UnityShader使用图像叠加实现运动模糊

using UnityEngine;
using System.Collections;
 
public class Translating : MonoBehaviour {
 
 public float speed = 10.0f;
 public Vector3 startPoint = Vector3.zero;
 public Vector3 endPoint = Vector3.zero;
 public Vector3 lookAt = Vector3.zero;
 public bool pingpong = true;
 
 private Vector3 curEndPoint = Vector3.zero;
 
 // Use this for initialization
 void Start () {
 transform.position = startPoint;
 curEndPoint = endPoint;
 }
 
 // Update is called once per frame
 void Update () {
 transform.position = Vector3.Slerp(transform.position, curEndPoint, Time.deltaTime * speed);
 transform.LookAt(lookAt);
 if (pingpong) {
 if (Vector3.Distance(transform.position, curEndPoint) < 0.001f) {
 curEndPoint = Vector3.Distance(curEndPoint, endPoint) < Vector3.Distance(curEndPoint, startPoint) ? startPoint : endPoint;
 }
 }
 }
}

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
 
public class MotionBlur : PostEffectsBase
{
 
 public Shader MotionBlurShader;
 private Material _motionBlurMaterial = null;
 
 public Material Material
 {
  get
  {
   _motionBlurMaterial = CheckShaderAndCreateMaterial(MotionBlurShader, _motionBlurMaterial);
   return _motionBlurMaterial;
  }
 } 
 
 //定义运动模糊在混合图像时使用的模糊参数,值越大，拖尾越明显，但过大会完全替代当前帧的渲染结果，所以最大为0.9
 [Range(0.0f, 0.9f)] public float BlurAmount = 0.5f;
 
 //定义一个RenderTexture类型的变量，保存之前图像叠加的结果
 private RenderTexture _accumulationTexture;
 //当脚本不运行时，立即销毁，这样在下一次开始运行时会重新叠加图像
 void OnDisable()
 {
  DestroyImmediate(_accumulationTexture);
 }
 
 void OnRenderImage(RenderTexture src, RenderTexture dest)
 {
  if (Material != null)
  {
   //判断用于混合图像的_accumulationTexture是否为空，或者是否与当前屏幕分辨率相等
   //如果不满足，需要重新创建
   if (_accumulationTexture == null || _accumulationTexture.width != src.width ||
    _accumulationTexture.height != src.height)
   {
    //立即销毁当前_accumulationTexture
    DestroyImmediate(_accumulationTexture);
    //创建一个与当前屏幕分辨率相等的
    _accumulationTexture = new RenderTexture(src.width, src.height, 0);
    //由于我们自己控制这个变量的销毁，所以不需要他显示在Hierarchy中，也不需要保存在场景中
    _accumulationTexture.hideFlags = HideFlags.HideAndDontSave;
    //使用当前的帧图像初始化_accumulationTexture
    Graphics.Blit(src, _accumulationTexture);
   }
 
   //对渲染纹理进行恢复操作，发生在渲染的纹理而该纹理又没有被提前清空或销毁的情况下
   //运动模糊每次调用OnRenderImage函数，都需要把当前纹理与_accumulationTexture中的图像混合，所以_accumulationTexture不需要被提前清空
   _accumulationTexture.MarkRestoreExpected();
 
   //将参数传给材质
   Material.SetFloat("_BlurAmount", 1.0f - BlurAmount);
 
   //把当前的屏幕图像叠加到_accumulationTexture
   Graphics.Blit(src, _accumulationTexture, Material);
   //把叠加后的图像输出到屏幕
   Graphics.Blit(_accumulationTexture, dest);
  }
  else
  {
   Graphics.Blit(src, dest);
  }
 }
}

Shader "Unity Shaders Book/Chapter 12/MotionBlur"
{
 Properties
 {
 _MainTex ("Base (RGB)", 2D) = "white" {}
  //混合系数
 _BlurAmount("Blur Amount", Float) = 1.0
 }
 SubShader
 {
 CGINCLUDE
 #include "UnityCG.cginc"
 
 sampler2D _MainTex;
 fixed _BlurAmount;
 
 //定义顶点着色器
 struct v2f {
 float4 pos : SV_POSITION;
 half2 uv : TEXCOORD0;
 };
 
 v2f vert(appdata_img v) {
 v2f o;
 o.pos = UnityObjectToClipPos(v.vertex);
 o.uv = v.texcoord;
 return o;
 }
 
 //定义第一个片元着色器，用于更新渲染纹理的RGB通道部分
 fixed4 fragRGB(v2f i) : SV_Target{
 //将A通道的值设为_BlurAmount,这样在后面混合时可直接使用透明通道进行混合
 return fixed4(tex2D(_MainTex, i.uv).rgb, _BlurAmount);
 }
 
 //定义第二个片元着色器，用于更新渲染纹理的A通道部分
 half4 fragA(v2f i) : SV_Target{
 //直接返回采样结果，为了维护渲染纹理的透明通道值，不让其受到混合时使用的透明度值的影响
 return tex2D(_MainTex, i.uv);
 }
 
 ENDCG
 
 ZTest Always Cull Off Zwrite Off
 //第一个Pass,用于更新渲染纹理的RGB通道
 Pass
 {
 Blend SrcAlpha OneMinusSrcAlpha
 ColorMask RGB
 CGPROGRAM
 #pragma vertex vert
 #pragma fragment fragRGB
 ENDCG
 }
 
 //第二个Pass,用于更新渲染纹理的A通道
 Pass
 {
 Blend One Zero
 ColorMask A
 CGPROGRAM
 #pragma vertex vert
 #pragma fragment fragA
 ENDCG
 }
 }
 Fallback Off
}