Propagate positions of secondary pointers in UP events on Android (flutter#6716)

Author: sbaranov

lib/ui/hooks.dart

@@ -196,7 +196,7 @@ 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 = 20;
+const int _kPointerDataFieldCount = 21;
 
 PointerDataPacket _unpackPointerDataPacket(ByteData packet) {
   const int kStride = Int64List.bytesPerElement;
@@ -226,7 +226,8 @@ PointerDataPacket _unpackPointerDataPacket(ByteData packet) {
       radiusMin: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
       radiusMax: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
       orientation: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
-      tilt: packet.getFloat64(kStride * offset++, _kFakeHostEndian)
+      tilt: packet.getFloat64(kStride * offset++, _kFakeHostEndian),
+      platformData: packet.getInt64(kStride * offset++, _kFakeHostEndian),
     );
     assert(offset == (i + 1) * _kPointerDataFieldCount);
   }

lib/ui/pointer.dart

@@ -77,7 +77,8 @@ class PointerData {
     this.radiusMin: 0.0,
     this.radiusMax: 0.0,
     this.orientation: 0.0,
-    this.tilt: 0.0
+    this.tilt: 0.0,
+    this.platformData: 0,
   });
 
   /// Time of event dispatch, relative to an arbitrary timeline.
@@ -199,6 +200,9 @@ class PointerData {
   /// the stylus is flat on that surface).
   final double tilt;
 
+  /// Opaque platform-specific data associated with the event.
+  final int platformData;
+
   @override
   String toString() => '$runtimeType(x: $physicalX, y: $physicalY)';
 
@@ -223,7 +227,8 @@ class PointerData {
              'radiusMin: $radiusMin, '
              'radiusMax: $radiusMax, '
              'orientation: $orientation, '
-             'tilt: $tilt'
+             'tilt: $tilt, '
+             'platformData: $platformData'
            ')';
   }
 }

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 = 20;
+static constexpr int kPointerDataFieldCount = 21;
 
 static_assert(sizeof(PointerData) == sizeof(int64_t) * kPointerDataFieldCount,
               "PointerData has the wrong size");

lib/ui/window/pointer_data.h

@@ -50,6 +50,7 @@ struct alignas(8) PointerData {
   double radius_max;
   double orientation;
   double tilt;
+  int64_t platformData;
 
   void Clear();
 };

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

@@ -447,8 +447,8 @@ private int getPointerDeviceTypeForToolType(int toolType) {
         }
     }
 
-    private void addPointerForIndex(MotionEvent event, int pointerIndex, ByteBuffer packet) {
-        int pointerChange = getPointerChangeForAction(event.getActionMasked());
+    private void addPointerForIndex(MotionEvent event, int pointerIndex, int pointerChange,
+                                    int pointerData, ByteBuffer packet) {
         if (pointerChange == -1) {
             return;
         }
@@ -503,6 +503,8 @@ private void addPointerForIndex(MotionEvent event, int pointerIndex, ByteBuffer
         } else {
             packet.putDouble(0.0); // tilt
         }
+
+        packet.putLong(pointerData); // platformData
     }
 
     @Override
@@ -521,26 +523,44 @@ public boolean onTouchEvent(MotionEvent event) {
         }
 
         // These values must match the unpacking code in hooks.dart.
-        final int kPointerDataFieldCount = 20;
+        final int kPointerDataFieldCount = 21;
         final int kBytePerField = 8;
 
+        // This value must match the value in framework's platform_view.dart.
+        // This flag indicates whether the original Android pointer events were batched together.
+        final int kPointerDataFlagBatched = 1;
+
         int pointerCount = event.getPointerCount();
 
         ByteBuffer packet = ByteBuffer.allocateDirect(pointerCount * kPointerDataFieldCount * kBytePerField);
         packet.order(ByteOrder.LITTLE_ENDIAN);
 
         int maskedAction = event.getActionMasked();
-        // ACTION_UP, ACTION_POINTER_UP, ACTION_DOWN, and ACTION_POINTER_DOWN
-        // only apply to a single pointer, other events apply to all pointers.
-        if (maskedAction == MotionEvent.ACTION_UP || maskedAction == MotionEvent.ACTION_POINTER_UP
-                || maskedAction == MotionEvent.ACTION_DOWN || maskedAction == MotionEvent.ACTION_POINTER_DOWN) {
-            addPointerForIndex(event, event.getActionIndex(), packet);
+        int pointerChange = getPointerChangeForAction(event.getActionMasked());
+        if (maskedAction == MotionEvent.ACTION_DOWN || maskedAction == MotionEvent.ACTION_POINTER_DOWN) {
+            // ACTION_DOWN and ACTION_POINTER_DOWN always apply to a single pointer only.
+            addPointerForIndex(event, event.getActionIndex(), pointerChange, 0, packet);
+        } else if (maskedAction == MotionEvent.ACTION_UP || maskedAction == MotionEvent.ACTION_POINTER_UP) {
+            // ACTION_UP and ACTION_POINTER_UP may contain position updates for other pointers.
+            // We are converting these updates to move events here in order to preserve this data.
+            // We also mark these events with a flag in order to help the framework reassemble
+            // the original Android event later, should it need to forward it to a PlatformView.
+            for (int p = 0; p < pointerCount; p++) {
+                if (p != event.getActionIndex()) {
+                    if (event.getToolType(p) == MotionEvent.TOOL_TYPE_FINGER) {
+                        addPointerForIndex(event, p, kPointerChangeMove, kPointerDataFlagBatched, packet);
+                    }
+                }
+            }
+            // It's important that we're sending the UP event last. This allows PlatformView
+            // to correctly batch everything back into the original Android event if needed.
+            addPointerForIndex(event, event.getActionIndex(), pointerChange, 0, packet);
         } else {
             // ACTION_MOVE may not actually mean all pointers have moved
             // but it's the responsibility of a later part of the system to
             // ignore 0-deltas if desired.
             for (int p = 0; p < pointerCount; p++) {
-                addPointerForIndex(event, p, packet);
+                addPointerForIndex(event, p, pointerChange, 0, packet);
             }
         }