GL_SGIS_texture_filter4
https://www.khronos.org/registry/OpenGL/extensions/SGIS/SGIS_texture_filter4.txt
GL_SGIS_texture_filter4

	void glGetTexFilterFuncSGIS (GLenum target, GLenum filter, GLfloat* weights)
	void glTexFilterFuncSGIS (GLenum target, GLenum filter, GLsizei n, const GLfloat* weights)
