Fix for negative padding from a curve in AnimatedPadding. (flutter#52072

)

* Fix for negative padding from a curve in AnimatedPadding.

* Added a EdgeInsets.clamp function that would return an EdgeInsets instance instead of a _MixedEdgeInsets used by the base class. This was causing some tests to fail that didn't have a text direction.

packages/flutter/lib/src/painting/edge_insets.dart

@@ -503,6 +503,16 @@ class EdgeInsets extends EdgeInsetsGeometry {
     return super.add(other);
   }
 
+  @override
+  EdgeInsetsGeometry clamp(EdgeInsetsGeometry min, EdgeInsetsGeometry max) {
+    return EdgeInsets.fromLTRB(
+      _left.clamp(min._left, max._left) as double,
+      _top.clamp(min._top, max._top) as double,
+      _right.clamp(min._right, max._right) as double,
+      _bottom.clamp(min._bottom, max._bottom) as double,
+    );
+  }
+
   /// Returns the difference between two [EdgeInsets].
   EdgeInsets operator -(EdgeInsets other) {
     return EdgeInsets.fromLTRB(

packages/flutter/lib/src/widgets/implicit_animations.dart

@@ -834,7 +834,9 @@ class _AnimatedPaddingState extends AnimatedWidgetBaseState<AnimatedPadding> {
   @override
   Widget build(BuildContext context) {
     return Padding(
-      padding: _padding.evaluate(animation),
+      padding: _padding
+        .evaluate(animation)
+        .clamp(EdgeInsets.zero, EdgeInsetsGeometry.infinity),
       child: widget.child,
     );
   }

packages/flutter/test/widgets/animated_padding_test.dart

@@ -58,4 +58,44 @@ void main() {
     expect(tester.getSize(find.byKey(target)), const Size(700.0, 600.0));
     expect(tester.getTopRight(find.byKey(target)), const Offset(700.0, 0.0));
   });
+
+  testWidgets('AnimatedPadding animated padding clamped to positive values', (WidgetTester tester) async {
+    final Key target = UniqueKey();
+
+    await tester.pumpWidget(
+      Directionality(
+        textDirection: TextDirection.rtl,
+        child: AnimatedPadding(
+          curve: Curves.easeInOutBack, // will cause negative padding during overshoot
+          duration: const Duration(milliseconds: 200),
+          padding: const EdgeInsets.only(right: 50.0),
+          child: SizedBox.expand(key: target),
+        ),
+      ),
+    );
+
+    expect(tester.getSize(find.byKey(target)), const Size(750.0, 600.0));
+    expect(tester.getTopRight(find.byKey(target)), const Offset(750.0, 0.0));
+
+    await tester.pumpWidget(
+      Directionality(
+        textDirection: TextDirection.rtl,
+        child: AnimatedPadding(
+          curve: Curves.easeInOutBack,
+          duration: const Duration(milliseconds: 200),
+          padding: const EdgeInsets.only(right: 0.0),
+          child: SizedBox.expand(key: target),
+        ),
+      ),
+    );
+
+    expect(tester.getSize(find.byKey(target)), const Size(750.0, 600.0));
+    expect(tester.getTopRight(find.byKey(target)), const Offset(750.0, 0.0));
+
+    await tester.pump(const Duration(milliseconds: 128));
+    // Curve would have made the padding negative a this point if it is not clamped.
+    expect(tester.getSize(find.byKey(target)), const Size(800.0, 600.0));
+    expect(tester.getTopRight(find.byKey(target)), const Offset(800.0, 0.0));
+  });
+
 }