랜던값을 필셀 셰이더에서 얻는 방법

http://stackoverflow.com/questions/5149544/can-i-generate-a-random-number-inside-a-pixel-shader

What you generally do when you want a random value in a pixel shader is to pass in a texture containing noise. While it's not actually "random" - it looks random.

For example, here's some code from a pixel shader I have lying around:

float3 random = (tex2D(noiseTexture, texCoord * noiseScale + noiseOffset));

The texture I use is an RGB-noise texture, which can come in handy some times. But the same technique would work for a grayscale one.

By scaling it I ensure that the pixels in the noise texture line up to on-screen pixels (you may also want to set the texture sampler to "point" mode so you don't blur the noise texture).

By using an offset you can scroll the texture - which is kind of like seeding a random number generator. Use a random offset if you want to avoid that "scrolling" look.