【Unity】URP自定义后处理效果

在新的URP（Universal Render Pipeline）下，Unity取消了OnRenderImage函数，也就是说原来的自定义后处理的方法被取消了。而且老的Post Processing插件也失效了。URP集成了一套内置的新的后处理效果，使用起来更加方便，不过自定义起来并不简单。

自带后处理效果

在Hierarchy中新建Volume -> Global Volume；

在细节面板中新建Profile

在Add Override中就可以看到很多自带的后处理效果

然后记得把摄像机的Rendering -> Post Processing勾上

然后就能一个个玩嘞

当然也可以看看官方的教程：https://docs.unity3d.com/Packages/com.unity.render-pipelines.universal@7.1/manual/VolumeOverrides.html

自定义后处理

但是有的时候我们要使用一些自定义效果，在URP中我们可以对Volume Override进行拓展。

这里做一个简单的反转颜色看看。

准备shader

URP抛弃了CG语言，只能使用hlsl进行shader编写：

Shader "Post Process/Invert Color"
{
	Properties
	{
		_MainTex("Base (RGB)", 2D) = "white" {}
	}
	SubShader
	{
        Tags {"RenderType" = "Opaque" "RenderPipeline" = "UniversalPipeline"}
	    ZTest Always Cull Off ZWrite Off

        Pass
        {
			Name "Invert Color"

			HLSLINCLUDE
			#include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"
			ENDHLSL
            			
			HLSLPROGRAM
			#pragma vertex vert
			#pragma fragment frag

			struct a2v
			{
				float4 positionOS : POSITION;
				float2 uv : TEXCOORD0;
			};

			struct v2f
			{
				float4 pos : SV_POSITION;
				float2 uv : TEXCOORD0;
			};

			CBUFFER_START(UnityPerMaterial)
			float4 _MainTex_ST;
			CBUFFER_END

			TEXTURE2D(_MainTex);
			SAMPLER(sampler_MainTex);

			v2f vert(a2v v)
			{
				v2f o;
				o.pos = TransformObjectToHClip(v.positionOS.xyz);
				o.uv = v.uv;
				return o;
			}

			half4 frag(v2f i) : SV_Target
			{
				half4 color = SAMPLE_TEXTURE2D(_MainTex,sampler_MainTex, i.uv);
				color = 1 - color;
				return color;
			}
			ENDHLSL
	     }
	}
}

拓展自定义Override

在Package/Universal RP/Runtime/Override文件夹下可以找到Unity自带的后处理的脚本，打开看看：

using System;

namespace UnityEngine.Rendering.Universal
{
    [Serializable, VolumeComponentMenu("Post-processing/Bloom")]
    public sealed class Bloom : VolumeComponent, IPostProcessComponent
    {
        [Tooltip("Filters out pixels under this level of brightness. Value is in gamma-space.")]
        public MinFloatParameter threshold = new MinFloatParameter(0.9f, 0f);

        [Tooltip("Strength of the bloom filter.")]
        public MinFloatParameter intensity = new MinFloatParameter(0f, 0f);

        [Tooltip("Changes the extent of veiling effects.")]
        public ClampedFloatParameter scatter = new ClampedFloatParameter(0.7f, 0f, 1f);

        [Tooltip("Clamps pixels to control the bloom amount.")]
        public MinFloatParameter clamp = new MinFloatParameter(65472f, 0f);

        [Tooltip("Global tint of the bloom filter.")]
        public ColorParameter tint = new ColorParameter(Color.white, false, false, true);

        [Tooltip("Use bicubic sampling instead of bilinear sampling for the upsampling passes. This is slightly more expensive but helps getting smoother visuals.")]
        public BoolParameter highQualityFiltering = new BoolParameter(false);

        [Tooltip("Dirtiness texture to add smudges or dust to the bloom effect.")]
        public TextureParameter dirtTexture = new TextureParameter(null);

        [Tooltip("Amount of dirtiness.")]
        public MinFloatParameter dirtIntensity = new MinFloatParameter(0f, 0f);

        public bool IsActive() => intensity.value > 0f;

        public bool IsTileCompatible() => false;
    }
}

大概能看懂，就是各种参数，直接抄一个：

using System;

namespace UnityEngine.Rendering.Universal
{
    [Serializable, VolumeComponentMenu("Addition-Post-Processing/Invert-Color")]
    public class InvertColor : VolumeComponent, IPostProcessComponent
    {
        public BoolParameter invert = new BoolParameter(false);
        
        public bool IsActive()
        {
            return (bool)invert;
        }
        public bool IsTileCompatible()
        {
            return false;
        }
    }
}

在Add Override中就可以找到嘞！

当然现在还没有效果，因为咱还什么都没做。

前期准备

Unity自带的后处理特效定义在Runtime/Passes的PostProcessPass.cs中，不过直接改管线不可取，所以我们可以使用RenderFeature进行扩展。

首先，为了方便管理，新建一个ScriptableObject叫AdditionPostProcessData，用于管理自定义后处理特效shader：

using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
#if UNITY_EDITOR
using UnityEditor;
using UnityEditor.ProjectWindowCallback;
#endif
using UnityEngine.Rendering.Universal;
using UnityEngine.Rendering;

namespace UnityEngine.Rendering.Universal
{
    [Serializable]
    public class AdditionPostProcessData : ScriptableObject
    {
#if UNITY_EDITOR
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Performance", "CA1812")]

        [MenuItem("Assets/Create/Rendering/Universal Render Pipeline/Additional Post-process Data", priority = CoreUtils.assetCreateMenuPriority3 + 1)]
        static void CreateAdditionalPostProcessData()
        {
            var instance = CreateInstance<AdditionPostProcessData>();
            AssetDatabase.CreateAsset(instance, $"Assets/Settings/{nameof(AdditionPostProcessData)}.asset");
            Selection.activeObject = instance;
        }
#endif
        [Serializable]
        public sealed class Shaders
        {
            public Shader invertColor = Shader.Find("Post Process/Invert Color");
        }
        public Shaders shaders;
    }
}

然后创建一个MaterialLibrary对象，负责动态创建每个自定义后处理效果所需要的材质：

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.Rendering;
using UnityEngine.Rendering.Universal;

namespace UnityEngine.Rendering.Universal
{
    public class MaterialLibrary
    {
        public readonly Material invertColor;

        public MaterialLibrary(AdditionPostProcessData data)
        {
            invertColor = Load(data.shaders.invertColor);
        }

        private Material Load(Shader shader)
        {
            if (shader == null)
            {
                Debug.LogErrorFormat($"Missing shader. {GetType().DeclaringType.Name} render pass will not execute. Check for missing reference in the renderer resources.");
                return null;
            }
            return shader.isSupported ? CoreUtils.CreateEngineMaterial(shader) : null;
        }
        internal void Cleanup()
        {
            CoreUtils.Destroy(invertColor);
        }
    }
}

这些都是为了后期方便处理进行的操作，下面进行Render Feature的编写。

在Render Feature中添加效果

右键 -> Rendering -> Universal Render Pipeline，新建一个Render Feature。

在下方新建一个AdditionPostProcessData的公开变量

public AdditionPostProcessData postData;

其中的AddRenderPasses函数需要重写，不过我们先写完ScriptableRenderPass再来写这个

在上方的ScriptableRenderPass中，我们需要重写Execute方法。我添加了SetUp和Render函数进行初始化和渲染，将反转色的效果分函数写，方便后期添加别的效果：

RenderTargetIdentifier m_ColorAttachment;
RenderTargetHandle m_Destination;

const string k_RenderPostProcessingTag = "Render AdditionalPostProcessing Effects";
const string k_RenderFinalPostProcessingTag = "Render Final AdditionalPostProcessing Pass";

InvertColor m_InvertColor;

MaterialLibrary m_Materials;

RenderTargetHandle m_TemporaryColorTexture01;
RenderTargetHandle m_TemporaryColorTexture02;
RenderTargetHandle m_TemporaryColorTexture03;

public CustomRenderPass(AdditionPostProcessData data)
{
    m_Materials = new MaterialLibrary(data);
    m_TemporaryColorTexture01.Init("_TemporaryColorTexture1");
    m_TemporaryColorTexture02.Init("_TemporaryColorTexture2");
    m_TemporaryColorTexture03.Init("_TemporaryColorTexture3");
}

public void Setup(RenderPassEvent @event, RenderTargetIdentifier source, RenderTargetHandle destination)
{
    renderPassEvent = @event;
    m_ColorAttachment = source;
    m_Destination = destination;
}

public override void Execute(ScriptableRenderContext context, ref RenderingData renderingData)
{
    var stack = VolumeManager.instance.stack;
    m_InvertColor = stack.GetComponent<InvertColor>();
    var cmd = CommandBufferPool.Get(k_RenderPostProcessingTag);
    Render(cmd, ref renderingData);
    context.ExecuteCommandBuffer(cmd);
    CommandBufferPool.Release(cmd);
}

private void Render(CommandBuffer cmd, ref RenderingData renderingData)
{
    ref var cameraData = ref renderingData.cameraData;
    if (m_InvertColor.IsActive() && !cameraData.isSceneViewCamera)
    {
    	SetupInvertColor(cmd, ref renderingData, m_Materials.invertColor);
    }
}

private void SetupInvertColor(CommandBuffer cmd, ref RenderingData renderingData, Material invertMaterial)
{
    RenderTextureDescriptor opaqueDesc = renderingData.cameraData.cameraTargetDescriptor;
    cmd.GetTemporaryRT(m_TemporaryColorTexture01.id, opaqueDesc);
    cmd.GetTemporaryRT(m_TemporaryColorTexture02.id, opaqueDesc);
    cmd.GetTemporaryRT(m_TemporaryColorTexture03.id, opaqueDesc);
    cmd.BeginSample("invertColor");
    cmd.Blit(this.m_ColorAttachment, m_TemporaryColorTexture01.Identifier());
    cmd.Blit(m_TemporaryColorTexture01.Identifier(), m_TemporaryColorTexture02.Identifier(), invertMaterial);
    cmd.Blit(m_TemporaryColorTexture02.Identifier(), m_ColorAttachment);
    cmd.Blit(m_TemporaryColorTexture02.Identifier(), this.m_Destination.Identifier());
    cmd.EndSample("invertColor");
}

然后重写AddRenderPasses函数

public override void Create()
{
    m_ScriptablePass = new CustomRenderPass(postData);
    m_ScriptablePass.renderPassEvent = RenderPassEvent.AfterRenderingTransparents;
}
public override void AddRenderPasses(ScriptableRenderer renderer, ref RenderingData renderingData)
{
    var cameraColorTarget = renderer.cameraColorTarget;
    var dest = RenderTargetHandle.CameraTarget;
    if (postData == null) return;
    m_ScriptablePass.Setup(cameraColorTarget, dest);
    renderer.EnqueuePass(m_ScriptablePass);
}

配置Render Feature完成后处理效果

• 在Edit -> Project Settings -> Graphics -> Scriptable Render Pipeline Settings或Project Settings -> Quality -> Rendering中找到项目的UniversalRenderPipelineAsset；

• 在UniversalRenderPipelineAsset的细节面板的Renderer List中找到自己的RendererData；

• 在自己的Renderer Data细节面板中点击Add Renderer Feature，添加自己的AdditionPostProcessRenderFeature，然后画面会变黑

• 在在资源面板右键，Creat -> Rendering -> Universial Render Pipeline -> Additional Post-process Data创建资源，这个资源创建在Asset/Settings文件夹里，找到这个文件，并且拖入Renderer Data细节面板中New Addition PP Render Feature的Post Data属性中。

  

• 现在画面应该是正常的

• 点击自己的AdditionPostProcessData，细节面板中检查一下Shader的值是否被正确赋予

  

现在就可以正确反色嘞：

后期加入别的效果

• 实现shader和VolumeComponent的CS文件；
• 在AdditionPostProcessData和MaterialLibrary中加入新的shader；
• 在ScriptableRenderPass中加入材质变量、效果Setup函数，然后在Render函数中调用；

脚本控制自定义后处理效果

using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class PostProcessControl : MonoBehaviour
{
    private UnityEngine.Rendering.Volume _ppv = null;
    
    private UnityEngine.Rendering.Universal.InvertColor _invertColor = null;

    private bool _invert = false;
    void Start()
    {
        _ppv = GetComponent<UnityEngine.Rendering.Volume>();
        
        if (!_ppv.profile.TryGet(out _invertColor))
        {
            _invertColor = ScriptableObject.CreateInstance<UnityEngine.Rendering.Universal.InvertColor>();
            _ppv.profile.components.Add(_invertColor);
        }
    }
    
    void Update()
    {
        if (Input.GetKeyDown(KeyCode.I))
        {
            _invert = !_invert;
        }
        
        ChangeOverride();
    }

    private void ChangeOverride()
    {
        _invertColor.invert.Override(_invert);
    }
}

资源

https://github.com/1keven1/Unity-URP-Post-Process-Effect#readme

参考文章

• https://zhuanlan.zhihu.com/p/161658349