Add engine support for scrollwheel events (#7494)

Adds support for pointer signals, in a way that will support both discrete events (e.g., scroll wheels, flutter/flutter#22762) and continuous gestures (e.g., trackpad scroll, flutter/flutter#21953).

Also exposes these new event options to the embedder. Does not include code to send the
new events from the platform shells.

lib/stub_ui/hooks.dart

@@ -213,7 +213,7 @@ void _invoke3<A1, A2, A3>(void callback(A1 a1, A2 a2, A3 a3), Zone zone, A1 arg1
 //
 //  * pointer_data.cc
 //  * FlutterView.java
-const int _kPointerDataFieldCount = 21;
+const int _kPointerDataFieldCount = 24;
 
 PointerDataPacket _unpackPointerDataPacket(ByteData packet) {
   const int kStride = Int64List.bytesPerElement;
@@ -227,6 +227,7 @@ PointerDataPacket _unpackPointerDataPacket(ByteData packet) {
       timeStamp: new Duration(microseconds: packet.getInt64(kStride * offset++, _kFakeHostEndian)),
       change: PointerChange.values[packet.getInt64(kStride * offset++, _kFakeHostEndian)],
       kind: PointerDeviceKind.values[packet.getInt64(kStride * offset++, _kFakeHostEndian)],
+      signalKind: PointerSignalKind.values[packet.getInt64(kStride * offset++, _kFakeHostEndian)],
       device: packet.getInt64(kStride * offset++, _kFakeHostEndian),
       physicalX: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
       physicalY: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
@@ -245,6 +246,8 @@ PointerDataPacket _unpackPointerDataPacket(ByteData packet) {
       orientation: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
       tilt: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
       platformData: packet.getInt64(kStride * offset++, _kFakeHostEndian),
+      scrollDeltaX: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
+      scrollDeltaY: packet.getFloat64(kStride * offset++, _kFakeHostEndian)
     );
     assert(offset == (i + 1) * _kPointerDataFieldCount);
   }

lib/stub_ui/pointer.dart

@@ -54,6 +54,18 @@ enum PointerDeviceKind {
   unknown
 }
 
+/// The kind of [PointerDeviceKind.signal].
+enum PointerSignalKind {
+  /// The event is not associated with a pointer signal.
+  none,
+
+  /// A pointer-generated scroll (e.g., mouse wheel or trackpad scroll).
+  scroll,
+
+  /// An unknown pointer signal kind.
+  unknown
+}
+
 /// Information about the state of a pointer.
 class PointerData {
   /// Creates an object that represents the state of a pointer.
@@ -61,6 +73,7 @@ class PointerData {
     this.timeStamp: Duration.zero,
     this.change: PointerChange.cancel,
     this.kind: PointerDeviceKind.touch,
+    this.signalKind,
     this.device: 0,
     this.physicalX: 0.0,
     this.physicalY: 0.0,
@@ -79,6 +92,8 @@ class PointerData {
     this.orientation: 0.0,
     this.tilt: 0.0,
     this.platformData: 0,
+    this.scrollDeltaX: 0.0,
+    this.scrollDeltaY: 0.0,
   });
 
   /// Time of event dispatch, relative to an arbitrary timeline.
@@ -90,6 +105,9 @@ class PointerData {
   /// The kind of input device for which the event was generated.
   final PointerDeviceKind kind;
 
+  /// The kind of signal for a pointer signal event.
+  final PointerSignalKind signalKind;
+
   /// Unique identifier for the pointing device, reused across interactions.
   final int device;
 
@@ -203,6 +221,16 @@ class PointerData {
   /// Opaque platform-specific data associated with the event.
   final int platformData;
 
+  /// For events with signalKind of PointerSignalKind.scroll:
+  ///
+  /// The amount to scroll in the x direction, in physical pixels.
+  final double scrollDeltaX;
+
+  /// For events with signalKind of PointerSignalKind.scroll:
+  ///
+  /// The amount to scroll in the y direction, in physical pixels.
+  final double scrollDeltaY;
+
   @override
   String toString() => '$runtimeType(x: $physicalX, y: $physicalY)';
 
@@ -212,6 +240,7 @@ class PointerData {
              'timeStamp: $timeStamp, '
              'change: $change, '
              'kind: $kind, '
+             'signalKind: $signalKind, '
              'device: $device, '
              'physicalX: $physicalX, '
              'physicalY: $physicalY, '
@@ -228,7 +257,9 @@ class PointerData {
              'radiusMax: $radiusMax, '
              'orientation: $orientation, '
              'tilt: $tilt, '
-             'platformData: $platformData'
+             'platformData: $platformData, '
+             'scrollDeltaX: $scrollDeltaX, '
+             'scrollDeltaY: $scrollDeltaY'
            ')';
   }
 }

lib/ui/hooks.dart

@@ -259,7 +259,7 @@ void _invoke3<A1, A2, A3>(void callback(A1 a1, A2 a2, A3 a3), Zone zone, A1 arg1
 //
 //  * pointer_data.cc
 //  * FlutterView.java
-const int _kPointerDataFieldCount = 21;
+const int _kPointerDataFieldCount = 24;
 
 PointerDataPacket _unpackPointerDataPacket(ByteData packet) {
   const int kStride = Int64List.bytesPerElement;
@@ -273,6 +273,7 @@ PointerDataPacket _unpackPointerDataPacket(ByteData packet) {
       timeStamp: new Duration(microseconds: packet.getInt64(kStride * offset++, _kFakeHostEndian)),
       change: PointerChange.values[packet.getInt64(kStride * offset++, _kFakeHostEndian)],
       kind: PointerDeviceKind.values[packet.getInt64(kStride * offset++, _kFakeHostEndian)],
+      signalKind: PointerSignalKind.values[packet.getInt64(kStride * offset++, _kFakeHostEndian)],
       device: packet.getInt64(kStride * offset++, _kFakeHostEndian),
       physicalX: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
       physicalY: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
@@ -291,6 +292,8 @@ PointerDataPacket _unpackPointerDataPacket(ByteData packet) {
       orientation: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
       tilt: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
       platformData: packet.getInt64(kStride * offset++, _kFakeHostEndian),
+      scrollDeltaX: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
+      scrollDeltaY: packet.getFloat64(kStride * offset++, _kFakeHostEndian)
     );
     assert(offset == (i + 1) * _kPointerDataFieldCount);
   }

lib/ui/pointer.dart

@@ -54,6 +54,18 @@ enum PointerDeviceKind {
   unknown
 }
 
+/// The kind of [PointerDeviceKind.signal].
+enum PointerSignalKind {
+  /// The event is not associated with a pointer signal.
+  none,
+
+  /// A pointer-generated scroll (e.g., mouse wheel or trackpad scroll).
+  scroll,
+
+  /// An unknown pointer signal kind.
+  unknown
+}
+
 /// Information about the state of a pointer.
 class PointerData {
   /// Creates an object that represents the state of a pointer.
@@ -61,6 +73,7 @@ class PointerData {
     this.timeStamp: Duration.zero,
     this.change: PointerChange.cancel,
     this.kind: PointerDeviceKind.touch,
+    this.signalKind,
     this.device: 0,
     this.physicalX: 0.0,
     this.physicalY: 0.0,
@@ -79,6 +92,8 @@ class PointerData {
     this.orientation: 0.0,
     this.tilt: 0.0,
     this.platformData: 0,
+    this.scrollDeltaX: 0.0,
+    this.scrollDeltaY: 0.0,
   });
 
   /// Time of event dispatch, relative to an arbitrary timeline.
@@ -90,6 +105,9 @@ class PointerData {
   /// The kind of input device for which the event was generated.
   final PointerDeviceKind kind;
 
+  /// The kind of signal for a pointer signal event.
+  final PointerSignalKind signalKind;
+
   /// Unique identifier for the pointing device, reused across interactions.
   final int device;
 
@@ -203,6 +221,16 @@ class PointerData {
   /// Opaque platform-specific data associated with the event.
   final int platformData;
 
+  /// For events with signalKind of PointerSignalKind.scroll:
+  ///
+  /// The amount to scroll in the x direction, in physical pixels.
+  final double scrollDeltaX;
+
+  /// For events with signalKind of PointerSignalKind.scroll:
+  ///
+  /// The amount to scroll in the y direction, in physical pixels.
+  final double scrollDeltaY;
+
   @override
   String toString() => '$runtimeType(x: $physicalX, y: $physicalY)';
 
@@ -212,6 +240,7 @@ class PointerData {
              'timeStamp: $timeStamp, '
              'change: $change, '
              'kind: $kind, '
+             'signalKind: $signalKind, '
              'device: $device, '
              'physicalX: $physicalX, '
              'physicalY: $physicalY, '
@@ -228,7 +257,9 @@ class PointerData {
              'radiusMax: $radiusMax, '
              'orientation: $orientation, '
              'tilt: $tilt, '
-             'platformData: $platformData'
+             'platformData: $platformData, '
+             'scrollDeltaX: $scrollDeltaX, '
+             'scrollDeltaY: $scrollDeltaY'
            ')';
   }
 }

lib/ui/window/pointer_data.cc

@@ -9,7 +9,7 @@
 namespace blink {
 
 // If this value changes, update the pointer data unpacking code in hooks.dart.
-static constexpr int kPointerDataFieldCount = 21;
+static constexpr int kPointerDataFieldCount = 24;
 
 static_assert(sizeof(PointerData) == sizeof(int64_t) * kPointerDataFieldCount,
               "PointerData has the wrong size");

lib/ui/window/pointer_data.h

@@ -28,11 +28,19 @@ struct alignas(8) PointerData {
     kMouse,
     kStylus,
     kInvertedStylus,
+    kSignal,
+  };
+
+  // Must match the PointerSignalKind enum in pointer.dart.
+  enum class SignalKind : int64_t {
+    kNone,
+    kScroll,
   };
 
   int64_t time_stamp;
   Change change;
   DeviceKind kind;
+  SignalKind signal_kind;
   int64_t device;
   double physical_x;
   double physical_y;
@@ -51,6 +59,8 @@ struct alignas(8) PointerData {
   double orientation;
   double tilt;
   int64_t platformData;
+  double scroll_delta_x;
+  double scroll_delta_y;
 
   void Clear();
 };

shell/platform/android/io/flutter/view/FlutterView.java

@@ -378,10 +378,16 @@ public class FlutterView extends SurfaceView
     private static final int kPointerDeviceKindMouse = 1;
     private static final int kPointerDeviceKindStylus = 2;
     private static final int kPointerDeviceKindInvertedStylus = 3;
-    private static final int kPointerDeviceKindUnknown = 4;
+    private static final int kPointerDeviceKindSignal = 4;
+    private static final int kPointerDeviceKindUnknown = 5;
+
+    // Must match the PointerSignalKind enum in pointer.dart.
+    private static final int kPointerSignalKindNone = 0;
+    private static final int kPointerSignalKindScroll = 1;
+    private static final int kPointerSignalKindUnknown = 2;
 
     // These values must match the unpacking code in hooks.dart.
-    private static final int kPointerDataFieldCount = 21;
+    private static final int kPointerDataFieldCount = 24;
     private static final int kPointerBytesPerField = 8;
 
     private int getPointerChangeForAction(int maskedAction) {
@@ -436,11 +442,14 @@ public class FlutterView extends SurfaceView
 
         int pointerKind = getPointerDeviceTypeForToolType(event.getToolType(pointerIndex));
 
+        int signalKind = kPointerSignalKindNone;
+
         long timeStamp = event.getEventTime() * 1000; // Convert from milliseconds to microseconds.
 
         packet.putLong(timeStamp); // time_stamp
         packet.putLong(pointerChange); // change
         packet.putLong(pointerKind); // kind
+        packet.putLong(signalKind); // signal_kind
         packet.putLong(event.getPointerId(pointerIndex)); // device
         packet.putDouble(event.getX(pointerIndex)); // physical_x
         packet.putDouble(event.getY(pointerIndex)); // physical_y
@@ -492,6 +501,9 @@ public class FlutterView extends SurfaceView
         }
 
         packet.putLong(pointerData); // platformData
+
+        packet.putDouble(0.0); // scroll_delta_x
+        packet.putDouble(0.0); // scroll_delta_y
     }
 
     @Override

shell/platform/embedder/embedder.cc

@@ -677,6 +677,19 @@ inline blink::PointerData::Change ToPointerDataChange(
   return blink::PointerData::Change::kCancel;
 }
 
+// Returns the blink::PointerData::SignalKind for the given
+// FlutterPointerSignaKind.
+inline blink::PointerData::SignalKind ToPointerDataSignalKind(
+    FlutterPointerSignalKind kind) {
+  switch (kind) {
+    case kFlutterPointerSignalKindNone:
+      return blink::PointerData::SignalKind::kNone;
+    case kFlutterPointerSignalKindScroll:
+      return blink::PointerData::SignalKind::kScroll;
+  }
+  return blink::PointerData::SignalKind::kNone;
+}
+
 FlutterEngineResult FlutterEngineSendPointerEvent(
     FlutterEngine engine,
     const FlutterPointerEvent* pointers,
@@ -699,6 +712,10 @@ FlutterEngineResult FlutterEngineSendPointerEvent(
     pointer_data.physical_x = SAFE_ACCESS(current, x, 0.0);
     pointer_data.physical_y = SAFE_ACCESS(current, y, 0.0);
     pointer_data.device = SAFE_ACCESS(current, device, 0);
+    pointer_data.signal_kind = ToPointerDataSignalKind(
+        SAFE_ACCESS(current, signal_kind, kFlutterPointerSignalKindNone));
+    pointer_data.scroll_delta_x = SAFE_ACCESS(current, scroll_delta_x, 0.0);
+    pointer_data.scroll_delta_y = SAFE_ACCESS(current, scroll_delta_y, 0.0);
     packet->SetPointerData(i, pointer_data);
     current = reinterpret_cast<const FlutterPointerEvent*>(
         reinterpret_cast<const uint8_t*>(current) + current->struct_size);

shell/platform/embedder/embedder.h

@@ -277,6 +277,7 @@ typedef struct {
   double pixel_ratio;
 } FlutterWindowMetricsEvent;
 
+// The phase of the pointer event.
 typedef enum {
   kCancel,
   kUp,
@@ -287,6 +288,12 @@ typedef enum {
   kHover,
 } FlutterPointerPhase;
 
+// The type of a pointer signal.
+typedef enum {
+  kFlutterPointerSignalKindNone,
+  kFlutterPointerSignalKindScroll,
+} FlutterPointerSignalKind;
+
 typedef struct {
   // The size of this struct. Must be sizeof(FlutterPointerEvent).
   size_t struct_size;
@@ -297,6 +304,9 @@ typedef struct {
   // An optional device identifier. If this is not specified, it is assumed that
   // the embedder has no multitouch capability.
   int32_t device;
+  FlutterPointerSignalKind signal_kind;
+  double scroll_delta_x;
+  double scroll_delta_y;
 } FlutterPointerEvent;
 
 struct _FlutterPlatformMessageResponseHandle;