function getDirection(x, y) {
	    if (x === y) {
	        return DIRECTION_NONE;
	    }
	
	    if (abs(x) >= abs(y)) {
	        return x < 0 ? DIRECTION_LEFT : DIRECTION_RIGHT;
	    }
	    return y < 0 ? DIRECTION_UP : DIRECTION_DOWN;
	}
get the direction between two points
@param {Number} x
@param {Number} y
@return {Number} direction