Workaround for magic mouse events which happen to be divisible by 120.

Author: moffatman

lib/web_ui/lib/src/engine/pointer_binding.dart

@@ -263,6 +263,7 @@ abstract class _BaseAdapter {
   final _PointerDataCallback _callback;
   final PointerDataConverter _pointerDataConverter;
   final KeyboardConverter _keyboardConverter;
+  DomWheelEvent? _lastWheelEvent;
 
   /// Each subclass is expected to override this method to attach its own event
   /// listeners and convert events into pointer events.
@@ -348,7 +349,7 @@ mixin _WheelEventListenerMixin on _BaseAdapter {
     return (wheelDelta - (-3 * delta)).abs() > 1;
   }
 
-  bool _isTrackpadEvent(DomWheelEvent event) {
+  bool _isTrackpadEvent(DomWheelEvent event, DomWheelEvent? lastWheelEvent) {
     // This function relies on deprecated and non-standard implementation
     // details. Useful reference material can be found below.
     //
@@ -366,9 +367,17 @@ mixin _WheelEventListenerMixin on _BaseAdapter {
     if ((event.deltaX % 120 == 0) && (event.deltaY % 120 == 0)) {
       // While not in any formal web standard, `blink` and `webkit` browsers use
       // a delta of 120 to represent one mouse wheel turn. If both dimensions of
-      // the delta are divisible by 120, this event is almost certainly not from
-      // a trackpad.
-      return false;
+      // the delta are divisible by 120, this event is probably from a mouse.
+      final num deltaXChange = (event.deltaX - (lastWheelEvent?.deltaX ?? 0)).abs();
+      final num deltaYChange = (event.deltaY - (lastWheelEvent?.deltaY ?? 0)).abs();
+      if ((lastWheelEvent == null) ||
+          (deltaXChange == 0 && deltaYChange == 0) ||
+          !(deltaXChange < 10 && deltaYChange < 10)) {
+        // A trackpad event might by chance have a delta of exactly 120, so
+        // make sure this event does not have a similar delta to the previous
+        // one before calling it a mouse event.
+        return false;
+      }
     }
     if (_isAcceleratedMouseWheelDelta(event.deltaX, event.wheelDeltaX) ||
         _isAcceleratedMouseWheelDelta(event.deltaY, event.wheelDeltaY)) {
@@ -385,7 +394,7 @@ mixin _WheelEventListenerMixin on _BaseAdapter {
     const int domDeltaPage = 0x02;
 
     ui.PointerDeviceKind kind = ui.PointerDeviceKind.mouse;
-    if (_isTrackpadEvent(event)) {
+    if (_isTrackpadEvent(event, _lastWheelEvent)) {
       kind = ui.PointerDeviceKind.trackpad;
     }
 
@@ -431,6 +440,7 @@ mixin _WheelEventListenerMixin on _BaseAdapter {
       scrollDeltaX: deltaX,
       scrollDeltaY: deltaY,
     );
+    _lastWheelEvent = event;
     return data;
   }
 

lib/web_ui/test/engine/pointer_binding_test.dart

@@ -1169,22 +1169,32 @@ void testMain() {
         buttons: 0,
         clientX: 10,
         clientY: 10,
-        deltaX: 10,
-        deltaY: 10,
-        wheelDeltaX: -30,
-        wheelDeltaY: -30,
+        deltaX: 119,
+        deltaY: 119,
+        wheelDeltaX: -357,
+        wheelDeltaY: -357,
       ));
 
       glassPane.dispatchEvent(context.wheel(
         buttons: 0,
         clientX: 10,
         clientY: 10,
-        deltaX: 0,
+        deltaX: 120,
         deltaY: 120,
-        wheelDeltaX: 0,
+        wheelDeltaX: -360,
         wheelDeltaY: -360,
       ));
 
+      glassPane.dispatchEvent(context.wheel(
+        buttons: 0,
+        clientX: 10,
+        clientY: 10,
+        deltaX: 0,
+        deltaY: -120,
+        wheelDeltaX: 0,
+        wheelDeltaY: 360,
+      ));
+
       glassPane.dispatchEvent(context.wheel(
         buttons: 0,
         clientX: 10,
@@ -1195,7 +1205,7 @@ void testMain() {
         wheelDeltaY: -360,
       ));
 
-      expect(packets, hasLength(3));
+      expect(packets, hasLength(4));
 
       // An add will be synthesized.
       expect(packets[0].data, hasLength(2));
@@ -1219,27 +1229,27 @@ void testMain() {
       expect(packets[0].data[1].physicalY, equals(10.0 * dpi));
       expect(packets[0].data[1].physicalDeltaX, equals(0.0));
       expect(packets[0].data[1].physicalDeltaY, equals(0.0));
-      expect(packets[0].data[1].scrollDeltaX, equals(10.0));
-      expect(packets[0].data[1].scrollDeltaY, equals(10.0));
+      expect(packets[0].data[1].scrollDeltaX, equals(119.0));
+      expect(packets[0].data[1].scrollDeltaY, equals(119.0));
 
-      // Because the delta is in increments of 120, it will be a mouse event.
-      expect(packets[1].data, hasLength(1));
+      // Because the delta is in increments of 120, but is similar to the
+      // previous event, it will be a trackpad event.
       expect(packets[1].data[0].change, equals(ui.PointerChange.hover));
       expect(
           packets[1].data[0].signalKind, equals(ui.PointerSignalKind.scroll));
       expect(
-          packets[1].data[0].kind, equals(ui.PointerDeviceKind.mouse));
+          packets[1].data[0].kind, equals(ui.PointerDeviceKind.trackpad));
       expect(packets[1].data[0].pointerIdentifier, equals(0));
       expect(packets[1].data[0].synthesized, isFalse);
       expect(packets[1].data[0].physicalX, equals(10.0 * dpi));
       expect(packets[1].data[0].physicalY, equals(10.0 * dpi));
       expect(packets[1].data[0].physicalDeltaX, equals(0.0));
       expect(packets[1].data[0].physicalDeltaY, equals(0.0));
-      expect(packets[1].data[0].scrollDeltaX, equals(0.0));
+      expect(packets[1].data[0].scrollDeltaX, equals(120.0));
       expect(packets[1].data[0].scrollDeltaY, equals(120.0));
 
-      // Because the delta is not in increments of 120 and has non-matching
-      // wheelDelta, it will be a mouse event.
+      // Because the delta is in increments of 120, and is not similar to
+      // the previous event, it will be a mouse event.
       expect(packets[2].data, hasLength(1));
       expect(packets[2].data[0].change, equals(ui.PointerChange.hover));
       expect(
@@ -1253,7 +1263,24 @@ void testMain() {
       expect(packets[2].data[0].physicalDeltaX, equals(0.0));
       expect(packets[2].data[0].physicalDeltaY, equals(0.0));
       expect(packets[2].data[0].scrollDeltaX, equals(0.0));
-      expect(packets[2].data[0].scrollDeltaY, equals(40.0));
+      expect(packets[2].data[0].scrollDeltaY, equals(-120.0));
+
+      // Because the delta is not in increments of 120 and has non-matching
+      // wheelDelta, it will be a mouse event.
+      expect(packets[3].data, hasLength(1));
+      expect(packets[3].data[0].change, equals(ui.PointerChange.hover));
+      expect(
+          packets[3].data[0].signalKind, equals(ui.PointerSignalKind.scroll));
+      expect(
+          packets[3].data[0].kind, equals(ui.PointerDeviceKind.mouse));
+      expect(packets[3].data[0].pointerIdentifier, equals(0));
+      expect(packets[3].data[0].synthesized, isFalse);
+      expect(packets[3].data[0].physicalX, equals(10.0 * dpi));
+      expect(packets[3].data[0].physicalY, equals(10.0 * dpi));
+      expect(packets[3].data[0].physicalDeltaX, equals(0.0));
+      expect(packets[3].data[0].physicalDeltaY, equals(0.0));
+      expect(packets[3].data[0].scrollDeltaX, equals(0.0));
+      expect(packets[3].data[0].scrollDeltaY, equals(40.0));
     },
   );