Unity6 URP17使用初探

1.简介

随着Unity6的发布，URP17也已经可以上手使用，相对旧的版本改动较大的是加入了

RenderGraph、STP、Foveated rendering、GPU Resident Drawer等功能，部分功能只需要开关参数即可使用，

而GRD更像是Gpu driven管线下的SRP Batches升级，RenderGraph相较于HDRP之前使用的版本换了一套API。

最大的不同是，使用URP17编写Feature时，必须依赖于RenderGraph进行编写，接下来就来介绍一下。

1.1 相关Demo

目前URP17比较容易找到的学习Demo如下：

• URP17 Package内自带的Samples
• Fantasy Kingdom (https://assetstore.unity.com/packages/essentials/tutorial-projects/fantasy-kingdom-in-unity-6-urp-298128)
• 在Unity Hub可以直接下载的Universal 3D sample（包含3个场景）

2.RenderGraph

打开任意URP的示例场景查看，RenderGraphView上各图标含义如下：

1. 说明这是一个外部置入的RenderTexture
2. 红色方块说明存在写入操作
3. 绿色方块指存在读取操作（红绿方块说明读写操作）
4. 该图标说明标记了全局RenderTexture

而顶部表明当前渲染一帧的各个Pass，左侧是各类RT。

URP17同时保留了旧的Feature逻辑与RenderGraph逻辑(随便打开一个pass为例)：

public class DistortTunnelPass_Tunnel : ScriptableRenderPass
{
    class PassData
    {
        public Renderer tunnelObject;
        public Material tunnelMaterial;
    }

#pragma warning disable 618, 672 // Type or member is obsolete, Member overrides obsolete member

    // Unity calls the Configure method in the Compatibility mode (non-RenderGraph path)
    public override void Configure(CommandBuffer cmd, RenderTextureDescriptor cameraTextureDescripor)
    {
    }

    // Unity calls the Execute method in the Compatibility mode
    public override void Execute(ScriptableRenderContext context, ref RenderingData renderingData)
    {
    }

#pragma warning restore 618, 672

    // Unity calls the RecordRenderGraph method to add and configure one or more render passes in the render graph system.
    public override void RecordRenderGraph(RenderGraph renderGraph, ContextContainer frameData)
    {
    }
}

参考时忽略掉Configure和Execute的逻辑，执行逻辑关注RecordRenderGraph函数。

2.1 操作方式的改变

在RenderGraph中，之前的RTHandle由于不在该系统中托管，进入RenderGraph的材质都需要调用API进行转换，

转换为RendeGraph的RT后，无需考虑释放操作：

RenderTextureDescriptor textureProperties = new RenderTextureDescriptor(Screen.width, Screen.height, RenderTextureFormat.Default, 0);
TextureHandle textureHandle = UniversalRenderer.CreateRenderGraphTexture(renderGraph, textureProperties, "My texture", false);

相关文档：

https://docs.unity3d.com/Manual/urp/render-graph-create-a-texture.html

此外RenderGraph对于空调用的pass，也会剔除进行优化，使用者需要手动标记以防止被剔除。

2.1 RecordRenderGraph

在该函数内可组织渲染逻辑，pass相关的逻辑需放在对应的代码块中，例如：

using (var builder = renderGraph.AddRasterRenderPass<PassData>(passName, out _))
{
    builder.UseTexture(rt1);
    builder.SetRenderAttachment(resourceData.activeColorTexture, 0);

    builder.SetRenderFunc<PassData>((data, context) =>
    {
        MaterialPropertyBlock materialPropertyBlock = new MaterialPropertyBlock();
        materialPropertyBlock.SetTexture("_BlitTexture", rt1);
        materialPropertyBlock.SetVector("_BlitScaleBias", new Vector4(1, 1, 0, 0));

        context.cmd.DrawProcedural(Matrix4x4.identity, material, 0, MeshTopology.Triangles, 3, 1, materialPropertyBlock);
    });
}

URP提供了多种RenderPass，例如处理光栅化相关逻辑使用RasterRenderPass组织相关逻辑。

在RenderPass的代码块中可使用builder对象配置RenderTarget、标记材质的读写等

而具体的pass绘制逻辑则在SetRenderFunc代码块中。

RecordRenderGraph内可以调用多次AddRenderPass，但URP并没有整理旧API的代码和相关工具类，

以至于容易使用旧的API导致报错，这点需要注意。

3.编写Feature

3.1 Blit与SetTarget

从前有句俗话“切RT的性能消耗相当于半个pass”，Unity SRP在几个版本的升级都在逐渐强调不切RenderTarget直接绘制，

如Cockpit Demo的屏幕空间描边。

3.2 屏幕模糊Demo

下面通过屏幕模糊Demo案例，演示URP17下pass的编写。

通过外部EnqueuePass的方式，在场景中通过控制器脚本添加该Pass，

MyBlurSceneController.cs：

using UnityEngine;
using UnityEngine.Rendering.Universal;
using UnityEngine.Rendering;

public class MyBlurSceneController : MonoBehaviour
{
    public Material material;
    [Range(2, 15)] public int blurPasses = 3;
    [Range(0, 4)] public int downSample = 0;
    [Range(0.0f, 10f)] public float offset = 0.2f;

    public RenderPassEvent injectionPoint = RenderPassEvent.BeforeRenderingPostProcessing;
    public int injectionPointOffset = 0;
    public ScriptableRenderPassInput inputRequirements = ScriptableRenderPassInput.Color;
    public CameraType cameraType = CameraType.Game;

    private MyBlurPass mMyBlurPass;

    private void OnEnable()
    {
        SetupPass();

        RenderPipelineManager.beginCameraRendering += OnBeginCamera;
    }

    private void OnDisable()
    {
        RenderPipelineManager.beginCameraRendering -= OnBeginCamera;
    }

    public virtual void SetupPass()
    {
        mMyBlurPass = new MyBlurPass();

        mMyBlurPass.renderPassEvent = injectionPoint + injectionPointOffset;
        mMyBlurPass.material = material;

        mMyBlurPass.ConfigureInput(inputRequirements);
    }

    public virtual void OnBeginCamera(ScriptableRenderContext ctx, Camera cam)
    {
        if (mMyBlurPass == null || material == null)
            return;

        if ((cam.cameraType & cameraType) == 0) return;

        mMyBlurPass.blurPasses = blurPasses;
        mMyBlurPass.downSample = downSample;
        mMyBlurPass.offset = offset;

        cam.GetUniversalAdditionalCameraData().scriptableRenderer.EnqueuePass(mMyBlurPass);
    }
}

MyBlurPass.cs：

using UnityEngine;
using UnityEngine.Rendering.RenderGraphModule;
using UnityEngine.Rendering;
using UnityEngine.Rendering.Universal;
using UnityEngine.Rendering.RenderGraphModule.Util;

public class MyBlurPass : ScriptableRenderPass
{
    public class PassData
    {
        public TextureHandle tempRt1;
        public TextureHandle tempRt2;
    }

    public Material material;
    [Range(2, 15)] public int blurPasses = 3;
    [Range(1, 4)] public int downSample = 1;
    [Range(0.0f, 10f)] public float offset = 0.2f;

    public override void RecordRenderGraph(RenderGraph renderGraph, ContextContainer frameData)
    {
        var resourceData = frameData.Get<UniversalResourceData>();
        var passData = new PassData();

        var w = Screen.width >> downSample;
        var h = Screen.height >> downSample;

        RenderTextureDescriptor textureProperties = new RenderTextureDescriptor(w, h, RenderTextureFormat.Default, 0);
        passData.tempRt1 = UniversalRenderer.CreateRenderGraphTexture(renderGraph, textureProperties, "MyBlurPassTempRt1", false);

        textureProperties = new RenderTextureDescriptor(w, h, RenderTextureFormat.Default, 0);
        passData.tempRt2 = UniversalRenderer.CreateRenderGraphTexture(renderGraph, textureProperties, "MyBlurPassTempRt2", false);

        var rt1 = passData.tempRt1;
        var rt2 = passData.tempRt2;

        //将屏幕RT Blit到rt1上
        var para = new RenderGraphUtils.BlitMaterialParameters(resourceData.activeColorTexture, rt1, material, 0);
        renderGraph.AddBlitPass(para, "MyBlurPassBlitFirst");

        material.SetFloat("_SampleOffset", offset);

        //模糊迭代
        for (int i = 0; i < blurPasses - 1; ++i)
        {
            para = new RenderGraphUtils.BlitMaterialParameters(rt1, rt2, material, 0);
            renderGraph.AddBlitPass(para, $"MyBlurPassBlit_{i}");

            var tmp = rt1;
            rt1 = rt2;
            rt2 = tmp;
        }

        //通过直接绘制的方式，将模糊RT绘制到屏幕上
        using (var builder = renderGraph.AddRasterRenderPass<PassData>(passName, out _))
        {
            builder.UseTexture(rt1);
            builder.SetRenderAttachment(resourceData.activeColorTexture, 0);

            builder.SetRenderFunc<PassData>((data, context) =>
            {
                MaterialPropertyBlock materialPropertyBlock = new MaterialPropertyBlock();
                materialPropertyBlock.SetTexture("_BlitTexture", rt1);
                materialPropertyBlock.SetVector("_BlitScaleBias", new Vector4(1, 1, 0, 0));

                context.cmd.DrawProcedural(Matrix4x4.identity, material, 0, MeshTopology.Triangles, 3, 1, materialPropertyBlock);
            });
        }
    }
}

最后在ShaderGraph中连出模糊的逻辑，注意Blit对应的参数_BlitTexture、_BlitScaleBias：

最后在场景中挂载控制器以及材质球，即可使用该模糊Pass。