Unity URP 简单的Renderer Feature

Unity 2019.4.30
URP 7.7.1
刚把测试项目升级到URP，本想看官方的Demo工程学习写一个简单后效，快速GettingStart
结果官方示例已经是 Unity 2020 URP 10.8.1 内容变化很多

最后还是结合Unity教程，终于把简单的后效跑起来了

创建Pipeline Asset之后，有一个同名的Forward Renderer Data

创建Forward Render Data，我命名的是DistortForwardData，扭曲的效果，测试的话默认ImageEffect就行。

添加到 PipelineAsset RenderList

回到DistortForwardData

Add Renderer Feature 可以添加Renderer Feature，但是此时只能添加Renderer Objects，还是实验性的

后效需要构建自己的Renderer Feature

创建DistortFeature类，继承ScriptableRendererFeature

再加两个类，逻辑比较简单直接作为内部类就行。

CustomPass类，继承ScriptableRenderPass，核心的渲染逻辑写在这里。

DistortSettings类，主要是用于传参，会出现在Renderer Feature的面板上，可以把材质参数放这里。

这时候在DistortForwardData就可以看到我们写的Feature啦

大致的代码结构如下：

Create()

可以在这里做初始化操作。

比如把Setting的参数赋值给CustomPass，我们会在CustomPass对材质参数进行设置。

    public override void Create()
    {
        customPass = new CustomPass();
        customPass.renderPassEvent = Settings.renderPassEvent;
        customPass.Material = Settings.Material;
        customPass.Distortion = Settings.Distortion;
        customPass.Scale = Settings.Scale;
    }

AddRenderPasses()

在这里将CustomPass加入队列

我们的CustomPass还需要相机的输出，就来自ScriptableRenderer.cameraColorTarget，

给CustomPass增加Setup方法，在加入队列之前，由Setup传给CustomPass

 public override void AddRenderPasses(ScriptableRenderer renderer, ref RenderingData renderingData)
 {
     customPass.Setup(renderer.cameraColorTarget);
     renderer.EnqueuePass(customPass);
 }

核心方法就是Execute，我们在这里创建CommandBuffer，由ScriptableRenderContext执行。

CustomPass的父类ScriptableRenderPass属性renderPassEvent指定执行的阶段。

public class DistortFeature : ScriptableRendererFeature
{
    [System.Serializable]
    public class DistortSettings
    {
        public RenderPassEvent renderPassEvent = RenderPassEvent.AfterRenderingTransparents;
        public Material Material = null;
        [Range(0.001f, 10)] public float Distortion;
        [Range(0.001f, 10)] public float Scale;
    }

    public class CustomPass : ScriptableRenderPass
    {
        static readonly string renderTag = "My Distort Effect";
        public Material Material = null;
        public float Distortion;
        public float Scale;

        RenderTargetIdentifier currentTarget;
        int TempTargetId = Shader.PropertyToID("_TempTarget");

        public void Setup(in RenderTargetIdentifier target)
        {
            currentTarget = target;
        }

        public override void Execute(ScriptableRenderContext context, ref RenderingData renderingData)
        {
            if (Material == null) return;

            var source = currentTarget;
            var destination = TempTargetId;

            Material.SetFloat("_distortion", Distortion);
            Material.SetFloat("_scale", Scale);

            CommandBuffer cmd = CommandBufferPool.Get(renderTag);
            cmd.Clear();

            cmd.GetTemporaryRT(destination, Screen.width, Screen.height, 0);
            cmd.Blit(source, destination, Material);
            cmd.Blit(destination, source);

            context.ExecuteCommandBuffer(cmd);
            CommandBufferPool.Release(cmd);
        }
    }

    public DistortSettings Settings = new DistortSettings();

    private CustomPass customPass;

    public override void Create()
    {
        customPass = new CustomPass();
        customPass.renderPassEvent = Settings.renderPassEvent;
        customPass.Material = Settings.Material;
        customPass.Distortion = Settings.Distortion;
        customPass.Scale = Settings.Scale;
    }

    public override void AddRenderPasses(ScriptableRenderer renderer, ref RenderingData renderingData)
    {
        customPass.Setup(renderer.cameraColorTarget);
        renderer.EnqueuePass(customPass);
    }
}

回到场景把相机设置上

然后就可以在Forward Renderer Data修改参数查看效果

参考资料：

[1] URP系列教程 | 如何使用Scriptable Renderer Feature来自定义后处理效果(https://zhuanlan.zhihu.com/p/373273390)