Native bindings to the EXT_shader_framebuffer_fetch extension.

Conventional OpenGL blending provides a configurable series of operations that can be used to combine the output values from a fragment shader with the values already in the framebuffer. While these operations are suitable for basic image compositing, other compositing operations or operations that treat fragment output as something other than a color (normals, for instance) may not be expressible without multiple passes or render-to-texture operations.

This extension provides a mechanism whereby a fragment shader may read existing framebuffer data as input. This can be used to implement compositing operations that would have been inconvenient or impossible with fixed-function blending. It can also be used to apply a function to the framebuffer color, by writing a shader which uses the existing framebuffer color as its only input.

This extension provides two alternative name strings:

• GL_EXT_shader_framebuffer_fetch guarantees full coherency between framebuffer reads and writes. If this extension string is exposed, the result of reading from the framebuffer from a fragment shader invocation is guaranteed to reflect values written by any previous overlapping samples in API primitive order, unless requested otherwise in the shader source using the noncoherent layout qualifier.
• GL_EXT_shader_framebuffer_fetch_non_coherent provides limited implicit coherency guarantees. Instead, the application is expected to call the FramebufferFetchBarrierEXT command for previous framebuffer writes to become visible to subsequent fragment shader invocations. For this extension to give well-defined results applications may have to split rendering into multiple passes separated with FramebufferFetchBarrierEXT calls. The functionality provided by this extension is requested in the shader source using the noncoherent layout qualifier.

Requires GLES 2.0.