unity3D 从摄像机发射射线，检测画线

                最近做项目的时候，有一个需要从摄像机发出一条射线，当射线检测到有碰撞物体的时候，点击鼠标左键开始画线。我是创立了一个平板drawing，当然Cube什么的也是可以的。

                c#脚本代码，将这个脚本拖到摄像机里，然后拖拽材质到画线材质，拖拽碰撞体到脚本那里即可以。

                代码脚本：

using UnityEngine;
using System.Collections;

public class test : MonoBehaviour {

    //-----------划线所能够用到材质
     public Material lineMaterial  ;
	//
      int maxPoints = 5000;
      //全局变量的定义方法
     public static float lineWidth = 4.0f;
	 int minPixelMove = 2;	// Must move at least this many pixels per sample for a new segment to be recorded
     public Vector2[] linePoints;
     private VectorLine  line ;
     private int  lineIndex = 0;
      private   Vector2   previousPosition;
      private int  sqrMinPixelMove ;
      private bool canDraw = false;
    //记录当下画板的位置，判断平板是否平移等
      public Vector3 boardPosition;
      public GameObject board;
	//记录当下画板的大小，判断画板是否缩放等	
	 public Vector3 boardScale;	
	//初始化平板的大小与位置
	void IntializeScaleAndPosition()
	{
		boardPosition=Camera.mainCamera.WorldToScreenPoint(board.transform.position);
	    boardScale=board.transform.localScale;
		
	}
	// 初始化
	void Start () {
        linePoints = new Vector2[maxPoints];
        line = new VectorLine("DrawnLine", linePoints,lineMaterial, lineWidth, LineType.Continuous);
        sqrMinPixelMove = minPixelMove * minPixelMove;
		IntializeScaleAndPosition();
	}
	// Update is called once per frame
	void Update () {
        Vector2 mousePos = Input.mousePosition;
		//当画板移动时，将所有的点按照统一方向移动相同的距离
		//当前画板的位置
	   Vector3 currentBoardPositon=Camera.mainCamera.WorldToScreenPoint(board.transform.position);
		
		//画板的移动距离
		Vector3  moveDistance=currentBoardPositon-boardPosition;
		
	    if(moveDistance.x!=0||moveDistance.y!=0)
		{
			//将所有的画下的点都平移
			for(int i=0;i sqrMinPixelMove && canDraw)
	        {
	            previousPosition = linePoints[++lineIndex] = mousePos;
	            line.minDrawIndex = lineIndex - 1;
	            line.maxDrawIndex = lineIndex;
	            if (lineIndex >= maxPoints - 1) canDraw = false;
	            Vector.DrawLine(line);
	        }				
		}	
	}