Remove outside of bezier path

Question

I have a function where I fill the image with a color and use a UIBezierPath to erase a point for corners.

CGRect rect = CGRectMake(0.0f, 0.0f, width, height);
UIGraphicsBeginImageContext(rect.size);
CGContextRef context = UIGraphicsGetCurrentContext();

CGContextSetBlendMode(context, kCGBlendModeCopy);

// Fill image
CGContextSetFillColorWithColor(context, [[UIColor redColor] CGColor]);
CGContextFillRect(context, rect);

// Round corners
UIBezierPath *bezierPath = [UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:15.0];
CGContextSetStrokeColorWithColor(context, [[UIColor clearColor] CGColor]);
[bezierPath stroke];

UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

With the above, I get an image that does have the Bézier path cut out, and the background filled.

However, how can I remove the corners outside of the path, or get at least some way to reference where they are so I can clear them?

Answer 1

A couple of options:

1. Use CoreGraphics, like you have, but clip it to a path:

   CGRect rect = CGRectMake(0.0f, 0.0f, width, height);
   
   UIGraphicsBeginImageContextWithOptions(rect.size, false, 0);
   CGContextRef context = UIGraphicsGetCurrentContext();
   CGContextSetBlendMode(context, kCGBlendModeCopy);
   
   // Round corners
   UIBezierPath *bezierPath = [UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:15.0];
   CGContextAddPath(context, bezierPath.CGPath);
   CGContextClip(context);
   
   // Fill image
   CGContextSetFillColorWithColor(context, [[UIColor redColor] CGColor]);
   CGContextFillRect(context, rect);
   
   UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
   UIGraphicsEndImageContext();
   

2. Alternatively, eliminate CoreGraphics and just fill the UIBezierPath:

   UIGraphicsBeginImageContextWithOptions(rect.size, false, 0);
   [[UIColor redColor] setFill];
   [[UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:15.0] fill];
   UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
   UIGraphicsEndImageContext();
   

Note, in both of those examples, I used UIGraphicsBeginImageContextWithOptions, supplying a scale of 0 (a scale optimized for display on the device in question). If you really want, you can supply a scale of 1, which obviously will be a bit pixelated when rendered on a retina device, but that's up to you.