GL_EXT_shadow_samplers
http://www.opengl.org/registry/specs/EXT/shadow_samplers.txt
GL_EXT_shadow_samplers

	GL_TEXTURE_COMPARE_MODE_EXT 0x884C
	GL_TEXTURE_COMPARE_FUNC_EXT 0x884D
	GL_COMPARE_REF_TO_TEXTURE_EXT 0x884E
	GL_SAMPLER_2D_SHADOW_EXT 0x8B62