func AlphaFunc(xfunc uint32, ref float32) {
	C.glowAlphaFunc(gpAlphaFunc, (C.GLenum)(xfunc), (C.GLfloat)(ref))
}
func AlphaFunc(xfunc uint32, ref float32) {
	C.glowAlphaFunc(gpAlphaFunc, (C.GLenum)(xfunc), (C.GLfloat)(ref))
}
// specify the alpha test function