Keep momentary input on the widget the cursor is on

Tests across layers, as asked, and the fifth one found a defect older than
this branch: a press fired on a widget the cursor had just left, because the
frame its hover ends is a frame it still gets dispatched on, and `should_run`
only ever looked at the cursor. A button in the corner of a list therefore
clicked when the press landed anywhere else in the row.

A widget that is not under the cursor now sees a cursor with nothing
momentary in it, which settles both halves of the question at once: it is not
its press to receive, and not its press to take from the layers below.

`CursorSense` and `CursorButton` derive `Debug`, so a failure says which
sense fired rather than `left != right`.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/default/sense.rs

@@ -4,14 +4,14 @@ use std::{
     rc::Rc,
 };
 
-#[derive(Clone, Copy, PartialEq)]
+#[derive(Debug, Clone, Copy, PartialEq)]
 pub enum CursorButton {
     Left,
     Right,
     Middle,
 }
 
-#[derive(Clone, Copy, PartialEq)]
+#[derive(Debug, Clone, Copy, PartialEq)]
 pub enum CursorSense {
     PressStart(CursorButton),
     Pressing(CursorButton),
@@ -205,6 +205,19 @@ impl SensorUi for UiRenderState {
                 }
                 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 {
+                    true => cursor.clone(),
+                    false => CursorState {
+                        pos: cursor.pos,
+                        exists: cursor.exists,
+                        ..Default::default()
+                    },
+                };
+
                 for senses in rsc.events_mut().get_type::<CursorSense>().registered(*id) {
                     for sense in senses.iter() {
                         if matches(sense, &cursor, sensor.hover) {
@@ -213,8 +226,6 @@ impl SensorUi for UiRenderState {
                     }
                 }
 
-                let cursor = cursor.clone();
-
                 let data = CursorData {
                     pos: cursor.pos - region.top_left,
                     size: region.bot_right - region.top_left,

tests/pointer_routing.rs

@@ -1,9 +1,9 @@
-//! A widget takes only what it answers to: a button over a list takes the
-//! click and leaves the scroll. These drive `run_sensors` directly, which
-//! needs no GPU and no window.
+//! Input across layers: what a widget takes, what passes through it, and
+//! where hovering stops. These drive `run_sensors` directly, which needs no
+//! GPU and no window.
 
 use iris::prelude::*;
-use std::{cell::Cell, rc::Rc};
+use std::{cell::RefCell, rc::Rc};
 
 struct SenseRsc {
     ui: UiData,
@@ -41,140 +41,215 @@ impl HasEvents for SenseRsc {
     }
 }
 
-fn cursor_at(pos: Vec2) -> CursorState {
-    CursorState {
-        pos,
-        exists: true,
-        buttons: Default::default(),
-        scroll_delta: Vec2::ZERO,
+const WINDOW: f32 = 100.0;
+
+/// Every sense that has fired on one widget since it was last read.
+#[derive(Default, Clone)]
+struct Fired(Rc<RefCell<Vec<CursorSense>>>);
+
+impl Fired {
+    fn take(&self) -> Vec<CursorSense> {
+        std::mem::take(&mut self.0.borrow_mut())
     }
 }
 
-/// A button covering a list, on the layer above it: the list scrolls, the
-/// button clicks, and the returned flags say which fired.
-fn button_over_list() -> (UiRenderState, SenseRsc, Rc<Cell<bool>>, Rc<Cell<bool>>) {
-    let mut rsc = SenseRsc {
-        ui: UiData::default(),
-        events: EventManager::default(),
-    };
+struct Ui {
+    rsc: SenseRsc,
+    render: UiRenderState,
+    state: (),
+}
 
-    // Both cover the whole window: the button "sitting over" the list.
-    let list = rsc.ui.widgets.add_strong(Rect::new(UiColor::WHITE));
-    let list_weak = list.weak();
-    let button = rsc.ui.widgets.add_strong(Rect::new(UiColor::RED));
-    let button_weak = button.weak();
-
-    let scrolled = Rc::new(Cell::new(false));
-    let clicked = Rc::new(Cell::new(false));
-    {
-        let scrolled = scrolled.clone();
-        rsc.register_event(list_weak, CursorSense::Scroll, move |_ctx, _rsc| {
-            scrolled.set(true);
-        });
-    }
-    {
-        let clicked = clicked.clone();
-        rsc.register_event(button_weak, CursorSense::click(), move |_ctx, _rsc| {
-            clicked.set(true);
-        });
+impl Ui {
+    fn new() -> Self {
+        Self {
+            rsc: SenseRsc {
+                ui: UiData::default(),
+                events: EventManager::default(),
+            },
+            render: UiRenderState::new(),
+            state: (),
+        }
     }
 
-    // A Stack draws each child on its own layer, in order.
-    let root = rsc
-        .ui
-        .widgets
-        .add_strong(Stack {
-            children: vec![list.any(), button.any()],
-            size: StackSize::default(),
-        })
-        .any();
+    fn listen<W: Widget + ?core::marker::Sized + 'static>(
+        &mut self,
+        widget: &StrongWidget<W>,
+        senses: impl Into<CursorSenses>,
+    ) -> Fired {
+        let fired = Fired::default();
+        let sink = fired.clone();
+        self.rsc
+            .register_event(widget.weak(), senses.into(), move |ctx, _rsc| {
+                sink.0.borrow_mut().push(ctx.data.sense)
+            });
+        fired
+    }
 
-    let mut render = UiRenderState::new();
-    render.resize((100.0, 100.0));
-    render.update(&root, &mut rsc);
+    /// Stacks the widgets bottom first, each on its own layer, and lays them
+    /// out in a square window.
+    fn stack(&mut self, children: Vec<StrongWidget>) {
+        let root = self
+            .rsc
+            .ui
+            .widgets
+            .add_strong(Stack {
+                children,
+                size: StackSize::default(),
+            })
+            .any();
+        self.render.resize((WINDOW, WINDOW));
+        self.render.update(&root, &mut self.rsc);
+    }
 
-    (render, rsc, scrolled, clicked)
+    fn cursor(&mut self, at: (f32, f32)) -> CursorState {
+        CursorState {
+            pos: at.into(),
+            exists: true,
+            buttons: Default::default(),
+            scroll_delta: Vec2::ZERO,
+        }
+    }
+
+    fn run(&mut self, cursor: CursorState) {
+        self.render.run_sensors(
+            &mut self.rsc,
+            &mut self.state,
+            cursor,
+            (WINDOW, WINDOW).into(),
+        );
+    }
+}
+
+fn full(ui: &mut Ui) -> StrongWidget<Rect> {
+    rect(UiColor::WHITE).add_strong(&mut ui.rsc)
 }
 
 #[test]
-fn a_button_over_a_list_scrolls_the_list_and_still_clicks() {
-    let (render, mut rsc, scrolled, clicked) = button_over_list();
-    let mut state = ();
+fn hover_stops_at_the_topmost_widget() {
+    let mut ui = Ui::new();
+    let (bottom, middle, top) = (full(&mut ui), full(&mut ui), full(&mut ui));
+    let bottom_hover = ui.listen(&bottom, CursorSense::HoverStart);
+    let middle_hover = ui.listen(&middle, CursorSense::HoverStart);
+    let top_hover = ui.listen(&top, CursorSense::HoverStart);
+    ui.stack(vec![bottom.any(), middle.any(), top.any()]);
 
-    let mut scroll = cursor_at((50.0, 50.0).into());
-    scroll.scroll_delta = (0.0, 10.0).into();
-    render.run_sensors(&mut rsc, &mut state, scroll, (100.0, 100.0).into());
+    let cursor = ui.cursor((50.0, 50.0));
+    ui.run(cursor);
 
-    assert!(
-        scrolled.get(),
-        "a scroll over the button must still reach the list underneath it"
-    );
-    assert!(
-        !clicked.get(),
-        "a scroll is not a click; the button must not have fired"
+    assert_eq!(top_hover.take(), [CursorSense::HoverStart]);
+    assert_eq!(
+        middle_hover.take(),
+        [],
+        "hover is not shared with a layer below"
     );
+    assert_eq!(bottom_hover.take(), []);
+}
 
-    let mut click = cursor_at((50.0, 50.0).into());
-    click.buttons.left = ActivationState::Start;
-    render.run_sensors(&mut rsc, &mut state, click, (100.0, 100.0).into());
+#[test]
+fn a_scroll_passes_through_every_widget_that_does_not_want_it() {
+    let mut ui = Ui::new();
+    let (list, button, overlay) = (full(&mut ui), full(&mut ui), full(&mut ui));
+    let scrolled = ui.listen(&list, CursorSense::Scroll);
+    let clicked = ui.listen(&button, CursorSense::click());
+    let overlay_clicked = ui.listen(&overlay, CursorSense::click());
+    ui.stack(vec![list.any(), button.any(), overlay.any()]);
 
-    assert!(
-        clicked.get(),
-        "the button on top must still receive an actual click"
+    let mut cursor = ui.cursor((50.0, 50.0));
+    cursor.scroll_delta = (0.0, 10.0).into();
+    ui.run(cursor);
+
+    assert_eq!(
+        scrolled.take(),
+        [CursorSense::Scroll],
+        "two layers of click-only widgets do not stop a scroll"
     );
+    assert_eq!(clicked.take(), []);
+    assert_eq!(overlay_clicked.take(), []);
 }
 
 #[test]
 fn a_click_and_a_scroll_in_one_frame_go_to_different_widgets() {
-    let (render, mut rsc, scrolled, clicked) = button_over_list();
-    let mut state = ();
+    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 both = cursor_at((50.0, 50.0).into());
-    both.scroll_delta = (0.0, 10.0).into();
-    both.buttons.left = ActivationState::Start;
-    render.run_sensors(&mut rsc, &mut state, both, (100.0, 100.0).into());
+    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!(
-        clicked.get(),
-        "the button takes the click it registered for"
-    );
-    assert!(
-        scrolled.get(),
+    assert_eq!(clicked.take(), [CursorSense::click()]);
+    assert_eq!(
+        scrolled.take(),
+        [CursorSense::Scroll],
         "taking the click must not take the scroll with it"
     );
 }
 
 #[test]
-fn leaving_a_widget_still_ends_its_hover() {
-    let mut rsc = SenseRsc {
-        ui: UiData::default(),
-        events: EventManager::default(),
-    };
-    let widget = rsc.ui.widgets.add_strong(Rect::new(UiColor::WHITE));
-    let ended = Rc::new(Cell::new(false));
-    {
-        let ended = ended.clone();
-        rsc.register_event(widget.weak(), CursorSense::HoverEnd, move |_ctx, _rsc| {
-            ended.set(true);
-        });
-    }
+fn only_the_topmost_listener_takes_a_press() {
+    let mut ui = Ui::new();
+    let (below, above) = (full(&mut ui), full(&mut ui));
+    let below_clicked = ui.listen(&below, CursorSense::click());
+    let above_clicked = ui.listen(&above, CursorSense::click());
+    ui.stack(vec![below.any(), above.any()]);
 
-    let root = widget.any();
-    let mut render = UiRenderState::new();
-    render.resize((100.0, 100.0));
-    render.update(&root, &mut rsc);
+    let mut cursor = ui.cursor((50.0, 50.0));
+    cursor.buttons.left = ActivationState::Start;
+    ui.run(cursor);
 
-    let mut state = ();
-    render.run_sensors(
-        &mut rsc,
-        &mut state,
-        cursor_at((50.0, 50.0).into()),
-        (100.0, 100.0).into(),
+    assert_eq!(above_clicked.take(), [CursorSense::click()]);
+    assert_eq!(below_clicked.take(), [], "one press goes to one widget");
+}
+
+#[test]
+fn a_press_beside_the_button_reaches_the_layer_below() {
+    let mut ui = Ui::new();
+    let list = full(&mut ui);
+    // The row above the list covers it, but only its left half is the button.
+    let button = full(&mut ui);
+    let gap = full(&mut ui);
+    let list_clicked = ui.listen(&list, CursorSense::click());
+    let button_clicked = ui.listen(&button, CursorSense::click());
+    let row = ui.rsc.ui.widgets.add_strong(Span {
+        children: vec![button.any(), gap.any()],
+        dir: Dir::RIGHT,
+        gap: 0.0,
+    });
+    ui.stack(vec![list.any(), row.any()]);
+
+    let mut on_button = ui.cursor((20.0, 50.0));
+    on_button.buttons.left = ActivationState::Start;
+    ui.run(on_button);
+    assert_eq!(button_clicked.take(), [CursorSense::click()]);
+    assert_eq!(list_clicked.take(), []);
+
+    let mut beside_it = ui.cursor((80.0, 50.0));
+    beside_it.buttons.left = ActivationState::Start;
+    ui.run(beside_it);
+    assert_eq!(button_clicked.take(), [], "the cursor is not on the button");
+    assert_eq!(
+        list_clicked.take(),
+        [CursorSense::click()],
+        "a press beside the button belongs to what is under it"
     );
-    assert!(!ended.get(), "the cursor is still on it");
+}
+
+#[test]
+fn leaving_a_widget_still_ends_its_hover() {
+    let mut ui = Ui::new();
+    let widget = full(&mut ui);
+    let hover = ui.listen(&widget, CursorSense::HoverStart | CursorSense::HoverEnd);
+    ui.stack(vec![widget.any()]);
+
+    let cursor = ui.cursor((50.0, 50.0));
+    ui.run(cursor);
+    assert_eq!(hover.take(), [CursorSense::HoverStart]);
 
-    let mut gone = cursor_at((50.0, 50.0).into());
+    let mut gone = ui.cursor((50.0, 50.0));
     gone.exists = false;
-    render.run_sensors(&mut rsc, &mut state, gone, (100.0, 100.0).into());
-    assert!(ended.get(), "leaving a widget ends its hover");
+    ui.run(gone);
+    assert_eq!(hover.take(), [CursorSense::HoverEnd]);
 }