iOS 蒙板，图片叠加显示漏空部分

-(UIImage*)maskImage:(UIImage *)image withMask:(UIImage *)maskImage {
    CGImageRef maskRef = maskImage.CGImage;
    CGImageRef mask = CGImageMaskCreate(CGImageGetWidth(maskRef),
                                        CGImageGetHeight(maskRef),
                                        CGImageGetBitsPerComponent(maskRef),
                                        CGImageGetBitsPerPixel(maskRef),
                                        CGImageGetBytesPerRow(maskRef),
                                        CGImageGetDataProvider(maskRef), NULL, false);
    
    CGImageRef sourceImage = [image CGImage];
    CGImageRef imageWithAlpha = sourceImage;
    //add alpha channel for images that don‘t have one (ie GIF, JPEG, etc...)
    //this however has a computational cost
    if (CGImageGetAlphaInfo(sourceImage) == kCGImageAlphaNone) {
//        imageWithAlpha =CopyImageAndAddAlphaChannel(sourceImage);
    }
    
    CGImageRef masked = CGImageCreateWithMask(imageWithAlpha, mask);

    CGImageRelease(mask);
    
        if (sourceImage != imageWithAlpha) {
            CGImageRelease(imageWithAlpha);
        }
    
    UIImage* retImage = [UIImage imageWithCGImage:masked];
    CGImageRelease(masked);
    
    return retImage;
}