fix: ensure animations finish at target value (#19)

blaugold · Sep 2, 2022 · 49126dc · 49126dc
1 parent ebec2a9
commit 49126dc
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Showing 2 changed files with 21 additions and 10 deletions.
diff --git a/packages/fleet/lib/src/animation.dart b/packages/fleet/lib/src/animation.dart
@@ -293,7 +293,8 @@ abstract class AnimationImpl<T> with Diagnosticable {
   ///
   /// The returned [Duration] must be negative or zero and represents the
   /// difference between when the animation reached its end value and [elapsed].
-  Duration? _isDone(Duration elapsed);
+  @protected
+  Duration? isAtEnd(Duration elapsed);
 
   /// Returns the value of this animation at the given [elapsed] time.
   ///
@@ -303,7 +304,8 @@ abstract class AnimationImpl<T> with Diagnosticable {
   /// actually returned value must always be assignable to [T] (if [T] is
   /// nullable returning `null` is fine). See [AnimatableValue.createTween] for
   /// more information.
-  T? _valueAt(Duration elapsed);
+  @protected
+  T? valueAt(Duration elapsed);
 
   void _onTick(Duration elapsed) {
     var elapsedForAllRepeats = elapsed * _spec._speed;
@@ -319,7 +321,7 @@ abstract class AnimationImpl<T> with Diagnosticable {
     var elapsedForRepeat = elapsedForAllRepeats - _lastRepeatEnd;
 
     if (_forward) {
-      final endDelta = _isDone(elapsedForRepeat);
+      final endDelta = isAtEnd(elapsedForRepeat);
       if (endDelta != null) {
         assert(endDelta.isNegative || endDelta.inMicroseconds == 0);
         elapsedForRepeat = elapsedForRepeat + endDelta;
@@ -345,7 +347,15 @@ abstract class AnimationImpl<T> with Diagnosticable {
       }
     }
 
-    _currentValue = _valueAt(elapsedForRepeat) as T;
+    if (_isStopped) {
+      // On the last tick we need to be exactly at the end of the animation.
+      // If the animation is repeated and reversing it is possible that the
+      // last tick is at the beginning of the animation.
+      _currentValue = _tween.end as T;
+    } else {
+      _currentValue = valueAt(elapsedForRepeat) as T;
+    }
+
     onChange?.call();
   }
 
@@ -406,15 +416,15 @@ class _CurveAnimation<T> extends AnimationImpl<T> {
   final _CurveAnimationProvider _provider;
 
   @override
-  Duration? _isDone(Duration elapsed) {
+  Duration? isAtEnd(Duration elapsed) {
     if (elapsed >= _provider.duration) {
       return _provider.duration - elapsed;
     }
     return null;
   }
 
   @override
-  T? _valueAt(Duration elapsed) {
+  T? valueAt(Duration elapsed) {
     var t = elapsed.inMicroseconds / _provider.duration.inMicroseconds;
     t = _provider.curve.transform(t);
     return _tween.transform(t);

diff --git a/...et/test/animated_widget_helpers_test.dart → ...es/fleet/test/animatable_widget_test.dart b/...et/test/animated_widget_helpers_test.dart → ...es/fleet/test/animatable_widget_test.dart
@@ -184,12 +184,13 @@ void main() {
           );
 
           await tester.pump(d500ms); // .5
-          await tester.pump(d500ms); // 1.
+          await tester.pump(d500ms); // 1
           await tester.pump(d500ms); // .5
-          await tester.pump(d500ms); // 0
+          await tester.pump(d250ms); // .25
+          await tester.pump(d250ms); // 1 (the last tick always goes to the end)
           await tester.pumpAndSettle();
 
-          expect(state.animationChanges, [.5, 1, .5, 0]);
+          expect(state.animationChanges, [.5, 1, .5, .25, 1]);
         });
 
         testWidgets('3 times', (tester) async {
@@ -202,7 +203,7 @@ void main() {
           );
 
           await tester.pump(d500ms); // .5
-          await tester.pump(d500ms); // 1.
+          await tester.pump(d500ms); // 1
           await tester.pump(d500ms); // .5
           await tester.pump(d500ms); // 0
           await tester.pump(d500ms); // .5