后处理之径向模糊

　　游戏中为了突出画面震撼或者突出移动速度快时，可以用径向模糊来提升表现的效果。例图如下：

　　

 　　径向模糊的原理是取一个中心点，然后沿着中心点----像素点的方向选取几个点采样，然后该像素点输出这几个采样点的平均值。因此约靠近中心越清晰，越远则越模糊。画图工具里瞎比划一下。。。

 　　

　　代码里进行了一些优化，思路是将图像渲染到了低分辨率的RenderTexture上，然后再进行模糊处理，最后将模糊后的RenderTexture和原始图像进行插值。

public class TestEffect : PostEffectsBase
{
    public Shader testShader;
    private Material testMaterial;
    public Material material
    {
        get
        {
            testMaterial = CheckShaderAndCreateMaterial(testShader, testMaterial);
            return testMaterial;
        }
    }

    [Range(0.0f, 0.05f)]
    public float blurFactor = 0.01f;
    public Vector2 blurCenter = new Vector2(0.5f, 0.5f);
    public int downSampleFactor = 2;//降低分辨率
    [Range(0f, 2f)]
    public float lerpFactor = 1;
 
    void OnRenderImage(RenderTexture src, RenderTexture dest)
    {
        if (material != null)
        {
            //用于中间存放降低分辨率的RT
            RenderTexture rtS = RenderTexture.GetTemporary(src.width >> downSampleFactor, src.width >> downSampleFactor);
            RenderTexture rtD = RenderTexture.GetTemporary(src.width >> downSampleFactor, src.width >> downSampleFactor);
            Graphics.Blit(src, rtS);

            material.SetFloat("_BlurFactor", blurFactor);
            material.SetVector("_BlurCenter", blurCenter);
            material.SetTexture("_BlurTex", rtD);
            material.SetFloat("_LerpFactor", lerpFactor);

            Graphics.Blit(rtS, rtD, material,0);            
            Graphics.Blit(src, dest,material, 1);

            RenderTexture.ReleaseTemporary(rtS);
            RenderTexture.ReleaseTemporary(rtD);
        }
        else
        {
            Graphics.Blit(src, dest);
        }
    }
}

 

Shader "TestEffectShader" {
    Properties {
        _MainTex ("Base (RGB)", 2D) = "white" {}
        _BlurFactor ("BlurFactor", Float) = 0.01
        _BlurCenter("BlurCenter",Color)=(0.5,0.5,0,0)
        _BlurTex("BlurTexture",2D)= "white" {}
        _LerpFactor("LerpFactor",Float)=1
    }
    SubShader {
        Pass {  
         
            ZTest Always Cull Off ZWrite Off
            
            CGPROGRAM  
            #pragma vertex vert  
            #pragma fragment frag  
              
            #include "UnityCG.cginc"  
              
            sampler2D _MainTex;  
            fixed _BlurFactor;
            fixed2 _BlurCenter;
            
              
            struct v2f {
                float4 pos : SV_POSITION;
                fixed2 uv: TEXCOORD0;
             
            };
            
            
            v2f vert(appdata_img v) {
                v2f o;
                o.pos = UnityObjectToClipPos(v.vertex);
                o.uv = v.texcoord.xy;
             
                return o;
            }
        
            fixed4 frag(v2f i) : SV_Target {
                 
                fixed2 dir=i.uv -_BlurCenter.xy;    
             
                fixed4 c=0;
                for(int    j=0;j<5;j++){
                    c+=tex2D(_MainTex, i.uv +dir*j*_BlurFactor);
                }
                c/=5;
                return c;
            }  
              
            ENDCG
        }  

        Pass {  
            ZTest Always Cull Off ZWrite Off
            CGPROGRAM  
            #pragma vertex vert  
            #pragma fragment frag  
              
            #include "UnityCG.cginc"  
              
            sampler2D _MainTex;  
            sampler2D _BlurTex;
            fixed _LerpFactor;
            fixed2 _BlurCenter;

            struct v2f {
                float4 pos : SV_POSITION;
                fixed2 uv1: TEXCOORD0;
                fixed2 uv2: TEXCOORD1;
            };

            v2f vert(appdata_img v) {
                v2f o;
                o.pos = UnityObjectToClipPos(v.vertex);
                o.uv1 = v.texcoord.xy;
                o.uv2 = v.texcoord.xy;
                return o;
            }

            fixed4 frag(v2f i) : SV_Target {
                 
                fixed2 dir=i.uv2 -_BlurCenter.xy;    
                fixed dis=length(dir);
                fixed4 normalColor=tex2D(_MainTex,i.uv1);
                fixed4 blurColor=tex2D(_BlurTex,i.uv2);
                return lerp(normalColor,blurColor,_LerpFactor*dis);

            }  
            ENDCG
        }
    }
    
    Fallback Off
}