Fixing nested collapse animations

CHANGELOG.md

@@ -13,6 +13,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - `Collapse`, `OverlayLayer`, and `Progress` all honor the theme components
   `EasingIn` and `EasingOut` rather than hard-coded easing functions.
+- `Collapse` widgets now apply child size changes immediately rather than
+  animating the transition. The previous behavior caused nested collapsed
+  widgets to grow and shrink in an accordian-like fashion rather than animating
+  together.
 
 ### Added
 

src/widgets/collapse.rs

@@ -6,8 +6,8 @@ use figures::{Size, Zero};
 use crate::animation::{AnimationHandle, AnimationTarget, Spawn};
 use crate::context::LayoutContext;
 use crate::styles::components::{EasingIn, EasingOut};
-use crate::value::{Dynamic, IntoDynamic, Source};
+use crate::value::{Destination, Dynamic, Generation, IntoDynamic, Source};
-use crate::widget::{MakeWidget, WidgetRef, WrappedLayout, WrapperWidget};
+use crate::widget::{MakeWidget, WidgetInstance, WidgetRef, WrappedLayout, WrapperWidget};
 use crate::ConstraintLimit;
 
 /// A widget that collapses/hides its contents based on a [`Dynamic<bool>`].
@@ -15,25 +15,32 @@ use crate::ConstraintLimit;
 pub struct Collapse {
     child: WidgetRef,
     collapse: Dynamic<bool>,
+    collapse_generation: Generation,
     size: Dynamic<Px>,
     collapse_animation: Option<CollapseAnimation>,
     vertical: bool,
 }
 
 impl Collapse {
+    fn new(collapse: Dynamic<bool>, child: WidgetInstance, vertical: bool) -> Self {
+        let collapse_generation = collapse.generation();
+        Self {
+            collapse,
+            collapse_generation,
+            child: WidgetRef::new(child),
+            size: Dynamic::default(),
+            vertical,
+            collapse_animation: None,
+        }
+    }
+
     /// Returns a widget that collapses `child` vertically based on the dynamic
     /// boolean value.
     ///
     /// This widget will be collapsed when the dynamic contains `true`, and
     /// revealed when the dynamic contains `false`.
     pub fn vertical(collapse_when: impl IntoDynamic<bool>, child: impl MakeWidget) -> Self {
-        Self {
+        Self::new(collapse_when.into_dynamic(), child.make_widget(), true)
-            collapse: collapse_when.into_dynamic(),
-            child: WidgetRef::new(child),
-            size: Dynamic::default(),
-            vertical: true,
-            collapse_animation: None,
-        }
     }
 
     /// Returns a widget that collapses `child` horizontally based on the
@@ -42,23 +49,33 @@ impl Collapse {
     /// This widget will be collapsed when the dynamic contains `true`, and
     /// revealed when the dynamic contains `false`.
     pub fn horizontal(collapse_when: impl IntoDynamic<bool>, child: impl MakeWidget) -> Self {
-        Self {
+        Self::new(collapse_when.into_dynamic(), child.make_widget(), false)
-            collapse: collapse_when.into_dynamic(),
-            child: WidgetRef::new(child),
-            size: Dynamic::default(),
-            vertical: false,
-            collapse_animation: None,
-        }
     }
 
-    fn note_child_size(&mut self, size: Px, context: &mut LayoutContext<'_, '_, '_, '_>) {
+    fn note_child_size(
-        let (easing, target) = if self.collapse.get_tracking_invalidate(context) {
+        &mut self,
+        size: Px,
+        current_size: Px,
+        context: &mut LayoutContext<'_, '_, '_, '_>,
+    ) -> Px {
+        context.invalidate_when_changed(&self.collapse);
+        let (generation, collapse) = self.collapse.map_generational(|c| (c.generation(), *c));
+        let (easing, target) = if collapse {
             (context.get(&EasingOut), Px::ZERO)
         } else {
             (context.get(&EasingIn), size)
         };
+        if generation == self.collapse_generation {}
         match &self.collapse_animation {
             Some(state) if state.target == target => {}
+            Some(_) if generation == self.collapse_generation => {
+                // The resize happened from a reason other than our toggle.
+                // Immediately apply it.
+                let mut stored_size = self.size.lock();
+                stored_size.prevent_notifications();
+                *stored_size = target;
+                return target;
+            }
             _ => {
                 // If this is our first setup, immediately give the child the
                 // space they request.
@@ -78,6 +95,8 @@ impl Collapse {
                 });
             }
         }
+        self.collapse_generation = generation;
+        current_size
     }
 }
 
@@ -94,13 +113,13 @@ impl WrapperWidget for Collapse {
     ) -> WrappedLayout {
         let clip_size = self.size.get_tracking_invalidate(context);
         if self.vertical {
-            self.note_child_size(size.height, context);
+            let height = self.note_child_size(size.height, clip_size, context);
 
-            Size::new(size.width, clip_size)
+            Size::new(size.width, height)
         } else {
-            self.note_child_size(size.width, context);
+            let width = self.note_child_size(size.width, clip_size, context);
 
-            Size::new(clip_size, size.height)
+            Size::new(width, size.height)
         }
         .into()
     }