Reverts "[ios][platform_view] Use CAShapeLayer as the mask to avoid software rendering (#53072)" (flutter/engine#53220)

Reverts: flutter/engine#53072
Initiated by: jason-simmons
Reason for reverting: compilation errors on iOS targets

```
FlutterPlatformViews_Internal.mm:277:10: error: ARC forbids explicit message send of 'dealloc'
  277 |   [super dealloc];
      |    ~~~~~ ^
 ```

(see https://logs.chromium.org/logs/flutter/buildbucket/cr-buildbucket/8746006425774972161/+/u/build_ci_ios_debug_unopt_sim_flutter_testing_scenario_app_flutter_shell_platform_darwin_ios:ios_test_flutter/st
Original PR Author: hellohuanlin

Reviewed By: {cbracken, jonahwilliams}

This change reverts the following previous change:
This PR uses `CAShapeLayer` as the mask to avoid software rendering. 

I kept `UIView` as the mask, so that we can measure just the improvement related to avoiding software rendering. This also allows me to land this change sooner. I created [a separate issue](https://github.com/flutter/flutter/issues/149212) to track removing UIView as the mask. 

Note: the previous behavior seems to be incorrect (or at least not pixel perfect). This PR fixed it. See comments. 

See design doc: https://docs.google.com/document/d/1TqG_N4GK_qctuk73Gk3zOdAiILUrwMqxoCMgroK_AeA/edit?resourcekey=0-jUiidfzIS642ngG2w9vSUA&tab=t.0

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

Fixes https://github.com/flutter/flutter/issues/142813
Fixes https://github.com/flutter/flutter/issues/142830

*If you had to change anything in the [flutter/tests] repo, include a link to the migration guide as per the [breaking change policy].*

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

engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterPlatformViewsTest.mm

@@ -1773,15 +1773,17 @@ fml::RefPtr<fml::TaskRunner> CreateNewThread(const std::string& name) {
   [mockFlutterView setNeedsLayout];
   [mockFlutterView layoutIfNeeded];
 
-  CGRect insideClipping = CGRectMake(2, 2, 3, 3);
   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:mockFlutterView];
+      // Edges of the clipping might have a semi transparent pixel, we only check the pixels that
+      // are fully inside the clipped area.
+      CGRect insideClipping = CGRectMake(3, 3, 1, 1);
       if (CGRectContainsPoint(insideClipping, point)) {
         XCTAssertEqual(alpha, 255);
       } else {
-        XCTAssertEqual(alpha, 0);
+        XCTAssertLessThan(alpha, 255);
       }
     }
   }
@@ -1846,42 +1848,17 @@ fml::RefPtr<fml::TaskRunner> CreateNewThread(const std::string& name) {
   [mockFlutterView setNeedsLayout];
   [mockFlutterView layoutIfNeeded];
 
-  /*
-  ClippingMask          outterClipping
-    2 3 4 5 6 7           2 3 4 5 6 7
-  2 / - - - - \         2 + - - - - +
-  3 |         |         3 |         |
-  4 |         |         4 |         |
-  5 |         |         5 |         |
-  6 |         |         6 |         |
-  7 \ - - - - /         7 + - - - - +
-
-  innerClipping1        innerClipping2
-    2 3 4 5 6 7           2 3 4 5 6 7
-  2   + - - +           2
-  3   |     |           3 + - - - - +
-  4   |     |           4 |         |
-  5   |     |           5 |         |
-  6   |     |           6 + - - - - +
-  7   + - - +           7
-  */
-  CGRect innerClipping1 = CGRectMake(3, 2, 4, 6);
-  CGRect innerClipping2 = CGRectMake(2, 3, 6, 4);
-  CGRect outterClipping = CGRectMake(2, 2, 6, 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:mockFlutterView];
-      if (CGRectContainsPoint(innerClipping1, point) ||
-          CGRectContainsPoint(innerClipping2, point)) {
-        // Pixels inside either of the 2 inner clippings should be fully opaque.
+      // Edges of the clipping might have a semi transparent pixel, we only check the pixels that
+      // are fully inside the clipped area.
+      CGRect insideClipping = CGRectMake(3, 3, 4, 4);
+      if (CGRectContainsPoint(insideClipping, point)) {
         XCTAssertEqual(alpha, 255);
-      } else if (CGRectContainsPoint(outterClipping, point)) {
-        // Corner pixels (i.e. (2, 2), (2, 7), (7, 2) and (7, 7)) should be partially transparent.
-        XCTAssert(0 < alpha && alpha < 255);
       } else {
-        // Pixels outside outterClipping should be fully transparent.
-        XCTAssertEqual(alpha, 0);
+        XCTAssertLessThan(alpha, 255);
       }
     }
   }
@@ -1947,42 +1924,17 @@ fml::RefPtr<fml::TaskRunner> CreateNewThread(const std::string& name) {
   [mockFlutterView setNeedsLayout];
   [mockFlutterView layoutIfNeeded];
 
-  /*
-  ClippingMask          outterClipping
-    2 3 4 5 6 7           2 3 4 5 6 7
-  2 / - - - - \         2 + - - - - +
-  3 |         |         3 |         |
-  4 |         |         4 |         |
-  5 |         |         5 |         |
-  6 |         |         6 |         |
-  7 \ - - - - /         7 + - - - - +
-
-  innerClipping1        innerClipping2
-    2 3 4 5 6 7           2 3 4 5 6 7
-  2   + - - +           2
-  3   |     |           3 + - - - - +
-  4   |     |           4 |         |
-  5   |     |           5 |         |
-  6   |     |           6 + - - - - +
-  7   + - - +           7
-  */
-  CGRect innerClipping1 = CGRectMake(3, 2, 4, 6);
-  CGRect innerClipping2 = CGRectMake(2, 3, 6, 4);
-  CGRect outterClipping = CGRectMake(2, 2, 6, 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:mockFlutterView];
-      if (CGRectContainsPoint(innerClipping1, point) ||
-          CGRectContainsPoint(innerClipping2, point)) {
-        // Pixels inside either of the 2 inner clippings should be fully opaque.
+      // Edges of the clipping might have a semi transparent pixel, we only check the pixels that
+      // are fully inside the clipped area.
+      CGRect insideClipping = CGRectMake(3, 3, 4, 4);
+      if (CGRectContainsPoint(insideClipping, point)) {
         XCTAssertEqual(alpha, 255);
-      } else if (CGRectContainsPoint(outterClipping, point)) {
-        // Corner pixels (i.e. (2, 2), (2, 7), (7, 2) and (7, 7)) should be partially transparent.
-        XCTAssert(0 < alpha && alpha < 255);
       } else {
-        // Pixels outside outterClipping should be fully transparent.
-        XCTAssertEqual(alpha, 0);
+        XCTAssertLessThan(alpha, 255);
       }
     }
   }
@@ -3037,69 +2989,6 @@ fml::RefPtr<fml::TaskRunner> CreateNewThread(const std::string& name) {
   XCTAssertNotEqual(maskView1, maskView2);
 }
 
-- (void)testMaskViewUsesCAShapeLayerAsTheBackingLayer {
-  flutter::FlutterPlatformViewsTestMockPlatformViewDelegate mock_delegate;
-  auto thread_task_runner = CreateNewThread("FlutterPlatformViewsTest");
-  flutter::TaskRunners runners(/*label=*/self.name.UTF8String,
-                               /*platform=*/thread_task_runner,
-                               /*raster=*/thread_task_runner,
-                               /*ui=*/thread_task_runner,
-                               /*io=*/thread_task_runner);
-  auto flutterPlatformViewsController = std::make_shared<flutter::FlutterPlatformViewsController>();
-  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" : @1, @"viewType" : @"MockFlutterPlatformView"}],
-      result);
-
-  XCTAssertNotNil(gMockPlatformView);
-  UIView* mockFlutterView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 10, 10)];
-  flutterPlatformViewsController->SetFlutterView(mockFlutterView);
-  // Create embedded view params
-  flutter::MutatorsStack stack1;
-  // Layer tree always pushes a screen scale factor to the stack
-  SkMatrix screenScaleMatrix =
-      SkMatrix::Scale([UIScreen mainScreen].scale, [UIScreen mainScreen].scale);
-  stack1.PushTransform(screenScaleMatrix);
-  // Push a clip rect
-  SkRect rect = SkRect::MakeXYWH(2, 2, 3, 3);
-  stack1.PushClipRect(rect);
-
-  auto embeddedViewParams1 = std::make_unique<flutter::EmbeddedViewParams>(
-      screenScaleMatrix, SkSize::Make(10, 10), stack1);
-
-  flutter::MutatorsStack stack2;
-  stack2.PushClipRect(rect);
-  auto embeddedViewParams2 = std::make_unique<flutter::EmbeddedViewParams>(
-      screenScaleMatrix, SkSize::Make(10, 10), stack2);
-
-  flutterPlatformViewsController->PrerollCompositeEmbeddedView(1, std::move(embeddedViewParams1));
-  flutterPlatformViewsController->CompositeEmbeddedView(1);
-  UIView* childClippingView = gMockPlatformView.superview.superview;
-
-  UIView* maskView = childClippingView.maskView;
-  XCTAssert([maskView.layer isKindOfClass:[CAShapeLayer class]],
-            @"Mask view must use CAShapeLayer as its backing layer.");
-}
-
 // Return true if a correct visual effect view is found. It also implies all the validation in this
 // method passes.
 //

engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterPlatformViews_Internal.mm

@@ -236,12 +236,12 @@ static BOOL _preparedOnce = NO;
 // information about screen scale.
 @property(nonatomic) CATransform3D reverseScreenScale;
 
-- (void)addTransformedPath:(CGPathRef)path matrix:(CATransform3D)matrix;
+- (fml::CFRef<CGPathRef>)getTransformedPath:(CGPathRef)path matrix:(CATransform3D)matrix;
 
 @end
 
 @implementation FlutterClippingMaskView {
-  CGMutablePathRef pathSoFar_;
+  std::vector<fml::CFRef<CGPathRef>> paths_;
 }
 
 - (instancetype)initWithFrame:(CGRect)frame {
@@ -252,31 +252,15 @@ static BOOL _preparedOnce = NO;
   if (self = [super initWithFrame:frame]) {
     self.backgroundColor = UIColor.clearColor;
     _reverseScreenScale = CATransform3DMakeScale(1 / screenScale, 1 / screenScale, 1);
-    pathSoFar_ = CGPathCreateMutable();
   }
   return self;
 }
 
-+ (Class)layerClass {
-  return [CAShapeLayer class];
-}
-
-- (CAShapeLayer*)shapeLayer {
-  return (CAShapeLayer*)self.layer;
-}
-
 - (void)reset {
-  CGPathRelease(pathSoFar_);
-  pathSoFar_ = CGPathCreateMutable();
-  [self shapeLayer].path = nil;
+  paths_.clear();
   [self setNeedsDisplay];
 }
 
-- (void)dealloc {
-  CGPathRelease(pathSoFar_);
-  [super dealloc];
-}
-
 // In some scenarios, when we add this view as a maskView of the ChildClippingView, iOS added
 // this view as a subview of the ChildClippingView.
 // This results this view blocking touch events on the ChildClippingView.
@@ -286,13 +270,28 @@ static BOOL _preparedOnce = NO;
   return NO;
 }
 
+- (void)drawRect:(CGRect)rect {
+  CGContextRef context = UIGraphicsGetCurrentContext();
+  CGContextSaveGState(context);
+
+  // For mask view, only the alpha channel is used.
+  CGContextSetAlpha(context, 1);
+
+  for (size_t i = 0; i < paths_.size(); i++) {
+    CGContextAddPath(context, paths_.at(i));
+    CGContextClip(context);
+  }
+  CGContextFillRect(context, rect);
+  CGContextRestoreGState(context);
+}
+
 - (void)clipRect:(const SkRect&)clipSkRect matrix:(const SkMatrix&)matrix {
   CGRect clipRect = flutter::GetCGRectFromSkRect(clipSkRect);
   CGPathRef path = CGPathCreateWithRect(clipRect, nil);
   // The `matrix` is based on the physical pixels, convert it to UIKit points.
   CATransform3D matrixInPoints =
       CATransform3DConcat(flutter::GetCATransform3DFromSkMatrix(matrix), _reverseScreenScale);
-  [self addTransformedPath:path matrix:matrixInPoints];
+  paths_.push_back([self getTransformedPath:path matrix:matrixInPoints]);
 }
 
 - (void)clipRRect:(const SkRRect&)clipSkRRect matrix:(const SkMatrix&)matrix {
@@ -361,7 +360,7 @@ static BOOL _preparedOnce = NO;
   // TODO(cyanglaz): iOS does not seem to support hard edge on CAShapeLayer. It clearly stated that
   // the CAShaperLayer will be drawn antialiased. Need to figure out a way to do the hard edge
   // clipping on iOS.
-  [self addTransformedPath:pathRef matrix:matrixInPoints];
+  paths_.push_back([self getTransformedPath:pathRef matrix:matrixInPoints]);
 }
 
 - (void)clipPath:(const SkPath&)path matrix:(const SkMatrix&)matrix {
@@ -426,15 +425,15 @@ static BOOL _preparedOnce = NO;
   // The `matrix` is based on the physical pixels, convert it to UIKit points.
   CATransform3D matrixInPoints =
       CATransform3DConcat(flutter::GetCATransform3DFromSkMatrix(matrix), _reverseScreenScale);
-  [self addTransformedPath:pathRef matrix:matrixInPoints];
+  paths_.push_back([self getTransformedPath:pathRef matrix:matrixInPoints]);
 }
 
-- (void)addTransformedPath:(CGPathRef)path matrix:(CATransform3D)matrix {
+- (fml::CFRef<CGPathRef>)getTransformedPath:(CGPathRef)path matrix:(CATransform3D)matrix {
   CGAffineTransform affine =
       CGAffineTransformMake(matrix.m11, matrix.m12, matrix.m21, matrix.m22, matrix.m41, matrix.m42);
-  CGPathAddPath(pathSoFar_, &affine, path);
-  [self shapeLayer].path = pathSoFar_;
+  CGPathRef transformedPath = CGPathCreateCopyByTransformingPath(path, &affine);
   CGPathRelease(path);
+  return fml::CFRef<CGPathRef>(transformedPath);
 }
 
 @end