grayscale.gxsl

//This shader takes a color from prev and makes it greyscale.
GX_ACCESS prev x -> reg3
GX_ACCESS prev y -> reg4
GX_ACCESS prev z -> reg5
//OK, prev is now exploded into reg3, reg4, and reg5
GX_ADD reg3 reg4 -> reg6
GX_ADD reg6 reg5 -> reg6
GX_DIV reg6 3 -> reg6
//construct a vec4 and store it in the prev register
GX_CALL_CONSTRUCT_VEC4 reg6 reg6 reg6 1 -> prev
//This should turn into:
//reg3 = prev.x;
//reg4 = prev.y;
//reg5 = prev.z;
//reg6 = reg3 + reg4;
//reg6 = reg6 + reg5;
//reg6 = reg6/3;
//prev = vec4(reg6,reg6,reg6,1);