Take a strong widget to depend on, and use the question mark

`depend_on_size` took a bare `WidgetId`, which any id at all satisfies. It takes a `&StrongWidget` now, so `DrawResult` carries the handle it was drawn from rather than an id copied out of it and nothing can claim a dependency on a widget it does not hold. `UiSpan::outside` matched on a pair of `Option`s where `?` says it. It was written that way while the method was still `const`, and it is not. No call site changed. Checked: fmt, clippy and 35 tests; `tabs`, `view`, `minimal` and `text` render unchanged, and the live sway resize round trip still matches a cold start at each size.
Say when a drawing cannot be taken out of its box, rather than guessing
2026-09-14 02:44:40 -04:00 · 2026-09-14 01:27:16 -04:00 · 2026-09-14 01:09:03 -04:00 · 2026-09-14 00:39:39 -04:00 · 2026-09-13 23:47:12 -04:00 · 2026-09-13 23:28:47 -04:00
39 changed files with 224 additions and 1869 deletions
@@ -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",
@@ -20,7 +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"
@@ -40,5 +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"] }
@@ -202,6 +202,14 @@ impl UiScalar {
        }
    }

+    /// Undoes `within`, and `None` where the span has a fixed length: every
+    /// fraction of it lands on the same `rel`, so none can be told apart.
+    pub fn outside(&self, span: &UiSpan) -> Option<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);
+        Some(Self { rel, abs })
+    }
+
    pub fn within_len(&self, len: UiScalar) -> Self {
        self.within(&UiSpan {
            start: UiScalar::ZERO,
@@ -270,6 +278,13 @@ impl UiSpan {
        }
    }

+    pub fn outside(&self, parent: &Self) -> Option<Self> {
+        Some(Self {
+            start: self.start.outside(parent)?,
+            end: self.end.outside(parent)?,
+        })
+    }
+
    pub const fn len(&self) -> UiScalar {
        self.end - self.start
    }
@@ -382,6 +397,50 @@ impl UiRegion {
    }
 }

+/// Taking a drawing out of one box and putting it in another, checked once
+/// for a whole subtree so that applying it cannot fail.
+///
+/// A box of a fixed length holds each part as an offset from its start rather
+/// than as a fraction of it, so those parts can be carried to a box of the
+/// same length but never stretched to a different one.
+#[derive(Debug, Copy, Clone, PartialEq)]
+pub struct Remap {
+    from: UiRegion,
+    to: UiRegion,
+}
+
+impl Remap {
+    pub fn new(from: UiRegion, to: UiRegion) -> Option<Self> {
+        [Axis::X, Axis::Y]
+            .into_iter()
+            .all(|axis| {
+                let (from, to) = (from.axis(axis), to.axis(axis));
+                from.start.rel != from.end.rel || from.len() == to.len()
+            })
+            .then_some(Self { from, to })
+    }
+
+    pub fn apply(&self, region: UiRegion) -> UiRegion {
+        UiRegion {
+            x: Self::span(region.x, self.from.x, self.to.x),
+            y: Self::span(region.y, self.from.y, self.to.y),
+        }
+    }
+
+    fn span(span: UiSpan, from: UiSpan, to: UiSpan) -> UiSpan {
+        match span.outside(&from) {
+            Some(out) => out.within(&to),
+            // `new` admits this only where the two are the same length, so
+            // the difference between their starts is the whole move.
+            None => {
+                let mut span = span;
+                span.shift(to.start - from.start);
+                span
+            }
+        }
+    }
+}
+
 impl Display for UiRegion {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(
@@ -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 }
-    }
 }
@@ -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 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,
-            );
+            if self.masks.update(device, queue, &ui.masks[..]) {
+                self.shared_group = Self::shared_group(
+                    device,
+                    &self.shared_layout,
+                    &self.window_buffer,
+                    &self.masks,
+                );
+            }
        }
    }

    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(
-            device,
-            BufferUsages::STORAGE | BufferUsages::COPY_DST,
-            "ui move offsets",
-        );
-        let shared_group =
-            Self::shared_group(device, &shared_layout, &window_buffer, &masks, &moves);
+        let shared_group = Self::shared_group(device, &shared_layout, &window_buffer, &masks);

        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
-    /// move chain every position is resolved through.
+    /// What every draw in the ui is given: the window and the masks.
    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"),
        })
@@ -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 {
-                    region,
-                    mask_idx,
-                    move_idx,
-                },
+                PrimitiveInstance { region, mask_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
-// here, which is how WGSL lays the struct out.
+// Manual rather than derived: the align(8) leaves four bytes of padding, which
+// is how WGSL lays the struct out.
 unsafe impl bytemuck::Pod for GlyphPrimitive {}
 unsafe impl bytemuck::Zeroable for GlyphPrimitive {}
 impl Primitive for GlyphPrimitive {
@@ -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(
-        UiSpan(UiScalar(in.x_start.x, in.x_start.y), UiScalar(in.x_end.x, in.x_end.y)),
-        UiSpan(UiScalar(in.y_start.x, in.y_start.y), UiScalar(in.y_end.x, 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_rel = vec2(in.x_start.x, in.y_start.x);
+    let top_left_abs = vec2(in.x_start.y, in.y_start.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 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
-    // clips content that moves inside it.
-    let m = resolve_move(mask.move_idx, Region(mask.x, mask.y));
-    let tl = vec2(m.x.start.rel, m.y.start.rel);
-    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 tl = vec2(mask.x.start.rel, mask.y.start.rel);
+    let tl_abs = vec2(mask.x.start.abs, mask.y.start.abs);
+    let br = vec2(mask.x.end.rel, mask.y.end.rel);
+    let br_abs = vec2(mask.x.end.abs, mask.y.end.abs);

    let top_left = floor(tl * window.dim) + floor(tl_abs);
    let bot_right = floor(br * window.dim) + floor(br_abs);
@@ -1,6 +1,4 @@
-use crate::{
-    LayerId, MaskIdx, MoveIdx, PrimitiveHandle, Size, TextureHandle, UiRegion, WidgetId, util::Vec2,
-};
+use crate::{LayerId, MaskIdx, PrimitiveHandle, Size, TextureHandle, UiRegion, WidgetId};

 /// important non rendering data for retained drawing
 #[derive(Debug)]
@@ -9,10 +7,6 @@ pub struct ActiveData {
    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>,
@@ -21,11 +15,6 @@ pub struct ActiveData {
    pub size_deps: Vec<WidgetId>,
    /// Whether it read the output's size, and so is wrong when that changes.
    pub reads_output: bool,
-    /// 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,
 }
@@ -1,14 +1,7 @@
 use crate::{
-    Mask, MoveIdx, MoveOffset, PrimitiveRegistry, TextData, Textures, UiRegion, WeakWidget,
-    WidgetId, Widgets,
-    util::{Arena, Id, TrackedArena},
+    Mask, PrimitiveRegistry, TextData, Textures, WeakWidget, WidgetId, Widgets, util::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 painter;
 mod render_state;
@@ -27,88 +20,6 @@ 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;
@@ -2,8 +2,8 @@ use crate::{
    Axis, Len, RenderedText, Size, StrongWidget, TextAttrs, TextBuffer, TextData, TextureHandle,
    UiRegion, UiRenderState, UiRsc, UiScalar, UiVec2, WidgetId,
    render::{
-        GlyphPrimitive, Mask, MaskIdx, MoveIdx, Primitive, PrimitiveHandle, PrimitiveInst,
-        PrimitiveKind, TexturePrimitive,
+        GlyphPrimitive, Mask, MaskIdx, Primitive, PrimitiveHandle, PrimitiveInst, PrimitiveKind,
+        TexturePrimitive,
    },
    util::Vec2,
 };
@@ -13,7 +13,6 @@ 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>,
@@ -22,9 +21,6 @@ pub struct Painter<'a> {
    /// The children whose size this widget read while drawing.
    pub(super) size_deps: Vec<WidgetId>,
    pub(super) reads_output: bool,
-    /// 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,
 }
@@ -45,7 +41,6 @@ impl<'a> Painter<'a> {
                primitive,
                region,
                mask_idx: self.mask,
-                move_idx: self.move_idx,
            },
        );
        self.push_primitive(h);
@@ -72,47 +67,29 @@ 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 {
-            region,
-            move_idx: self.move_idx,
-        });
+        self.mask = self.rsc.ui_mut().masks.push(Mask { region });
    }

    /// 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> {
-        self.widget_at(id, self.region, false)
+        self.widget_at(id, self.region)
    }

-    /// Draws a widget somewhere within this one.
+    /// Draws a widget somewhere within this one. Drawing one a second time
+    /// gives it a new box, keeping the drawing it already has where it can.
    pub fn widget_within<'s, W: ?Sized>(
        &'s mut self,
        id: &'s StrongWidget<W>,
        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
-    /// 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> {
-        let region = region.within(&self.region);
-        self.widget_at(id, region, true)
+        self.widget_at(id, region)
    }

    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()) {
@@ -123,8 +100,6 @@ impl<'a> Painter<'a> {
            id.id(),
            region,
            Some(self.id),
-            self.move_idx,
-            slotted,
            self.mask,
            None,
            self.rsc,
@@ -184,8 +159,6 @@ 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
    }
@@ -197,13 +170,11 @@ impl<'a> Painter<'a> {
        self.state.output_size
    }

-    /// 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.
+    /// This widget's box in pixels. Resolved against the output's size, so a
+    /// widget that reads it draws again when the output changes.
    pub fn px_size(&mut self) -> Vec2 {
        self.reads_output = true;
-        let region = self.state.moves.resolve(self.move_idx, self.region);
-        region.size().to_abs(self.state.output_size)
+        self.region.size().to_abs(self.state.output_size)
    }

    pub fn text_data(&mut self) -> &mut TextData {
@@ -1,11 +1,9 @@
 use crate::{
-    ActiveData, Axis, DrawLayers, IdLike, MaskIdx, MoveIdx, Moves, OnResize, Painter, PixelRegion,
-    Size, StrongWidget, UiRegion, UiRsc, WidgetId, Widgets,
-    util::{HashMap, HashSet, Vec2},
+    ActiveData, Axis, DrawLayers, IdLike, MaskIdx, OnResize, Painter, PixelRegion, Remap, Size,
+    StrongWidget, UiRegion, UiRsc, WidgetId, Widgets,
+    util::{HashMap, HashSet, Vec2, forget_ref},
 };

-const AXES: [Axis; 2] = [Axis::X, Axis::Y];
-
 pub struct UiRenderState {
    pub active: HashMap<WidgetId, ActiveData>,
    pub layers: DrawLayers,
@@ -14,10 +12,6 @@ pub struct UiRenderState {
    old_root: Option<WidgetId>,
    resized: bool,
    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 {
@@ -29,8 +23,6 @@ impl UiRenderState {
            old_root: None,
            resized: false,
            draw_started: Default::default(),
-            slots: Default::default(),
-            moves: Default::default(),
        }
    }

@@ -84,17 +76,7 @@ impl UiRenderState {
        self.clear(rsc);
        // free all resources & cache
        if let Some(id) = root {
-            self.draw_inner(
-                0,
-                id.id(),
-                UiRegion::FULL,
-                None,
-                MoveIdx::NONE,
-                false,
-                MaskIdx::NONE,
-                None,
-                rsc,
-            );
+            self.draw_inner(0, id.id(), UiRegion::FULL, None, MaskIdx::NONE, None, rsc);
        }
    }

@@ -106,15 +88,13 @@ 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 {
        let mut old_children = old_children.unwrap_or_default();
        if self.active.contains_key(&id) {
-            if let Some(size) = self.try_reuse(id, region, parent_move, rsc) {
+            if let Some(size) = self.try_reuse(id, region, rsc) {
                return size;
            }
            // if not, then maintain resize and track old children to remove unneeded
@@ -123,22 +103,12 @@ 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,
@@ -147,7 +117,6 @@ impl UiRenderState {
            children: Vec::new(),
            size_deps: Vec::new(),
            reads_output: false,
-            move_idx,
            rsc,
        };

@@ -158,14 +127,13 @@ impl UiRenderState {
        let Painter {
            state: _,
            rsc: _,
-            region: _,
+            region,
            mask,
            textures,
            primitives,
            children,
            size_deps,
            reads_output,
-            move_idx,
            layer,
            id,
        } = painter;
@@ -181,15 +149,12 @@ impl UiRenderState {
            id,
            region,
            size,
-            px,
            parent,
            textures,
            primitives,
            children,
            size_deps,
            reads_output,
-            move_idx,
-            parent_move,
            mask,
            layer,
        };
@@ -206,138 +171,49 @@ impl UiRenderState {
        size
    }

-    /// The slot a widget's box is held in, made on its first placed draw and
-    /// 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)
-    }
-
    /// 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> {
+    fn try_reuse(&mut self, id: WidgetId, region: UiRegion, rsc: &dyn UiRsc) -> Option<Size> {
        if rsc.widgets().needs_redraw.contains(&id) {
            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 {
-            return None;
-        }
-        let (size, old, slot, was) = (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 = px.axis(axis) != was.axis(axis);
-        }
-        if !changed.iter().any(|&c| c) && old == region {
+        let (size, old) = (active.size, active.region);
+        if old == region {
            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 {
+        // TODO: epsilon?
+        if old.size() != region.size() && !self.reusable(id, region, rsc) {
            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 || self.redraws_under(id, changed, rsc) {
-                return None;
-            }
-        }
-        self.moves.set(slot, region);
-        let active = self.active.get_mut(&id).unwrap();
-        active.region = region;
-        active.px = px;
+        // Its drawing stands, if the new box can be reached from the old one.
+        self.mov(id, &Remap::new(old, region)?);
        Some(size)
    }

-    /// 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 {
+    /// Whether the widget can keep the drawing it has and be given `region`
+    /// instead, asked one axis at a time: a change on an axis it does not
+    /// depend on costs nothing, whatever it depends on elsewhere.
+    fn reusable(&self, id: WidgetId, region: UiRegion, rsc: &dyn UiRsc) -> bool {
        let Some(active) = self.active.get(&id) else {
            return false;
        };
-        let size_deps = &active.size_deps;
-        active.children.iter().any(|&child| {
-            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 Some(widget) = rsc.widgets().get_dyn(id) else {
+            return false;
+        };
+        [Axis::X, Axis::Y].into_iter().all(|axis| {
+            let offered = region.axis(axis).len();
+            let had = active.region.axis(axis).len();
+            match widget.on_resize(axis) {
+                OnResize::Scale => true,
+                // `Translate` is not acted on yet, and cannot be until a
+                // drawing can sit somewhere other than its box. `region` is
+                // both the box a widget was given and the box its primitives
+                // are in, and `mov` remaps from it -- so carrying a drawing at
+                // its old size while the box grows makes the next move stretch
+                // it. The offset chain is what separates the two.
+                OnResize::Translate | OnResize::Redraw => offered == had,
            }
-            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)
        })
    }

@@ -345,13 +221,27 @@ impl UiRenderState {
        let Some(widget) = rsc.widgets().get_dyn(id) else {
            return true;
        };
-        AXES.into_iter().all(|axis| {
+        [Axis::X, Axis::Y].into_iter().all(|axis| {
            widget
                .size_hint(axis)
                .is_none_or(|hint| hint == size.axis(axis))
        })
    }

+    fn mov(&mut self, id: WidgetId, remap: &Remap) {
+        let active = self.active.get_mut(&id).unwrap();
+        for h in &active.primitives {
+            let region = self.layers[h.layer].region_mut(h);
+            *region = remap.apply(*region);
+        }
+        active.region = remap.apply(active.region);
+        // SAFETY: children cannot be recursive
+        let children = unsafe { forget_ref(&active.children) };
+        for child in children {
+            self.mov(*child, remap);
+        }
+    }
+
    /// NOTE: instance textures are cleared and self.textures freed
    fn remove(&mut self, id: WidgetId, undraw: bool, rsc: &mut dyn UiRsc) -> Option<ActiveData> {
        let mut active = self.active.remove(&id);
@@ -378,10 +268,6 @@ impl UiRenderState {
                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
    }

@@ -389,8 +275,6 @@ impl UiRenderState {
        for (_, active) in self.active.drain() {
            rsc.on_undraw(&active);
        }
-        self.slots.clear();
-        self.moves.clear();
        self.layers.clear();
        rsc.widgets_mut().needs_redraw.clear();
        rsc.free();
@@ -438,11 +322,8 @@ 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.moves.resolve(active.parent_move, active.region);
+        let region = self.active.get(&id.id())?.region;
        Some(region.to_px(self.output_size))
    }

@@ -475,8 +356,6 @@ impl UiRenderState {
            id,
            active.region,
            active.parent,
-            active.parent_move,
-            active.move_idx != active.parent_move,
            active.mask,
            Some(active.children),
            rsc,
@@ -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> {
@@ -1,5 +1,6 @@
-pub const trait LerpUtil {
+pub const trait LerpUtil: Sized {
    fn lerp(self, from: Self, to: Self) -> Self;
+    fn lerp_inv(self, from: Self, to: Self) -> Option<Self>;
 }

 const impl LerpUtil for f32 {
@@ -8,6 +9,14 @@ const impl LerpUtil for f32 {
    fn lerp(self, from: Self, to: Self) -> Self {
        from + (to - from) * self
    }
+    /// inverse of lerp, and `None` where `from` and `to` are the same point:
+    /// every input lerps to it, so there is no one answer to come back to.
+    fn lerp_inv(self, from: Self, to: Self) -> Option<Self> {
+        match to == from {
+            true => None,
+            false => Some((self - from) / (to - from)),
+        }
+    }
 }

 macro_rules! impl_op {
@@ -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) }
@@ -1,11 +1,7 @@
 use crate::util::impl_op;
 use std::{hash::Hash, ops::*};

-/// `align(8)` because that is WGSL's alignment for a `vec2<f32>`, so any GPU
-/// 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))]
+#[repr(C)]
 #[derive(Clone, Copy, PartialEq, Default, bytemuck::Pod, bytemuck::Zeroable)]
 pub struct Vec2 {
    pub x: f32,
@@ -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 std::collections::HashMap;
-
-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, &HashMap::new());
-        ui_state.set_root(root);
-        Self { ui_state }
-    }
-}
@@ -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 }
@@ -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);
-}
@@ -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
@@ -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"
@@ -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 {
@@ -270,51 +178,3 @@ impl Harness {
        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}");
-    }
-}
@@ -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;
@@ -1,161 +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];
-
-/// 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,
-];
-
-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>>,
-}
-
-/// 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: &HashMap<usize, Lens>,
-) -> (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 HashMap<usize, Lens>,
-}
-
-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,
-        }
-    }
-
-    /// 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.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 count = 2 + self.rng.below(2);
-        let mut children = Vec::with_capacity(count);
-        for _ in 0..count {
-            let child = self.node(depth - 1);
-            children.push(self.sized(child));
-        }
-        let id: StrongWidget = match self.rng.below(3) {
-            0 => Stack {
-                children,
-                size: StackSize::Child(0),
-            }
-            .add_strong(self.rsc),
-            _ => {
-                let dir = [Dir::RIGHT, Dir::DOWN, Dir::LEFT, Dir::UP][self.rng.below(4)];
-                Span {
-                    children,
-                    dir,
-                    gap: self.rng.below(3) as f32 * 4.0,
-                }
-                .add_strong(self.rsc)
-            }
-        };
-        self.tree.ids.push(id.id());
-        id
-    }
-}
@@ -9,20 +9,14 @@ impl Widget for Aligned {
    fn draw(&mut self, painter: &mut Painter) -> Size {
        // Drawn where it may be too big, then given its aligned box once its
        // size is known.
-        let size = painter.place(&self.inner, UiRegion::FULL).size();
+        let size = painter.widget(&self.inner).size();
        let region = match self.align.tuple() {
            (Some(x), Some(y)) => size.to_uivec2().align(RegionAlign { x, y }),
            (Some(x), None) => UiRegion::new(size.x.apply_rest().align(x), UiSpan::FULL),
            (None, Some(y)) => UiRegion::new(UiSpan::FULL, size.y.apply_rest().align(y)),
            (None, None) => UiRegion::FULL,
        };
-        painter.place(&self.inner, region);
+        painter.widget_within(&self.inner, region);
        size
    }
-
-    /// The aligned box is a fraction of its own, so the child keeps its
-    /// length and stays against the edge it was aligned to.
-    fn on_resize(&self, _: Axis) -> OnResize {
-        OnResize::Scale
-    }
 }
@@ -12,8 +12,4 @@ impl Widget for LayerOffset {
        }
        painter.widget(&self.inner).size()
    }
-
-    fn on_resize(&self, _: Axis) -> OnResize {
-        OnResize::Scale
-    }
 }
@@ -10,8 +10,4 @@ impl Widget for Offset {
        let region = UiRegion::FULL.offset(self.amt);
        painter.widget_within(&self.inner, region).size()
    }
-
-    fn on_resize(&self, _: Axis) -> OnResize {
-        OnResize::Scale
-    }
 }
@@ -21,12 +21,6 @@ impl Widget for Pad {
            },
        }
    }
-
-    /// The padding is an offset from each edge, so a longer box pads the same
-    /// amount and the child takes the rest.
-    fn on_resize(&self, _: Axis) -> OnResize {
-        OnResize::Scale
-    }
 }

 pub struct Padding {
@@ -12,10 +12,10 @@ pub struct Scroll {
 impl Widget for Scroll {
    fn draw(&mut self, painter: &mut Painter) -> Size {
        let output_len = painter.output_size().axis(self.axis);
-        let container_len = UiScalar::abs(painter.px_size().axis(self.axis));
+        let container_len = painter.region().axis(self.axis).len();
        // Drawn in the whole container to learn its length, then placed at
        // the scrolled offset.
-        let child = painter.place(&self.inner, UiRegion::FULL).size();
+        let child = painter.widget(&self.inner).size();
        let content_len = child
            .axis(self.axis)
            .apply_rest()
@@ -31,7 +31,7 @@ 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);
-        painter.place(&self.inner, region);
+        painter.widget_within(&self.inner, region);
        child
    }
 }
@@ -23,8 +23,4 @@ impl Widget for SetSize {
            Axis::Y => self.y,
        }
    }
-
-    fn on_resize(&self, _: Axis) -> OnResize {
-        OnResize::Scale
-    }
 }
@@ -17,7 +17,7 @@ impl Widget for Span {
            .iter()
            .map(|child| match painter.size_hint(child, axis) {
                Some(len) => len,
-                None => painter.place(child, UiRegion::FULL).len(axis),
+                None => painter.widget(child).len(axis),
            })
            .collect();

@@ -42,7 +42,7 @@ impl Widget for Span {
            if self.dir.sign == Sign::Neg {
                region.flip(axis);
            }
-            let used = painter.place(child, region).size().axis(!axis);
+            let used = painter.widget_within(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;
@@ -58,12 +58,6 @@ impl Widget for Span {
        };
        Size::from_axis(axis, along, ortho)
    }
-
-    /// Every child is placed in fractions and offsets of the span's own box,
-    /// so a longer box holds the same layout and the children follow it.
-    fn on_resize(&self, _: Axis) -> OnResize {
-        OnResize::Scale
-    }
 }

 impl Span {
@@ -28,10 +28,6 @@ impl Widget for Stack {
        }
        size
    }
-
-    fn on_resize(&self, _: Axis) -> OnResize {
-        OnResize::Scale
-    }
 }

 #[derive(Default, Debug)]
@@ -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
-        );
-    }
-}
@@ -22,8 +22,8 @@ use std::time::Instant;

 use iris::prelude::*;
 use iris_core::{
-    GlyphPrimitive, MaskIdx, MoveIdx, PrimitiveInst, RectPrimitive, TextureHandle,
-    TexturePrimitive, UiData, UiRegion, UiRenderNode, UiRenderState,
+    GlyphPrimitive, MaskIdx, PrimitiveInst, RectPrimitive, TextureHandle, TexturePrimitive, UiData,
+    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,
                },
            );
        }
@@ -1,169 +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::{Lens, Rng, Tree, grow};
-
-const DEPTH: usize = 4;
-const SEEDS: [u64; 6] = [1, 2, 3, 5, 8, 13];
-
-fn plant(h: &mut Harness, seed: u64, edits: &HashMap<usize, Lens>) -> 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
-}
-
-/// 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());
-        if 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, &HashMap::new());
-
-    let mut rng = Rng::new(seed ^ 0x5eed);
-    let edits = edit(&mut warm, &grown, &mut rng);
-    warm.frame();
-
-    let mut cold = Harness::new((900, 1200));
-    let same = plant(&mut cold, seed, &edits);
-
-    assert_same(seed, "a size change", (&warm, &grown), (&cold, &same));
-}
-
-fn resized(seed: u64) {
-    let mut warm = Harness::new((1920, 1200));
-    let grown = plant(&mut warm, seed, &HashMap::new());
-    warm.resize((640, 900));
-    warm.frame();
-
-    let mut cold = Harness::new((640, 900));
-    let same = plant(&mut cold, seed, &HashMap::new());
-
-    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, &HashMap::new());
-    warm.resize((640, 900));
-    warm.frame();
-
-    let mut rng = Rng::new(seed ^ 0xb0a7);
-    let edits = edit(&mut warm, &grown, &mut rng);
-    warm.frame();
-
-    let mut cold = Harness::new((640, 900));
-    let same = plant(&mut cold, seed, &edits);
-
-    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);
-}
-
-/// 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 six the others check"]
-fn a_long_run_of_seeds_agrees() {
-    for seed in 1..=100 {
-        changed_size(seed);
-        resized(seed);
-        resized_then_changed(seed);
-    }
-}
@@ -109,76 +109,3 @@ fn a_fixed_box_is_drawn_again_rather_than_stretched() {

    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");
-}
@@ -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"]);
-}
@@ -0,0 +1,27 @@
+//! What a drawing can be taken out of, and what it cannot.
+
+use iris::core::{Remap, UiRegion, UiScalar, UiSpan};
+
+/// A box `size` tall whose top is `rel` of the way down the window.
+fn fixed(rel: f32, size: f32) -> UiRegion {
+    UiRegion::new(
+        UiSpan::FULL,
+        UiSpan::new(UiScalar { rel, abs: 0.0 }, UiScalar { rel, abs: size }),
+    )
+}
+
+#[test]
+fn a_fixed_box_can_be_carried_but_not_stretched() {
+    let from = fixed(0.0, 164.0);
+    assert!(Remap::new(from, UiRegion::FULL).is_none());
+    assert!(Remap::new(from, fixed(0.5, 164.0)).is_some());
+    assert!(Remap::new(from, fixed(0.0, 98.0)).is_none());
+}
+
+#[test]
+fn a_relative_box_can_be_stretched_to_any_other() {
+    let remap = Remap::new(UiRegion::FULL, fixed(0.0, 98.0)).expect("relative boxes remap");
+    // A part that filled the window keeps filling what replaced it, which is
+    // exactly what `outside` could not say for a box of a fixed length.
+    assert_eq!(remap.apply(UiRegion::FULL), fixed(0.0, 98.0));
+}
@@ -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();
-    }
-}
@@ -250,93 +250,3 @@ fn a_change_two_levels_under_its_reader_still_reaches_it() {

    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));
-}
Author	SHA1	Message	Date
iris-ai	46547563c1	Take a strong widget to depend on, and use the question mark `depend_on_size` took a bare `WidgetId`, which any id at all satisfies. It takes a `&StrongWidget` now, so `DrawResult` carries the handle it was drawn from rather than an id copied out of it and nothing can claim a dependency on a widget it does not hold. `UiSpan::outside` matched on a pair of `Option`s where `?` says it. It was written that way while the method was still `const`, and it is not. No call site changed. Checked: fmt, clippy and 35 tests; `tabs`, `view`, `minimal` and `text` render unchanged, and the live sway resize round trip still matches a cold start at each size.	2026-09-14 02:44:40 -04:00
iris-ai	53e61289f5	Say when a drawing cannot be taken out of its box, rather than guessing `lerp_inv` returns `Option`. Inverting a lerp over a range of zero length has no one answer, and `div_or`'s fallback picked one: the start of the range. Measured, that is not a wrong number so much as a plausible one -- taking a part out of a box fixed at the top of the window hands back exactly what went in, and out of a box fixed at the middle hands back the parent's own `rel` of 0.5 as if it were the child's fraction. Either way the caller cannot tell that nothing was recovered, which is the defect; the previous commit's claim that it "returns a rel of 0" is right only for the first case. `UiScalar::outside` and `UiSpan::outside` follow it to `Option`, and `Remap` is the answer at the region level: `new` says whether a drawing in one box can be put in another and `apply` then cannot fail, so `try_reuse` asks once for a whole subtree and `reusable` goes back to reporting only what the widget claims. That replaces the predicate the last commit put in `reusable`, which stated the same rule in a second place. `DivOr` existed only for the fallback and is gone, along with `UiRegion::outside` and `UiVec2::outside`, which had no callers once `Remap` owned the operation. `UiRegion::axis` took `&mut self` to return a shared reference; `Remap::new` needs it on a shared one. This does not redraw less. `Remap::new` refuses exactly what the predicate refused; what it buys is one statement of the rule and a remap that cannot half-apply. Counted on a resize, with the old wipe-everything for comparison: 20 padded rows, 101 widgets 101 draws -> 0 the `tabs` example 73 draws -> 0 the `text` example 49 draws -> 48 So the saving is whole where a resize does not change any widget's size, and nil in `text`, where both paragraphs rewrap to a different height and the relayout that forces reaches the root. The last commit's message oversold that case. Checked: fmt, clippy and 35 tests. `tabs` (with the image replay), `view` and `minimal` still byte-identical to `upstream/main`, `text` unchanged, and the live sway resize round trip still matches a cold start at each size.	2026-09-14 01:27:16 -04:00
iris-ai	984f482a7f	Move a resized drawing instead of redrawing it A region is a fraction of the output plus an offset and the shader resolves it against the window every frame, so a resize already moves the whole drawing without the CPU. Wiping the tree and drawing it again was throwing that away. `Painter::output_size` and `px_size` now record that a widget read pixels, the way reading a child's size records a dependency on it, and a resize marks only those. In the `text` example that is the two wrapping paragraphs out of forty-odd widgets; everything else keeps its drawing and the window uniform puts it in the right place. Two defects the change surfaced, both of which made a resize land somewhere a cold start would not: `redraw` climbed to the highest reader of the changed widget and drew from there, trusting that draw to reach back down. It does not: an intermediate whose own box has not changed is reused as it stands and the draw stops there. Everything between the two is now marked as well, which is the only thing that stops the reuse. Not resize-specific -- `a_change_two_levels_under_its_reader_still_reaches_it` fails on the mutation path too. `mov` cannot stretch a drawing out of a box with no relative extent. `UiScalar::within` puts a part into such a box as a plain offset from its start, and `lerp_inv`'s divide-by-zero fallback then returns a rel of 0 rather than saying it cannot invert, so the remap silently leaves the drawing its old size. `OnResize::Scale` now only reuses across a length change when the old box had a relative extent. The underlying loss belongs to the position chain, which separates the drawn box from the offered one; until then this is the honest predicate. Checked: fmt, clippy and 33 tests. `tabs` (with the image replay), `view`, `minimal` still byte-identical to `upstream/main`, and `text` unchanged at 1920x1200 and 900x1200. Driven live under the GPU as well: started at 1920x1200, resized to 900x1200 and back through sway, and each screenshot matches a cold start at that size byte for byte.	2026-09-14 01:09:03 -04:00
iris-ai	9520996623	Return the size from draw, and fold placing back into drawing Review response. `Painter::set_size` is gone: `Widget::draw` returns the `Size` instead, so a widget that does not say what it used cannot compile rather than panicking at the widget that forgot. That also settles setting it twice -- a branch that learns something late just returns a different value. `Painter::place` and `UiRenderState::place` are gone too. `draw_inner` already tried to reuse an active widget's drawing before redrawing it, so `place` was `widget_within` with its own bookkeeping bolted on; drawing a child a second time now is how a parent puts it where it belongs, and a child is deduplicated in `children` because listing one twice would move it twice. The unification also drops `place`'s use of `ActiveData::layer`, which is the layer a widget's own `child_layer()` left the painter on rather than the layer it was drawn into. What `place` did unconditionally and `widget_within` did not is record the size dependency, so `Painter::size_hint` now records one: reading a child's length to lay out around it is reading its size, whether it came from a draw or from a hint. `tests/retained.rs` has a parent that only ever reads the hint, which is the case no existing widget exercises. `()` sizes itself `Size::default()` -- rest -- rather than zero, so it is a gap that takes an even share of a span; `WidgetPtr` with nothing in it does the same, since it is the same situation. `Widget::on_resize`'s default body said `Translate` while the enum's `#[default]` said `Redraw`; it now defers to the enum. `was` is `old` throughout, the `OnResize` variant comments are gone, and so are two empty `impl` blocks. Checked: fmt, clippy and 27 tests across the workspace; `tabs` on each of its five tabs, and `tabs` with a replay that adds two images, all byte-identical to `upstream/main`; `view` and `minimal` likewise; and the `text` example rendered at 1920x1200 and 900x1200 to see the paragraph reflow and its container follow.	2026-09-14 00:39:39 -04:00
iris	b108645240	Say what may be done to a drawing, and default to nothing `SizeDependence::{None, Internal, External}` becomes `OnResize::{Scale, Translate, Redraw}`, which says what the retained path may do rather than leaving the reader to work it out from a dependency. `Redraw` is now the default, and that is the substance of this rather than the naming. `Translate` was, and nothing opted into it: `SetSize` reports one size and hands its child the whole box, so its pixels change with the box and carrying them stretched a 100x100 rect across half the window. A default that is only right for widgets that happen to qualify is the same fault as an unchecked reuse flag. `Translate` still does nothing, and now for the reason rather than the one I gave before: `mov` translates perfectly well, but `ActiveData`'s `region` is both the box a widget was given and the box its primitives occupy, and `mov` remaps out of it. Keeping a drawing at its old size while the box grows leaves those two disagreeing, and the next move stretches it. Separating them is what the offset chain does. Caught by rendering `tabs` against `main` rather than by a test, which is the argument for keeping that check in the loop.	2026-09-13 23:47:12 -04:00
iris	ec012c4552	Text depends on its box for where it sits, not only for shaping Alignment was not accounted for. Glyphs anchored to the start of an axis stay where they are when that extent changes, but the default is `CENTER_LEFT`: a label in a box that grows taller has to re-centre, even though its shaping is untouched. Saying `Internal` there would keep a drawing that belongs somewhere else once the retained path can act on it. It costs nothing today, since neither `Internal` nor `External` reuses anything yet. It would be silent when the move chain lands, which is why the classification wants to be right while it is being written rather than when something starts trusting it.	2026-09-13 23:28:47 -04:00
iris	f192f75b25	Size a widget while drawing it, not in a pass of its own `desired_width`/`desired_height`, `WidgetAxisFns`, `SizeCtx` and the size cache are gone. A widget states what it used with `Painter::set_size` while it draws, and `Painter::widget` hands back a `DrawResult` whose `size()` both reads the child and records that this widget's size depends on it. Reading nothing keeps the parent independent of what the child came to. `Span` is what the change is for. It takes each child's `size_hint` where there is one, draws only the children that cannot answer, allocates the flexible space, then places everything -- which deletes `desired_ortho`, whose own comment said it "literally copies draw ... which makes this slow and not cool". Invalidation follows the dependency edges the draw recorded: a widget that needs redrawing hands off to the highest ancestor that read its size, instead of re-running a measurement to find out whether anything changed. `Widget::size_dependence(axis)` says how much of its box a widget's drawing depends on -- none of it, its own extent, or the whole box -- so the retained path can keep a drawing and write a new box into it. Asked per axis, because wrapped text depends on the width it is offered and not on the height. `Internal` does not yet buy more than `External`: keeping a drawing when only the room around it changed is a translation, which waits for the move chain. `tests/retained.rs` covers the second frame rather than the first, which is where the bugs were: a placed child that was not recorded as one got pruned as departed on the next draw. `examples/text.rs` is new, since wrapping was the one thing here with no way to see it on its own.	2026-09-13 22:51:05 -04:00