OpenGL Programming Guide: The Official Guide to Learning OpenGL, Version 4.3, Eighth Edition

The Blending Equation

With standard blending, colors in the framebuffer are combined (using addition) with incoming fragment colors to produce the new framebuffer color. Either glBlendEquation() or glBlendEquationSeparate() may be used to select other mathematical operations to compute the difference, minimum, or maximum between color fragments and framebuffer pixels.

void glBlendEquation(GLenum mode);void glBlendEquationi(GLuint buffer, GLenum mode);

Specifies how framebuffer and source colors are blended together. The allowable values for mode are GL_FUNC_ADD (the default), GL_FUNC_SUBTRACT, GL_FUNC_REVERSE_SUBTRACT, GL_MIN, and GL_MAX. The possible modes are described in Table 4.4.

Table 4.4. Blending Equation Mathematical Operations