【原创】使用Unity在屏幕上画个框

直接放在相机上！　　

Unity3D使用的图形引擎是DirectX，OpenGL和自带的APi（Wii），这里使用OpenGL的渲染方式

（使用过OpenGl的应该相对容易理解。另外：代码中使用Shader是因为矩形框中部的透明部分需要）　
using UnityEngine;
using System.Collections;

public class NewBehaviourScript : MonoBehaviour {

 private Vector2 mMouseStart, mMouseEnd; 
 private bool mBDrawMouseRect; 
 
 private Material rectMat = null;//画线的材质 不设定系统会用当前材质画线 结果不可控 
 
 void Start() 
 { 
  
  mBDrawMouseRect = false; 
  
  rectMat = new Material("Shader \"Lines/Colored Blended\" {" + 
                         "SubShader { Pass { " + 
                         "    Blend SrcAlpha OneMinusSrcAlpha " + 
                         "    ZWrite Off Cull Off Fog { Mode Off } " + 
                         "    BindChannels {" + 
                         "      Bind \"vertex\", vertex Bind \"color\", color }" + 
                         "} } }");//生成画线的材质 
  rectMat.hideFlags = HideFlags.HideAndDontSave; 
  rectMat.shader.hideFlags = HideFlags.HideAndDontSave; 
 } //Unity3D教程手册：www.unitymanual.com
 
 void Update() 
 { 
  if (Input.GetMouseButtonDown(0)) 
   //按下鼠标左键 
  { 
   Vector3 mousePosition = Input.mousePosition; 
   mMouseStart = new Vector2(mousePosition.x, mousePosition.y); 
  } 
  
  if (Input.GetMouseButton(0)) 
   //持续按下鼠标左键 
  { 
   mBDrawMouseRect = true; 
   Vector3 mousePosition = Input.mousePosition; 
   mMouseEnd = new Vector2(mousePosition.x, mousePosition.y); 
  } 
  
  if (Input.GetMouseButtonUp(0))