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

Controlling Blending Factors

You have two different ways to choose the source and destination blending factors. You may call glBlendFunc() and choose two blending factors: the first factor for the source RGBA and the second for the destination RGBA. Or, you may use glBlendFuncSeparate() and choose four blending factors, which allows you to use one blending operation for RGB and a different one for its corresponding alpha.

Note

We also list the functions glBlendFunci() and glBlendFuncSeparatei(), which are used when you’re drawing to multiple buffers simultaneously. This is an advanced topic that we describe in “Framebuffer Objects” on Page 180, but since the functions are virtually identical actions to glBlendFunc() and glBlendFuncSeparate() ...