Draggable feedback positioning (#145647)

Fixes a calculation in Draggable that was previously wrong when the target was transformed.

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

@@ -833,6 +833,7 @@ class _DragAvatar<T extends Object> extends Drag {
   final List<_DragTargetState<Object>> _enteredTargets = <_DragTargetState<Object>>[];
   Offset _position;
   Offset? _lastOffset;
+  late Offset _overlayOffset;
   OverlayEntry? _entry;
 
   @override
@@ -858,6 +859,10 @@ class _DragAvatar<T extends Object> extends Drag {
 
   void updateDrag(Offset globalPosition) {
     _lastOffset = globalPosition - dragStartPoint;
+    final RenderBox box = overlayState.context.findRenderObject()! as RenderBox;
+    final Offset overlaySpaceOffset = box.globalToLocal(globalPosition);
+    _overlayOffset = overlaySpaceOffset - dragStartPoint;
+
     _entry!.markNeedsBuild();
     final HitTestResult result = HitTestResult();
     WidgetsBinding.instance.hitTestInView(result, globalPosition + feedbackOffset, viewId);
@@ -943,11 +948,9 @@ class _DragAvatar<T extends Object> extends Drag {
   }
 
   Widget _build(BuildContext context) {
-    final RenderBox box = overlayState.context.findRenderObject()! as RenderBox;
-    final Offset overlayTopLeft = box.localToGlobal(Offset.zero);
     return Positioned(
-      left: _lastOffset!.dx - overlayTopLeft.dx,
+      left: _overlayOffset.dx,
-      top: _lastOffset!.dy - overlayTopLeft.dy,
+      top: _overlayOffset.dy,
       child: ExcludeSemantics(
         excluding: ignoringFeedbackSemantics,
         child: IgnorePointer(

packages/flutter/test/widgets/draggable_test.dart

@@ -967,6 +967,10 @@ void main() {
       await gesture.moveTo(thirdLocation);
       await tester.pump();
       expect(tester.getTopLeft(find.text('N')), thirdLocation);
+
+      // Finish gesture to release resources.
+      await gesture.up();
+      await tester.pump();
     });
 
     testWidgets('Horizontal axis draggable moves horizontally', (WidgetTester tester) async {
@@ -982,6 +986,10 @@ void main() {
       await gesture.moveTo(thirdLocation);
       await tester.pump();
       expect(tester.getTopLeft(find.text('H')), thirdLocation);
+
+      // Finish gesture to release resources.
+      await gesture.up();
+      await tester.pump();
     });
 
     testWidgets('Horizontal axis draggable does not move vertically', (WidgetTester tester) async {
@@ -1000,6 +1008,10 @@ void main() {
       await gesture.moveTo(thirdDragLocation);
       await tester.pump();
       expect(tester.getTopLeft(find.text('H')), thirdWidgetLocation);
+
+      // Finish gesture to release resources.
+      await gesture.up();
+      await tester.pump();
     });
 
     testWidgets('Vertical axis draggable moves vertically', (WidgetTester tester) async {
@@ -1015,6 +1027,10 @@ void main() {
       await gesture.moveTo(thirdLocation);
       await tester.pump();
       expect(tester.getTopLeft(find.text('V')), thirdLocation);
+
+      // Finish gesture to release resources.
+      await gesture.up();
+      await tester.pump();
     });
 
     testWidgets('Vertical axis draggable does not move horizontally', (WidgetTester tester) async {
@@ -1033,6 +1049,10 @@ void main() {
       await gesture.moveTo(thirdDragLocation);
       await tester.pump();
       expect(tester.getTopLeft(find.text('V')), thirdWidgetLocation);
+
+      // Finish gesture to release resources.
+      await gesture.up();
+      await tester.pump();
     });
   });
 
@@ -1666,6 +1686,10 @@ void main() {
     expect(find.text('Dragging'), findsOneWidget);
     expect(find.text('Target'), findsOneWidget);
     expect(find.text('Rejected'), findsNothing);
+
+    // Finish gesture to release resources.
+    await gesture.up();
+    await tester.pump();
   });
 
 
@@ -3099,6 +3123,10 @@ void main() {
         ),
         findsNothing,
       );
+
+      // Finish gesture to release resources.
+      await gesture.up();
+      await tester.pump();
     });
 
   testWidgets('Drag feedback is put on root overlay with [rootOverlay] flag', (WidgetTester tester) async {
@@ -3497,6 +3525,93 @@ void main() {
     await tester.pumpAndSettle();
   });
 
+  testWidgets('Drag and drop - feedback matches pointer in scaled MaterialApp', (WidgetTester tester) async {
+    await tester.pumpWidget(Transform.scale(
+      scale: 0.5,
+      child: const MaterialApp(
+        home: Scaffold(
+          body: Draggable<int>(
+            data: 42,
+            feedback: Text('Feedback'),
+            child: Text('Source'),
+          ),
+        ),
+      ),
+    ));
+
+    final Offset location = tester.getTopLeft(find.text('Source'));
+    final TestGesture gesture = await tester.startGesture(location);
+    final Offset secondLocation = location + const Offset(100, 100);
+    await gesture.moveTo(secondLocation);
+    await tester.pump();
+    final Offset appTopLeft = tester.getTopLeft(find.byType(MaterialApp));
+    expect(tester.getTopLeft(find.text('Source')), appTopLeft);
+    expect(tester.getTopLeft(find.text('Feedback')), secondLocation);
+
+    // Finish gesture to release resources.
+    await gesture.up();
+    await tester.pumpAndSettle();
+  });
+
+  testWidgets('Drag and drop - childDragAnchorStrategy works in scaled MaterialApp', (WidgetTester tester) async {
+    final Key sourceKey = UniqueKey();
+    final Key feedbackKey = UniqueKey();
+    await tester.pumpWidget(Transform.scale(
+      scale: 0.5,
+      child:  MaterialApp(
+        home: Scaffold(
+          body: Draggable<int>(
+            data: 42,
+            feedback: Text('Text', key: feedbackKey),
+            child: Text('Text', key: sourceKey),
+          ),
+        ),
+      ),
+    ));
+    final Finder source = find.byKey(sourceKey);
+    final Finder feedback = find.byKey(feedbackKey);
+
+    final TestGesture gesture = await tester.startGesture(tester.getCenter(source));
+    await tester.pump();
+    expect(tester.getTopLeft(source), tester.getTopLeft(feedback));
+
+    // Finish gesture to release resources.
+    await gesture.up();
+    await tester.pumpAndSettle();
+  });
+
+  testWidgets('Drag and drop - feedback matches pointer in rotated MaterialApp', (WidgetTester tester) async {
+    await tester.pumpWidget(Transform.rotate(
+      angle: 1, // ~57 degrees
+      child: const MaterialApp(
+        home: Scaffold(
+          body: Draggable<int>(
+            data: 42,
+            feedback: Text('Feedback'),
+            child: Text('Source'),
+          ),
+        ),
+      ),
+    ));
+
+    final Offset location = tester.getTopLeft(find.text('Source'));
+    final TestGesture gesture = await tester.startGesture(location);
+    final Offset secondLocation = location + const Offset(100, 100);
+    await gesture.moveTo(secondLocation);
+    await tester.pump();
+    final Offset appTopLeft = tester.getTopLeft(find.byType(MaterialApp));
+    expect(tester.getTopLeft(find.text('Source')), appTopLeft);
+    final Offset feedbackTopLeft =  tester.getTopLeft(find.text('Feedback'));
+
+    // Different rotations can incur rounding errors, this makes it more robust
+    expect(feedbackTopLeft.dx, moreOrLessEquals(secondLocation.dx));
+    expect(feedbackTopLeft.dy, moreOrLessEquals(secondLocation.dy));
+
+    // Finish gesture to release resources.
+    await gesture.up();
+    await tester.pumpAndSettle();
+  });
+
   testWidgets('configurable Draggable hit test behavior', (WidgetTester tester) async {
     const HitTestBehavior hitTestBehavior = HitTestBehavior.deferToChild;
 
@@ -3573,6 +3688,10 @@ void main() {
 
     await tester.tap(find.text('Draggable'));
     expect(onTap, true);
+
+    // Finish gesture to release resources.
+    await gesture.up();
+    await tester.pump();
   });
 
   testWidgets('configurable feedback ignore pointer behavior - LongPressDraggable', (WidgetTester tester) async {
@@ -3604,6 +3723,10 @@ void main() {
 
     await tester.tap(find.text('Draggable'));
     expect(onTap, true);
+
+    // Finish gesture to release resources.
+    await gesture.up();
+    await tester.pump();
   });
 
   testWidgets('configurable DragTarget hit test behavior', (WidgetTester tester) async {
@@ -3811,6 +3934,10 @@ Future<void> _testChildAnchorFeedbackPosition({ required WidgetTester tester, do
   final Offset sourceTopLeft = tester.getTopLeft(find.text('Source'));
   final Offset dragOffset = secondLocation - firstLocation;
   expect(feedbackTopLeft, equals(sourceTopLeft + dragOffset));
+
+  // Finish gesture to release resources.
+  await gesture.up();
+  await tester.pump();
 }
 
 class DragTargetData { }