MotionBlur运动模糊

• 首先为accumulationTexture进行一个恢复操作，以取得上一步混合得到的纹理。
• 然后用shader把原图像和上一步的纹理进行混合
• 最后把混合后的纹理显示在屏幕上。

  accumulationTexture.MarkRestoreExpected();
  material.SetFloat("_BlurAmount", 1.0f - blurAmount);
  Graphics.Blit(src, accumulationTexture, material);
  Graphics.Blit(accumulationTexture, dest);
  

  shader混合图像的方式为(last.rgb BlurAmount + src.rgb (1 - blurAmount), last.a)

  Shader "UnityShaderLearning/MotionBlur"
  {
    Properties
    {
        _MainTex ("Base (RGB)", 2D) = "white" {}
        _BlurAmount("Blur Amount", FLoat) = 1.0
    }
    SubShader
    {
        CGINCLUDE
        #include "UnityCG.cginc"
        sampler2D _MainTex;
        fixed _BlurAmount;
        struct v2f
        {
            float4 pos : SV_POSITION;
            half2 uv : TEXCOORD0;
        };
        v2f vert(appdata_img v)
        {
            v2f o;
            o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
            o.uv = v.texcoord;
            return o;
        }
        fixed fragRGB(v2f i) : SV_Target
        {
            return fixed4(tex2D(_MainTex, i.uv).rgb, _BlurAmount);
        }
            half4 fragA(v2f i) : SV_Target
        {
            return tex2D(_MainTex, i.uv);
        }
        ENDCG
        ZTest Always Cull Off ZWrite Off
        Pass
        {
            Blend SrcAlpha OneMinusSrcAlpha
            ColorMask RGB
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment fragRGB
            ENDCG
        }
        Pass
        {
            Blend One Zero
            ColorMask A
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment fragA
            ENDCG
        }
    }
  Fallback Off
  }