GL_EXT_texture_rg
https://www.khronos.org/registry/OpenGL/extensions/EXT/EXT_texture_rg.txt
GL_EXT_texture_rg

	GL_RED_EXT 0x1903
	GL_RG_EXT 0x8227
	GL_R8_EXT 0x8229
	GL_RG8_EXT 0x822B