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