func BlendFunc(sfactor uint32, dfactor uint32) {
	syscall.Syscall(gpBlendFunc, 2, uintptr(sfactor), uintptr(dfactor), 0)
}
func BlendFunc(sfactor uint32, dfactor uint32) {
	syscall.Syscall(gpBlendFunc, 2, uintptr(sfactor), uintptr(dfactor), 0)
}
// specify pixel arithmetic