理解 Unity3D RenderWithShader Api

主要参考：

unity, 替换shader渲染（Rendering with Replaced Shaders） ： http://www.cnblogs.com/wantnon/p/4528677.html

测试例子：

Test.cs挂到Camera上

using UnityEngine;
using System.Collections;

public class Test1 : MonoBehaviour {

    private Camera shaderCamera;
    private RenderTexture replaceRenderTexture;

    public void Start()
    {
        shaderCamera = new GameObject("Test", typeof(Camera)).GetComponent<Camera>();
        Camera origCamera = GetComponent<Camera>();
        replaceRenderTexture = new RenderTexture((int)origCamera.pixelWidth, (int)origCamera.pixelHeight, 16, RenderTextureFormat.ARGB32);
        replaceRenderTexture.wrapMode = TextureWrapMode.Clamp