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Perlin noise
Wednesday, December 18, 2002 | Permalink

Executable
Source code
PerlinNoise.zip (88 KB)

Required:
GL_ARB_fragment_program
This demos does perlin noise in a fragment program. The output of the demo doesn't look like much, but it isn't nearly as interesting as the fact that you can actually do this kind of stuff in a fragment program. There is a wide range of applications to Perlin noise, especially in graphics. I already have an idea how to use it in a more useful manner.

For doing Perlin noise you use a table of random values on which you apply a band pass filter. In this case the table is obviously a texture. In order to reduce the amount of texture accesses I have instead of just using a single channel texture mirrored the neighbor values in the other channels. So R it this texel, G is the one to the right, B is the one below and A is below right. This way I only need 2 texture accesses instead of 8 for each pixel.
This demo does the 2D noise function, but extending it to the 3D version should be straight-forward, with performance implication of course though. To get some kind of animation in this demo I just let the output be a simple function of the Perlin function and time.