Masking a transparent image with another actual image in iOS - ios

Question

I have two images, one is a mask that is transparent with some edges / borders and the other is the actual image. I want to merge both of them.
I have used the following code to mask and combine the image:
- (UIImage*) maskImage:(UIImage *)image withMask:(UIImage *)maskImage {
// create a bitmap graphics context the size of the image
CGFloat dim = MIN(image.size.width, image.size.height);
CGSize size = CGSizeMake(dim, dim);
UIGraphicsBeginImageContextWithOptions(size, NO, .0);
UIBezierPath *bezierPath = [UIBezierPath bezierPathWithOvalInRect:(CGRect){ CGPointZero, size }];
[bezierPath fill];
[bezierPath addClip];
CGPoint offset = CGPointMake((dim - image.size.width) * 0.5, (dim - image.size.height) * 0.5);
[image drawInRect:(CGRect){ offset, image.size }];
UIImage *ret = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return ret;
}
The result:
In the result image, the border of the image used as a mask is missing. Can someone please help me with this?

Answer 1

I wrote a masking category for ios (well it is basically cross platform because CoreImage is on both platforms anyway:
github project
the core functionality boils down to this (for your example)
UIImage *person = ...
UIImage *circle = ...
UIImage *result = [person imageMaskedWith:circle];
UIImageView *redbox = [[UIImageView alloc] initWithImage:result];
redbox.backgroundColor = [UIColor redColor]; //this can be a gradient!
the main part of the code from the category:
CGImageRef imageReference = image.CGImage;
CGImageRef maskReference = mask.CGImage;
CGRect rect = CGRectMake(0, 0, CGImageGetWidth(imageReference), CGImageGetHeight(imageReference));
// draw with Core Graphics
UIGraphicsBeginImageContext(rect.size);
CGContextRef bitmap = UIGraphicsGetCurrentContext();
CGContextTranslateCTM(bitmap, 0.0, rect.size.height);
CGContextScaleCTM(bitmap, 1.0, -1.0);
CGContextClipToMask(bitmap, rect, maskReference);
CGContextDrawImage(bitmap, rect, imageReference);
newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();