这里Canvas(1)设置为Overlay能渲染出指定UI高清，其他UI模糊，然而这做法非常不好，如果此时再打开UI 以及 关闭模糊效果 要将这些置顶UI 恢复到原本Canvas里，也就是要管理2套Canvas

using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.Rendering;
using UnityEngine.Rendering.Universal;public class Blur : ScriptableRendererFeature
{[Serializable] //序列化 会在ForwardRenderer下创建Blur时看到m_Data就是它public class BlurData{//blur材质public Material material;public RenderPassEvent renderPassEvent = RenderPassEvent.AfterRenderingPostProcessing;//渲染次数,次数越大图像会越模糊[Range(0, 4)]public int iterations = 3;//模糊采样间距,越大越模糊[Range(0.2f, 3.0f)]public float blurSpread = 0.6f;//缩小比例（2代表缩小1/2) 越大越模糊，性能越好，但是会逐渐像素化！[Range(1, 8)]public int downSample = 2;}public class BlurRenderPass : ScriptableRenderPass{private BlurData m_Data; //ForwardRenderer下Blur（ScriptableRendererFeature）资源的序列化参数数据private RenderTargetIdentifier m_Source;//屏幕图private RenderTargetHandle m_Buffer0;//缓冲区1private RenderTargetHandle m_Buffer1;//缓冲区2private int m_BlurSize = Shader.PropertyToID("_BlurSize");public BlurRenderPass(BlurData data){this.m_Data = data;}public void Setup(RenderTargetIdentifier cameraColorTarget){m_Buffer0.Init("_Buffer0");m_Buffer1.Init("_Buffer1");this.m_Source = cameraColorTarget;//该pass所在管线 ForwardRenderer 所处的摄像机主纹理}public override void Configure(CommandBuffer cmd, RenderTextureDescriptor cameraTextureDescriptor){var width = cameraTextureDescriptor.width / m_Data.downSample;var height = cameraTextureDescriptor.height / m_Data.downSample;cmd.GetTemporaryRT(m_Buffer0.id, width, height, 0, FilterMode.Bilinear, RenderTextureFormat.ARGB32);cmd.GetTemporaryRT(m_Buffer1.id, width, height, 0, FilterMode.Bilinear, RenderTextureFormat.ARGB32);}public override void FrameCleanup(CommandBuffer cmd){cmd.ReleaseTemporaryRT(m_Buffer0.id);cmd.ReleaseTemporaryRT(m_Buffer1.id);}public override void Execute(ScriptableRenderContext context, ref RenderingData renderingData){var mat = m_Data.material;if (mat == null) return;//renderingData.cameraData.camera 可获取摄像机判定哪个摄像机才进行处理渲染(每个摄像机都会进一遍pass 如果摄像机有多个且都有这个Blur(ScriptableRendererFeature资源)CommandBuffer cmd = CommandBufferPool.Get("MyBlurCmd"); //从池获取一个cmd 命名为MyBlurCmd 能在FrameDebugger看到cmd.Blit(m_Source, m_Buffer0.Identifier());//将摄像机图渲染至buffer0//开始iterations次渲染,每次都会进行2次Pass操作：横向、纵向（谁先谁后都无所谓for (int i = 0; i < m_Data.iterations; i++){mat.SetFloat(m_BlurSize, 1.0f + i * m_Data.blurSpread);//指定采样间距,逐级递增的形式cmd.Blit(m_Buffer0.Identifier(), m_Buffer1.Identifier(), mat, 0);var tmp = m_Buffer0;m_Buffer0 = m_Buffer1; //注意最终都会将渲染结果输出到m_Buffer0m_Buffer1 = tmp;}cmd.Blit(m_Buffer0.Identifier(), m_Source); //将最终结果渲染到摄像机上//执行cmdcontext.ExecuteCommandBuffer(cmd);//清空回收cmdcmd.Clear();CommandBufferPool.Release(cmd);}}public BlurData data = new BlurData();private BlurRenderPass m_Pass;public override void AddRenderPasses(ScriptableRenderer renderer, ref RenderingData renderingData){var src = renderer.cameraColorTarget;m_Pass.Setup(src); //设置摄像机输出的颜色纹理renderer.EnqueuePass(m_Pass); //入队渲染pass}public override void Create(){m_Pass = new BlurRenderPass(data); //创建一个passm_Pass.renderPassEvent = data.renderPassEvent; //设置pass的渲染时机在某个节点后（导致问题，无法类似grab一样在某一个UI渲染时进行渲染 而必须等到所有UI渲染完成才进行渲染。。//无法做到置顶UI高清，底下UI模糊的效果.//所以下一步是思考如何实现这个吧..}
}

Shader代码实现模糊 

//注意 注释掉的CGINCLUDE CDEND UnityCG.cginc 等一系列带cg或注释的方法都是传统CG管线的内容
// 新内容会是HLSLxxx字眼形式出现 (目的是演示如何将CG代码改为URP管线代码)
Shader "MilkShader/Twently/G_GaussianBlur"
{Properties{_MainTex("Texture", 2D) = "white" {}//采样间距系数_BlurSize("Blur Size", Float) = 1.0}SubShader{Tags { "RenderType" = "Opaque" }LOD 100//CGINCLUDE ... ENDCG 是一种组织结构，放在它里面的方法可以被任意Pass直接使用..相当于所有Pass都会有这些内容//CGINCLUDE //CGHLSLINCLUDE//#include "UnityCG.cginc" //CG#include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"sampler2D _MainTex;half4 _MainTex_TexelSize;float _BlurSize;//URP下没有appdata_img结构 要自定义struct a2v{float4 vertex : POSITION;float2 texcoord : TEXCOORD0;};struct v2f{float4 pos : SV_POSITION;half2 uv[5] : TEXCOORD0;};//我们只需要appdata_img内置结构的数据传入即可（有顶点、纹理坐标）v2f vertBlurVertical(a2v v) {v2f o;//o.pos = UnityObjectToClipPos(v.vertex); //CGVertexPositionInputs vertexInputs = GetVertexPositionInputs(v.vertex.xyz);o.pos = vertexInputs.positionCS;half2 uv = v.texcoord;//纵向的5个像素点纹理坐标o.uv[0] = uv;o.uv[1] = uv + float2(0.0, _MainTex_TexelSize.y * 1.0) * _BlurSize;o.uv[2] = uv - float2(0.0, _MainTex_TexelSize.y * 1.0) * _BlurSize;o.uv[3] = uv + float2(0.0, _MainTex_TexelSize.y * 2.0) * _BlurSize;o.uv[4] = uv - float2(0.0, _MainTex_TexelSize.y * 2.0) * _BlurSize;return o;}v2f vertBlurHorizontal(a2v v) {v2f o;//o.pos = UnityObjectToClipPos(v.vertex); //CGVertexPositionInputs vertexInputs = GetVertexPositionInputs(v.vertex.xyz);o.pos = vertexInputs.positionCS;half2 uv = v.texcoord;//横向的5个像素点纹理坐标o.uv[0] = uv;o.uv[1] = uv + float2(_MainTex_TexelSize.x * 1.0, 0.0) * _BlurSize;o.uv[2] = uv - float2(_MainTex_TexelSize.x * 1.0, 0.0) * _BlurSize;o.uv[3] = uv + float2(_MainTex_TexelSize.x * 2.0, 0.0) * _BlurSize;o.uv[4] = uv - float2(_MainTex_TexelSize.x * 2.0, 0.0) * _BlurSize;return o;}//无论是纵向还是横向，它们都会使用这个片元着色器，处理手法一样half4 fragBlur(v2f i) : SV_Target{float weight[3] = {0.4026, 0.2442, 0.0545};//采样RGB然后进行乘以对应的权重累加到sumhalf3 sum = tex2D(_MainTex, i.uv[0]).rgb * weight[0];for (int it = 1; it < 3; it++) {sum += tex2D(_MainTex, i.uv[it * 2 - 1]).rgb * weight[it];sum += tex2D(_MainTex, i.uv[it * 2]).rgb * weight[it];}//是的这样就完成了，模糊。。。。return half4(sum, 1.0);}//ENDCG //CGENDHLSL//上面都是INCLUDE内容即下面Pass都可使用的内容//标配写法ZTest Always Cull Off ZWrite Off//第一个PASS,纵向模糊处理Pass{NAME "GAUSSIAN_BLUR_VERTICAL"//CGPROGRAM //CGHLSLPROGRAM//纵向的顶点着色器#pragma vertex vertBlurVertical//片元着色器#pragma fragment fragBlur//ENDCG //CGENDHLSL}//第二个Pass 横向模糊处理Pass{NAME "GAUSSIAN_BLUR_HORIZONTAL"//CGPROGRAMHLSLPROGRAM//横向的顶点着色器#pragma vertex vertBlurHorizontal//片元着色器#pragma fragment fragBlur//ENDCGENDHLSL}}//完成SubShaderFallback Off
}

1个Canvas和2个摄像机

主要以上内容，实际上就是因为Render Pass Event是只能After Rendering Transpanrets在透明物体渲染完成后进行屏幕后处理模糊，导致无法实现置顶UI高清，底下UI模糊的需求，如果可以控制这个后处理时机是在置顶UI渲染之前进行后处理，等后处理完成后再渲染指定UI 那就可以，然而...

TODO！！！