MESA GLSL Notes

tests.glsl

// Ran with MESA_GLSL=dump, "Mesa 11.0.0-devel (git-1bba29e) is supported"

#version 130


uniform vec4 ua;
uniform vec4 ub;

float add(float a, float b) { 

#if 1 // GOOD! (Inlined + this is the only one which does vector math!)
	return a + b;
#endif

#if 0 // OKISH! (Puts a > 0.0 in a temporary)
	float c = mix(a + b, a + b, a > 0.0);
	return mix(c, a + b,  a > 0.0);
#endif

#if 0 // OKISH! (CSEL)
	return mix(a + b, a + b, a > 0.0);
#endif

#if 0 // OKISH! (CSEL, same as before)
	return mix(a + b, a + b, greaterThan(a, 0.0));
#endif

#if 0 // BAD! (IF + ASSIGN)
	return (a > 0.0) ? a + b : a + b;
#endif

#if 0 // BAD! (IF + ASSIGN)
	if (a > 0.0) {
		return a + b;
	} else {
		return a + b;
	}
#endif

}

vec4 add4(vec4 va, vec4 vb) {
#if 0 // TESTS
 return vec4(add(va.x,vb.x),
             add(va.y,vb.y),
             add(va.z,vb.z),
             add(va.w,vb.w));
#endif
#if 1 // GOOD! (Inlined + vector math)
  bvec4 vc = greaterThan(va, vec4(0.0));
  return mix(va, vb, vc);
#endif

}

void main()
{
	gl_Position  = add4(ua,ub);
}