I didn't test this (basically cut and pasted from some existing code I have)
but it should run plenty fast
#define RGB_BYTES_PER_PIXEL 3
- (NSBitmapImageRep *) noiseImageRepWithBaseRed:(float) inRed
green:(float) inGreen
blue:(float) inBlue
width:(NSUInteger) inWidth
height:(NSUInteger) inHeight
{
NSUInteger resultSize = RGB_BYTES_PER_PIXEL *
width * height;
// allocate buffer, init pointers and convert input floats to 8 bit ints
unsigned char *buffer = (unsigned char *)
calloc(resultSize, 1),
*pr =
buffer,
*pg = pr +
1,
*pb = pg +
1,
*e =
buffer + resultSize - RGB_BYTES_PER_PIXEL;
r = inRed
* 255,
g =
inGreen * 255,
b =
inBlue * 255,
noise;
// it looked from your code that you only wanted the random
// number to contribute 10% to the color, so if you pre-divide
// the byte max (255) by 10 here, that's one less calculation
// needed inside the loop
float byteMax = 26;
// seed the random function
srandom(time(0));
// add random value to source rgb values
while (pr < e)
{
noise = ((float)random() * byteMax);
// add noise to r,g,b values, save in buffer and increment
pointer to next slot
*pr = r + noise; pr += RGB_BYTES_PER_PIXEL;
*pg = g + noise; pg += RGB_BYTES_PER_PIXEL;
*pb = b + noise; pb += RGB_BYTES_PER_PIXEL;
}
// now create an image rep with your raw byte array
NSBitmapImageRep *result = [[[NSBitmapImageRep alloc]
initWithBitmapDataPlanes: &buffer
pixelsWide: inWidth
pixelsHigh: inHeight
bitsPerSample: 8
samplesPerPixel: RGB_BYTES_PER_PIXEL
hasAlpha: NO
isPlanar: NO
colorSpaceName: NSCalibratedRGBColorSpace
bytesPerRow: RGB_BYTES_PER_PIXEL * width
bitsPerPixel: RGB_BYTES_PER_PIXEL * 8] autorelease];
NSLog(@"result: %@", result);
// clean up
free(buffer);
return result;
}
On Jun 14, 2011, at 6:20 PM, Stephen Blinkhorn wrote:
> Thanks for all the Core Image tips. Completely missed that somehow. At the
> moment I'm drawing a lot of stuff into CGLayers to save redrawing the same
> thing over and over. I see CIImage provides imageWithCGLayer: so this could
> be very fruitful.
>
> Thanks!
> Stephen
>
> On 14 Jun 2011, at 16:07, Quincey Morris wrote:
>
>> On Jun 14, 2011, at 14:56, Stephen Blinkhorn wrote:
>>
>>> I'm looking to fill a large custom view with noise. The solution I have
>>> arrived at so far is taking much too long to draw for it to be useable.
>>> Does anyone know any better ways of achieving this in Cocoa? The basic idea
>>> is to add an amount of noise to a base color pixel by pixel, for example:
>>
>> Have you looked into using Core Image, e.g. the CIRandomGenerator filter
>> composited onto an image filled with the base color?
>>
>> For something trivial (in Core Image terms) like this, there's a fairly
>> steep learning curve, but the point of Core Image *is* performance.
>
>
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