void glBlendEquation(GLenum mode)
Blending combines corresponding source and destination color components according to the blending operation specified by the mode. The blend equations are:
|GL_FUNC_ADD||min(Cs*sf + Cd*df, 1)|
|GL_FUNC_SUBTRACT||max(Cs*sf - Cd*df, 0)|
|GL_FUNC_REVERSE_SUBTRACT||max(Cd*df - Cs*sf, 0)|
|GL_LOGIC_OP||Cs Lop Cd|
where Cs and Cd are the source and destination color components, respectively; sf and df are the source and destination blending factors are specified by glBlendFunc; Lop is one of the 16 bitwise operators specified by glLogicOp.