[SOLVED] How to use a UIImage as a mask over a color in Objective-C

How to use a UIImage as a mask over a color in Objective-C

I have a UIImage that is all black with an alpha channel so some parts are grayish and some parts are completely see-through. I want to use that images as a mask over some other color (let's say white to make it easy), so the final product is now a white image with parts of it transparent.

I've been looking around on the Apple documentation site here: https://developer.apple.com/library/archive/documentation/GraphicsImaging/Conceptual/drawingwithquartz2d/dq_images/dq_images.html#//apple_ref/doc/uid/TP30001066-CH212-CJBHIJEB

But I don't can't really make sense of those examples.

Solution

In iOS 7+ you should use UIImageRenderingModeAlwaysTemplate instead. See https://stackoverflow.com/a/26965557/870313

Creating arbitrarily-colored icons from a black-with-alpha master image (iOS).

// Usage: UIImage *buttonImage = [UIImage ipMaskedImageNamed:@"UIButtonBarAction.png" color:[UIColor redColor]];

+ (UIImage *)ipMaskedImageNamed:(NSString *)name color:(UIColor *)color
{
    UIImage *image = [UIImage imageNamed:name];
    CGRect rect = CGRectMake(0, 0, image.size.width, image.size.height);
    UIGraphicsBeginImageContextWithOptions(rect.size, NO, image.scale);
    CGContextRef c = UIGraphicsGetCurrentContext();
    [image drawInRect:rect];
    CGContextSetFillColorWithColor(c, [color CGColor]);
    CGContextSetBlendMode(c, kCGBlendModeSourceAtop);
    CGContextFillRect(c, rect);
    UIImage *result = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return result;
}

Credits to Ole Zorn: https://gist.github.com/1102091