OpenGL extension ARB.blend_func_extended
This module customises the behaviour of the OpenGL.raw.GL.ARB.blend_func_extended to provide a more Python-friendly API
Overview (from the spec)
Traditional OpenGL includes fixed-function blending that combines source colors with the existing content of a render buffer in a variety of ways. A number of extensions have enhanced this functionality by adding further sources of blending weights and methods to combine them. However, the inputs to the fixed-function blending units are constrained to a source color (as output from fragment shading), destination color (as the current content of the frame buffer) or constants that may be used in their place.
This extension adds new blending functions whereby a fragment shader may output two colors, one of which is treated as the source color, and the other used as a blending factor for either source or destination colors. Furthermore, this extension increases orthogonality by allowing the SRC_ALPHA_SATURATE function to be used as the destination weight.
The official definition of this extension is available here:


glBindFragDataLocationIndexed( program , colorNumber , index , name )
glGetFragDataIndex( program , name ) -> <class 'ctypes.c_int'>


GL_SRC1_ALPHA (34185)
GL_SRC1_COLOR (35065)