Better solution for boolean mixing?

Question

Sorry if this question has been asked in the past, but searching Google and here didn't yield relevant results, so here goes.

I'm working on a fragment shader that implements both conditional/boolean diffuse and bump mapping (that is to say, you don't need a diffuse texture or a normals texture, and if they're not present, they're simply changed to default values).

My current solution is to use a uniform float to say "mix amount". For example, computing the diffuse texel works as:

// Compute diffuse amount scaled by vCol
// If no texture is present (mDif = 0.0), then DiffuseTexel = vCol
// kT[0] is the diffuse texture
// vTex is the texture co-ordinates
// mDif is the uniform float containing the mix amount (either 0.0 or 1.0)
vec4 DiffuseTexel = vCol*mix(vec4(1.0), texture2D(kT[0], vTex), mDif);

While that works great and all, I was wondering if there's a better way of doing this, as I will never have any use for in-between values for funky effects. I know that perhaps the best solution is to simply write separate shaders for mDif=0.0 and mDif=1.0, but I'd like a more elegant solution than splicing shaders before compiling or writing multiple shader files and keeping each one updated.

Any ideas are greatly appreciated. =)

Answer 1

Branching should be sufficiently fast on modern cards that you don't need to worry about it, and you can always profile it if you think there's a bottleneck. Branching will also make for somewhat more readable code, since your intent is much clearer, and the code you're currently using does imply the possibility of a "25% mix" between the two, for example.

Your current example also causes the texture to be sampled, even if it would be the "default" value, which you could avoid with an actual branch, potentially.

But there's really nothing horrible with your current solution, and if you have a need to support cards/versions that are old enough that branching isn't very fast, it's probably better.