GL_NV_fog_distance
http://www.opengl.org/registry/specs/gl/NV/fog_distance.txt
GL_NV_fog_distance
	GL_FOG_DISTANCE_MODE_NV 0x855A
	GL_EYE_RADIAL_NV 0x855B
	GL_EYE_PLANE_ABSOLUTE_NV 0x855C