问题
I'm creating an iPad app for 3.2 and later. My app has an overlay view which has a semi-transparency that makes everything below it darker. In the middle of this view I am chopping a hole in this semi-transparency to let part of the background filter through unscathed, with this code:
- (void)drawRect:(CGRect)rect {
CGContextRef context = UIGraphicsGetCurrentContext();
CGRect intersection = CGRectIntersection(hole.frame, rect);
CGContextClearRect(context, intersection);
}
Additionally, the 'hole' view has rounded corners, applied via:
self.layer.cornerRadius = 4.25;
This works great except for one small problem - these rounded corners are not taken into account, so the hole that gets chopped out has square corners instead of rounded. I need to fix this, but I have no idea how. Any ideas, examples, thoughts?
回答1:
Here's how I ended up getting it to work. This produces a hole with the same frame as the 'hole' UIView, cutting it out from self (UIView). This lets you see whatever is behind the 'hole' unhindered.
- (void)drawRect:(CGRect)rect {
CGFloat radius = self.hole.layer.cornerRadius;
CGRect c = self.hole.frame;
CGContextRef context = UIGraphicsGetCurrentContext();
// this simply draws a path the same shape as the 'hole' view
CGContextMoveToPoint(context, c.origin.x, c.origin.y + radius);
CGContextAddLineToPoint(context, c.origin.x, c.origin.y + c.size.height - radius);
CGContextAddArc(context, c.origin.x + radius, c.origin.y + c.size.height - radius, radius, M_PI_4, M_PI_2, 1);
CGContextAddLineToPoint(context, c.origin.x + c.size.width - radius, c.origin.y + c.size.height);
CGContextAddArc(context, c.origin.x + c.size.width - radius, c.origin.y + c.size.height - radius, radius, M_PI_2, 0.0f, 1);
CGContextAddLineToPoint(context, c.origin.x + c.size.width, c.origin.y + radius);
CGContextAddArc(context, c.origin.x + c.size.width - radius, c.origin.y + radius, radius, 0.0f, -M_PI_2, 1);
CGContextAddLineToPoint(context, c.origin.x + radius, c.origin.y);
CGContextAddArc(context, c.origin.x + radius, c.origin.y + radius, radius, -M_PI_2, M_PI, 1);
// finish
CGContextClosePath(context);
CGContextClip(context); // this is the secret sauce
CGContextClearRect(context, c);
}
回答2:
What you're trying to do is called masking. You can use Core Graphics to mask the current graphics context. See Apple's documentation on the subject here:
http://developer.apple.com/library/ios/documentation/GraphicsImaging/Conceptual/drawingwithquartz2d/dq_images/dq_images.html#//apple_ref/doc/uid/TP30001066-CH212-CJBHDDBE
回答3:
If you change the cornerRadius
property of a layer, you must also set clipsToBounds
to YES
on the associated view in order for the content to be clipped to the rounded corners.
来源:https://stackoverflow.com/questions/4349400/how-can-i-remove-a-uiview-with-rounded-corners-from-its-parent-view