[ios][platform_view]use cashapelayer as the backing layer for mask view

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

@@ -255,12 +255,12 @@ @interface FlutterClippingMaskView ()
 // information about screen scale.
 @property(nonatomic) CATransform3D reverseScreenScale;
 
-- (fml::CFRef<CGPathRef>)getTransformedPath:(CGPathRef)path matrix:(CATransform3D)matrix;
+- (void)addTransformedPath:(CGPathRef)path matrix:(CATransform3D)matrix;
 
 @end
 
 @implementation FlutterClippingMaskView {
-  std::vector<fml::CFRef<CGPathRef>> paths_;
+  CGMutablePathRef pathSoFar_;
 }
 
 - (instancetype)initWithFrame:(CGRect)frame {
@@ -271,15 +271,32 @@ - (instancetype)initWithFrame:(CGRect)frame screenScale:(CGFloat)screenScale {
   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 {
-  paths_.clear();
+  CGPathRelease(pathSoFar_);
+  pathSoFar_ = CGPathCreateMutable();
+  [self shapeLayer].path = nil;
   [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.
@@ -289,28 +306,13 @@ - (BOOL)pointInside:(CGPoint)point withEvent:(UIEvent*)event {
   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);
-  paths_.push_back([self getTransformedPath:path matrix:matrixInPoints]);
+  [self addTransformedPath:path matrix:matrixInPoints];
 }
 
 - (void)clipRRect:(const SkRRect&)clipSkRRect matrix:(const SkMatrix&)matrix {
@@ -379,7 +381,7 @@ - (void)clipRRect:(const SkRRect&)clipSkRRect matrix:(const SkMatrix&)matrix {
   // 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.
-  paths_.push_back([self getTransformedPath:pathRef matrix:matrixInPoints]);
+  [self addTransformedPath:pathRef matrix:matrixInPoints];
 }
 
 - (void)clipPath:(const SkPath&)path matrix:(const SkMatrix&)matrix {
@@ -444,15 +446,15 @@ - (void)clipPath:(const SkPath&)path matrix:(const SkMatrix&)matrix {
   // The `matrix` is based on the physical pixels, convert it to UIKit points.
   CATransform3D matrixInPoints =
       CATransform3DConcat(flutter::GetCATransform3DFromSkMatrix(matrix), _reverseScreenScale);
-  paths_.push_back([self getTransformedPath:pathRef matrix:matrixInPoints]);
+  [self addTransformedPath:pathRef matrix:matrixInPoints];
 }
 
-- (fml::CFRef<CGPathRef>)getTransformedPath:(CGPathRef)path matrix:(CATransform3D)matrix {
+- (void)addTransformedPath:(CGPathRef)path matrix:(CATransform3D)matrix {
   CGAffineTransform affine =
       CGAffineTransformMake(matrix.m11, matrix.m12, matrix.m21, matrix.m22, matrix.m41, matrix.m42);
-  CGPathRef transformedPath = CGPathCreateCopyByTransformingPath(path, &affine);
+  CGPathAddPath(pathSoFar_, &affine, path);
+  [self shapeLayer].path = pathSoFar_;
   CGPathRelease(path);
-  return fml::CFRef<CGPathRef>(transformedPath);
 }
 
 @end