Native bindings to the EXT_blend_func_extended extension.

This extension provides an ES version of the ARB_blend_func_extended functionality.

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.

Because of the limitations of the OpenGL ES 2.0 shading language, new built-in variables (gl_SecondaryFragColorEXT, gl_SecondaryFragDataEXT) are added to the ES 1.00 shading language rather than introduce more complex features for user-defined fragment outputs. Because such built-in variable are deprecated in ES 3.0, these variables are NOT available in the OpenGL ES 3.xx shading language verisons.