mask UIImage

gistfile1.txt

#define Mask8(__x__) ((__x__) & 0xFF)
#define R(__x__)     (Mask8(__x__))
#define G(__x__)     (Mask8(__x__ >> 8))
#define B(__x__)     (Mask8(__x__ >> 16))
#define A(__x__)     (Mask8(__x__ >> 24))
#define __RGBA(r, g, b, a)       (Mask8(r) | Mask8(g)<<8 | Mask8(b)<<16 | Mask8(a)<<24)

- (UIImage *)maskImage:(UIImage *)maskImage {
    if (!maskImage) {
        return self;
    }
    
    UInt32 *inputPixels;
    UInt32 *maskPixels;
    
    CGImageRef maskImageRef = [maskImage CGImage];
    CGImageRef inputImageRef = [self CGImage];
    NSUInteger inputWidth = CGImageGetWidth(inputImageRef);
    NSUInteger inputHeight = CGImageGetHeight(inputImageRef);
    
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    
    NSUInteger bytesPerPixel = 4;
    NSUInteger bitsPerComponent = 8;
    
    NSUInteger inputBytesPerRow = bytesPerPixel * inputWidth;
    
    inputPixels = (UInt32 *)calloc(inputHeight * inputWidth, sizeof(UInt32));
    maskPixels = (UInt32 *)calloc(inputHeight * inputWidth, sizeof(UInt32));
    
    CGContextRef context = CGBitmapContextCreate(inputPixels, inputWidth, inputHeight, bitsPerComponent, inputBytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
    CGContextDrawImage(context, CGRectMake(0, 0, inputWidth, inputHeight), inputImageRef);
    
    CGContextRef maskContext = CGBitmapContextCreate(maskPixels, inputWidth, inputHeight, bitsPerComponent, inputBytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
    CGContextDrawImage(maskContext, CGRectMake(0, 0, inputWidth, inputHeight), maskImageRef);
    
    for (NSUInteger i = 0; i<inputHeight; i++) {
        for (NSUInteger j = 0; j<inputWidth; j++) {
            
            UInt32 *currentPixel = inputPixels + (i*inputWidth)+j;
            UInt32 *currentMaskPixel = maskPixels + (i * inputWidth)+j;
            
            UInt32 color = *currentMaskPixel;
            
            NSInteger alpha = A(color);
            if (alpha != 0) {
                *currentPixel = __RGBA(0, 0, 0, 0);
            }
        }
    }
    
    CGImageRef destImageRef = CGBitmapContextCreateImage(context);
    UIImage *destImage = [UIImage imageWithCGImage:destImageRef];
    
    CGColorSpaceRelease(colorSpace);
    CGContextRelease(context);
    CGContextRelease(maskContext);
    free(inputPixels);
    free(maskPixels);
    
    return destImage;
}