建立射線，如下，表示只在2D  layer下建立射線，表示只能檢測2D下的物件

	        Ray ray =  Camera.main.ScreenPointToRay( Input.mousePosition );
		RaycastHit _hitItem;
		int layer = 1 << LayerMask.NameToLayer("2D");
		if( Physics.Raycast( ray, out _hitItem ,Mathf.Infinity,layer) )//只接收2Dlayer下的碰撞物件
		{
			_ContentsPanel.transform.position = _hitItem.point;
			transform.position = _hitItem.point;
		}
 

建立射線，檢測所有射線碰撞到的物件

                        Ray ray = Camera.main.ScreenPointToRay( Input.mousePosition );
			RaycastHit hit;
			if( Physics.Raycast( ray, out hit ) )
			{}