Native bindings to the KHR_blend_equation_advanced extension.

This extension adds a number of "advanced" blending equations that can be used to perform new color blending operations, many of which are more complex than the standard blend modes provided by unextended OpenGL. This extension provides two different extension string entries:

• KHR_blend_equation_advanced:Provides the new blending equations, but guarantees defined results only if each sample is touched no more than once in any single rendering pass. The command BlendBarrierKHR is provided to indicate a boundary between passes.
• KHR_blend_equation_advanced_coherent: Provides the new blending equations, and guarantees that blending is done coherently and in API primitive order. An enable is provided to allow implementations to opt out of fully coherent blending and instead behave as though only KHR_blend_equation_advanced were supported.

Some implementations may support KHR_blend_equation_advanced without supporting KHR_blend_equation_advanced_coherent.

In unextended OpenGL, the set of blending equations is limited, and can be expressed very simply. The MIN and MAX blend equations simply compute component-wise minimums or maximums of source and destination color components. The FUNC_ADD, FUNC_SUBTRACT, and FUNC_REVERSE_SUBTRACT multiply the source and destination colors by source and destination factors and either add the two products together or subtract one from the other. This limited set of operations supports many common blending operations but precludes the use of more sophisticated transparency and blending operations commonly available in many dedicated imaging APIs.

This extension provides a number of new "advanced" blending equations. Unlike traditional blending operations using the FUNC_ADD equation, these blending equations do not use source and destination factors specified by BlendFunc. Instead, each blend equation specifies a complete equation based on the source and destination colors. These new blend equations are used for both RGB and alpha components; they may not be used to perform separate RGB and alpha blending (via functions like BlendEquationSeparate).

These blending operations are performed using premultiplied source and destination colors, where RGB colors produced by the fragment shader and stored in the framebuffer are considered to be multiplied by alpha (coverage). Many of these advanced blending equations are formulated where the result of blending source and destination colors with partial coverage have three separate contributions: from the portions covered by both the source and the destination, from the portion covered only by the source, and from the portion covered only by the destination. Such equations are defined assuming that the source and destination coverage have no spatial correlation within the pixel.

In addition to the coherency issues on implementations not supporting KHR_blend_equation_advanced_coherent, this extension has several limitations worth noting. First, the new blend equations are not supported while rendering to more than one color buffer at once; an INVALID_OPERATION will be generated if an application attempts to render any primitives in this unsupported configuration. Additionally, blending precision may be limited to 16-bit floating-point, which could result in a loss of precision and dynamic range for framebuffer formats with 32-bit floating-point components, and in a loss of precision for formats with 12- and 16-bit signed or unsigned normalized integer components.

Requires GLES 2.0 and EXT_blend_minmax.