BezierPath and masking

问题

I want to set up UIBezierPath as mask into my view: The goal is something like this:

So i draw the View with frame:

CGFloat round = 80;
UIView *myView = [[UIView alloc] initWithFrame:CGRectMake(self.frame.size.width/2-105, 0, 210, 60+round)];
myView.backgroundColor = [UIColor redColor];

And then try to add BezierMask:

UIBezierPath *aPath = [UIBezierPath bezierPath];

CGSize viewSize = CGSizeMake(myView.frame.size.width, myView.frame.size.height); //(210,80)
CGPoint startPoint = CGPointMake(myView.frame.origin.x,myView.frame.origin.y); //(279,0)

[aPath moveToPoint:startPoint]; //(279,0)

[aPath addLineToPoint:CGPointMake(startPoint.x+viewSize.width,startPoint.y)]; //(489,0)
[aPath addLineToPoint:CGPointMake(startPoint.x+viewSize.width,startPoint.y+viewSize.height-round)]; //(489,60)
[aPath addQuadCurveToPoint:CGPointMake(startPoint.x,startPoint.y+viewSize.height-round) controlPoint:CGPointMake(startPoint.x+(viewSize.width/2),80)]; //(279,60) : (384,80)

[aPath closePath];

CAShapeLayer *layer = [CAShapeLayer layer];
layer.frame = myView.bounds;
layer.path = aPath.CGPath;
myView.layer.mask = layer;

[self addSubview:myView];

But my view is disappearing after that. Why?

回答1:

I guess you are using improper coordinations for your mask layer. Your mask layer must be positioned within the view which it masks, not in the view's superview.

Try these changes:

CGSize viewSize = myView.bounds.size;
CGPoint startPoint = CGPointZero;

Your code with those little modifications works OK for me.

来源：https://stackoverflow.com/questions/16773753/bezierpath-and-masking