Question

Is there any efficient way to fetch texture data in a random way? That is, I’d like to use a texture as a look-up table and I need random access to its elements. Therefore I’d be sampling it in a random fashion. Is it a completely lost cause?

Answer 1

Random access is a basic feature of GLSL. E.g.

vec2 someLocation = ... whatever you like ...;
vec4 sampledColour = texture2D(sampler, someLocation);

Depending on your hardware, it may cost more to read a texture if you’ve calculated the sample locations directly in the pixel shader rather than out in the vertex shader and allowed them to be interpolated automatically as a varying, but that’s just an immutable hardware cost relating to the decreased predictability of what you’re doing.