Efficient pixel shader when only u-axis varies?

Question

I'm writing a pixel shader that has the property where for a given quad the values returned only vary by u-axis value. I.e. for a fixed u, then the color output is constant as v varies.

The computation to calculate the color at a pixel is relatively expensive - i.e. does multiple samples per pixel / loops etc..

Is there a way to take advantage of the v-invariance property? If I was doing this on a CPU then you'd obviously just cache the values once calculated but guess that doesn't apply because of parallelism. It might be possible for me to move the texture generation to the CPU side and have the shader access a Texture1D but I'm not sure how fast that will be.

Is there a paradigm that fits this situation on GPU cards?

cheers

Answer 1

Storing your data in a 1D texture and sampling it in your pixel shader looks like a good solution. Your GPU will be able to use texture caching features, allowing it to make use of the fact that many of you pixels are using the same value from your 1D texture. This should be really fast, texture fetching and caching is one of the main reasons your gpu is so efficient at rendering.

It is commonpractice to make a trade-off between calculating the value in the pixel shader, or using a lookup table texture. You are doing complex calculations by the sound of it, so using a lookup texture with certainly improve performance.

Note that you could still generate this texture by the GPU, there is no need to move it to the CPU. Just render to this 1D texture using your existing shader code as a prepass.