GL_EXT_texture_swizzle http://www.opengl.org/registry/specs/EXT/texture_swizzle.txt GL_EXT_texture_swizzle GL_TEXTURE_SWIZZLE_R_EXT 0x8E42 GL_TEXTURE_SWIZZLE_G_EXT 0x8E43 GL_TEXTURE_SWIZZLE_B_EXT 0x8E44 GL_TEXTURE_SWIZZLE_A_EXT 0x8E45 GL_TEXTURE_SWIZZLE_RGBA_EXT 0x8E46