InteractiveViewer parameter to return to pre-3.3 trackpad/Magic Mouse behaviour (#114280)

* trackpadPanShouldActAsZoom

* Address feedback

* Move constant, add blank lines

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

@@ -288,6 +288,8 @@ class GestureDetector extends StatelessWidget {
     this.behavior,
     this.excludeFromSemantics = false,
     this.dragStartBehavior = DragStartBehavior.start,
+    this.trackpadScrollCausesScale = false,
+    this.trackpadScrollToScaleFactor = kDefaultTrackpadScrollToScaleFactor,
     this.supportedDevices,
   }) : assert(excludeFromSemantics != null),
        assert(dragStartBehavior != null),
@@ -1014,6 +1016,12 @@ class GestureDetector extends StatelessWidget {
   /// If set to null, events from all device types will be recognized. Defaults to null.
   final Set<PointerDeviceKind>? supportedDevices;
 
+  /// {@macro flutter.gestures.scale.trackpadScrollCausesScale}
+  final bool trackpadScrollCausesScale;
+
+  /// {@macro flutter.gestures.scale.trackpadScrollToScaleFactor}
+  final Offset trackpadScrollToScaleFactor;
+
   @override
   Widget build(BuildContext context) {
     final Map<Type, GestureRecognizerFactory> gestures = <Type, GestureRecognizerFactory>{};
@@ -1186,7 +1194,9 @@ class GestureDetector extends StatelessWidget {
             ..onUpdate = onScaleUpdate
             ..onEnd = onScaleEnd
             ..dragStartBehavior = dragStartBehavior
-            ..gestureSettings = gestureSettings;
+            ..gestureSettings = gestureSettings
+            ..trackpadScrollCausesScale = trackpadScrollCausesScale
+            ..trackpadScrollToScaleFactor = trackpadScrollToScaleFactor;
         },
       );
     }

packages/flutter/test/gestures/scale_test.dart

@@ -1173,4 +1173,196 @@ void main() {
       ),
     );
   });
+
+  testGesture('scale trackpadScrollCausesScale', (GestureTester tester) {
+    final ScaleGestureRecognizer scale = ScaleGestureRecognizer(
+      dragStartBehavior: DragStartBehavior.start,
+      trackpadScrollCausesScale: true
+    );
+
+    bool didStartScale = false;
+    Offset? updatedFocalPoint;
+    scale.onStart = (ScaleStartDetails details) {
+      didStartScale = true;
+      updatedFocalPoint = details.focalPoint;
+    };
+
+    double? updatedScale;
+    Offset? updatedDelta;
+    scale.onUpdate = (ScaleUpdateDetails details) {
+      updatedScale = details.scale;
+      updatedFocalPoint = details.focalPoint;
+      updatedDelta = details.focalPointDelta;
+    };
+
+    bool didEndScale = false;
+    scale.onEnd = (ScaleEndDetails details) {
+      didEndScale = true;
+    };
+
+    final TestPointer pointer1 = TestPointer(2, PointerDeviceKind.trackpad);
+
+    final PointerPanZoomStartEvent start = pointer1.panZoomStart(Offset.zero);
+    scale.addPointerPanZoom(start);
+
+    tester.closeArena(2);
+    expect(didStartScale, isFalse);
+    expect(updatedScale, isNull);
+    expect(updatedFocalPoint, isNull);
+    expect(updatedDelta, isNull);
+    expect(didEndScale, isFalse);
+
+    tester.route(start);
+    expect(didStartScale, isTrue);
+    didStartScale = false;
+    expect(updatedScale, isNull);
+    expect(updatedFocalPoint, Offset.zero);
+    updatedFocalPoint = null;
+    expect(updatedDelta, isNull);
+    expect(didEndScale, isFalse);
+
+    // Zoom in by scrolling up.
+    tester.route(pointer1.panZoomUpdate(Offset.zero, pan: const Offset(0, -200)));
+    expect(didStartScale, isFalse);
+    expect(updatedFocalPoint, Offset.zero);
+    updatedFocalPoint = null;
+    expect(updatedScale, math.e);
+    updatedScale = null;
+    expect(updatedDelta, Offset.zero);
+    updatedDelta = null;
+    expect(didEndScale, isFalse);
+
+    // A horizontal scroll should do nothing.
+    tester.route(pointer1.panZoomUpdate(Offset.zero, pan: const Offset(200, -200)));
+    expect(didStartScale, isFalse);
+    expect(updatedFocalPoint, Offset.zero);
+    updatedFocalPoint = null;
+    expect(updatedScale, math.e);
+    updatedScale = null;
+    expect(updatedDelta, Offset.zero);
+    updatedDelta = null;
+    expect(didEndScale, isFalse);
+
+    // End.
+    tester.route(pointer1.panZoomEnd());
+    expect(didStartScale, isFalse);
+    expect(updatedFocalPoint, isNull);
+    expect(updatedScale, isNull);
+    expect(updatedDelta, isNull);
+    expect(didEndScale, isTrue);
+    didEndScale = false;
+
+    // Try with a different trackpadScrollToScaleFactor
+    scale.trackpadScrollToScaleFactor = const Offset(1/125, 0);
+
+    final PointerPanZoomStartEvent start2 = pointer1.panZoomStart(Offset.zero);
+    scale.addPointerPanZoom(start2);
+
+    tester.closeArena(2);
+    expect(didStartScale, isFalse);
+    expect(updatedScale, isNull);
+    expect(updatedFocalPoint, isNull);
+    expect(updatedDelta, isNull);
+    expect(didEndScale, isFalse);
+
+    tester.route(start2);
+    expect(didStartScale, isTrue);
+    didStartScale = false;
+    expect(updatedScale, isNull);
+    expect(updatedFocalPoint, Offset.zero);
+    updatedFocalPoint = null;
+    expect(updatedDelta, isNull);
+    expect(didEndScale, isFalse);
+
+    // Zoom in by scrolling left.
+    tester.route(pointer1.panZoomUpdate(Offset.zero, pan: const Offset(125, 0)));
+    expect(didStartScale, isFalse);
+    didStartScale = false;
+    expect(updatedFocalPoint, Offset.zero);
+    updatedFocalPoint = null;
+    expect(updatedScale, math.e);
+    updatedScale = null;
+    expect(updatedDelta, Offset.zero);
+    updatedDelta = null;
+    expect(didEndScale, isFalse);
+
+    // A vertical scroll should do nothing.
+    tester.route(pointer1.panZoomUpdate(Offset.zero, pan: const Offset(125, 125)));
+    expect(didStartScale, isFalse);
+    expect(updatedFocalPoint, Offset.zero);
+    updatedFocalPoint = null;
+    expect(updatedScale, math.e);
+    updatedScale = null;
+    expect(updatedDelta, Offset.zero);
+    updatedDelta = null;
+    expect(didEndScale, isFalse);
+
+    // End.
+    tester.route(pointer1.panZoomEnd());
+    expect(didStartScale, isFalse);
+    expect(updatedFocalPoint, isNull);
+    expect(updatedScale, isNull);
+    expect(updatedDelta, isNull);
+    expect(didEndScale, isTrue);
+    didEndScale = false;
+
+    scale.dispose();
+  });
+
+  testGesture('scale ending velocity', (GestureTester tester) {
+    final ScaleGestureRecognizer scale = ScaleGestureRecognizer(
+      dragStartBehavior: DragStartBehavior.start,
+      trackpadScrollCausesScale: true
+    );
+
+    bool didStartScale = false;
+    Offset? updatedFocalPoint;
+    scale.onStart = (ScaleStartDetails details) {
+      didStartScale = true;
+      updatedFocalPoint = details.focalPoint;
+    };
+
+    bool didEndScale = false;
+    double? scaleEndVelocity;
+    scale.onEnd = (ScaleEndDetails details) {
+      didEndScale = true;
+      scaleEndVelocity = details.scaleVelocity;
+    };
+
+    final TestPointer pointer1 = TestPointer(2, PointerDeviceKind.trackpad);
+
+    final PointerPanZoomStartEvent start = pointer1.panZoomStart(Offset.zero);
+    scale.addPointerPanZoom(start);
+
+    tester.closeArena(2);
+    expect(didStartScale, isFalse);
+    expect(updatedFocalPoint, isNull);
+    expect(didEndScale, isFalse);
+
+    tester.route(start);
+    expect(didStartScale, isTrue);
+    didStartScale = false;
+    expect(updatedFocalPoint, Offset.zero);
+    updatedFocalPoint = null;
+    expect(didEndScale, isFalse);
+
+    // Zoom in by scrolling up.
+    for (int i = 0; i < 100; i++) {
+      tester.route(pointer1.panZoomUpdate(
+        Offset.zero,
+        pan: Offset(0, i * -10),
+        timeStamp: Duration(milliseconds: i * 25)
+      ));
+    }
+
+    // End.
+    tester.route(pointer1.panZoomEnd(timeStamp: const Duration(milliseconds: 2500)));
+    expect(didStartScale, isFalse);
+    expect(updatedFocalPoint, isNull);
+    expect(didEndScale, isTrue);
+    didEndScale = false;
+    expect(scaleEndVelocity, moreOrLessEquals(281.41454098027765));
+
+    scale.dispose();
+  });
 }

packages/flutter/test/widgets/interactive_viewer_test.dart

@@ -1802,6 +1802,78 @@ void main() {
       await tester.pump();
       expect(transformationController.value.getMaxScaleOnAxis(), 2.5); // capped at maxScale (2.5)
     });
+
+    testWidgets('trackpadScrollCausesScale', (WidgetTester tester) async {
+      final TransformationController transformationController = TransformationController();
+      const double boundaryMargin = 50.0;
+      await tester.pumpWidget(
+        MaterialApp(
+          home: Scaffold(
+            body: Center(
+              child: InteractiveViewer(
+                boundaryMargin: const EdgeInsets.all(boundaryMargin),
+                transformationController: transformationController,
+                trackpadScrollCausesScale: true,
+                child: const SizedBox(width: 200.0, height: 200.0),
+              ),
+            ),
+          ),
+        ),
+      );
+
+      expect(transformationController.value.getMaxScaleOnAxis(), 1.0);
+
+      // Send a vertical scroll.
+      final TestPointer pointer = TestPointer(1, PointerDeviceKind.trackpad);
+      final Offset center = tester.getCenter(find.byType(SizedBox));
+      await tester.sendEventToBinding(pointer.panZoomStart(center));
+      await tester.pump();
+      expect(transformationController.value.getMaxScaleOnAxis(), 1.0);
+      await tester.sendEventToBinding(pointer.panZoomUpdate(center, pan: const Offset(0, -81)));
+      await tester.pump();
+      expect(transformationController.value.getMaxScaleOnAxis(), moreOrLessEquals(1.499302500056767));
+
+      // Send a horizontal scroll (should have no effect).
+      await tester.sendEventToBinding(pointer.panZoomUpdate(center, pan: const Offset(81, -81)));
+      await tester.pump();
+      expect(transformationController.value.getMaxScaleOnAxis(), moreOrLessEquals(1.499302500056767));
+    });
+
+    testWidgets('Scaling inertia', (WidgetTester tester) async {
+      final TransformationController transformationController = TransformationController();
+      const double boundaryMargin = 50.0;
+      await tester.pumpWidget(
+        MaterialApp(
+          home: Scaffold(
+            body: Center(
+              child: InteractiveViewer(
+                boundaryMargin: const EdgeInsets.all(boundaryMargin),
+                transformationController: transformationController,
+                trackpadScrollCausesScale: true,
+                child: const SizedBox(width: 200.0, height: 200.0),
+              ),
+            ),
+          ),
+        ),
+      );
+
+      expect(transformationController.value.getMaxScaleOnAxis(), 1.0);
+
+      // Send a vertical scroll fling, which will cause inertia.
+      await tester.trackpadFling(
+        find.byType(InteractiveViewer),
+        const Offset(0, -100),
+        3000
+      );
+      await tester.pump();
+      expect(transformationController.value.getMaxScaleOnAxis(), moreOrLessEquals(1.6487212707001282));
+      await tester.pump(const Duration(milliseconds: 80));
+      expect(transformationController.value.getMaxScaleOnAxis(), moreOrLessEquals(1.7966838346780103));
+      await tester.pumpAndSettle();
+      expect(transformationController.value.getMaxScaleOnAxis(), moreOrLessEquals(1.9984509673751225));
+      await tester.pump(const Duration(seconds: 10));
+      expect(transformationController.value.getMaxScaleOnAxis(), moreOrLessEquals(1.9984509673751225));
+    });
   });
 
   group('getNearestPointOnLine', () {