self.dir.axis {
-    fn on_resize(&self, _: Axis) -> OnResize {
+            Axis::X => self.desired_len(ctx),
-        OnResize::Scale
+            Axis::Y => self.desired_ortho(ctx),
+        }
+    }
+
+    fn desired_height(&mut self, ctx: &mut SizeCtx) -> Len {
+        match self.dir.axis {
+            Axis::X => self.desired_ortho(ctx),
+            Axis::Y => self.desired_len(ctx),
+        }
     }
 }
 
@@ -95,6 +69,87 @@ impl Span {
     pub fn pop(&mut self) -> Option<StrongWidget> {
         self.children.pop()
     }
+
+    fn len_sum(&mut self, ctx: &mut SizeCtx) -> Len {
+        let gap = self.gap * self.children.len().saturating_sub(1) as f32;
+        self.children.iter().fold(Len::abs(gap), |mut s, id| {
+            // it's tempting to subtract the abs & rel from the ctx outer,
+            // but that would create inconsistent sizing if you put
+            // a rest first vs last & only speed up in one direction.
+            // I think this is only solvable by restricting how you can
+            // compute size, bc currently you need child to define parent's
+            // sectioning and you need parent's sectioning to define child.
+            // Fortunately, that doesn't matter in most cases
+            let len = ctx.len_axis(id, self.dir.axis);
+            s += len;
+            s
+        })
+    }
+
+    fn desired_len(&mut self, ctx: &mut SizeCtx) -> Len {
+        let len = self.len_sum(ctx);
+        if len.rest == 0.0 && len.rel == 0.0 {
+            len
+        } else {
+            Len::default()
+        }
+    }
+
+    fn desired_ortho(&mut self, ctx: &mut SizeCtx) -> Len {
+        // this is a weird hack to get text wrapping to work properly when in a downward span
+        // the correct solution here is to add a function to widget that lets them
+        // request that ctx.outer has an axis "resolved" before checking the other,
+        // and panicking or warning if two request opposite axis (unsolvable in that case)
+        let outer = ctx.outer.axis(self.dir.axis);
+        if self.dir.axis == Axis::X {
+            // so....... this literally copies draw so that the lengths are correctly set in the
+            // context, which makes this slow and not cool
+            let total = self.len_sum(ctx);
+            let mut start = UiScalar::rel_min();
+            let mut ortho_len = Len::ZERO;
+            for child in &self.children {
+                let mut span = UiSpan::FULL;
+                span.start = start;
+                let len = ctx.len_axis(child, self.dir.axis);
+                if len.rest > 0.0 {
+                    let offset = UiScalar::new(total.rel, total.abs);
+                    let rel_end = UiScalar::rel(len.rest / total.rest);
+                    let end = (UiScalar::rel_max() + start) - offset;
+                    start = rel_end.within(&start.to(end));
+                }
+                start.abs += len.abs;
+                start.rel += len.rel;
+                span.end = start;
+
+                let scalar = span.len();
+                *ctx.outer.axis_mut(self.dir.axis) = outer.select_len(scalar);
+                let ortho = ctx.len_axis(child, !self.dir.axis);
+                // TODO: rel shouldn't do this, but no easy way before actually calculating pixels
+                if ortho.rel > 0.0 || ortho.rest > 0.0 {
+                    ortho_len.rest = 1.0;
+                    ortho_len.abs = 0.0;
+                    break;
+                }
+                ortho_len.abs = ortho_len.abs.max(ortho.abs);
+                start.abs += self.gap;
+            }
+            ortho_len
+        } else {
+            let mut ortho_len = Len::ZERO;
+            let ortho = !self.dir.axis;
+            for child in &self.children {
+                let len = ctx.len_axis(child, ortho);
+                // TODO: rel shouldn't do this, but no easy way before actually calculating pixels
+                if len.rel > 0.0 || len.rest > 0.0 {
+                    ortho_len.rest = 1.0;
+                    ortho_len.abs = 0.0;
+                    break;
+                }
+                ortho_len.abs = ortho_len.abs.max(len.abs);
+            }
+            ortho_len
+        }
+    }
 }
 
 pub struct SpanBuilder<State, const LEN: usize, Wa: WidgetArrLike<State, LEN, Tag>, Tag> {

src/widget/position/stack.rs

@@ -8,29 +8,30 @@ pub struct Stack {
 }
 
 impl Widget for Stack {
-    fn draw(&mut self, painter: &mut Painter) -> Size {
+    fn draw(&mut self, painter: &mut Painter) {
-        let sizing = match self.size {
+        let mut iter = self.children.iter();
-            StackSize::Default => None,
+        if let Some(child) = iter.next() {
-            StackSize::Child(i) => Some(i),
+            painter.child_layer();
-        };
+            painter.widget(child);
-        let mut size = Size::default();
-        for (i, child) in self.children.iter().enumerate() {
-            match i {
-                0 => painter.child_layer(),
-                _ => painter.next_layer(),
         }
-            let drawn = painter.widget(child);
+        for child in iter {
-            // Only the child that sizes the stack is read, so the others
+            painter.next_layer();
-            // changing size does not redraw it.
+            painter.widget(child);
-            if sizing == Some(i) {
-                size = drawn.size();
         }
     }
-        size
-    }
 
-    fn on_resize(&self, _: Axis) -> OnResize {
+    fn desired_width(&mut self, ctx: &mut SizeCtx) -> Len {
-        OnResize::Scale
+        match self.size {
+            StackSize::Default => Len::default(),
+            StackSize::Child(i) => ctx.width(&self.children[i]),
+        }
+    }
+
+    fn desired_height(&mut self, ctx: &mut SizeCtx) -> Len {
+        match self.size {
+            StackSize::Default => Len::default(),
+            StackSize::Child(i) => ctx.height(&self.children[i]),
+        }
     }
 }
 

src/widget/ptr.rs

@@ -6,10 +6,25 @@ pub struct WidgetPtr {
 }
 
 impl Widget for WidgetPtr {
-    fn draw(&mut self, painter: &mut Painter) -> Size {
+    fn draw(&mut self, painter: &mut Painter) {
-        match &self.inner {
+        if let Some(id) = &self.inner {
-            Some(id) => painter.widget(id).size(),
+            painter.widget(id);
-            None => Size::default(),
+        }
+    }
+
+    fn desired_width(&mut self, ctx: &mut SizeCtx) -> Len {
+        if let Some(id) = &self.inner {
+            ctx.width(id)
+        } else {
+            Len::ZERO
+        }
+    }
+
+    fn desired_height(&mut self, ctx: &mut SizeCtx) -> Len {
+        if let Some(id) = &self.inner {
+            ctx.height(id)
+        } else {
+            Len::ZERO
         }
     }
 }

src/widget/rect.rs

@@ -28,23 +28,21 @@ impl Rect {
 }
 
 impl Widget for Rect {
-    fn draw(&mut self, painter: &mut Painter) -> Size {
+    fn draw(&mut self, painter: &mut Painter) {
         painter.primitive(RectPrimitive {
             color: self.color,
             radius: self.radius,
             thickness: self.thickness,
             inner_radius: self.inner_radius,
         });
-        Size::REST
     }
 
-    fn size_hint(&self, _: Axis) -> Option<Len> {
+    fn desired_width(&mut self, _: &mut SizeCtx) -> Len {
-        Some(Len::REST)
+        Len::rest(1)
     }
 
-    /// Its box is its primitive's own region, so a new one is written there.
+    fn desired_height(&mut self, _: &mut SizeCtx) -> Len {
-    fn on_resize(&self, _: Axis) -> OnResize {
+        Len::rest(1)
-        OnResize::Scale
     }
 }
 

src/widget/text/edit.rs

@@ -55,47 +55,44 @@ impl TextEdit {
 }
 
 impl Widget for TextEdit {
-    fn draw(&mut self, painter: &mut Painter) -> Size {
+    fn draw(&mut self, painter: &mut Painter) {
         let base = painter.layer;
         painter.child_layer();
-        let (_, size) = self.view.draw(painter);
+        self.view.draw(painter);
         painter.layer = base;
         let region = self.region();
 
         let Some(selection) = self.selection else {
-            return size;
+            return;
         };
         let layout = self.view.buf.layout();
 
         // parley reports selection as boxes in layout space, so bidi and
         // wrapped lines come out right without this code knowing about either.
         for (rect, _) in selection.geometry(layout) {
-            let rect_size = vec2(rect.width() as f32, rect.height() as f32);
+            let size = vec2(rect.width() as f32, rect.height() as f32);
             let top_left = vec2(rect.x0 as f32, rect.y0 as f32);
             painter.primitive_within(
                 RectPrimitive::color(Color::SKY),
-                rect_size
+                size.align(Align::TOP_LEFT).offset(top_left).within(&region),
-                    .align(Align::TOP_LEFT)
-                    .offset(top_left)
-                    .within(&region),
             );
         }
 
         let caret = selection.focus().geometry(layout, CARET_WIDTH);
-        let caret_size = vec2(caret.width() as f32, caret.height() as f32);
+        let size = vec2(caret.width() as f32, caret.height() as f32);
         let top_left = vec2(caret.x0 as f32, caret.y0 as f32);
         painter.primitive_within(
             RectPrimitive::color(Color::WHITE),
-            caret_size
+            size.align(Align::TOP_LEFT).offset(top_left).within(&region),
-                .align(Align::TOP_LEFT)
-                .offset(top_left)
-                .within(&region),
         );
-        size
     }
 
-    fn on_resize(&self, axis: Axis) -> OnResize {
+    fn desired_width(&mut self, ctx: &mut SizeCtx) -> Len {
-        self.view.on_resize(axis)
+        self.view.desired_width(ctx)
+    }
+
+    fn desired_height(&mut self, ctx: &mut SizeCtx) -> Len {
+        self.view.desired_height(ctx)
     }
 }
 

src/widget/text/mod.rs

@@ -52,15 +52,15 @@ impl TextView {
             .align(self.align)
     }
 
-    fn render(&mut self, painter: &mut Painter) -> &RenderedText {
+    fn render(&mut self, ctx: &mut SizeCtx) -> &RenderedText {
         let width = if self.attrs.wrap {
-            Some(painter.px_len(Axis::X))
+            Some(ctx.px_size().x)
         } else {
             None
         };
         if width != self.width || self.tex.is_none() || self.attrs.changed || self.buf.changed {
             self.width = width;
-            self.tex = Some(painter.render_text(&mut self.buf, &self.attrs, width));
+            self.tex = Some(ctx.draw_text(&mut self.buf, &self.attrs, width));
             self.attrs.changed = false;
             self.buf.changed = false;
         }
@@ -69,40 +69,39 @@ impl TextView {
     pub fn tex(&self) -> Option<&RenderedText> {
         self.tex.as_ref()
     }
-    /// Draws the text, and says where the glyphs went and what they use.
+    pub fn desired_width(&mut self, ctx: &mut SizeCtx) -> Len {
-    pub fn draw(&mut self, painter: &mut Painter) -> (UiRegion, Size) {
+        if self.is_empty()
+            && let Some(hint) = &self.hint
+        {
+            ctx.width(hint)
+        } else {
+            Len::abs(self.render(ctx).size.x)
+        }
+    }
+    pub fn desired_height(&mut self, ctx: &mut SizeCtx) -> Len {
+        if self.is_empty()
+            && let Some(hint) = &self.hint
+        {
+            ctx.height(hint)
+        } else {
+            Len::abs(self.render(ctx).size.y)
+        }
+    }
+    pub fn draw(&mut self, painter: &mut Painter) -> UiRegion {
         let align = self.align;
         if self.is_empty() && self.hint.is_some() {
-            let region = self.render(painter).size.align(align);
+            let region = self.render(&mut painter.size_ctx()).size.align(align);
-            let size = match &self.hint {
+            if let Some(hint) = &self.hint {
-                Some(hint) => painter.widget(hint).size(),
+                painter.widget(hint);
-                None => Size::ZERO,
+            }
-            };
+            return region;
-            return (region, size);
         }
 
-        let tex = self.render(painter);
+        let tex = self.render(&mut painter.size_ctx());
         let region = tex.size.align(align);
-        let size = Size::abs(tex.size);
         let within = region.within(&painter.region());
         painter.glyphs(tex, within);
-        (region, size)
+        region
-    }
-
-    /// Wrapping reads the width it is offered, so a wider box reshapes it and
-    /// a taller one does not. Alignment matters too, and separately: glyphs
-    /// anchored to the start of an axis stay put when that extent changes,
-    /// but centred or end-aligned ones move even though the shaping stands.
-    pub fn on_resize(&self, axis: Axis) -> OnResize {
-        let reshapes = axis == Axis::X && self.attrs.wrap;
-        let anchored = match axis {
-            Axis::X => self.align.x,
-            Axis::Y => self.align.y,
-        } == AxisAlign::Neg;
-        match reshapes || !anchored {
-            true => OnResize::Redraw,
-            false => OnResize::Translate,
-        }
     }
 
     pub fn content(&self) -> String {
@@ -118,7 +117,7 @@ impl Text {
             content: content.into(),
         }
     }
-    fn update_buf(&mut self) {
+    fn update_buf(&mut self, _ctx: &mut SizeCtx) {
         if self.content.changed {
             self.content.changed = false;
             self.view.buf.set_text(self.content.as_str());
@@ -127,13 +126,19 @@ impl Text {
 }
 
 impl Widget for Text {
-    fn draw(&mut self, painter: &mut Painter) -> Size {
+    fn draw(&mut self, painter: &mut Painter) {
-        self.update_buf();
+        self.update_buf(&mut painter.size_ctx());
-        self.view.draw(painter).1
+        self.view.draw(painter);
     }
 
-    fn on_resize(&self, axis: Axis) -> OnResize {
+    fn desired_width(&mut self, ctx: &mut SizeCtx) -> Len {
-        self.view.on_resize(axis)
+        self.update_buf(ctx);
+        self.view.desired_width(ctx)
+    }
+
+    fn desired_height(&mut self, ctx: &mut SizeCtx) -> Len {
+        self.update_buf(ctx);
+        self.view.desired_height(ctx)
     }
 }
 

tests/chain_cost.rs

@@ -1,224 +0,0 @@
-//! What the vertex shader's move-chain walk costs, against how deep the chain
-//! is. Every active widget owns a slot, so the depth a primitive resolves
-//! through is its depth in the widget tree.
-//!
-//!     cargo test --release --test chain_cost -- --ignored --nocapture
-//!
-//! Timed on the GPU with timestamp queries rather than by the clock: wall time
-//! here varied by 2x between runs of one unchanged binary. The pass is
-//! submitted and waited on, so this is the GPU's cost and not the recording
-//! loop's -- which is what `draw_cost.rs` measures instead.
-//!
-//! The instances are two pixels wide so that vertex work dominates; a chain
-//! walk that does not show up against small quads will not show up against
-//! anything.
-//!
-//! The instance is leaked deliberately, for the reason `draw_cost.rs` gives.
-
-use iris::prelude::*;
-use iris_core::{
-    MaskIdx, MoveIdx, PrimitiveInst, RectPrimitive, UiData, UiRegion, UiRenderNode, UiRenderState,
-    UiScalar, UiSpan,
-};
-use wgpu::{Color as GpuColor, *};
-
-const SIZE: u32 = 1024;
-const INSTANCES: usize = 200_000;
-const FRAMES: u32 = 20;
-/// Reported as the best of this many batches, since the mean moves by more
-/// than the thing being measured.
-const BATCHES: u32 = 8;
-
-fn gpu() -> Option<(Device, Queue, f32)> {
-    let all = Instance::new(InstanceDescriptor::new_without_display_handle());
-    let instance = match pollster::block_on(all.request_adapter(&RequestAdapterOptions::default()))
-    {
-        Ok(_) => all,
-        Err(_) => Instance::new(InstanceDescriptor {
-            backends: Backends::GL,
-            ..InstanceDescriptor::new_without_display_handle()
-        }),
-    };
-    let instance: &'static Instance = Box::leak(Box::new(instance));
-    let adapter =
-        pollster::block_on(instance.request_adapter(&RequestAdapterOptions::default())).ok()?;
-    if !adapter.features().contains(Features::TIMESTAMP_QUERY) {
-        println!("no timestamp queries on {:?}", adapter.get_info().name);
-        return None;
-    }
-    println!("adapter: {:?}", adapter.get_info().name);
-    let (device, queue) = pollster::block_on(adapter.request_device(&DeviceDescriptor {
-        required_features: Features::TIMESTAMP_QUERY,
-        ..Default::default()
-    }))
-    .ok()?;
-    let period = queue.get_timestamp_period();
-    Some((device, queue, period))
-}
-
-fn config(format: TextureFormat) -> SurfaceConfiguration {
-    SurfaceConfiguration {
-        usage: TextureUsages::RENDER_ATTACHMENT,
-        format,
-        color_space: SurfaceColorSpace::Auto,
-        width: SIZE,
-        height: SIZE,
-        present_mode: PresentMode::Fifo,
-        desired_maximum_frame_latency: 2,
-        alpha_mode: CompositeAlphaMode::Auto,
-        view_formats: vec![],
-    }
-}
-
-/// A chain `depth` slots long, and instances that all resolve through its end.
-fn fill(ui: &mut UiData, render: &mut UiRenderState, depth: usize) {
-    let kind = ui.primitives.kind::<RectPrimitive>();
-    let id = ui.widgets.add_strong(Rect::new(UiColor::WHITE)).id();
-
-    let mut slot = MoveIdx::NONE;
-    for _ in 0..depth {
-        slot = render.moves.push(slot, UiRegion::FULL);
-    }
-
-    let px = |v: f32| UiScalar { rel: 0.0, abs: v };
-    for i in 0..INSTANCES {
-        let x = (i % (SIZE as usize / 2)) as f32 * 2.0;
-        let y = (i / (SIZE as usize / 2)) as f32;
-        render.layers.write(
-            0,
-            PrimitiveInst {
-                kind,
-                id,
-                primitive: RectPrimitive::color(UiColor::WHITE),
-                region: UiRegion::new(
-                    UiSpan::new(px(x), px(x + 2.0)),
-                    UiSpan::new(px(y), px(y + 1.0)),
-                ),
-                mask_idx: MaskIdx::NONE,
-                move_idx: slot,
-            },
-        );
-    }
-}
-
-/// Nanoseconds the pass took on the GPU, best of `BATCHES`.
-fn pass_cost(device: &Device, queue: &Queue, period: f32, depth: usize) -> f64 {
-    let format = TextureFormat::Bgra8Unorm;
-    let mut node = UiRenderNode::new(device, &config(format));
-    let mut ui = UiData::default();
-    let mut render = UiRenderState::new();
-    fill(&mut ui, &mut render, depth);
-    node.update(device, queue, &mut ui, &mut render);
-
-    let target = device.create_texture(&TextureDescriptor {
-        label: Some("chain cost"),
-        size: Extent3d {
-            width: SIZE,
-            height: SIZE,
-            depth_or_array_layers: 1,
-        },
-        mip_level_count: 1,
-        sample_count: 1,
-        dimension: TextureDimension::D2,
-        format,
-        usage: TextureUsages::RENDER_ATTACHMENT,
-        view_formats: &[],
-    });
-    let view = target.create_view(&TextureViewDescriptor::default());
-
-    let queries = device.create_query_set(&QuerySetDescriptor {
-        label: Some("chain cost"),
-        ty: QueryType::Timestamp,
-        count: 2,
-    });
-    let resolved = device.create_buffer(&BufferDescriptor {
-        label: Some("resolved"),
-        size: 16,
-        usage: BufferUsages::QUERY_RESOLVE | BufferUsages::COPY_SRC,
-        mapped_at_creation: false,
-    });
-    let readback = device.create_buffer(&BufferDescriptor {
-        label: Some("readback"),
-        size: 16,
-        usage: BufferUsages::MAP_READ | BufferUsages::COPY_DST,
-        mapped_at_creation: false,
-    });
-
-    let frame = || {
-        let mut encoder = device.create_command_encoder(&CommandEncoderDescriptor::default());
-        {
-            let pass = &mut encoder.begin_render_pass(&RenderPassDescriptor {
-                label: None,
-                color_attachments: &[Some(RenderPassColorAttachment {
-                    view: &view,
-                    resolve_target: None,
-                    ops: Operations {
-                        load: LoadOp::Clear(GpuColor::BLACK),
-                        store: StoreOp::Store,
-                    },
-                    depth_slice: None,
-                })],
-                depth_stencil_attachment: None,
-                timestamp_writes: Some(RenderPassTimestampWrites {
-                    query_set: &queries,
-                    beginning_of_pass_write_index: Some(0),
-                    end_of_pass_write_index: Some(1),
-                }),
-                occlusion_query_set: None,
-                multiview_mask: None,
-            });
-            node.draw(pass);
-        }
-        encoder.resolve_query_set(&queries, 0..2, &resolved, 0);
-        encoder.copy_buffer_to_buffer(&resolved, 0, &readback, 0, 16);
-        queue.submit(Some(encoder.finish()));
-
-        let slice = readback.slice(..);
-        slice.map_async(MapMode::Read, |_| {});
-        let _ = device.poll(PollType::Wait {
-            submission_index: None,
-            timeout: None,
-        });
-        let ns = {
-            let view = slice.get_mapped_range().expect("timestamps did not map");
-            let stamps: [u64; 2] = [
-                u64::from_le_bytes(view[..8].try_into().unwrap()),
-                u64::from_le_bytes(view[8..16].try_into().unwrap()),
-            ];
-            (stamps[1].saturating_sub(stamps[0])) as f64 * period as f64
-        };
-        readback.unmap();
-        ns
-    };
-
-    frame();
-    let mut best = f64::MAX;
-    for _ in 0..BATCHES {
-        let mut total = 0.0;
-        for _ in 0..FRAMES {
-            total += frame();
-        }
-        best = best.min(total / FRAMES as f64);
-    }
-    best
-}
-
-#[test]
-#[ignore = "measurement, not a check"]
-fn chain_cost_by_depth() {
-    let Some((device, queue, period)) = gpu() else {
-        println!("no gpu with timestamps; nothing measured");
-        return;
-    };
-    println!("{INSTANCES} instances, {SIZE}x{SIZE}, best of {BATCHES} batches");
-    let mut base = None;
-    for depth in [1, 2, 4, 8, 16, 32, 64] {
-        let ns = pass_cost(&device, &queue, period, depth);
-        let base = *base.get_or_insert(ns);
-        println!(
-            "depth {depth:>3}: {:>9.1} us   {:+6.1}% against depth 1",
-            ns / 1000.0,
-            (ns - base) / base * 100.0
-        );
-    }
-}

tests/draw_cost.rs

@@ -22,8 +22,8 @@ use std::time::Instant;
 
 use iris::prelude::*;
 use iris_core::{
-    GlyphPrimitive, MaskIdx, MoveIdx, PrimitiveInst, RectPrimitive, TextureHandle,
+    GlyphPrimitive, MaskIdx, PrimitiveInst, RectPrimitive, TextureHandle, TexturePrimitive, UiData,
-    TexturePrimitive, UiData, UiRegion, UiRenderNode, UiRenderState,
+    UiRegion, UiRenderNode, UiRenderState,
 };
 use wgpu::{Color as GpuColor, *};
 
@@ -95,7 +95,6 @@ fn fill(
                     primitive: RectPrimitive::color(UiColor::WHITE),
                     region: UiRegion::FULL,
                     mask_idx: MaskIdx::NONE,
-                    move_idx: MoveIdx::NONE,
                 },
             );
             render.layers.write(
@@ -112,7 +111,6 @@ fn fill(
                     },
                     region: UiRegion::FULL,
                     mask_idx: MaskIdx::NONE,
-                    move_idx: MoveIdx::NONE,
                 },
             );
         }
@@ -125,7 +123,6 @@ fn fill(
                     primitive: TexturePrimitive::from(h),
                     region: UiRegion::FULL,
                     mask_idx: MaskIdx::NONE,
-                    move_idx: MoveIdx::NONE,
                 },
             );
         }

tests/generated.rs

@@ -1,337 +0,0 @@
-//! Random trees, checked against building the same tree cold.
-//!
-//! A frame reaches its layout by keeping most of the last one: slots
-//! rewritten, some widgets drawn again, the rest untouched. The property here
-//! is that what comes out is the tree a cold start would have produced, so
-//! anything the retained path carried over that it should not have shows up
-//! as a difference in somebody's box.
-//!
-//! `iris::random` grows the tree and `examples/random.rs` draws one. A seed is
-//! the whole reproduction; `a_long_run_of_seeds_agrees` is the ignored sweep
-//! for when it is worth spending the time.
-
-use std::collections::HashMap;
-
-use iris::harness::Harness;
-use iris::prelude::*;
-use iris::random::{Edits, Lens, Rng, SpanEdit, Tree, grow};
-
-const DEPTH: usize = 4;
-const SEEDS: [u64; 7] = [1, 2, 3, 5, 8, 13, 98];
-const REGION_EPSILON_PX: f32 = 0.05;
-
-fn same_coordinate(got: f32, want: f32) -> bool {
-    (got - want).abs() <= REGION_EPSILON_PX
-}
-
-fn same_region(got: Option<PixelRegion>, want: Option<PixelRegion>) -> bool {
-    match (got, want) {
-        (Some(got), Some(want)) => {
-            same_coordinate(got.top_left.x, want.top_left.x)
-                && same_coordinate(got.top_left.y, want.top_left.y)
-                && same_coordinate(got.bot_right.x, want.bot_right.x)
-                && same_coordinate(got.bot_right.y, want.bot_right.y)
-        }
-        (None, None) => true,
-        _ => false,
-    }
-}
-
-fn plant(h: &mut Harness, seed: u64, edits: &Edits) -> Tree {
-    let (root, tree) = grow(&mut h.rsc, seed, DEPTH, edits);
-    h.state.root = Some(root);
-    h.frame();
-    tree
-}
-
-/// Changes a few of the declared sizes, and says which, so the cold tree can
-/// be grown with the same ones.
-fn edit(h: &mut Harness, tree: &Tree, rng: &mut Rng) -> HashMap<usize, Lens> {
-    let mut edits = HashMap::new();
-    for _ in 0..4 {
-        let idx = rng.below(tree.sized.len());
-        let lens = [
-            Some(Len::abs(20.0 + rng.below(180) as f32)),
-            Some(Len::abs(20.0 + rng.below(180) as f32)),
-        ];
-        edits.insert(idx, lens);
-        let sized = &mut h.rsc[tree.sized[idx]];
-        sized.x = lens[0];
-        sized.y = lens[1];
-    }
-    edits
-}
-
-/// A way of changing what a span holds. Each is a shape worth its own case:
-/// taking a child out of the middle is not the same as emptying a span, and
-/// adding one is not the same as adding three.
-#[derive(Clone, Copy, Debug)]
-enum Shuffle {
-    /// Every other child, so what is left is interleaved with what went.
-    EveryOther,
-    /// Everything but the first, which is the last step before empty.
-    AllButFirst,
-    /// Three more on the end at once.
-    AddThree,
-    /// The first out and three more on, so the count moves both ways.
-    SwapForThree,
-    /// One out of the middle and one on the end.
-    TradeOne,
-}
-
-const SHUFFLES: [Shuffle; 5] = [
-    Shuffle::EveryOther,
-    Shuffle::AllButFirst,
-    Shuffle::AddThree,
-    Shuffle::SwapForThree,
-    Shuffle::TradeOne,
-];
-
-impl Shuffle {
-    fn of(self, grown: usize) -> SpanEdit {
-        let all = |step: usize, from: usize| (from..grown).step_by(step).collect();
-        match self {
-            Self::EveryOther => SpanEdit {
-                detach: all(2, 0),
-                attach: 0,
-            },
-            Self::AllButFirst => SpanEdit {
-                detach: all(1, 1),
-                attach: 0,
-            },
-            Self::AddThree => SpanEdit {
-                detach: Vec::new(),
-                attach: 3,
-            },
-            Self::SwapForThree => SpanEdit {
-                detach: vec![0],
-                attach: 3,
-            },
-            Self::TradeOne => SpanEdit {
-                detach: vec![grown / 2],
-                attach: 1,
-            },
-        }
-    }
-}
-
-/// Applies `shuffle` to every third span, and says what it did so the cold
-/// tree can be grown that way. The widgets it takes out are given back: the
-/// last share of one must outlive the comparison, or its id is handed to
-/// something else and the two trees stop lining up.
-fn reshuffle(
-    h: &mut Harness,
-    tree: &mut Tree,
-    shuffle: Shuffle,
-) -> (HashMap<usize, SpanEdit>, Vec<StrongWidget>) {
-    let mut edits = HashMap::new();
-    let mut detached = Vec::new();
-    for (idx, span) in tree.spans.iter_mut().enumerate().step_by(3) {
-        let span_edit = shuffle.of(span.grown);
-        let mut take = span_edit.detach.clone();
-        take.sort_unstable();
-        let children = &mut h.rsc[span.id].children;
-        // Highest first, so an index means the same child however many of
-        // its neighbours are going too.
-        for j in take.into_iter().rev() {
-            if j < children.len() {
-                detached.push(children.remove(j));
-            }
-        }
-        let attach = span_edit.attach.min(span.spares.len());
-        children.extend(span.spares.drain(..attach));
-        edits.insert(idx, span_edit);
-    }
-    (edits, detached)
-}
-
-/// Every widget in one tree against the matching widget in the other. A
-/// mismatch prints the widget's ancestry, marking the ones that own a slot,
-/// since where two trees disagree is rarely where the cause is.
-fn assert_same(seed: u64, what: &str, warm: (&Harness, &Tree), cold: (&Harness, &Tree)) {
-    let ((wh, wt), (ch, ct)) = (warm, cold);
-    assert_eq!(wt.ids.len(), ct.ids.len(), "seed {seed}: different trees");
-    let mut drawn = 0;
-    let mut wrong = 0;
-    for (i, (&w, &c)) in wt.ids.iter().zip(&ct.ids).enumerate() {
-        let (got, want) = (wh.region(&w), ch.region(&c));
-        drawn += usize::from(got.is_some());
-        // This oracle cares where rasterization lands, not whether equivalent
-        // arithmetic produced the same f32. Keep the tolerance to one
-        // twentieth of a physical pixel, while whether a widget drew remains
-        // exact.
-        if same_region(got, want) {
-            continue;
-        }
-        wrong += 1;
-        if wrong <= 3 {
-            let mut chain = Vec::new();
-            let mut at = Some(w);
-            while let Some(id) = at {
-                let active = &wh.render.active[&id];
-                let slot = match active.move_idx == active.parent_move {
-                    true => "",
-                    false => "*",
-                };
-                chain.push(format!("{}{slot}", wh.rsc.widgets().label(id)));
-                at = active.parent;
-            }
-            println!(
-                "seed {seed} after {what}: widget {i}\n  warm {got:?}\n  cold {want:?}\n  {}",
-                chain.join(" < ")
-            );
-        }
-    }
-    assert!(drawn > 0, "seed {seed}: nothing was drawn");
-    assert_eq!(wrong, 0, "seed {seed}: {wrong} widgets differ after {what}");
-}
-
-fn changed_size(seed: u64) {
-    let mut warm = Harness::new((900, 1200));
-    let grown = plant(&mut warm, seed, &Edits::default());
-
-    let mut rng = Rng::new(seed ^ 0x5eed);
-    let sizes = edit(&mut warm, &grown, &mut rng);
-    warm.frame();
-
-    let mut cold = Harness::new((900, 1200));
-    let same = plant(
-        &mut cold,
-        seed,
-        &Edits {
-            sizes,
-            ..Default::default()
-        },
-    );
-
-    assert_same(seed, "a size change", (&warm, &grown), (&cold, &same));
-}
-
-fn reshuffled(seed: u64, shuffle: Shuffle) {
-    let mut warm = Harness::new((900, 1200));
-    let mut grown = plant(&mut warm, seed, &Edits::default());
-    // Some seeds grow nothing but wrappers, and a shuffle with no span to
-    // shuffle is not the same thing as one that had no effect.
-    if grown.spans.is_empty() {
-        return;
-    }
-    let before: Vec<_> = grown.ids.iter().map(|id| warm.region(id)).collect();
-
-    let (spans, _held) = reshuffle(&mut warm, &mut grown, shuffle);
-    warm.frame();
-
-    // Or the two trees would agree for want of anything having happened.
-    let after = grown.ids.iter().map(|id| warm.region(id));
-    let moved = before.iter().zip(after).filter(|(a, b)| *a != b).count();
-    assert!(moved > 0, "seed {seed}: {shuffle:?} changed nothing");
-
-    let mut cold = Harness::new((900, 1200));
-    let same = plant(
-        &mut cold,
-        seed,
-        &Edits {
-            spans,
-            ..Default::default()
-        },
-    );
-
-    let what = format!("{shuffle:?}");
-    assert_same(seed, &what, (&warm, &grown), (&cold, &same));
-}
-
-fn resized(seed: u64) {
-    let mut warm = Harness::new((1920, 1200));
-    let grown = plant(&mut warm, seed, &Edits::default());
-    warm.resize((640, 900));
-    warm.frame();
-
-    let mut cold = Harness::new((640, 900));
-    let same = plant(&mut cold, seed, &Edits::default());
-
-    assert_same(seed, "a resize", (&warm, &grown), (&cold, &same));
-}
-
-fn resized_then_changed(seed: u64) {
-    let mut warm = Harness::new((1920, 1200));
-    let grown = plant(&mut warm, seed, &Edits::default());
-    warm.resize((640, 900));
-    warm.frame();
-
-    let mut rng = Rng::new(seed ^ 0xb0a7);
-    let sizes = edit(&mut warm, &grown, &mut rng);
-    warm.frame();
-
-    let mut cold = Harness::new((640, 900));
-    let same = plant(
-        &mut cold,
-        seed,
-        &Edits {
-            sizes,
-            ..Default::default()
-        },
-    );
-
-    let what = "a resize then a size change";
-    assert_same(seed, what, (&warm, &grown), (&cold, &same));
-}
-
-#[test]
-fn a_changed_size_lands_where_growing_it_that_way_would() {
-    SEEDS.into_iter().for_each(changed_size);
-}
-
-#[test]
-fn a_resize_lands_where_starting_at_that_size_would() {
-    SEEDS.into_iter().for_each(resized);
-}
-
-#[test]
-fn a_size_change_after_a_resize_lands_the_same_way() {
-    SEEDS.into_iter().for_each(resized_then_changed);
-}
-
-#[test]
-fn adding_and_removing_span_children_lands_where_growing_it_that_way_would() {
-    for shuffle in SHUFFLES {
-        for seed in SEEDS {
-            reshuffled(seed, shuffle);
-        }
-    }
-}
-
-/// Reproduces a divergence that predates the position chain: laying a tree out
-/// again does not always land where growing it cold does.
-///
-/// Every one seen so far is a wrapping text on a span's *own* axis, where the
-/// two draws do not agree. The span measures the child in the whole box, the
-/// child shapes to that width and reports the width it used, the span then
-/// places it in exactly that width -- which is a length change, so the child
-/// shapes again, and its longest line is shorter than the box it was just
-/// given. Each pass narrows it, so where the tree ends up depends on how many
-/// passes it has had, and a warm tree has had a different number from a cold
-/// one. Layout is supposed to be a function of the state alone.
-///
-/// A span whose axis is not the wrap axis is stable, which is every real
-/// column of text, and why nothing else has run into this.
-///
-/// 7 of these 90 diverge on `db1751f`, before the chain; 30 do with it, since
-/// a placed child reaches the second shaping more often. Both numbers are the
-/// same defect, and it wants fixing where the two draws meet -- LAYOUT.md §4 --
-/// rather than anywhere in the chain.
-#[test]
-#[ignore = "a hundred seeds, rather than the seven the others check"]
-fn a_long_run_of_seeds_agrees() {
-    let seeds = std::env::var("IRIS_GENERATED_SEED")
-        .ok()
-        .and_then(|seed| seed.parse().ok())
-        .map(|seed| seed..=seed)
-        .unwrap_or(1..=100);
-    for seed in seeds {
-        changed_size(seed);
-        resized(seed);
-        resized_then_changed(seed);
-        for shuffle in SHUFFLES {
-            reshuffled(seed, shuffle);
-        }
-    }
-}

tests/layout.rs

@@ -32,153 +32,3 @@ fn resizing_relays_out_against_the_new_output() {
     assert_corners!(h, left, (0, 0), (100, 100));
     assert_corners!(h, right, (100, 0), (800, 100));
 }
-
-#[test]
-fn an_empty_widget_takes_a_share_of_a_span() {
-    let mut h = Harness::new((400, 200));
-    let gap = ().add(&mut h.rsc);
-    let right = rect(Color::BLUE).width(100).add(&mut h.rsc);
-    h.set_root((gap, right).span(Dir::RIGHT));
-
-    assert_corners!(h, gap, (0, 0), (300, 200));
-    assert_corners!(h, right, (300, 0), (400, 200));
-}
-
-#[test]
-fn a_child_drawn_twice_moves_once() {
-    let mut h = Harness::new((400, 200));
-    // `Aligned` draws its child twice; listing it twice would move it twice.
-    let inner = rect(Color::BLUE).add(&mut h.rsc);
-    let centered = inner.center().width(200).add(&mut h.rsc);
-    let left = rect(Color::RED).width(100).add(&mut h.rsc);
-    h.set_root((left, centered).span(Dir::RIGHT));
-    assert_corners!(h, inner, (100, 0), (300, 200));
-
-    h.rsc[left].x = Some(Len::abs(150));
-    h.frame();
-
-    assert_corners!(h, inner, (150, 0), (350, 200));
-}
-
-#[test]
-fn a_resize_lands_where_a_cold_start_would() {
-    let build = |h: &mut Harness| {
-        let para = wtext(
-            "Wrapping shapes one source into as many lines as its container leaves room \
-             for, so the height of a paragraph is an answer rather than a setting.",
-        )
-        .size(20)
-        .wrap(true)
-        .pad(16)
-        .add(&mut h.rsc);
-        let below = rect(Color::RED).add(&mut h.rsc);
-        let root = (para, below).span(Dir::DOWN).pad(12);
-        h.set_root(root);
-        (para, below)
-    };
-
-    let mut cold = Harness::new((900, 1200));
-    let (cold_para, cold_below) = build(&mut cold);
-
-    let mut resized = Harness::new((1920, 1200));
-    let (para, below) = build(&mut resized);
-    resized.resize((900, 1200));
-    resized.frame();
-
-    assert_eq!(resized.region(&para), cold.region(&cold_para), "paragraph");
-    assert_eq!(resized.region(&below), cold.region(&cold_below), "below");
-}
-
-#[test]
-fn a_fixed_box_is_drawn_again_rather_than_stretched() {
-    let mut h = Harness::new((400, 400));
-    // The panel fills a stack sized by its sibling, so it is drawn in the
-    // whole box and then placed in the shorter one. Reusing it in that fixed
-    // box afterwards would leave it whatever height it happened to have.
-    let panel = rect(Color::BLUE).add(&mut h.rsc);
-    let leaf = rect(Color::RED).height(100).add(&mut h.rsc);
-    let stack = (panel, leaf)
-        .stack()
-        .size(StackSize::Child(1))
-        .add(&mut h.rsc);
-    h.set_root(stack.align(Align::TOP));
-    assert_corners!(h, panel, (0, 0), (400, 100));
-
-    h.rsc[leaf].y = Some(Len::abs(250));
-    h.frame();
-
-    assert_corners!(h, panel, (0, 0), (400, 250));
-}
-
-#[test]
-fn a_moved_subtree_takes_its_children_with_it() {
-    let mut h = Harness::new((400, 400));
-    let first = rect(Color::RED).height(40).add(&mut h.rsc);
-    let inner = rect(Color::BLUE).add(&mut h.rsc);
-    let row = inner.pad(10).height(40).add(&mut h.rsc);
-    h.set_root((first, row).span(Dir::DOWN));
-    assert_corners!(h, inner, (10, 50), (390, 70));
-
-    h.rsc[first].y = Some(Len::abs(80));
-    h.frame();
-
-    // The row is the same shape somewhere else, so one slot moved it and
-    // `inner`'s own region was never rewritten.
-    assert_corners!(h, inner, (10, 90), (390, 110));
-}
-
-#[test]
-fn a_fixed_length_child_keeps_it_when_the_box_around_it_grows() {
-    let mut h = Harness::new((400, 200));
-    let fixed = rect(Color::BLUE).width(50).add(&mut h.rsc);
-    let rest = rect(Color::GREEN).add(&mut h.rsc);
-    let panel = (fixed, rest).span(Dir::RIGHT).add(&mut h.rsc);
-    // Changing the bar's width is the only thing that changes the box the
-    // panel and everything under it was drawn for.
-    let bar = rect(Color::RED).width(100).add(&mut h.rsc);
-    h.set_root((bar, panel).span(Dir::RIGHT));
-    assert_corners!(h, fixed, (100, 0), (150, 200));
-    assert_corners!(h, rest, (150, 0), (400, 200));
-
-    h.rsc[bar].x = Some(Len::abs(200));
-    h.frame();
-
-    // The panel's box is 100 shorter, so the fixed child is the same 50 wide
-    // against its new start and the one taking the rest absorbs the change.
-    assert_corners!(h, fixed, (200, 0), (250, 200));
-    assert_corners!(h, rest, (250, 0), (400, 200));
-}
-
-#[test]
-fn a_box_with_a_fixed_length_can_be_stretched_on_its_other_axis() {
-    let mut h = Harness::new((400, 200));
-    // The row is 40 tall whatever happens, which used to make its drawing
-    // impossible to take out of: recovering a fraction of a box needs a
-    // relative extent, and it has none on that axis.
-    let inner = rect(Color::BLUE).add(&mut h.rsc);
-    let row = inner.pad(10).height(40).add(&mut h.rsc);
-    let filler = rect(Color::GREEN).add(&mut h.rsc);
-    let column = (row, filler).span(Dir::DOWN).add(&mut h.rsc);
-    let bar = rect(Color::RED).width(100).add(&mut h.rsc);
-    h.set_root((bar, column).span(Dir::RIGHT));
-    assert_corners!(h, inner, (110, 10), (390, 30));
-
-    h.rsc[bar].x = Some(Len::abs(200));
-    h.frame();
-
-    assert_corners!(h, inner, (210, 10), (390, 30));
-}
-
-#[test]
-fn only_a_container_that_places_its_children_lengthens_the_chain() {
-    let mut h = Harness::new((400, 200));
-    let leaf = rect(Color::BLUE).add(&mut h.rsc);
-    // Four widgets between the span and the leaf, none of which places what
-    // it draws, so all of them share the span's slot.
-    let buried = leaf.pad(4).pad(4).pad(4).pad(4).add(&mut h.rsc);
-    let bar = rect(Color::RED).width(100).add(&mut h.rsc);
-    h.set_root((bar, buried).span(Dir::RIGHT));
-
-    let slot = h.render.active[&leaf.id()].parent_move;
-    assert_eq!(h.render.moves.depth(slot), 1, "one span above the leaf");
-}

tests/layout_diagnostics.rs

@@ -1,218 +0,0 @@
-//! Retained CPU-layout diagnostics on one reproducible random tree.
-//!
-//! Counters and phase timers:
-//!
-//!     cargo test --release --features layout-diagnostics \
-//!       --test layout_diagnostics -- --ignored --nocapture
-//!
-//! Uninstrumented hardware totals for one phase:
-//!
-//!     IRIS_PHASE=resize IRIS_FRAMES=1000 perf stat \
-//!       -e cycles:u,instructions:u cargo test --release \
-//!       --test layout_diagnostics -- --ignored --nocapture
-//!
-//! `IRIS_PHASE` is `cold`, `repaint`, `size`, `scroll`, `resize`, or `all`.
-//! `IRIS_SEED`, `IRIS_DEPTH`, and `IRIS_FRAMES` select the load.
-
-use iris::harness::Harness;
-use iris::prelude::*;
-use iris::random::{Edits, Tree, grow};
-use std::time::Instant;
-
-const OUTPUT: (f32, f32) = (1920.0, 1200.0);
-
-#[cfg(feature = "layout-diagnostics")]
-#[test]
-fn a_selected_widget_retains_its_layout_events() {
-    use iris::core::layout_diagnostics::{self as diagnostics, TraceEvent};
-
-    diagnostics::clear_traced_widgets();
-    let _ = diagnostics::take();
-    let mut harness = Harness::new((400, 200));
-    let leaf = rect(Color::RED).add(&mut harness.rsc);
-    let other = rect(Color::BLUE).add(&mut harness.rsc);
-    let root = (leaf, other).span(Dir::RIGHT).add(&mut harness.rsc);
-    harness.set_root(root);
-    diagnostics::trace_widget(leaf.id());
-    let _ = diagnostics::take();
-
-    let _ = harness.rsc.widgets_mut().get_dyn_mut(root.id());
-    let _ = harness.rsc.widgets_mut().get_dyn_mut(leaf.id());
-    harness.frame();
-
-    let report = diagnostics::take();
-    assert!(
-        report
-            .traces()
-            .iter()
-            .any(|event| matches!(event, TraceEvent::Placed { id, .. } if *id == leaf.id()))
-    );
-    assert!(
-        report
-            .traces()
-            .iter()
-            .any(|event| matches!(event, TraceEvent::DrawRequest { id, .. } if *id == leaf.id()))
-    );
-    assert!(
-        report
-            .traces()
-            .iter()
-            .any(|event| matches!(event, TraceEvent::SizeRead { id, .. } if *id == leaf.id()))
-    );
-    assert!(
-        report
-            .traces()
-            .iter()
-            .any(|event| matches!(event, TraceEvent::SizeReported { id, .. } if *id == leaf.id()))
-    );
-    diagnostics::clear_traced_widgets();
-}
-
-fn env<T: std::str::FromStr>(name: &str, fallback: T) -> T {
-    std::env::var(name)
-        .ok()
-        .and_then(|value| value.parse().ok())
-        .unwrap_or(fallback)
-}
-
-#[cfg(feature = "layout-diagnostics")]
-fn trace_selected(tree: &Tree) {
-    let Ok(value) = std::env::var("IRIS_TRACE_INDEX") else {
-        return;
-    };
-    let index = value
-        .parse::<usize>()
-        .expect("IRIS_TRACE_INDEX must be a tree.ids index");
-    let id = tree.ids[index];
-    iris::core::layout_diagnostics::trace_widget(id);
-    println!("tracing tree.ids[{index}] = {id:?}");
-}
-
-#[cfg(not(feature = "layout-diagnostics"))]
-fn trace_selected(_: &Tree) {}
-
-fn warm(seed: u64, depth: usize) -> (Harness, Tree) {
-    let mut harness = Harness::new(OUTPUT);
-    let (root, tree) = grow(&mut harness.rsc, seed, depth, &Edits::default());
-    harness.state.root = Some(root);
-    harness.frame();
-    println!(
-        "fixture: seed {seed}, depth {depth}, {} widgets, {} active",
-        tree.ids.len(),
-        harness.render.active_widgets()
-    );
-    #[cfg(feature = "layout-diagnostics")]
-    let _ = iris::core::layout_diagnostics::take();
-    (harness, tree)
-}
-
-fn report(label: &str, mut elapsed: Vec<f64>, _harness: &Harness) {
-    elapsed.sort_by(|a, b| a.partial_cmp(b).unwrap());
-    let frames = elapsed.len();
-    println!(
-        "{label}: {frames} frame(s), min {:.3} ms, median {:.3} ms, total {:.1} ms",
-        elapsed[0],
-        elapsed[frames / 2],
-        elapsed.iter().sum::<f64>(),
-    );
-    #[cfg(feature = "layout-diagnostics")]
-    {
-        let diagnostics = iris::core::layout_diagnostics::take();
-        print!("{}", diagnostics.per_frame(frames));
-        for callsite in diagnostics.hot_text().iter().take(3) {
-            let mut ancestry = Vec::new();
-            let mut id = Some(callsite.id);
-            while let Some(widget) = id {
-                ancestry.push(_harness.rsc.widgets().label(widget).as_str());
-                id = _harness
-                    .render
-                    .active
-                    .get(&widget)
-                    .and_then(|active| active.parent);
-            }
-            println!("    text ancestry: {}", ancestry.join(" < "));
-        }
-    }
-}
-
-fn run(
-    label: &str,
-    frames: usize,
-    harness: &mut Harness,
-    mut change: impl FnMut(&mut Harness, usize),
-) {
-    let mut elapsed = Vec::with_capacity(frames);
-    for frame in 0..frames {
-        change(harness, frame);
-        let start = Instant::now();
-        harness.frame();
-        elapsed.push(start.elapsed().as_secs_f64() * 1_000.0);
-    }
-    report(label, elapsed, harness);
-}
-
-#[test]
-#[ignore = "measurement, not a check"]
-fn layout_cost() {
-    let seed = env("IRIS_SEED", 1_u64);
-    let depth = env("IRIS_DEPTH", 7_usize);
-    let frames = env("IRIS_FRAMES", 100_usize);
-    assert!(frames > 0, "IRIS_FRAMES must be greater than zero");
-    let phase = env("IRIS_PHASE", String::from("all"));
-    assert!(
-        ["all", "cold", "repaint", "size", "scroll", "resize"].contains(&phase.as_str()),
-        "unknown IRIS_PHASE {phase:?}"
-    );
-    let selected = |name| phase == "all" || phase == name;
-
-    if selected("cold") {
-        let mut harness = Harness::new(OUTPUT);
-        let (root, tree) = grow(&mut harness.rsc, seed, depth, &Edits::default());
-        harness.state.root = Some(root);
-        println!(
-            "fixture: seed {seed}, depth {depth}, {} widgets",
-            tree.ids.len()
-        );
-        trace_selected(&tree);
-        #[cfg(feature = "layout-diagnostics")]
-        let _ = iris::core::layout_diagnostics::take();
-        run("cold", 1, &mut harness, |_, _| {});
-        drop(tree);
-    }
-
-    if selected("repaint") {
-        let (mut harness, tree) = warm(seed, depth);
-        trace_selected(&tree);
-        let leaf = tree.ids[0];
-        run("repaint", frames, &mut harness, move |harness, _| {
-            let _ = harness.rsc.widgets_mut().get_dyn_mut(leaf);
-        });
-    }
-
-    if selected("size") {
-        let (mut harness, tree) = warm(seed, depth);
-        trace_selected(&tree);
-        let sized = tree.sized[0];
-        run("size", frames, &mut harness, move |harness, frame| {
-            harness.rsc[sized].x = Some(Len::abs(100.0 + (frame % 2) as f32 * 40.0));
-        });
-    }
-
-    if selected("scroll") {
-        let (mut harness, tree) = warm(seed, depth);
-        trace_selected(&tree);
-        let scroll = tree.scrolls[0];
-        run("scroll", frames, &mut harness, move |harness, frame| {
-            harness.rsc[scroll].scroll(if frame % 2 == 0 { 12.0 } else { -12.0 });
-        });
-    }
-
-    if selected("resize") {
-        let (mut harness, tree) = warm(seed, depth);
-        trace_selected(&tree);
-        run("resize", frames, &mut harness, |harness, frame| {
-            harness.resize((OUTPUT.0 - ((frame + 1) % 2) as f32 * 8.0, OUTPUT.1));
-        });
-        drop(tree);
-    }
-}

tests/pointer.rs

@@ -2,7 +2,7 @@
 
 use std::{cell::RefCell, rc::Rc};
 
-use iris::harness::{Harness, TouchScript};
+use iris::harness::Harness;
 use iris::prelude::*;
 
 #[test]
@@ -58,28 +58,3 @@ fn hover_ends_when_the_cursor_leaves_the_window() {
     h.leave();
     assert_eq!((*hovered.borrow(), *ended.borrow()), (1, 1));
 }
-
-#[test]
-fn a_recorded_gesture_presses_where_it_says() {
-    let mut h = Harness::new((400, 200));
-    let clicks = Rc::new(RefCell::new(Vec::new()));
-
-    let (on_left, on_right) = (clicks.clone(), clicks.clone());
-    let left = rect(Color::RED)
-        .width(100)
-        .on(CursorSense::click(), move |_, _| {
-            on_left.borrow_mut().push("left")
-        })
-        .add(&mut h.rsc);
-    let right = rect(Color::BLUE)
-        .on(CursorSense::click(), move |_, _| {
-            on_right.borrow_mut().push("right")
-        })
-        .add(&mut h.rsc);
-    h.set_root((left, right).span(Dir::RIGHT));
-
-    let script = TouchScript::parse("0 down 300 100\n80 up 300 100").unwrap();
-    h.replay(&script);
-
-    assert_eq!(*clicks.borrow(), ["right"]);
-}

tests/pointer_routing.rs

@@ -1,225 +0,0 @@
-//! Input across layers: what stops at a layer, what passes through it, and
-//! where hovering stops.
-
-use std::{cell::RefCell, rc::Rc};
-
-use iris::harness::Harness;
-use iris::prelude::*;
-
-const WINDOW: f32 = 100.0;
-
-/// Every sense that has fired on one widget since it was last read.
-#[derive(Default, Clone)]
-struct Fired(Rc<RefCell<Vec<CursorSense>>>);
-
-impl Fired {
-    fn take(&self) -> Vec<CursorSense> {
-        std::mem::take(&mut self.0.borrow_mut())
-    }
-}
-
-/// A widget filling whatever it is given, recording the senses it is sent.
-fn listener(h: &mut Harness, senses: impl Into<CursorSenses>) -> (WeakWidget<Rect>, Fired) {
-    let fired = Fired::default();
-    let record = fired.clone();
-    let id = rect(Color::WHITE)
-        .on(senses.into(), move |ctx, _| {
-            record.0.borrow_mut().push(ctx.data.sense)
-        })
-        .add(&mut h.rsc);
-    (id, fired)
-}
-
-/// A widget with no senses of its own, to leave a gap beside one that has.
-fn blank(h: &mut Harness) -> WeakWidget<Rect> {
-    rect(Color::WHITE).add(&mut h.rsc)
-}
-
-fn harness() -> Harness {
-    Harness::new((WINDOW, WINDOW))
-}
-
-#[test]
-fn hover_stops_at_the_topmost_widget() {
-    let mut h = harness();
-    let (bottom, bottom_hover) = listener(&mut h, CursorSense::HoverStart);
-    let (middle, middle_hover) = listener(&mut h, CursorSense::HoverStart);
-    let (top, top_hover) = listener(&mut h, CursorSense::HoverStart);
-    h.set_root((bottom, middle, top).stack());
-
-    h.move_to((50, 50));
-
-    assert_eq!(top_hover.take(), [CursorSense::HoverStart]);
-    assert_eq!(
-        middle_hover.take(),
-        [],
-        "hover is not shared with a layer below"
-    );
-    assert_eq!(bottom_hover.take(), []);
-}
-
-#[test]
-fn a_scroll_passes_through_every_widget_that_does_not_want_it() {
-    let mut h = harness();
-    let (list, scrolled) = listener(&mut h, CursorSense::Scroll);
-    let (button, clicked) = listener(&mut h, CursorSense::click());
-    let (overlay, overlay_clicked) = listener(&mut h, CursorSense::click());
-    h.set_root((list, button, overlay).stack());
-
-    h.move_to((50, 50));
-    h.scroll((0, 10));
-
-    assert_eq!(
-        scrolled.take(),
-        [CursorSense::Scroll],
-        "two layers of click-only widgets do not stop a scroll"
-    );
-    assert_eq!(clicked.take(), []);
-    assert_eq!(overlay_clicked.take(), []);
-}
-
-#[test]
-fn hovering_a_button_above_does_not_stop_a_later_scroll() {
-    let mut h = harness();
-    let (list, scrolled) = listener(&mut h, CursorSense::Scroll);
-    let (button, _clicked) = listener(&mut h, CursorSense::click());
-    h.set_root((list, button).stack());
-
-    // The hover arrives in its own frame, as a window delivers it.
-    h.move_to((50, 50));
-    assert_eq!(scrolled.take(), []);
-
-    h.scroll((0, 10));
-    assert_eq!(
-        scrolled.take(),
-        [CursorSense::Scroll],
-        "a hover already resting on the button must not consume the wheel"
-    );
-}
-
-#[test]
-fn only_the_topmost_listener_takes_a_press() {
-    let mut h = harness();
-    let (below, below_clicked) = listener(&mut h, CursorSense::click());
-    let (above, above_clicked) = listener(&mut h, CursorSense::click());
-    h.set_root((below, above).stack());
-
-    h.click((50, 50));
-
-    assert_eq!(above_clicked.take(), [CursorSense::click()]);
-    assert_eq!(below_clicked.take(), [], "one press goes to one widget");
-}
-
-#[test]
-fn a_press_beside_the_button_reaches_the_layer_below() {
-    let mut h = harness();
-    let (list, list_clicked) = listener(&mut h, CursorSense::click());
-    // The row above the list covers it, but only its left half is the button.
-    let (button, button_clicked) = listener(&mut h, CursorSense::click());
-    let row = (button, blank(&mut h)).span(Dir::RIGHT).add(&mut h.rsc);
-    h.set_root((list, row).stack());
-
-    h.click((20, 50));
-    assert_eq!(button_clicked.take(), [CursorSense::click()]);
-    assert_eq!(list_clicked.take(), []);
-
-    h.click((80, 50));
-    assert_eq!(button_clicked.take(), [], "the cursor is not on the button");
-    assert_eq!(
-        list_clicked.take(),
-        [CursorSense::click()],
-        "a press beside the button belongs to what is under it"
-    );
-}
-
-#[test]
-fn leaving_a_widget_still_ends_its_hover() {
-    let mut h = harness();
-    let (widget, hover) = listener(&mut h, CursorSense::HoverStart | CursorSense::HoverEnd);
-    h.set_root(widget);
-
-    h.move_to((50, 50));
-    assert_eq!(hover.take(), [CursorSense::HoverStart]);
-
-    h.leave();
-    assert_eq!(hover.take(), [CursorSense::HoverEnd]);
-}
-
-#[test]
-fn leaving_a_widget_does_not_block_the_layer_below() {
-    let mut h = harness();
-    let (below, below_hover) = listener(&mut h, CursorSense::HoverStart);
-    // Only the left half of the layer above is a widget, so the cursor can
-    // leave it without leaving the one underneath.
-    let (above, above_hover) = listener(&mut h, CursorSense::HoverStart | CursorSense::HoverEnd);
-    let row = (above, blank(&mut h)).span(Dir::RIGHT).add(&mut h.rsc);
-    h.set_root((below, row).stack());
-
-    h.move_to((20, 50));
-    assert_eq!(above_hover.take(), [CursorSense::HoverStart]);
-    assert_eq!(below_hover.take(), [], "the layer above is over it");
-
-    h.move_to((80, 50));
-    assert_eq!(above_hover.take(), [CursorSense::HoverEnd]);
-    assert_eq!(
-        below_hover.take(),
-        [CursorSense::HoverStart],
-        "ending a hover above must not stop the hover below"
-    );
-}
-
-#[test]
-fn covering_a_widget_ends_its_hover() {
-    let mut h = harness();
-    let (below, below_hover) = listener(&mut h, CursorSense::HoverStart | CursorSense::HoverEnd);
-    let (above, above_hover) = listener(&mut h, CursorSense::HoverStart);
-    let row = (above, blank(&mut h)).span(Dir::RIGHT).add(&mut h.rsc);
-    h.set_root((below, row).stack());
-
-    h.move_to((80, 50));
-    assert_eq!(below_hover.take(), [CursorSense::HoverStart]);
-
-    h.move_to((20, 50));
-    assert_eq!(above_hover.take(), [CursorSense::HoverStart]);
-    assert_eq!(
-        below_hover.take(),
-        [CursorSense::HoverEnd],
-        "a widget covered by one that took the input is no longer hovered"
-    );
-
-    h.move_to((80, 50));
-    assert_eq!(
-        below_hover.take(),
-        [CursorSense::HoverStart],
-        "uncovering it hovers it again"
-    );
-}
-
-#[test]
-fn hover_starts_and_ends_once_each() {
-    let mut h = harness();
-    // Only the left half is the widget, so the cursor can leave it without
-    // leaving the window.
-    let (widget, hover) = listener(&mut h, CursorSense::HoverStart | CursorSense::HoverEnd);
-    let row = (widget, blank(&mut h)).span(Dir::RIGHT).add(&mut h.rsc);
-    h.set_root(row);
-
-    h.move_to((20, 50));
-    assert_eq!(hover.take(), [CursorSense::HoverStart]);
-
-    h.move_to((30, 50));
-    assert_eq!(hover.take(), [], "staying inside is not a second start");
-
-    h.move_to((80, 50));
-    assert_eq!(hover.take(), [CursorSense::HoverEnd]);
-
-    h.move_to((90, 50));
-    assert_eq!(hover.take(), [], "an ended hover does not end again");
-
-    h.move_to((20, 50));
-    assert_eq!(
-        hover.take(),
-        [CursorSense::HoverStart],
-        "re-entering starts it"
-    );
-}

tests/replace_cost.rs

@@ -1,43 +0,0 @@
-//! What re-placing a subtree costs per frame, as a load for a counter rather
-//! than a check. A span of 200 fixed-height rows, five primitives each, with
-//! the row above them changing height every frame, so every row below is
-//! offered a box the same shape somewhere else.
-//!
-//!     cargo test --release --test replace_cost -- --ignored
-//!     perf stat -e instructions:u target/release/.../replace_cost-* --ignored
-//!
-//! Wall time is the wrong number here; see `draw_cost.rs`. Measured on
-//! 2026-09-14 at 1.98M instructions per frame, against 2.38M for rewriting
-//! each row's regions instead and 7.13M for redrawing them.
-
-use iris::harness::Harness;
-use iris::prelude::*;
-
-const ROWS: usize = 200;
-const FRAMES: usize = 200;
-
-#[test]
-#[ignore = "measurement, not a check"]
-fn replacing_rows_every_frame() {
-    let mut h = Harness::new((1920, 1200));
-    let first = rect(Color::RED).height(40).add(&mut h.rsc);
-    let mut span = Span::empty(Dir::DOWN);
-    span.push(first.add_strong(&mut h.rsc));
-    for i in 0..ROWS {
-        let row = (
-            rect(Color::BLUE.darker(i as f32 / (ROWS * 2) as f32)),
-            rect(Color::GREEN).pad(2),
-            wtext("row").size(16).pad(2),
-        )
-            .span(Dir::RIGHT)
-            .pad(4)
-            .height(40)
-            .add(&mut h.rsc);
-        span.push(row.add_strong(&mut h.rsc));
-    }
-    h.set_root(span);
-    for i in 0..FRAMES {
-        h.rsc[first].y = Some(Len::abs(40.0 + (i % 2) as f32));
-        h.frame();
-    }
-}

tests/retained.rs

@@ -1,445 +0,0 @@
-//! What a second frame draws again, and what it keeps.
-
-use std::{cell::Cell, rc::Rc};
-
-use iris::harness::{Harness, assert_corners};
-use iris::prelude::*;
-
-/// A leaf that counts its draws and reports whatever size it is given, so a
-/// test can see what the retained path skipped.
-struct Counted {
-    draws: Rc<Cell<usize>>,
-    size: Size,
-    dependence: OnResize,
-}
-
-impl Widget for Counted {
-    fn draw(&mut self, _: &mut Painter) -> Size {
-        self.draws.set(self.draws.get() + 1);
-        self.size
-    }
-
-    fn on_resize(&self, _: Axis) -> OnResize {
-        self.dependence
-    }
-}
-
-struct Counts(Rc<Cell<usize>>);
-
-impl Counts {
-    fn get(&self) -> usize {
-        self.0.get()
-    }
-}
-
-fn counted(h: &mut Harness, size: Size, dependence: OnResize) -> (WeakWidget<Counted>, Counts) {
-    let draws = Rc::new(Cell::new(0));
-    let id = Counted {
-        draws: draws.clone(),
-        size,
-        dependence,
-    }
-    .add(&mut h.rsc);
-    (id, Counts(draws))
-}
-
-/// A fixed-width leaf beside one that takes the rest, so changing the first
-/// hands the second a different box without the output changing.
-fn pair(h: &mut Harness, rest: OnResize) -> (WeakWidget<Counted>, Counts, WidgetId) {
-    let (first, _) = counted(h, Size::from((100, 200)), OnResize::Translate);
-    let (second, draws) = counted(h, Size::REST, rest);
-    h.set_root((first, second).span(Dir::RIGHT));
-    (first, draws, second.id())
-}
-
-#[test]
-fn a_leaf_that_ignores_its_box_is_not_drawn_again_when_the_box_changes() {
-    let mut h = Harness::new((400, 200));
-    let (first, draws, second) = pair(&mut h, OnResize::Scale);
-    let settled = draws.get();
-    assert_corners!(h, second, (100, 0), (400, 200));
-
-    h.rsc[first].size = Size::from((150, 200));
-    h.frame();
-
-    assert_eq!(
-        draws.get(),
-        settled,
-        "its box is a field to write, not a reason to draw"
-    );
-    assert_corners!(h, second, (150, 0), (400, 200));
-}
-
-#[test]
-fn a_leaf_that_depends_on_its_box_is_drawn_again_when_the_box_changes() {
-    let mut h = Harness::new((400, 200));
-    let (first, draws, second) = pair(&mut h, OnResize::Redraw);
-    let settled = draws.get();
-
-    h.rsc[first].size = Size::from((150, 200));
-    h.frame();
-
-    // The preceding fixed child makes the remaining box this child's real
-    // box, so measuring it also draws it in its final place.
-    assert_eq!(draws.get(), settled + 1);
-    assert_corners!(h, second, (150, 0), (400, 200));
-}
-
-#[test]
-fn a_span_child_that_declares_its_length_is_drawn_once() {
-    let mut h = Harness::new((400, 200));
-    let (told, told_draws) = counted(&mut h, Size::from((100, 200)), OnResize::Translate);
-    let (asked, asked_draws) = counted(&mut h, Size::from((100, 200)), OnResize::Translate);
-    // The span takes one child's length from its hint and has to draw the
-    // other to find out, so only the second is drawn before it is placed.
-    let hinted = told.width(100).add(&mut h.rsc);
-    h.set_root((hinted, asked).span(Dir::RIGHT));
-
-    assert_eq!(told_draws.get(), 1);
-    assert_eq!(
-        asked_draws.get(),
-        2,
-        "drawn to be measured, then again to be placed"
-    );
-}
-
-#[test]
-fn a_span_relays_out_when_a_child_it_measured_changes() {
-    let mut h = Harness::new((400, 200));
-    let (first, _, second) = pair(&mut h, OnResize::Translate);
-
-    h.rsc[first].size = Size::from((250, 200));
-    h.frame();
-
-    assert_corners!(h, first, (0, 0), (250, 200));
-    assert_corners!(h, second, (250, 0), (400, 200));
-}
-
-#[test]
-fn a_repaint_that_keeps_its_size_does_not_relay_out() {
-    let mut h = Harness::new((400, 200));
-    let (first, draws) = counted(&mut h, Size::from((100, 200)), OnResize::Translate);
-    let (second, _) = counted(&mut h, Size::REST, OnResize::Translate);
-    h.set_root((first, second).span(Dir::RIGHT));
-    let settled = draws.get();
-
-    // Taking mutable access is the ordinary content-change signal. This
-    // widget returns the same size, so the parent has nothing to lay out.
-    let _ = h.rsc.widgets_mut().get_dyn_mut(first.id());
-    h.frame();
-
-    assert_eq!(draws.get(), settled + 1);
-}
-
-#[test]
-fn a_placed_child_survives_the_next_frame() {
-    let mut h = Harness::new((400, 200));
-    // Both children declare a length, so the span places them from their hints
-    // rather than drawing them to find out.
-    let top = rect(Color::RED).height(80).add(&mut h.rsc);
-    let bottom = rect(Color::BLUE).height(120).add(&mut h.rsc);
-    h.set_root((top, bottom).span(Dir::DOWN));
-
-    h.rsc.widgets_mut().get_dyn_mut(top.id());
-    h.frame();
-
-    assert_corners!(h, top, (0, 0), (400, 80));
-    assert_corners!(h, bottom, (0, 80), (400, 200));
-}
-
-/// Lays its child out from the hint alone, never reading what it drew.
-struct FromHint {
-    inner: StrongWidget,
-}
-
-impl Widget for FromHint {
-    fn draw(&mut self, painter: &mut Painter) -> Size {
-        let len = painter.size_hint(&self.inner, Axis::Y).unwrap();
-        let mut region = UiRegion::FULL;
-        region.y.end = region.y.start.offset(len.abs);
-        painter.widget_within(&self.inner, region);
-        Size::REST
-    }
-}
-
-#[test]
-fn a_parent_that_only_read_a_hint_relays_out_when_the_hint_changes() {
-    let mut h = Harness::new((400, 200));
-    let inner = rect(Color::RED).height(80).add(&mut h.rsc);
-    let parent = FromHint {
-        inner: inner.add_strong(&mut h.rsc),
-    }
-    .add(&mut h.rsc);
-    h.set_root(parent);
-    assert_corners!(h, inner, (0, 0), (400, 80));
-
-    h.rsc[inner].y = Some(Len::abs(120));
-    h.frame();
-
-    assert_corners!(h, inner, (0, 0), (400, 120));
-}
-
-/// Reads the output's size, which nothing but its own draw can put right.
-struct ReadsOutput {
-    draws: Rc<Cell<usize>>,
-}
-
-impl Widget for ReadsOutput {
-    fn draw(&mut self, painter: &mut Painter) -> Size {
-        self.draws.set(self.draws.get() + 1);
-        Size::abs(painter.output_size() / 4.0)
-    }
-}
-
-struct ReadsWidth {
-    draws: Rc<Cell<usize>>,
-}
-
-impl Widget for ReadsWidth {
-    fn draw(&mut self, painter: &mut Painter) -> Size {
-        self.draws.set(self.draws.get() + 1);
-        Size::abs((painter.output_len(Axis::X) / 4.0, 20.0).into())
-    }
-}
-
-#[test]
-fn a_resize_does_not_redraw_what_the_shader_can_move() {
-    let mut h = Harness::new((400, 200));
-    let (leaf, draws) = counted(&mut h, Size::REST, OnResize::Redraw);
-    h.set_root(leaf);
-    let settled = draws.get();
-
-    h.resize((800, 100));
-    assert!(h.needs_redraw());
-    h.frame();
-
-    assert_eq!(
-        draws.get(),
-        settled,
-        "its box is the same fraction of a different output"
-    );
-    assert_corners!(h, leaf, (0, 0), (800, 100));
-}
-
-#[test]
-fn a_resize_redraws_what_read_the_output() {
-    let mut h = Harness::new((400, 200));
-    let draws = Rc::new(Cell::new(0));
-    let leaf = ReadsOutput {
-        draws: draws.clone(),
-    }
-    .add(&mut h.rsc);
-    h.set_root(leaf);
-    let settled = draws.get();
-
-    h.resize((800, 100));
-    h.frame();
-
-    assert_eq!(draws.get(), settled + 1);
-}
-
-#[test]
-fn a_resize_only_redraws_read_output_axes() {
-    let mut h = Harness::new((400, 200));
-    let draws = Rc::new(Cell::new(0));
-    let leaf = ReadsWidth {
-        draws: draws.clone(),
-    }
-    .add(&mut h.rsc);
-    h.set_root(leaf);
-    let settled = draws.get();
-
-    h.resize((400, 300));
-    h.frame();
-    assert_eq!(draws.get(), settled, "height was never read");
-
-    h.resize((800, 300));
-    h.frame();
-    assert_eq!(draws.get(), settled + 1, "width changes its answer");
-}
-
-#[test]
-fn subpixel_resize_changes_accumulate_from_the_last_layout() {
-    let mut h = Harness::new((400, 200));
-    let draws = Rc::new(Cell::new(0));
-    let leaf = ReadsWidth {
-        draws: draws.clone(),
-    }
-    .add(&mut h.rsc);
-    h.set_root(leaf);
-    let settled = draws.get();
-
-    for width in [400.02, 400.04, 400.05] {
-        h.resize((width, 200.0));
-        h.frame();
-        assert_eq!(draws.get(), settled);
-    }
-
-    h.resize((400.06, 200.0));
-    h.frame();
-    assert_eq!(draws.get(), settled + 1);
-}
-
-#[test]
-fn subpixel_box_changes_accumulate_from_the_last_draw() {
-    let mut h = Harness::new((400, 200));
-    let (first, draws, _) = pair(&mut h, OnResize::Redraw);
-    let settled = draws.get();
-
-    for width in [100.02, 100.04, 100.05] {
-        h.rsc[first].size.x = Len::abs(width);
-        h.frame();
-        assert_eq!(draws.get(), settled);
-    }
-
-    h.rsc[first].size.x = Len::abs(100.06);
-    h.frame();
-    assert_eq!(draws.get(), settled + 1);
-}
-
-#[test]
-fn reporting_the_same_output_size_does_not_start_a_resize() {
-    let mut h = Harness::new((400, 200));
-    let draws = Rc::new(Cell::new(0));
-    let leaf = ReadsOutput {
-        draws: draws.clone(),
-    }
-    .add(&mut h.rsc);
-    h.set_root(leaf);
-    let settled = draws.get();
-
-    h.resize((400, 200));
-
-    assert!(!h.needs_redraw());
-    h.frame();
-    assert_eq!(draws.get(), settled);
-}
-
-#[test]
-fn narrowing_the_output_reflows_text_and_relays_out_around_it() {
-    let mut h = Harness::new((600, 400));
-    let para = wtext(
-        "Wrapping shapes one source into as many lines as its container leaves \
-        room for, so the height of a paragraph is an answer rather than a setting.",
-    )
-    .size(20)
-    .wrap(true)
-    .add(&mut h.rsc);
-    let below = rect(Color::RED).add(&mut h.rsc);
-    h.set_root((para, below).span(Dir::DOWN));
-    let top = h.region(&below).expect("drew nothing").top_left.y;
-
-    h.resize((300, 400));
-    h.frame();
-
-    let lower = h.region(&below).expect("drew nothing").top_left.y;
-    assert!(lower > top, "same words, half the width: {top} -> {lower}");
-}
-
-#[test]
-fn a_change_two_levels_under_its_reader_still_reaches_it() {
-    let mut h = Harness::new((400, 400));
-    // Every wrapper up to the outer pad read the size below it, so the outer
-    // pad is what draws again -- and the span it hands the box to is the same
-    // size as before, which is what lets a draw reuse its way past the leaf.
-    let (leaf, _) = counted(&mut h, Size::abs((100, 100).into()), OnResize::Redraw);
-    let padded = leaf.pad(10).add(&mut h.rsc);
-    let below = rect(Color::RED).add(&mut h.rsc);
-    h.set_root((padded, below).span(Dir::DOWN).pad(12));
-    assert_corners!(h, below, (12, 132), (388, 388));
-
-    h.rsc[leaf].size = Size::abs((100, 200).into());
-    h.frame();
-
-    assert_corners!(h, below, (12, 232), (388, 388));
-}
-
-/// Claims its drawing survives its box changing length, and has a child so
-/// that the walk looking for what does not has one to reach.
-struct Stretchy {
-    inner: StrongWidget,
-    draws: Rc<Cell<usize>>,
-}
-
-impl Widget for Stretchy {
-    fn draw(&mut self, painter: &mut Painter) -> Size {
-        self.draws.set(self.draws.get() + 1);
-        painter.widget(&self.inner).size()
-    }
-
-    fn on_resize(&self, _: Axis) -> OnResize {
-        OnResize::Scale
-    }
-}
-
-#[test]
-fn stretching_a_subtree_carries_the_children_in_it() {
-    let mut h = Harness::new((400, 400));
-    let first = rect(Color::RED).height(40).add(&mut h.rsc);
-    let inner = rect(Color::BLUE).add(&mut h.rsc);
-    let draws = Rc::new(Cell::new(0));
-    let outer = Stretchy {
-        inner: inner.add_strong(&mut h.rsc),
-        draws: draws.clone(),
-    }
-    .add(&mut h.rsc);
-    h.set_root((first, outer).span(Dir::DOWN));
-    let settled = draws.get();
-    assert_corners!(h, inner, (0, 40), (400, 400));
-
-    h.rsc[first].y = Some(Len::abs(80));
-    h.frame();
-
-    assert_eq!(
-        draws.get(),
-        settled,
-        "its drawing follows its box, rather than being made again"
-    );
-    assert_corners!(h, outer, (0, 80), (400, 400));
-    assert_corners!(h, inner, (0, 80), (400, 400));
-}
-
-#[test]
-fn a_widened_row_redraws_what_reads_its_length_and_nothing_else() {
-    let mut h = Harness::new((400, 200));
-    // What a transcript row is: something whose shaping depends on the width
-    // it is given, beside something that only has to be the right shape.
-    let (wraps, wrap_draws) = counted(&mut h, Size::REST, OnResize::Redraw);
-    let (backing, back_draws) = counted(&mut h, Size::REST, OnResize::Scale);
-    let row = (backing, wraps).span(Dir::RIGHT).add(&mut h.rsc);
-    let bar = rect(Color::RED).width(100).add(&mut h.rsc);
-    h.set_root((bar, row).span(Dir::RIGHT));
-    let (settled_wrap, settled_back) = (wrap_draws.get(), back_draws.get());
-
-    h.rsc[bar].x = Some(Len::abs(200));
-    h.frame();
-
-    // The span reads every child's size, so redrawing one takes the span
-    // with it -- and the span then measures and places the redrawn child.
-    assert!(wrap_draws.get() > settled_wrap, "reads the width it got");
-    assert_eq!(back_draws.get(), settled_back, "only has to be the shape");
-    assert_corners!(h, backing, (200, 0), (300, 200));
-    assert_corners!(h, wraps, (300, 0), (400, 200));
-}
-
-#[test]
-fn a_declared_length_child_is_not_redrawn_when_the_box_around_it_grows() {
-    let mut h = Harness::new((400, 200));
-    // Its box is a fixed 80 wherever the row's edges end up, so drawing it
-    // again would be for a width it does not have. The declared width is what
-    // lets the span say that without drawing it: a width the span learnt by
-    // drawing the child in its own box is only an answer for that box.
-    let (counter, draws) = counted(&mut h, Size::from((80, 200)), OnResize::Redraw);
-    let fixed = counter.width(80).add(&mut h.rsc);
-    let (rest, _) = counted(&mut h, Size::REST, OnResize::Scale);
-    let row = (fixed, rest).span(Dir::RIGHT).add(&mut h.rsc);
-    let bar = rect(Color::RED).width(100).add(&mut h.rsc);
-    h.set_root((bar, row).span(Dir::RIGHT));
-    let settled = draws.get();
-
-    h.rsc[bar].x = Some(Len::abs(200));
-    h.frame();
-
-    assert_eq!(draws.get(), settled, "its own length did not change");
-    assert_corners!(h, fixed, (200, 0), (280, 200));
-}