GL_EXT_shader_framebuffer_fetch
https://www.khronos.org/registry/OpenGL/extensions/EXT/EXT_shader_framebuffer_fetch.txt
GL_EXT_shader_framebuffer_fetch

	GL_FRAGMENT_SHADER_DISCARDS_SAMPLES_EXT 0x8A52
	void glFramebufferFetchBarrierEXT (void)