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@kgn
Created June 28, 2012 18:11
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Noise in Cocoa
+ (void)drawNoiseWithOpacity:(CGFloat)opacity inRect:(CGRect)rect{
static UIImage *noiseImage = nil;
static dispatch_once_t oncePredicate;
dispatch_once(&oncePredicate, ^{
NSUInteger width = 64, height = 64;
NSUInteger size = width*height;
char *rgba = (char *)malloc(size); srand(124);
for(NSUInteger i=0; i < size; ++i){rgba[i] = rand()%256;}
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();
CGContextRef bitmapContext =
CGBitmapContextCreate(rgba, width, height, 8, width, colorSpace, kCGImageAlphaNone);
CFRelease(colorSpace);
CGImageRef noiseImageRef = CGBitmapContextCreateImage(bitmapContext);
CFRelease(bitmapContext);
free(rgba);
if([[UIScreen mainScreen] respondsToSelector:@selector(scale)] && [[UIScreen mainScreen] scale] == 2){
noiseImage = [UIImage imageWithCGImage:noiseImageRef scale:2 orientation:UIImageOrientationUp];
}else{
noiseImage = [UIImage imageWithCGImage:noiseImageRef];
}
CGImageRelease(noiseImageRef);
});
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSaveGState(context);
CGContextSetAlpha(context, opacity);
CGContextSetBlendMode(context, kCGBlendModeScreen);
[noiseImage drawAsPatternInRect:rect];
CGContextRestoreGState(context);
}
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