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（附有注释）：
<pre><code>
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<linePoints.Length;i++)
{
Vector2 dis=new Vector2(moveDistance.x,moveDistance.y);
linePoints[i]+=dis;
}
//销毁当前画下的线
Vector.DestroyLine(ref line);
//距离平移后，所有的点的位置已经重新获得，重新画下新的线
line = new VectorLine("DrawnLine", linePoints, lineMaterial, lineWidth, LineType.Continuous);
line.minDrawIndex = 1;
line.maxDrawIndex = lineIndex;
Vector.DrawLine(line);
}
boardPosition=Camera.mainCamera.WorldToScreenPoint(board.transform.position);
//平板的缩放操作，对平板进行缩放，同时画出的线也要能够实现缩放。
//检测平板是否已经开始缩放
float currentScale=board.transform.localScale.x;
float scaleFactor=currentScale/(boardScale.x);
//Debug.Log("scaleFactor "+scaleFactor+" currentScale "+currentScale+" boardScale "+boardScale.x);
boardScale=board.transform.localScale;
if(scaleFactor!=1||scaleFactor!=1)
{
// 求出画板中心的位置
Vector3 boardPostionToSceern=Camera.mainCamera.WorldToScreenPoint(board.transform.position);
//当平板缩放时，所有的点都要同比例缩放。
for(int i=0;i<linePoints.Length;i++)
{
Vector3 pointPositon=new Vector3(linePoints[i].x,linePoints[i].y,0);
Vector3 PointToCenterDistance=(pointPositon-boardPostionToSceern)*scaleFactor;
linePoints[i]=new Vector2((boardPostionToSceern+PointToCenterDistance).x,(boardPostionToSceern+PointToCenterDistance).y);
}
//销毁当前画下的线
Vector.DestroyLine(ref line);
//画板缩放后，所有的点的位置已经重新获得，重新画下新的线
line = new VectorLine("DrawnLine", linePoints, lineMaterial, lineWidth, LineType.Continuous);
line.minDrawIndex = 1;
line.maxDrawIndex = lineIndex;
Vector.DrawLine(line);
}
//从摄像头发出一条射线
Ray ray=Camera.mainCamera.ScreenPointToRay(Input.mousePosition);
RaycastHit hit;
if(Physics.Raycast(ray,out hit,1000))
{
//检测到物体时才开始画
if(hit.transform.gameObject.name=="drawing")
{
if (Input.GetMouseButtonDown(0))
{
// Vector.ZeroPointsInLine(line);
// line.minDrawIndex = lineIndex;
// Vector.DrawLine(line);
// linePoints[lineIndex] = mousePos;
previousPosition = mousePos;
lineIndex++;
linePoints[lineIndex] = mousePos;
canDraw = true;
}
else if (Input.GetMouseButton(0) && (mousePos - previousPosition).sqrMagnitude > sqrMinPixelMove && canDraw)
{
previousPosition = linePoints[++lineIndex] = mousePos;
line.minDrawIndex = lineIndex - 1;
line.maxDrawIndex = lineIndex;
if (lineIndex >= maxPoints - 1) canDraw = false;
Vector.DrawLine(line);
}
}
}
</code></pre>
