public void step(Direction d) {
		if (moveIsAllowed(d))
			currentDirection = d;

		spriteForDirection(currentDirection);

		if (currentDirection == Direction.UP) {
			motion(0, 0 - speed);
		} else if (currentDirection == Direction.DOWN) {
			motion(0, speed);
		} else if (currentDirection == Direction.LEFT) {
			motion(0 - speed, 0);
		} else if (currentDirection == Direction.RIGHT) {
			motion(speed, 0);
		}
	}