前言

本篇将介绍如何通过添加RenderFeature实现自定义的postprocess——KawaseBlur

关于RenderFeature的基础可以看这篇https://www.cnblogs.com/chenglixue/p/17816447.html

KawaseBlur介绍

因为毛神对于十大模糊算法的介绍已经整理得十分详细了，所以这里不会深入，但会大致讲讲它的思想
思想：对距离目标pixel越来越远的地方的四个点进行sample，且在两个Render Target Texture间进行Blit。与高斯模糊不同的是，KawaseBlur采样随循环次数变化的Blur Kernel
随循环次数增加，Blur Kernel逐渐变大

Shader

Shader很简单，重点在于Render Pass中的循环迭代

实现

Shader "Custom/PP_KawaseBlur"
{
    Properties
    {
        _MainTex("Main Tex", 2D) = "white" {}
        _BlurIntensity("Blur Intensity", Range(0, 10)) = 1
    }
    
    SubShader
    {
        Tags
        {
            "RenderPipeline" = "UniversalPipeline"
        }
        
        HLSLINCLUDE
        #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"

        CBUFFER_START(UnityPerMaterial)
        half _BlurIntensity;
        float4 _MainTex_TexelSize;
        CBUFFER_END

        TEXTURE2D(_MainTex);
        SAMPLER(sampler_MainTex);
        ENDHLSL

        Pass
        {
            Cull Off
            ZWrite Off
            ZTest Always
            
            HLSLPROGRAM
            #pragma vertex VS
            #pragma fragment PS
            
            struct VSInput
            {
                float4 postionL : POSITION;
                float2 uv : TEXCOORD0;
            };

            struct PSInput
            {
                float4 positionH : SV_POSITION;
                float2 uv : TEXCOORD0;
            };

            PSInput VS(VSInput vsInput)
            {
                PSInput vsOutput;

                vsOutput.positionH = TransformObjectToHClip(vsInput.postionL);
                vsOutput.uv = vsInput.uv;

                return vsOutput;
            }

            float4 PS(PSInput psInput) : SV_TARGET
            {
                float4 outputColor = 0;

                // 经典卷积
                outputColor += SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, psInput.uv);
                outputColor += SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, psInput.uv + float2(-1, -1) * _MainTex_TexelSize.xy * _BlurIntensity);
                outputColor += SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, psInput.uv + float2(-1, 1) * _MainTex_TexelSize.xy * _BlurIntensity);
                outputColor += SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, psInput.uv + float2(1, -1) * _MainTex_TexelSize.xy * _BlurIntensity);
                outputColor += SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, psInput.uv + float2(1, 1) * _MainTex_TexelSize.xy * _BlurIntensity);

                return outputColor / 5.f;
            }
            ENDHLSL
        }
    }
}

Render Feature

整体实现

public class KawaseBlurRenderFeature : ScriptableRendererFeature
{
    // render feature Inspector 显示内容
    [System.Serializable]
    public class PassSetting
    {
        // profiler tag will show up in frame debugger
        public readonly string m_ProfilerTag = "Kawase Blur Pass";
        // 安插位置
        public RenderPassEvent m_passEvent = RenderPassEvent.AfterRenderingTransparents;

        // 控制分辨率
        [Range(1, 5)] 
        public int m_sampleWeaken = 1;

        [Range(0, 5)] 
        public int m_PassLoop = 2;

        // 模糊强度
        [Range(0, 10)] 
        public float m_BlurIntensity = 5;
    }
    
    public PassSetting m_Setting = new PassSetting();
    KawaseBlurRenderPass m_KawaseBlurPass;
    
    // 初始化 Pass
    public override void Create()
    {
        m_KawaseBlurPass = new KawaseBlurRenderPass(m_Setting);
    }

    // 添加Pass
    // Here you can inject one or multiple render passes in the renderer.
    // This method is called when setting up the renderer once per-camera.
    public override void AddRenderPasses(ScriptableRenderer renderer, ref RenderingData renderingData)
    {
        // can queue up multiple passes after each other
        renderer.EnqueuePass(m_KawaseBlurPass);
    }
}

PassSetting：创建一个PassSetting class，用于存储后续计算必要的变量
Create()：初始化Pass
AddRenderPasses()：添加一个或多个Pass

Render Pass

整体实现

class KawaseBlurRenderPass : ScriptableRenderPass
{
    // 用于存储pass setting
    private KawaseBlurRenderFeature.PassSetting m_passSetting;

    // render target texture
    private RenderTargetIdentifier m_TargetBuffer, m_TempBuffer1, m_TempBuffer2;

    private Material m_Material;

    static class ShaderIDs
    {
        // int 相较于 string可以获得更好的性能，因为这是预处理的
        internal static readonly int m_BlurIntensityProperty = Shader.PropertyToID("_BlurIntensity");
        // 关于这里的_BufferRT,应该是shader自带的内容，笔者google也未查到，还望知道的大佬指点迷津
        internal static readonly int m_TempBufferRT1Property = Shader.PropertyToID("_BufferRT1");
        internal static readonly int m_TempBufferRT2Property = Shader.PropertyToID("_BufferRT2");
    }

    // 用于设置material 属性
    public KawaseBlurRenderPass(KawaseBlurRenderFeature.PassSetting passSetting)
    {
        this.m_passSetting = passSetting;

        renderPassEvent = m_passSetting.m_passEvent;

        if (m_Material == null) m_Material = CoreUtils.CreateEngineMaterial("Custom/PP_KawaseBlur");

        // 基于pass setting设置material Properties
        m_Material.SetFloat(ShaderIDs.m_BlurIntensityProperty, m_passSetting.m_BlurIntensity);
    }

    // Gets called by the renderer before executing the pass.
    // Can be used to configure render targets and their clearing state.
    // Can be used to create temporary render target textures.
    // If this method is not overriden, the render pass will render to the active camera render target.
    public override void OnCameraSetup(CommandBuffer cmd, ref RenderingData renderingData)
    {
        // camera target descriptor will be used when creating a temporary render texture
        RenderTextureDescriptor descriptor = renderingData.cameraData.cameraTargetDescriptor;

        // 降低分辨率，改善模糊效果
        // Downsample original camera target descriptor
        descriptor.width /= m_passSetting.m_sampleWeaken;
        descriptor.height /= m_passSetting.m_sampleWeaken;

        // Set the number of depth bits we need for temporary render texture
        descriptor.depthBufferBits = 0;

        // Enable these if pass requires access to the CameraDepthTexture or the CameraNormalsTexture.
        // ConfigureInput(ScriptableRenderPassInput.Depth);
        // ConfigureInput(ScriptableRenderPassInput.Normal);

        // Grab the color buffer from the renderer camera color target
        m_TargetBuffer = renderingData.cameraData.renderer.cameraColorTarget;

        // Create a temporary render texture using the descriptor from above
        cmd.GetTemporaryRT(ShaderIDs.m_TempBufferRT1Property, descriptor, FilterMode.Bilinear);
        cmd.GetTemporaryRT(ShaderIDs.m_TempBufferRT2Property, descriptor, FilterMode.Bilinear);
        m_TempBuffer1 = new RenderTargetIdentifier(ShaderIDs.m_TempBufferRT1Property);
        m_TempBuffer2 = new RenderTargetIdentifier(ShaderIDs.m_TempBufferRT2Property);
    }

    // The actual execution of the pass. This is where custom rendering occurs
    public override void Execute(ScriptableRenderContext context, ref RenderingData renderingData)
    {
        // Grab a command buffer. We put the actual execution of the pass inside of a profiling scope
        CommandBuffer cmd = CommandBufferPool.Get();

        using (new ProfilingScope(cmd, new ProfilingSampler(m_passSetting.m_ProfilerTag)))
        {
            // Blit from the color buffer to a temporary buffer and back
            Blit(cmd, m_TargetBuffer, m_TempBuffer1, m_Material, 0);

            for (uint i = 1; i <= m_passSetting.m_PassLoop; ++i)
            {
                // 增大Blur Kernel.从而影响shader
                cmd.SetGlobalFloat(ShaderIDs.m_BlurIntensityProperty, i * m_passSetting.m_BlurIntensity + 1);

                Blit(cmd, m_TempBuffer1, m_TempBuffer2, m_Material, 0);

                // 交换 tempbuffer1 和 tempbuffer2，使得下个循环继续使用tempbuffer1进行计算
                var tempRT = m_TempBuffer1;
                m_TempBuffer1 = m_TempBuffer2;
                m_TempBuffer2 = tempRT;
            }

            // 最后将最终的模糊图像传给要输出的Render Target
            cmd.SetGlobalFloat(ShaderIDs.m_BlurIntensityProperty, m_passSetting.m_PassLoop * m_passSetting.m_BlurIntensity + 1);
            Blit(cmd, m_TempBuffer1, m_TargetBuffer, m_Material, 0);
        }

        // Execute the command buffer and release it
        context.ExecuteCommandBuffer(cmd);
        CommandBufferPool.Release(cmd);
    }

    // Called when the camera has finished rendering
    // release/cleanup any allocated resources that were created by this pass
    public override void OnCameraCleanup(CommandBuffer cmd)
    {
        if(cmd == null) throw new ArgumentNullException("cmd");

        // Since created a temporary render texture in OnCameraSetup, we need to release the memory here to avoid a leak
        cmd.ReleaseTemporaryRT(ShaderIDs.m_TempBufferRT1Property);
        cmd.ReleaseTemporaryRT(ShaderIDs.m_TempBufferRT2Property);
    }
}