Fix `Response::interact` and `Ui:interact_with_hovered` (#4013)

These broke in 0.26

* #3989
* #4006

crates/egui/src/context.rs

@@ -234,7 +234,18 @@ impl WidgetRects {
 
     /// Insert the given widget rect in the given layer.
     pub fn insert(&mut self, layer_id: LayerId, widget_rect: WidgetRect) {
-        self.by_layer.entry(layer_id).or_default().push(widget_rect);
+        let layer_widgets = self.by_layer.entry(layer_id).or_default();
+
+        if let Some(last) = layer_widgets.last_mut() {
+            if last.id == widget_rect.id {
+                // e.g. calling `response.interact(…)` right after interacting.
+                last.sense |= widget_rect.sense;
+                last.rect = last.rect.union(widget_rect.rect);
+                return;
+            }
+        }
+
+        layer_widgets.push(widget_rect);
     }
 }
 
@@ -1089,7 +1100,19 @@ impl Context {
 
         let clicked_elsewhere = res.clicked_elsewhere();
         self.write(|ctx| {
-            let input = &ctx.viewports.entry(ctx.viewport_id()).or_default().input;
+            let viewport = ctx.viewports.entry(ctx.viewport_id()).or_default();
+
+            // We need to remember this widget.
+            // `widget_contains_pointer` also does this, but in case of e.g. `Response::interact`,
+            // that won't be called.
+            // We add all widgets here, even non-interactive ones,
+            // because we need this list not only for checking for blocking widgets,
+            // but also to know when we have reached the widget we are checking for cover.
+            viewport
+                .layer_rects_this_frame
+                .insert(layer_id, WidgetRect { id, rect, sense });
+
+            let input = &viewport.input;
             let memory = &mut ctx.memory;
 
             if sense.focusable {
@@ -2292,9 +2315,10 @@ impl Context {
                 let pointer_pos = viewport.input.pointer.interact_pos();
                 if let Some(pointer_pos) = pointer_pos {
                     if let Some(rects) = viewport.layer_rects_prev_frame.by_layer.get(&layer_id) {
+                        // Iterate backwards, i.e. topmost widgets first.
                         for blocking in rects.iter().rev() {
                             if blocking.id == id {
-                                // There are no earlier widgets before this one,
+                                // We've checked all widgets there were added after this one last frame,
                                 // which means there are no widgets covering us.
                                 break;
                             }

crates/egui/src/response.rs

@@ -607,7 +607,7 @@ impl Response {
             self.rect,
             sense,
             self.enabled,
-            self.hovered,
+            self.contains_pointer,
         )
     }
 

crates/egui/src/sense.rs

@@ -85,3 +85,19 @@ impl Sense {
         self.click || self.drag
     }
 }
+
+impl std::ops::BitOr for Sense {
+    type Output = Self;
+
+    #[inline]
+    fn bitor(self, rhs: Self) -> Self {
+        self.union(rhs)
+    }
+}
+
+impl std::ops::BitOrAssign for Sense {
+    #[inline]
+    fn bitor_assign(&mut self, rhs: Self) {
+        *self = self.union(rhs);
+    }
+}

crates/egui_demo_lib/src/demo/tests.rs

@@ -357,6 +357,8 @@ pub struct InputTest {
     #[cfg_attr(feature = "serde", serde(skip))]
     history: [DeduplicatedHistory; 4],
 
+    late_interaction: bool,
+
     show_hovers: bool,
 }
 
@@ -394,6 +396,8 @@ impl super::View for InputTest {
             ui.checkbox(&mut self.show_hovers, "Show hover state");
         });
 
+        ui.checkbox(&mut self.late_interaction, "Use Response::interact");
+
         ui.label("This tests how egui::Response reports events.\n\
         The different buttons are sensitive to different things.\n\
         Try interacting with them with any mouse button by clicking, double-clicking, triple-clicking, or dragging them.");
@@ -409,7 +413,13 @@ impl super::View for InputTest {
             .enumerate()
             {
                 columns[i].push_id(i, |ui| {
-                    let response = ui.add(egui::Button::new(sense_name).sense(sense));
+                    let response = if self.late_interaction {
+                        let first_response =
+                            ui.add(egui::Button::new(sense_name).sense(egui::Sense::hover()));
+                        first_response.interact(sense)
+                    } else {
+                        ui.add(egui::Button::new(sense_name).sense(sense))
+                    };
                     let info = response_summary(&response, self.show_hovers);
                     self.history[i].add(info.trim().to_owned());
                     self.history[i].ui(ui);