func (d Dir) Vector() (x, y int) {
	switch d {
	case DirUp:
		return 0, -1
	case DirRight:
		return 1, 0
	case DirDown:
		return 0, 1
	case DirLeft:
		return -1, 0
	}
	panic("not reach")
}
func (d Dir) Vector() (x, y int) {
	switch d {
	case DirUp:
		return 0, -1
	case DirRight:
		return 1, 0
	case DirDown:
		return 0, 1
	case DirLeft:
		return -1, 0
	}
	panic("not reach")
}
func ( d Dir ) Vector ( ) ( x , y int ) { switch d { case DirUp : return 0 , - 1 case DirRight : return 1 , 0 case DirDown : return 0 , 1 case DirLeft : return - 1 , 0 } panic ( " " ) }
// Vector returns a [-1, 1] value for each axis.
Vector returns a [ - 1 1 ] value for each axis .