Consume by layer, not by widget

Replaces the taking mechanism with `CursorSenses::consumes`, which
decides only whether a layer stops the input reaching the layer below.
Nothing is removed from the cursor, and senses on one layer no longer
block each other: every sensor the pointer is inside runs.

Where the cursor rests stops at the top layer under it. Something
happening to the cursor stops only at a widget that answers to it, so a
click-only child does not swallow a scroll -- which is what `main` gets
wrong, where any hovered sensor blocks the layer below.

A widget the cursor has left still hears its hover ending, but is handed
no press or scroll: that input landed somewhere else. This is a hit test
rather than a consumption rule, and without it a press beside a button
fires the button it just left.

`a_click_and_a_scroll_in_one_frame_go_to_different_widgets` goes with the
per-kind taking it tested. Of the five that remain, two fail on `main`.

src/default/mod.rs

@@ -1,10 +1,6 @@
 use crate::prelude::*;
 use arboard::Clipboard;
-use std::{
-    marker::{PhantomData, Sized},
-    sync::Arc,
-    time::Instant,
-};
+use std::{marker::PhantomData, sync::Arc, time::Instant};
 use winit::{
     event::{Ime, WindowEvent},
     event_loop::{ActiveEventLoop, EventLoopProxy},

src/default/sense.rs

@@ -39,6 +39,19 @@ impl Event for CursorSenses {
     }
 }
 
+impl CursorSenses {
+    /// Whether a widget with these senses stops the input reaching the layer
+    /// below it. Where the cursor rests stops at the top layer that is under
+    /// it; something happening to the cursor stops only at a widget that
+    /// answers to that, so a click-only child does not swallow a scroll.
+    fn consumes(&self, cursor: &CursorState, hover: ActivationState, momentary: bool) -> bool {
+        if !momentary {
+            return true;
+        }
+        should_run(self, cursor, hover).is_some_and(|sense| sense.is_momentary())
+    }
+}
+
 impl CursorSense {
     pub fn click() -> Self {
         Self::PressStart(CursorButton::Left)
@@ -53,17 +66,10 @@ impl CursorSense {
         matches!(self, CursorSense::Pressing(CursorButton::Left))
     }
 
-    /// Takes what this sense answers to out of `cursor`, so a widget below
-    /// does not also get it. Hovering takes nothing: it goes to the topmost
-    /// widget in shape, which is not a question about the input.
-    fn take(&self, cursor: &mut CursorState) {
-        match self {
-            Self::PressStart(button) | Self::Pressing(button) | Self::PressEnd(button) => {
-                *cursor.buttons.select_mut(button) = ActivationState::Off
-            }
-            Self::Scroll => cursor.scroll_delta = Vec2::ZERO,
-            Self::HoverStart | Self::Hovering | Self::HoverEnd => {}
-        }
+    /// Whether this sense is about something happening to the cursor, rather
+    /// than about where it rests.
+    fn is_momentary(&self) -> bool {
+        !matches!(self, Self::HoverStart | Self::Hovering | Self::HoverEnd)
     }
 }
 
@@ -91,14 +97,6 @@ impl CursorButtons {
         }
     }
 
-    pub fn select_mut(&mut self, button: &CursorButton) -> &mut ActivationState {
-        match button {
-            CursorButton::Left => &mut self.left,
-            CursorButton::Right => &mut self.right,
-            CursorButton::Middle => &mut self.middle,
-        }
-    }
-
     pub fn end_frame(&mut self) {
         self.left.end_frame();
         self.middle.end_frame();
@@ -117,6 +115,11 @@ impl CursorButtons {
 }
 
 impl CursorState {
+    /// Whether anything is happening to the cursor beyond where it rests.
+    pub fn has_momentary_input(&self) -> bool {
+        self.scroll_delta != Vec2::ZERO || self.buttons.iter().any(|(_, state)| !state.is_off())
+    }
+
     pub fn end_frame(&mut self) {
         self.buttons.end_frame();
         self.scroll_delta = Vec2::ZERO;
@@ -185,31 +188,20 @@ impl SensorUi for UiRenderState {
         // state like thing, but local to render state, and is passed to UiRsc events so you can
         // update it there?
         let mut active = std::mem::take(&mut rsc.events_mut().get_type::<CursorSense>().active);
-        // Narrowed as it descends: a widget takes what it answers to, and
-        // what is left is what the layers below see.
-        let mut cursor = cursor;
-        let mut hovered = false;
+        let momentary = cursor.has_momentary_input();
         for layer in self.layers.indices().rev() {
-            let mut below = cursor.clone();
-            let mut hovered_here = false;
+            let mut consumed = false;
             for (id, sensor) in active.get_mut(&layer).into_flat_iter() {
                 let shape = self.active.get(id).unwrap().region;
                 let region = shape.to_px(window_size);
-                let over = cursor.exists && region.contains(cursor.pos);
-                // Hover goes to the topmost widget in shape and no further.
-                sensor.hover.update(over && !hovered);
-                // `is_off` would be wrong here: it counts `End`, which is
-                // the one frame a hover-end handler has to run on.
-                if !over && sensor.hover == ActivationState::Off {
+                let in_shape = cursor.exists && region.contains(cursor.pos);
+                sensor.hover.update(in_shape);
+                if sensor.hover == ActivationState::Off {
                     continue;
                 }
-                hovered_here |= over;
-
-                // Momentary input belongs to whatever the cursor is on. A
-                // widget it has just left still hears its hover ending, but
-                // a press landing elsewhere is neither its press to receive
-                // nor its press to take.
-                let cursor = match over {
+                // A widget the cursor has left still hears its hover ending,
+                // but a press or a scroll landing elsewhere is not its input.
+                let cursor = match in_shape {
                     true => cursor.clone(),
                     false => CursorState {
                         pos: cursor.pos,
@@ -217,14 +209,12 @@ impl SensorUi for UiRenderState {
                         ..Default::default()
                     },
                 };
-
-                for senses in rsc.events_mut().get_type::<CursorSense>().registered(*id) {
-                    for sense in senses.iter() {
-                        if matches(sense, &cursor, sensor.hover) {
-                            sense.take(&mut below);
-                        }
-                    }
-                }
+                consumed = consumed
+                    || rsc
+                        .events_mut()
+                        .get_type::<CursorSense>()
+                        .registered(*id)
+                        .any(|senses| senses.consumes(&cursor, sensor.hover, momentary));
 
                 let data = CursorData {
                     pos: cursor.pos - region.top_left,
@@ -239,9 +229,7 @@ impl SensorUi for UiRenderState {
                 };
                 rsc.run_event::<CursorSense>(*id, data, state);
             }
-            hovered |= hovered_here;
-            cursor = below;
-            if hovered && !is_momentary(&cursor) {
+            if consumed {
                 break;
             }
         }
@@ -254,14 +242,8 @@ pub fn should_run(
     cursor: &CursorState,
     hover: ActivationState,
 ) -> Option<CursorSense> {
-    senses
-        .iter()
-        .find(|sense| matches(sense, cursor, hover))
-        .copied()
-}
-
-fn matches(sense: &CursorSense, cursor: &CursorState, hover: ActivationState) -> bool {
-    match sense {
+    for sense in senses.iter() {
+        if match sense {
             CursorSense::PressStart(button) => cursor.buttons.select(button).is_start(),
             CursorSense::Pressing(button) => cursor.buttons.select(button).is_on(),
             CursorSense::PressEnd(button) => cursor.buttons.select(button).is_end(),
@@ -269,12 +251,11 @@ fn matches(sense: &CursorSense, cursor: &CursorState, hover: ActivationState) ->
             CursorSense::Hovering => hover.is_on(),
             CursorSense::HoverEnd => hover.is_end(),
             CursorSense::Scroll => cursor.scroll_delta != Vec2::ZERO,
+        } {
+            return Some(*sense);
         }
-}
-
-/// Whether anything is happening to the cursor beyond where it rests.
-fn is_momentary(cursor: &CursorState) -> bool {
-    cursor.scroll_delta != Vec2::ZERO || cursor.buttons.iter().any(|(_, state)| !state.is_off())
+    }
+    None
 }
 
 impl ActivationState {

src/widget/position/mod.rs

@@ -4,7 +4,7 @@ mod max_size;
 mod offset;
 mod pad;
 mod scroll;
-mod sized;
+mod set_size;
 mod span;
 mod stack;
 
@@ -14,6 +14,6 @@ pub use max_size::*;
 pub use offset::*;
 pub use pad::*;
 pub use scroll::*;
-pub use sized::*;
+pub use set_size::*;
 pub use span::*;
 pub use stack::*;

src/widget/position/set_size.rs

@@ -1,12 +1,12 @@
 use crate::prelude::*;
 
-pub struct Sized {
+pub struct SetSize {
     pub inner: StrongWidget,
     pub x: Option<Len>,
     pub y: Option<Len>,
 }
 
-impl Sized {
+impl SetSize {
     fn apply_to_outer(&self, ctx: &mut SizeCtx) {
         if let Some(x) = self.x {
             ctx.outer.x.select_len(x.apply_rest());
@@ -17,7 +17,7 @@ impl Sized {
     }
 }
 
-impl Widget for Sized {
+impl Widget for SetSize {
     fn draw(&mut self, painter: &mut Painter) {
         painter.widget(&self.inner);
     }

src/widget/ptr.rs

@@ -1,5 +1,5 @@
 use crate::prelude::*;
-use std::marker::{Sized, Unsize};
+use std::marker::Unsize;
 
 pub struct WidgetPtr {
     pub inner: Option<StrongWidget>,

src/widget/text/build.rs

@@ -1,5 +1,5 @@
 use crate::prelude::*;
-use std::marker::{PhantomData, Sized};
+use std::marker::PhantomData;
 
 pub struct TextBuilder<State, O = TextOutput, H: WidgetOption<State> = ()> {
     pub content: String,

src/widget/trait_fns.rs

@@ -31,9 +31,9 @@ widget_trait! {
         }
     }
 
-    fn sized(self, size: impl Into<Size>) -> impl WidgetFn<Rsc, Sized> {
+    fn sized(self, size: impl Into<Size>) -> impl WidgetFn<Rsc, SetSize> {
         let size = size.into();
-        move |state| Sized {
+        move |state| SetSize {
             inner: self.add_strong(state),
             x: Some(size.x),
             y: Some(size.y),
@@ -58,18 +58,18 @@ widget_trait! {
         }
     }
 
-    fn width(self, len: impl Into<Len>) -> impl WidgetFn<Rsc, Sized> {
+    fn width(self, len: impl Into<Len>) -> impl WidgetFn<Rsc, SetSize> {
         let len = len.into();
-        move |state| Sized {
+        move |state| SetSize {
             inner: self.add_strong(state),
             x: Some(len),
             y: None,
         }
     }
 
-    fn height(self, len: impl Into<Len>) -> impl WidgetFn<Rsc, Sized> {
+    fn height(self, len: impl Into<Len>) -> impl WidgetFn<Rsc, SetSize> {
         let len = len.into();
-        move |state| Sized {
+        move |state| SetSize {
             inner: self.add_strong(state),
             x: None,
             y: Some(len),

tests/pointer_routing.rs

@@ -1,4 +1,4 @@
-//! Input across layers: what a widget takes, what passes through it, and
+//! Input across layers: what stops at a layer, what passes through it, and
 //! where hovering stops. These drive `run_sensors` directly, which needs no
 //! GPU and no window.
 
@@ -167,27 +167,6 @@ fn a_scroll_passes_through_every_widget_that_does_not_want_it() {
     assert_eq!(overlay_clicked.take(), []);
 }
 
-#[test]
-fn a_click_and_a_scroll_in_one_frame_go_to_different_widgets() {
-    let mut ui = Ui::new();
-    let (list, button) = (full(&mut ui), full(&mut ui));
-    let scrolled = ui.listen(&list, CursorSense::Scroll);
-    let clicked = ui.listen(&button, CursorSense::click());
-    ui.stack(vec![list.any(), button.any()]);
-
-    let mut cursor = ui.cursor((50.0, 50.0));
-    cursor.scroll_delta = (0.0, 10.0).into();
-    cursor.buttons.left = ActivationState::Start;
-    ui.run(cursor);
-
-    assert_eq!(clicked.take(), [CursorSense::click()]);
-    assert_eq!(
-        scrolled.take(),
-        [CursorSense::Scroll],
-        "taking the click must not take the scroll with it"
-    );
-}
-
 #[test]
 fn only_the_topmost_listener_takes_a_press() {
     let mut ui = Ui::new();