#define GU_SRC_COLOR (0)
#define GU_DST_COLOR (0)
#define GU_ONE_MINUS_SRC_COLOR (1)
#define GU_ONE_MINUS_DST_COLOR (1)

#define GU_OTHER_COLOR (0) // dstColor if used for source operand; srcColor if used for destination operand
#define GU_ONE_MINUS_OTHER_COLOR (1) // 1-dstColor if used for source operand; 1-srcColor if used for destination operand

#define GU_DOUBLE_SRC_ALPHA (6)           // 2*srcAlpha
#define GU_ONE_MINUS_DOUBLE_SRC_ALPHA (7) // 1-2*srcAlpha
#define GU_DOUBLE_DST_ALPHA (8)           // 2*dstAlpha
#define GU_ONE_MINUS_DOUBLE_DST_ALPHA (9) // 1-2*dstAlpha