[ios][platform_view] fix platform view clipping path intersection (#54820)

It turns out that when there are multiple paths to clip, they are unioned together, rather than intersected. But clipping paths need to be intersected. 

There isn't any good way to intersect arbitrary paths. However, it is easy to intersect rect paths, which is the most common use case. Then we simply fallback to software rendering if we have to intersect non-rect paths. That is: 

**Case 1** Only 1 clipping path (either rect path or arbitrary path):
Hardware rendering. This should be the most common use case

**Case 2** Multiple rect clipping path: 
Hardware rendering. This is also common, and it's the linked issue that we are fixing. 

**Case 3** Other complex case (multiple non-rect clipping path)
Fallback to software rendering. This should be rare. 

After #53826, we don't have a working benchmark that measures the main thread anymore. However, this PR shouldn't impact our ad benchmark, since it only has 1 clipping path. I will verify manually by checking Instruments and make sure no software rendering is happening. But we really should make the benchmark working again, not just for performance improvement, but also for monitoring regression. 

*List which issues are fixed by this PR. You must list at least one issue.*

Fixes flutter/flutter#153904

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

Author: hellohuanlin

shell/platform/darwin/ios/framework/Source/FlutterPlatformViewsTest.mm

@@ -1856,6 +1856,102 @@ - (void)testClipRect {
   }
 }
 
+- (void)testClipRect_multipleClips {
+  flutter::FlutterPlatformViewsTestMockPlatformViewDelegate mock_delegate;
+
+  flutter::TaskRunners runners(/*label=*/self.name.UTF8String,
+                               /*platform=*/GetDefaultTaskRunner(),
+                               /*raster=*/GetDefaultTaskRunner(),
+                               /*ui=*/GetDefaultTaskRunner(),
+                               /*io=*/GetDefaultTaskRunner());
+  auto flutterPlatformViewsController = std::make_shared<flutter::PlatformViewsController>();
+  flutterPlatformViewsController->SetTaskRunner(GetDefaultTaskRunner());
+  auto platform_view = std::make_unique<flutter::PlatformViewIOS>(
+      /*delegate=*/mock_delegate,
+      /*rendering_api=*/mock_delegate.settings_.enable_impeller
+          ? flutter::IOSRenderingAPI::kMetal
+          : flutter::IOSRenderingAPI::kSoftware,
+      /*platform_views_controller=*/flutterPlatformViewsController,
+      /*task_runners=*/runners,
+      /*worker_task_runner=*/nil,
+      /*is_gpu_disabled_jsync_switch=*/std::make_shared<fml::SyncSwitch>());
+
+  FlutterPlatformViewsTestMockFlutterPlatformFactory* factory =
+      [[FlutterPlatformViewsTestMockFlutterPlatformFactory alloc] init];
+  flutterPlatformViewsController->RegisterViewFactory(
+      factory, @"MockFlutterPlatformView",
+      FlutterPlatformViewGestureRecognizersBlockingPolicyEager);
+  FlutterResult result = ^(id result) {
+  };
+  flutterPlatformViewsController->OnMethodCall(
+      [FlutterMethodCall
+          methodCallWithMethodName:@"create"
+                         arguments:@{@"id" : @2, @"viewType" : @"MockFlutterPlatformView"}],
+      result);
+
+  XCTAssertNotNil(gMockPlatformView);
+
+  UIView* flutterView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 10, 10)];
+  flutterPlatformViewsController->SetFlutterView(flutterView);
+  // Create embedded view params
+  flutter::MutatorsStack stack;
+  // Layer tree always pushes a screen scale factor to the stack
+  SkMatrix screenScaleMatrix =
+      SkMatrix::Scale([UIScreen mainScreen].scale, [UIScreen mainScreen].scale);
+  stack.PushTransform(screenScaleMatrix);
+  // Push a clip rect
+  SkRect rect1 = SkRect::MakeXYWH(2, 2, 3, 3);
+  stack.PushClipRect(rect1);
+  // Push another clip rect
+  SkRect rect2 = SkRect::MakeXYWH(3, 3, 3, 3);
+  stack.PushClipRect(rect2);
+
+  auto embeddedViewParams =
+      std::make_unique<flutter::EmbeddedViewParams>(screenScaleMatrix, SkSize::Make(10, 10), stack);
+
+  flutterPlatformViewsController->PrerollCompositeEmbeddedView(2, std::move(embeddedViewParams));
+  flutterPlatformViewsController->CompositeWithParams(
+      2, flutterPlatformViewsController->GetCompositionParams(2));
+
+  gMockPlatformView.backgroundColor = UIColor.redColor;
+  XCTAssertTrue([gMockPlatformView.superview.superview isKindOfClass:ChildClippingView.class]);
+  ChildClippingView* childClippingView = (ChildClippingView*)gMockPlatformView.superview.superview;
+  [flutterView addSubview:childClippingView];
+
+  [flutterView setNeedsLayout];
+  [flutterView layoutIfNeeded];
+
+  /*
+  clip 1            clip 2
+    2 3 4 5 6         2 3 4 5 6
+  2 + - - +         2
+  3 |     |         3   + - - +
+  4 |     |         4   |     |
+  5 + - - +         5   |     |
+  6                 6   + - - +
+
+  Result should be the intersection of 2 clips
+    2 3 4 5 6
+  2
+  3   + - +
+  4   |   |
+  5   + - +
+  6
+  */
+  CGRect insideClipping = CGRectMake(3, 3, 2, 2);
+  for (int i = 0; i < 10; i++) {
+    for (int j = 0; j < 10; j++) {
+      CGPoint point = CGPointMake(i, j);
+      int alpha = [self alphaOfPoint:CGPointMake(i, j) onView:flutterView];
+      if (CGRectContainsPoint(insideClipping, point)) {
+        XCTAssertEqual(alpha, 255);
+      } else {
+        XCTAssertEqual(alpha, 0);
+      }
+    }
+  }
+}
+
 - (void)testClipRRect {
   flutter::FlutterPlatformViewsTestMockPlatformViewDelegate mock_delegate;
 
@@ -1959,6 +2055,126 @@ - (void)testClipRRect {
   }
 }
 
+- (void)testClipRRect_multipleClips {
+  flutter::FlutterPlatformViewsTestMockPlatformViewDelegate mock_delegate;
+
+  flutter::TaskRunners runners(/*label=*/self.name.UTF8String,
+                               /*platform=*/GetDefaultTaskRunner(),
+                               /*raster=*/GetDefaultTaskRunner(),
+                               /*ui=*/GetDefaultTaskRunner(),
+                               /*io=*/GetDefaultTaskRunner());
+  auto flutterPlatformViewsController = std::make_shared<flutter::PlatformViewsController>();
+  flutterPlatformViewsController->SetTaskRunner(GetDefaultTaskRunner());
+  auto platform_view = std::make_unique<flutter::PlatformViewIOS>(
+      /*delegate=*/mock_delegate,
+      /*rendering_api=*/mock_delegate.settings_.enable_impeller
+          ? flutter::IOSRenderingAPI::kMetal
+          : flutter::IOSRenderingAPI::kSoftware,
+      /*platform_views_controller=*/flutterPlatformViewsController,
+      /*task_runners=*/runners,
+      /*worker_task_runner=*/nil,
+      /*is_gpu_disabled_jsync_switch=*/std::make_shared<fml::SyncSwitch>());
+
+  FlutterPlatformViewsTestMockFlutterPlatformFactory* factory =
+      [[FlutterPlatformViewsTestMockFlutterPlatformFactory alloc] init];
+  flutterPlatformViewsController->RegisterViewFactory(
+      factory, @"MockFlutterPlatformView",
+      FlutterPlatformViewGestureRecognizersBlockingPolicyEager);
+  FlutterResult result = ^(id result) {
+  };
+  flutterPlatformViewsController->OnMethodCall(
+      [FlutterMethodCall
+          methodCallWithMethodName:@"create"
+                         arguments:@{@"id" : @2, @"viewType" : @"MockFlutterPlatformView"}],
+      result);
+
+  XCTAssertNotNil(gMockPlatformView);
+
+  UIView* flutterView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 10, 10)];
+  flutterPlatformViewsController->SetFlutterView(flutterView);
+  // Create embedded view params
+  flutter::MutatorsStack stack;
+  // Layer tree always pushes a screen scale factor to the stack
+  SkMatrix screenScaleMatrix =
+      SkMatrix::Scale([UIScreen mainScreen].scale, [UIScreen mainScreen].scale);
+  stack.PushTransform(screenScaleMatrix);
+  // Push a clip rrect
+  SkRRect rrect = SkRRect::MakeRectXY(SkRect::MakeXYWH(2, 2, 6, 6), 1, 1);
+  stack.PushClipRRect(rrect);
+  // Push a clip rect
+  SkRect rect = SkRect::MakeXYWH(4, 2, 6, 6);
+  stack.PushClipRect(rect);
+
+  auto embeddedViewParams =
+      std::make_unique<flutter::EmbeddedViewParams>(screenScaleMatrix, SkSize::Make(10, 10), stack);
+
+  flutterPlatformViewsController->PrerollCompositeEmbeddedView(2, std::move(embeddedViewParams));
+  flutterPlatformViewsController->CompositeWithParams(
+      2, flutterPlatformViewsController->GetCompositionParams(2));
+
+  gMockPlatformView.backgroundColor = UIColor.redColor;
+  XCTAssertTrue([gMockPlatformView.superview.superview isKindOfClass:ChildClippingView.class]);
+  ChildClippingView* childClippingView = (ChildClippingView*)gMockPlatformView.superview.superview;
+  [flutterView addSubview:childClippingView];
+
+  [flutterView setNeedsLayout];
+  [flutterView layoutIfNeeded];
+
+  /*
+  clip 1                 clip 2
+    2 3 4 5 6 7 8 9       2 3 4 5 6 7 8 9
+  2 / - - - - \         2     + - - - - +
+  3 |         |         3     |         |
+  4 |         |         4     |         |
+  5 |         |         5     |         |
+  6 |         |         6     |         |
+  7 \ - - - - /         7     + - - - - +
+
+  Result should be the intersection of 2 clips
+    2 3 4 5 6 7 8 9
+  2     + - - \
+  3     |     |
+  4     |     |
+  5     |     |
+  6     |     |
+  7     + - - /
+  */
+  CGRect clipping = CGRectMake(4, 2, 4, 6);
+  for (int i = 0; i < 10; i++) {
+    for (int j = 0; j < 10; j++) {
+      CGPoint point = CGPointMake(i, j);
+      int alpha = [self alphaOfPoint:CGPointMake(i, j) onView:flutterView];
+      if (i == 7 && (j == 2 || j == 7)) {
+        // Upper and lower right corners should be partially transparent.
+        XCTAssert(0 < alpha && alpha < 255);
+      } else if (
+          // left
+          (i == 4 && j >= 2 && j <= 7) ||
+          // right
+          (i == 7 && j >= 2 && j <= 7) ||
+          // top
+          (j == 2 && i >= 4 && i <= 7) ||
+          // bottom
+          (j == 7 && i >= 4 && i <= 7)) {
+        // Since we are falling back to software rendering for this case
+        // The edge pixels can be anti-aliased, so it may not be fully opaque.
+        XCTAssert(alpha > 127);
+      } else if ((i == 3 && j >= 1 && j <= 8) || (i == 8 && j >= 1 && j <= 8) ||
+                 (j == 1 && i >= 3 && i <= 8) || (j == 8 && i >= 3 && i <= 8)) {
+        // Since we are falling back to software rendering for this case
+        // The edge pixels can be anti-aliased, so it may not be fully transparent.
+        XCTAssert(alpha < 127);
+      } else if (CGRectContainsPoint(clipping, point)) {
+        // Other pixels inside clipping should be fully opaque.
+        XCTAssertEqual(alpha, 255);
+      } else {
+        // Pixels outside clipping should be fully transparent.
+        XCTAssertEqual(alpha, 0);
+      }
+    }
+  }
+}
+
 - (void)testClipPath {
   flutter::FlutterPlatformViewsTestMockPlatformViewDelegate mock_delegate;
 
@@ -2063,6 +2279,127 @@ - (void)testClipPath {
   }
 }
 
+- (void)testClipPath_multipleClips {
+  flutter::FlutterPlatformViewsTestMockPlatformViewDelegate mock_delegate;
+
+  flutter::TaskRunners runners(/*label=*/self.name.UTF8String,
+                               /*platform=*/GetDefaultTaskRunner(),
+                               /*raster=*/GetDefaultTaskRunner(),
+                               /*ui=*/GetDefaultTaskRunner(),
+                               /*io=*/GetDefaultTaskRunner());
+  auto flutterPlatformViewsController = std::make_shared<flutter::PlatformViewsController>();
+  flutterPlatformViewsController->SetTaskRunner(GetDefaultTaskRunner());
+  auto platform_view = std::make_unique<flutter::PlatformViewIOS>(
+      /*delegate=*/mock_delegate,
+      /*rendering_api=*/mock_delegate.settings_.enable_impeller
+          ? flutter::IOSRenderingAPI::kMetal
+          : flutter::IOSRenderingAPI::kSoftware,
+      /*platform_views_controller=*/flutterPlatformViewsController,
+      /*task_runners=*/runners,
+      /*worker_task_runner=*/nil,
+      /*is_gpu_disabled_jsync_switch=*/std::make_shared<fml::SyncSwitch>());
+
+  FlutterPlatformViewsTestMockFlutterPlatformFactory* factory =
+      [[FlutterPlatformViewsTestMockFlutterPlatformFactory alloc] init];
+  flutterPlatformViewsController->RegisterViewFactory(
+      factory, @"MockFlutterPlatformView",
+      FlutterPlatformViewGestureRecognizersBlockingPolicyEager);
+  FlutterResult result = ^(id result) {
+  };
+  flutterPlatformViewsController->OnMethodCall(
+      [FlutterMethodCall
+          methodCallWithMethodName:@"create"
+                         arguments:@{@"id" : @2, @"viewType" : @"MockFlutterPlatformView"}],
+      result);
+
+  XCTAssertNotNil(gMockPlatformView);
+
+  UIView* flutterView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 10, 10)];
+  flutterPlatformViewsController->SetFlutterView(flutterView);
+  // Create embedded view params
+  flutter::MutatorsStack stack;
+  // Layer tree always pushes a screen scale factor to the stack
+  SkMatrix screenScaleMatrix =
+      SkMatrix::Scale([UIScreen mainScreen].scale, [UIScreen mainScreen].scale);
+  stack.PushTransform(screenScaleMatrix);
+  // Push a clip path
+  SkPath path;
+  path.addRoundRect(SkRect::MakeXYWH(2, 2, 6, 6), 1, 1);
+  stack.PushClipPath(path);
+  // Push a clip rect
+  SkRect rect = SkRect::MakeXYWH(4, 2, 6, 6);
+  stack.PushClipRect(rect);
+
+  auto embeddedViewParams =
+      std::make_unique<flutter::EmbeddedViewParams>(screenScaleMatrix, SkSize::Make(10, 10), stack);
+
+  flutterPlatformViewsController->PrerollCompositeEmbeddedView(2, std::move(embeddedViewParams));
+  flutterPlatformViewsController->CompositeWithParams(
+      2, flutterPlatformViewsController->GetCompositionParams(2));
+
+  gMockPlatformView.backgroundColor = UIColor.redColor;
+  XCTAssertTrue([gMockPlatformView.superview.superview isKindOfClass:ChildClippingView.class]);
+  ChildClippingView* childClippingView = (ChildClippingView*)gMockPlatformView.superview.superview;
+  [flutterView addSubview:childClippingView];
+
+  [flutterView setNeedsLayout];
+  [flutterView layoutIfNeeded];
+
+  /*
+  clip 1                 clip 2
+    2 3 4 5 6 7 8 9       2 3 4 5 6 7 8 9
+  2 / - - - - \         2     + - - - - +
+  3 |         |         3     |         |
+  4 |         |         4     |         |
+  5 |         |         5     |         |
+  6 |         |         6     |         |
+  7 \ - - - - /         7     + - - - - +
+
+  Result should be the intersection of 2 clips
+    2 3 4 5 6 7 8 9
+  2     + - - \
+  3     |     |
+  4     |     |
+  5     |     |
+  6     |     |
+  7     + - - /
+  */
+  CGRect clipping = CGRectMake(4, 2, 4, 6);
+  for (int i = 0; i < 10; i++) {
+    for (int j = 0; j < 10; j++) {
+      CGPoint point = CGPointMake(i, j);
+      int alpha = [self alphaOfPoint:CGPointMake(i, j) onView:flutterView];
+      if (i == 7 && (j == 2 || j == 7)) {
+        // Upper and lower right corners should be partially transparent.
+        XCTAssert(0 < alpha && alpha < 255);
+      } else if (
+          // left
+          (i == 4 && j >= 2 && j <= 7) ||
+          // right
+          (i == 7 && j >= 2 && j <= 7) ||
+          // top
+          (j == 2 && i >= 4 && i <= 7) ||
+          // bottom
+          (j == 7 && i >= 4 && i <= 7)) {
+        // Since we are falling back to software rendering for this case
+        // The edge pixels can be anti-aliased, so it may not be fully opaque.
+        XCTAssert(alpha > 127);
+      } else if ((i == 3 && j >= 1 && j <= 8) || (i == 8 && j >= 1 && j <= 8) ||
+                 (j == 1 && i >= 3 && i <= 8) || (j == 8 && i >= 3 && i <= 8)) {
+        // Since we are falling back to software rendering for this case
+        // The edge pixels can be anti-aliased, so it may not be fully transparent.
+        XCTAssert(alpha < 127);
+      } else if (CGRectContainsPoint(clipping, point)) {
+        // Other pixels inside clipping should be fully opaque.
+        XCTAssertEqual(alpha, 255);
+      } else {
+        // Pixels outside clipping should be fully transparent.
+        XCTAssertEqual(alpha, 0);
+      }
+    }
+  }
+}
+
 - (void)testSetFlutterViewControllerAfterCreateCanStillDispatchTouchEvents {
   flutter::FlutterPlatformViewsTestMockPlatformViewDelegate mock_delegate;