func PointSize(size float32) {
	syscall.Syscall(gpPointSize, 1, uintptr(math.Float32bits(size)), 0, 0)
}
func PointSize(size float32) {
	syscall.Syscall(gpPointSize, 1, uintptr(math.Float32bits(size)), 0, 0)
}
// specify the diameter of rasterized points