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 |
| GL_MIN | min(Cs, Cd) |
| GL_MAX | max(Cs, 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.