Component-wise GLSL vector branching
- by Gustavo Maciel
I'm aware that it usually is a BAD idea to operate separately on GLSL vec's components separately.
For example:
//use instrinsic functions, they do the calculation on 4 components at a time.
float dot = v1.x*v2.x + v1.y * v2.y + v1.z * v2.z; //NEVER
float dot = dot(v1, v2); //YES
//Multiply one by one is not good too, since the ALU can do the 4 components at a time too.
vec3 mul = vec3(v1.x * v2.x, v1.y * v2.y, v1.z * v2.z); //NEVER
vec3 mul = v1 * v2;
I've been struggling thinking, are there equivalent operations for branching?
For example:
vec4 Overlay(vec4 v1, vec4 v2, vec4 opacity)
{
bvec4 less = lessThan(v1, vec4(0.5));
vec4 blend;
for(int i = 0; i < 4; ++i)
{
if(less[i])
blend[i] = 2.0 * v1[i]*v2[i];
else
blend[i] = 1.0 - 2.0 * (1.0 - v1[i])*(1.0 - v2[i]);
}
return v1 + (blend-v1)*opacity;
}
This is a Overlay operator that works component wise. I'm not sure if this is the best way to do it, since I'm afraid these for and if can be a bottleneck later.
Tl;dr, Can I branch component wise? If yes, how can I optimize that Overlay function with it?
