GL_EXT_stencil_two_side
https://www.khronos.org/registry/OpenGL/extensions/EXT/EXT_stencil_two_side.txt
GL_EXT_stencil_two_side

	GL_STENCIL_TEST_TWO_SIDE_EXT 0x8910
	GL_ACTIVE_STENCIL_FACE_EXT 0x8911
	void glActiveStencilFaceEXT (GLenum face)