[skwasm] Fix platform view placement. (flutter/engine#53845)

Previously, each platform view contained styling/placement information from the entire stack of the layer builder. This caused issues when using `addRetained`, since it would contain stale styling/placement information from its old parent layers. I have changed it so that platform views only contain local styling information, and that styling is combined with the parent only when the layers are merged.

engine/src/flutter/lib/web_ui/lib/src/engine/layers.dart

@@ -385,14 +385,14 @@ class ShaderMaskOperation implements LayerOperation {
 }
 
 class PlatformView {
-  PlatformView(this.viewId, this.size, this.styling);
+  PlatformView(this.viewId, this.bounds, this.styling);
 
-  int viewId;
+  final int viewId;
 
   // The bounds of this platform view, in the layer's local coordinate space.
-  ui.Size size;
+  final ui.Rect bounds;
 
-  PlatformViewStyling styling;
+  final PlatformViewStyling styling;
 }
 
 sealed class LayerSlice {
@@ -606,20 +606,8 @@ class LayerBuilder {
 
   PlatformViewStyling? _memoizedPlatformViewStyling;
 
-  PlatformViewStyling _createPlatformViewStyling() {
-    final PlatformViewStyling? innerStyling = operation?.createPlatformViewStyling();
-    final PlatformViewStyling? outerStyling = parent?.platformViewStyling;
-    if (innerStyling == null) {
-      return outerStyling ?? const PlatformViewStyling();
-    }
-    if (outerStyling == null) {
-      return innerStyling;
-    }
-    return PlatformViewStyling.combine(outerStyling, innerStyling);
-  }
-
   PlatformViewStyling get platformViewStyling {
-    return _memoizedPlatformViewStyling ??= _createPlatformViewStyling();
+    return _memoizedPlatformViewStyling ??= operation?.createPlatformViewStyling() ?? const PlatformViewStyling();
   }
 
   (ui.PictureRecorder, SceneCanvas) _createRecorder(ui.Rect rect) {
@@ -713,16 +701,7 @@ class LayerBuilder {
   }) {
     final ui.Rect bounds = ui.Rect.fromLTWH(offset.dx, offset.dy, width, height);
     platformViewRect = platformViewRect?.expandToInclude(bounds) ?? bounds;
-    final PlatformViewStyling layerStyling = platformViewStyling;
-    final PlatformViewStyling viewStyling = offset == ui.Offset.zero
-      ? layerStyling
-      : PlatformViewStyling.combine(
-        layerStyling,
-        PlatformViewStyling(
-          position: PlatformViewPosition.offset(offset),
-        ),
-      );
-    pendingPlatformViews.add(PlatformView(viewId, ui.Size(width, height), viewStyling));
+    pendingPlatformViews.add(PlatformView(viewId, bounds, platformViewStyling));
   }
 
   void mergeLayer(PictureEngineLayer layer) {
@@ -738,7 +717,15 @@ class LayerBuilder {
           if (occlusionRect != null) {
             platformViewRect = platformViewRect?.expandToInclude(occlusionRect) ?? occlusionRect;
           }
-          pendingPlatformViews.addAll(slice.views);
+          for (final PlatformView view in slice.views) {
+            // Merge the platform view styling of this layer with the nested
+            // platform views.
+            final PlatformViewStyling styling = PlatformViewStyling.combine(
+              platformViewStyling,
+              view.styling,
+            );
+            pendingPlatformViews.add(PlatformView(view.viewId, view.bounds, styling));
+          }
       }
     }
   }

engine/src/flutter/lib/web_ui/lib/src/engine/scene_view.dart

@@ -179,7 +179,7 @@ class EngineSceneView {
               }
             }
             container ??= PlatformViewContainer(view.viewId);
-            container.size = view.size;
+            container.bounds = view.bounds;
             container.styling = view.styling;
             container.updateContents();
             newContainers.add(container);
@@ -281,7 +281,7 @@ final class PlatformViewContainer extends SliceContainer {
 
   final int viewId;
   PlatformViewStyling? _styling;
-  ui.Size? _size;
+  ui.Rect? _bounds;
   bool _dirty = false;
 
   @override
@@ -294,9 +294,9 @@ final class PlatformViewContainer extends SliceContainer {
     }
   }
 
-  set size(ui.Size size) {
-    if (_size != size) {
-      _size = size;
+  set bounds(ui.Rect bounds) {
+    if (_bounds != bounds) {
+      _bounds = bounds;
       _dirty = true;
     }
   }
@@ -305,23 +305,28 @@ final class PlatformViewContainer extends SliceContainer {
   @override
   void updateContents() {
     assert(_styling != null);
-    assert(_size != null);
+    assert(_bounds != null);
     if (_dirty) {
       final DomCSSStyleDeclaration style = container.style;
       final double devicePixelRatio = EngineFlutterDisplay.instance.devicePixelRatio;
-      final double logicalWidth = _size!.width / devicePixelRatio;
-      final double logicalHeight = _size!.height / devicePixelRatio;
+      final double logicalWidth = _bounds!.width / devicePixelRatio;
+      final double logicalHeight = _bounds!.height / devicePixelRatio;
       style.width = '${logicalWidth}px';
       style.height = '${logicalHeight}px';
       style.position = 'absolute';
 
-      final ui.Offset? offset = _styling!.position.offset;
-      final double logicalLeft = (offset?.dx ?? 0) / devicePixelRatio;
-      final double logicalTop = (offset?.dy ?? 0) / devicePixelRatio;
+      final PlatformViewPosition position = PlatformViewPosition.combine(
+        _styling!.position,
+        PlatformViewPosition.offset(_bounds!.topLeft),
+      );
+
+      final ui.Offset offset = position.offset ?? ui.Offset.zero;
+      final double logicalLeft = offset.dx / devicePixelRatio;
+      final double logicalTop = offset.dy / devicePixelRatio;
       style.left = '${logicalLeft}px';
       style.top = '${logicalTop}px';
 
-      final Matrix4? transform = _styling!.position.transform;
+      final Matrix4? transform = position.transform;
       style.transform = transform != null ? float64ListToCssTransform3d(transform.storage) : '';
       style.opacity = _styling!.opacity != 1.0 ? '${_styling!.opacity}' : '';
       // TODO(jacksongardner): Implement clip styling for platform views

engine/src/flutter/lib/web_ui/test/engine/scene_builder_test.dart

@@ -72,9 +72,7 @@ void testMain() {
       expect(slices.length, 2);
       expect(slices[0], pictureSliceWithRect(pictureRect));
       expect(slices[1], platformViewSliceWithViews(<PlatformView>[
-        PlatformView(1, platformViewRect.size, PlatformViewStyling(
-          position: PlatformViewPosition.offset(platformViewRect.topLeft)
-        ))
+        PlatformView(1, platformViewRect, const PlatformViewStyling())
       ]));
     });
 
@@ -95,9 +93,7 @@ void testMain() {
       final List<LayerSlice> slices = scene.rootLayer.slices;
       expect(slices.length, 2);
       expect(slices[0], platformViewSliceWithViews(<PlatformView>[
-        PlatformView(1, platformViewRect.size, PlatformViewStyling(
-          position: PlatformViewPosition.offset(platformViewRect.topLeft)
-        ))
+        PlatformView(1, platformViewRect, const PlatformViewStyling())
       ]));
       expect(slices[1], pictureSliceWithRect(pictureRect));
     });
@@ -122,9 +118,7 @@ void testMain() {
       expect(slices.length, 3);
       expect(slices[0], pictureSliceWithRect(pictureRect1));
       expect(slices[1], platformViewSliceWithViews(<PlatformView>[
-        PlatformView(1, platformViewRect.size, PlatformViewStyling(
-          position: PlatformViewPosition.offset(platformViewRect.topLeft)
-        ))
+        PlatformView(1, platformViewRect, const PlatformViewStyling())
       ]));
       expect(slices[2], pictureSliceWithRect(pictureRect2));
     });
@@ -153,9 +147,7 @@ void testMain() {
       expect(slices.length, 2);
       expect(slices[0], pictureSliceWithRect(const ui.Rect.fromLTRB(50, 50, 200, 200)));
       expect(slices[1], platformViewSliceWithViews(<PlatformView>[
-        PlatformView(1, platformViewRect.size, PlatformViewStyling(
-          position: PlatformViewPosition.offset(platformViewRect.topLeft)
-        ))
+        PlatformView(1, platformViewRect, const PlatformViewStyling())
       ]));
     });
   });
@@ -219,7 +211,7 @@ class PlatformViewSliceMatcher extends Matcher {
       if (expectedView.viewId != actualView.viewId) {
         return false;
       }
-      if (expectedView.size != actualView.size) {
+      if (expectedView.bounds != actualView.bounds) {
         return false;
       }
       if (expectedView.styling != actualView.styling) {

engine/src/flutter/lib/web_ui/test/engine/scene_view_test.dart

@@ -152,10 +152,8 @@ void testMain() {
 
     final PlatformView platformView = PlatformView(
         1,
-        const ui.Size(100, 120),
-        const PlatformViewStyling(
-          position: PlatformViewPosition.offset(ui.Offset(50, 80)),
-        ));
+        const ui.Rect.fromLTWH(50, 80, 100, 120),
+        const PlatformViewStyling());
     final EngineRootLayer rootLayer = EngineRootLayer();
     rootLayer.slices.add(PlatformViewSlice(<PlatformView>[platformView], null));
     final EngineScene scene = EngineScene(rootLayer);

engine/src/flutter/lib/web_ui/test/ui/platform_view_test.dart

@@ -132,6 +132,47 @@ Future<void> testMain() async {
     await matchGoldenFile('platformview_transformed.png', region: region);
   });
 
+  test('offset platformview', () async {
+    await _createPlatformView(1, platformViewType);
+
+    final ui.PictureRecorder recorder = ui.PictureRecorder();
+    final ui.Canvas canvas = ui.Canvas(recorder);
+    canvas.drawCircle(
+      const ui.Offset(50, 50),
+      50,
+      ui.Paint()
+        ..style = ui.PaintingStyle.fill
+        ..color = const ui.Color(0xFFFF0000)
+    );
+
+    final ui.Picture picture = recorder.endRecording();
+
+    final ui.SceneBuilder sb = ui.SceneBuilder();
+    sb.pushOffset(50, 50);
+    sb.addPicture(const ui.Offset(100, 100), picture);
+
+    final ui.EngineLayer retainedPlatformView = sb.pushOffset(50, 50);
+    sb.addPlatformView(
+      1,
+      offset: const ui.Offset(125, 125),
+      width: 50,
+      height: 50,
+    );
+    await renderScene(sb.build());
+
+    await matchGoldenFile('platformview_offset.png', region: region);
+
+    final ui.SceneBuilder sb2 = ui.SceneBuilder();
+    sb2.pushOffset(0, 0);
+    sb2.addPicture(const ui.Offset(100, 100), picture);
+
+    sb2.addRetained(retainedPlatformView);
+    await renderScene(sb2.build());
+
+    await matchGoldenFile('platformview_offset_moved.png', region: region);
+  });
+
+
   test('platformview with opacity', () async {
     await _createPlatformView(1, platformViewType);
 
@@ -149,7 +190,7 @@ Future<void> testMain() async {
     sb.pushOffset(0, 0);
     sb.addPicture(const ui.Offset(100, 100), recorder.endRecording());
 
-    sb.pushOpacity(127);
+    sb.pushOpacity(127, offset: const ui.Offset(50, 50));
     sb.addPlatformView(
       1,
       offset: const ui.Offset(125, 125),