func StencilFunc(xfunc uint32, ref int32, mask uint32) {
	syscall.Syscall(gpStencilFunc, 3, uintptr(xfunc), uintptr(ref), uintptr(mask))
}
func StencilFunc(xfunc uint32, ref int32, mask uint32) {
	syscall.Syscall(gpStencilFunc, 3, uintptr(xfunc), uintptr(ref), uintptr(mask))
}
// set front and back function and reference value for stencil testing