[DONT LAND][ios][platform_view]round in layers and round out platform views

display_list/geometry/dl_rtree.cc

@@ -201,18 +201,30 @@ void DlRTree::search(const Node& parent,
   }
 }
 
-const DlRegion& DlRTree::region() const {
+const DlRegion& DlRTree::region(bool useRoundIn) const {
   if (!region_) {
     std::vector<SkIRect> rects;
     rects.resize(leaf_count_);
     for (int i = 0; i < leaf_count_; i++) {
-      nodes_[i].bounds.roundOut(&rects[i]);
+      if (useRoundIn) {
+        nodes_[i].bounds.roundIn(&rects[i]);
+      } else {
+        nodes_[i].bounds.roundOut(&rects[i]);
+      }
     }
     region_.emplace(rects);
   }
   return *region_;
 }
 
+const DlRegion& DlRTree::region() const {
+  return region(/*useRoundIn=*/false);
+}
+
+const DlRegion& DlRTree::roundedInRegion() const {
+  return region(/*useRoundIn=*/true);
+}
+
 const SkRect& DlRTree::bounds() const {
   if (!nodes_.empty()) {
     return nodes_.back().bounds;

display_list/geometry/dl_rtree.h

@@ -127,8 +127,11 @@ class DlRTree : public SkRefCnt {
                                               bool deband = true) const;
 
   /// Returns DlRegion that represents the union of all rectangles in the
-  /// R-Tree.
+  /// R-Tree. Each rectangle is rounded out.
   const DlRegion& region() const;
+  /// Returns DlRegion that represents the union of all rectangles in the
+  /// R-Tree. Each rectangle is rounded in.
+  const DlRegion& roundedInRegion() const;
 
   /// Returns DlRegion that represents the union of all rectangles in the
   /// R-Tree intersected with the query rect.
@@ -147,6 +150,7 @@ class DlRTree : public SkRefCnt {
   int leaf_count_ = 0;
   int invalid_id_;
   mutable std::optional<DlRegion> region_;
+  const DlRegion& region(bool useRoundIn) const;
 };
 
 }  // namespace flutter

flow/embedded_views.cc

@@ -26,6 +26,10 @@ const DlRegion& DisplayListEmbedderViewSlice::getRegion() const {
   return display_list_->rtree()->region();
 }
 
+const DlRegion& DisplayListEmbedderViewSlice::getRoundedInRegion() const {
+  return display_list_->rtree()->roundedInRegion();
+}
+
 void DisplayListEmbedderViewSlice::render_into(DlCanvas* canvas) {
   canvas->DrawDisplayList(display_list_);
 }

flow/embedded_views.h

@@ -338,7 +338,13 @@ class EmbedderViewSlice {
   virtual ~EmbedderViewSlice() = default;
   virtual DlCanvas* canvas() = 0;
   virtual void end_recording() = 0;
+  // TODO(hellohuanlin): deprecate `getRegion` and migrate to
+  // `getRoundedInRegion`. Then we should rename `getRoundedInRegion` to just
+  // `getRegion`.
   virtual const DlRegion& getRegion() const = 0;
+  // TODO(hellohuanlin): iOS only for now. Try on other platforms.
+  virtual const DlRegion& getRoundedInRegion() const = 0;
+
   // TODO(hellohuanlin): We should deprecate this function if we migrate
   // all platforms to use `roundedInRegion`. Then we should rename
   // `roundedInRegion` to just `region`.
@@ -355,13 +361,13 @@ class EmbedderViewSlice {
     // result in an intersection region of 1 px height, which is then used to
     // create an overlay layer. For each overlay, we acquire a surface frame,
     // paint the pixels and submit the frame. This resulted in performance
-    // issues since the surface frame acquisition is expensive. Since slice
-    // regions are already rounded out (see:
-    // https://github.com/flutter/engine/blob/5f40c9f49f88729bc3e71390356209dbe29ec788/display_list/geometry/dl_rtree.cc#L209),
-    // we can simply round in the queried rect to avoid the situation.
-    // After rounding in, it will ignore a single (or partial) pixel overlap,
-    // and give the ownership to the platform view.
-    return DlRegion::MakeIntersection(getRegion(), DlRegion(query.roundIn()));
+    // issues since the surface frame acquisition is expensive.
+    // We round in the layers and round out the platform view, rather than the
+    // opposite, so that the edge pixel overlay is guaranteed to be displayed
+    // on top of the platform view. After rounding in, layers will give the
+    // ownership of a single (or partial) pixel on the edge to platform views.
+    return DlRegion::MakeIntersection(getRoundedInRegion(),
+                                      DlRegion(query.roundOut()));
   }
 
   virtual void render_into(DlCanvas* canvas) = 0;
@@ -375,6 +381,7 @@ class DisplayListEmbedderViewSlice : public EmbedderViewSlice {
   DlCanvas* canvas() override;
   void end_recording() override;
   const DlRegion& getRegion() const override;
+  const DlRegion& getRoundedInRegion() const override;
 
   void render_into(DlCanvas* canvas) override;
   void dispatch(DlOpReceiver& receiver);

testing/scenario_app/ios/Scenarios/Scenarios/AppDelegate.m

@@ -52,7 +52,10 @@ - (BOOL)application:(UIApplication*)application
         @"platform_view_one_overlay_two_intersecting_overlays",
     @"--platform-view-multiple-without-overlays" : @"platform_view_multiple_without_overlays",
     @"--platform-view-max-overlays" : @"platform_view_max_overlays",
-    @"--platform-view-surrounding-layers" : @"platform_view_surrounding_layers",
+    @"--platform-view-surrounding-layers-fractional-coordinate" :
+        @"platform_view_surrounding_layers_fractional_coordinate",
+    @"--platform-view-partial-intersection-fractional-coordinate" :
+        @"platform_view_partial_intersection_fractional_coordinate",
     @"--platform-view-multiple" : @"platform_view_multiple",
     @"--platform-view-multiple-background-foreground" :
         @"platform_view_multiple_background_foreground",

testing/scenario_app/ios/Scenarios/ScenariosUITests/UnobstructedPlatformViewTests.m

@@ -313,9 +313,9 @@ - (void)testPlatformViewsMaxOverlays {
 //  +---+----+---+
 //      | D  |
 //      +----+
-- (void)testPlatformViewsWithAdjacentSurroundingLayers {
+- (void)testPlatformViewsWithAdjacentSurroundingLayersAndFractionalCoordinate {
   XCUIApplication* app = [[XCUIApplication alloc] init];
-  app.launchArguments = @[ @"--platform-view-surrounding-layers" ];
+  app.launchArguments = @[ @"--platform-view-surrounding-layers-fractional-coordinate" ];
   [app launch];
 
   XCUIElement* platform_view = app.otherElements[@"platform_view[0]"];
@@ -331,4 +331,36 @@ - (void)testPlatformViewsWithAdjacentSurroundingLayers {
   XCTAssertFalse(overlay.exists);
 }
 
+// Platform view partially intersect with a layer in fractional coordinate.
+// +-------+
+// |       |
+// | PV +--+--+
+// |    |     |
+// +----+  A  |
+//      |     |
+//      +-----+
+- (void)testPlatformViewsWithPartialIntersectionAndFractionalCoordinate {
+  XCUIApplication* app = [[XCUIApplication alloc] init];
+  app.launchArguments = @[ @"--platform-view-partial-intersection-fractional-coordinate" ];
+  [app launch];
+
+  XCUIElement* platform_view = app.otherElements[@"platform_view[0]"];
+  XCTAssertTrue([platform_view waitForExistenceWithTimeout:1.0]);
+
+  CGFloat scale = [UIScreen mainScreen].scale;
+  XCTAssertEqual(platform_view.frame.origin.x * scale, 0.5);
+  XCTAssertEqual(platform_view.frame.origin.y * scale, 0.5);
+  XCTAssertEqual(platform_view.frame.size.width * scale, 100);
+  XCTAssertEqual(platform_view.frame.size.height * scale, 100);
+
+  XCUIElement* overlay = app.otherElements[@"platform_view[0].overlay[0]"];
+  XCTAssert(overlay.exists);
+
+  // 51 since layer is rounded in.
+  XCTAssertEqual(CGRectGetMinX(overlay.frame) * scale, 51);
+  XCTAssertEqual(CGRectGetMinY(overlay.frame) * scale, 51);
+  // 101 since platform view is rounded out.
+  XCTAssertEqual(CGRectGetMaxX(overlay.frame) * scale, 101);
+  XCTAssertEqual(CGRectGetMaxY(overlay.frame) * scale, 101);
+}
 @end

testing/scenario_app/lib/src/platform_view.dart

@@ -367,10 +367,10 @@ class PlatformViewMaxOverlaysScenario extends Scenario
 }
 
 /// A platform view with adjacent surrounding layers should not create overlays.
-class PlatformViewSurroundingLayersScenario extends Scenario
+class PlatformViewSurroundingLayersFractionalCoordinateScenario extends Scenario
     with _BasePlatformViewScenarioMixin {
   /// Creates the PlatformView scenario.
-  PlatformViewSurroundingLayersScenario(
+  PlatformViewSurroundingLayersFractionalCoordinateScenario(
     super.view, {
     required this.id,
   });
@@ -438,6 +438,55 @@ class PlatformViewSurroundingLayersScenario extends Scenario
   }
 }
 
+/// A platform view partially intersect with a layer, both with fractional coordinates.
+class PlatformViewPartialIntersectionFractionalCoordinateScenario extends Scenario
+    with _BasePlatformViewScenarioMixin {
+  /// Creates the PlatformView scenario.
+  PlatformViewPartialIntersectionFractionalCoordinateScenario(
+    super.view, {
+    required this.id,
+  });
+
+  /// The platform view identifier.
+  final int id;
+
+  @override
+  void onBeginFrame(Duration duration) {
+    final SceneBuilder builder = SceneBuilder();
+
+    // Simulate partial pixel offsets as we would see while scrolling.
+    // All objects in the scene below are then on sub-pixel boundaries.
+    builder.pushOffset(0.5, 0.5);
+
+    // a platform view from (0, 0) to (100, 100)
+    addPlatformView(
+      id,
+      width: 100,
+      height: 100,
+      dispatcher: view.platformDispatcher,
+      sceneBuilder: builder,
+    );
+
+    final PictureRecorder recorder = PictureRecorder();
+    final Canvas canvas = Canvas(recorder);
+
+    canvas.drawRect(
+      Rect.fromLTWH(50, 50, 100, 100),
+      Paint()..color = const Color(0x22FF0000),
+    );
+
+    final Picture picture = recorder.endRecording();
+    builder.addPicture(Offset.zero, picture);
+
+    // Pop the (0.5, 0.5) offset.
+    builder.pop();
+
+    final Scene scene = builder.build();
+    view.render(scene);
+    scene.dispose();
+  }
+}
+
 /// Builds a scene with 2 platform views.
 class MultiPlatformViewScenario extends Scenario
     with _BasePlatformViewScenarioMixin {

testing/scenario_app/lib/src/scenarios.dart

@@ -34,7 +34,8 @@ Map<String, _ScenarioFactory> _scenarios = <String, _ScenarioFactory>{
   'platform_view_one_overlay_two_intersecting_overlays': (FlutterView view) => PlatformViewOneOverlayTwoIntersectingOverlaysScenario(view, id: _viewId++),
   'platform_view_multiple_without_overlays': (FlutterView view) => MultiPlatformViewWithoutOverlaysScenario(view, firstId: _viewId++, secondId: _viewId++),
   'platform_view_max_overlays': (FlutterView view) => PlatformViewMaxOverlaysScenario(view, id: _viewId++),
-  'platform_view_surrounding_layers': (FlutterView view) => PlatformViewSurroundingLayersScenario(view, id: _viewId++),
+  'platform_view_surrounding_layers_fractional_coordinate': (FlutterView view) => PlatformViewSurroundingLayersFractionalCoordinateScenario(view, id: _viewId++),
+  'platform_view_partial_intersection_fractional_coordinate': (FlutterView view) => PlatformViewPartialIntersectionFractionalCoordinateScenario(view, id: _viewId++),
   'platform_view_cliprect': (FlutterView view) => PlatformViewClipRectScenario(view, id: _viewId++),
   'platform_view_cliprect_with_transform': (FlutterView view) => PlatformViewClipRectWithTransformScenario(view, id: _viewId++),
   'platform_view_cliprect_after_moved': (FlutterView view) => PlatformViewClipRectAfterMovedScenario(view, id: _viewId++),