Version: Unity 6.1 Alpha (6000.1)
Language : English
Enable HDR Output in URP
Troubleshooting Scriptable Render Passes with HDR Output in URP

Implement an HDR Output compatible custom overlay in URP

This page demonstrates how to create a Scriptable Renderer Feature that does the following:

  • Composites the output of one cameraA component which creates an image of a particular viewpoint in your scene. The output is either drawn to the screen or captured as a texture. More info
    See in Glossary     onto another camera.
  • Applies tonemappingThe process of remapping HDR values of an image into a range suitable to be displayed on screen. More info
    See in Glossary     to make the custom overlay consistent with the effects of HDRhigh dynamic range
    See in Glossary     output.

This includes the shaderA program that runs on the GPU. More info
See in Glossary that applies tonemapping to the overlay, depending on frame order.

Refer to Introduction to Scriptable Renderer Features and Introduction to Scriptable Render Passes for more information.

This example is split into the following sections:

Prerequisites

This example assumes the following:

  • The Unity project uses URP as the active render pipelineA series of operations that take the contents of a Scene, and displays them on a screen. Unity lets you choose from pre-built render pipelines, or write your own. More info
    See in Glossary    .
  • The project is set up for HDR rendering with the following settings:
  • The active URP Asset has Grading Mode set to High Dynamic Range.
  • The active URP Asset has HDR enabled.
  • The Project SettingsA broad collection of settings which allow you to configure how Physics, Audio, Networking, Graphics, Input and many other areas of your project behave. More info
    See in Glossary     have HDR Output enabled.

Set up the scene

For the example to work correctly, you must first set up a sample sceneA Scene contains the environments and menus of your game. Think of each unique Scene file as a unique level. In each Scene, you place your environments, obstacles, and decorations, essentially designing and building your game in pieces. More info
See in Glossary as shown in the following instructions.

  1. Create a Cube GameObjectThe fundamental object in Unity scenes, which can represent characters, props, scenery, cameras, waypoints, and more. A GameObject’s functionality is defined by the Components attached to it. More info
    See in Glossary     and set its position to the origin point in the scene (X: 0, Y: 0, Z: 0).

  2. Align the Main Camera so that the cube is clearly visible.

  3. Create a new camera and call it Overlay Camera.

  4. Position the overlay camera to the right of the Main Camera and align it so the cube is clearly visible.

  5. Set the overlay camera Background Type property to Solid Color in the InspectorA Unity window that displays information about the currently selected GameObject, asset or project settings, allowing you to inspect and edit the values. More info
    See in Glossary     window.

  6. Set the color of the overlay camera background to a clear black with the RGBA values of 0, 0, 0, 0.

  7. Create a render texture and call it OverlayRenderTexture. To create a render texture, go to Assets > Create > Rendering > Render Texture.

    Note: For better HDR precision, use a signed float format for the render texture format. To do this, select the render texture, then in the Inspector window change Color Format to a format with the _SFLOAT suffix.

  8. Assign the overlay render texture to the overlay camera’s Output Texture property. To do this, open the Overlay Camera in the Inspector and go to Output > Output Texture and select OverlayRenderTexture from the asset list.

  9. Create a new Universal Renderer asset for the overlay camera and call it OverlayRenderer. To do this, go to Assets > Create > Rendering > URP Universal Renderer.

  10. Select the active URP Asset, then in the Inspector window go to Rendering > Renderer List > +. Select OverlayRenderer. This adds the overlay renderer to the renderer list.

  11. Select the overlay camera, then in the Inspector window go to Rendering > Renderer. Select OverlayRenderer. This sets the overlay camera to use the overlay renderer.

The scene is now ready for you to create a custom overlay with Scriptable Renderer Features.

Create the custom overlay Render Pass

To create a custom overlay that’s compatible with HDR Output, you must use a Scriptable Render Pass to create the overlay. HDR Output applies tonemapping to the output of the main camera during post-processingA process that improves product visuals by applying filters and effects before the image appears on screen. You can use post-processing effects to simulate physical camera and film properties, for example Bloom and Depth of Field. More info post processing, postprocessing, postprocess
See in Glossary. As a result of this, the output of the main camera and the overlay camera have different tonemapping. This render pass then occurs after post-processing to apply tonemapping to the output of the overlay camera.

To create the render pass for this example, use the following steps:

  1. Create a C# script and call it CustomOverlayRenderPass.

  2. In the script, remove the code that Unity inserted in the CustomOverlayRenderPass class.

  3. Add the following using directives.

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

  4. Create a new CustomOverlayRenderPass class that inherits from the ScriptableRenderPass class and has the attribute [SupportedOnRenderer(typeof(UniversalRendererData) -->.

    [SupportedOnRenderer(typeof(UniversalRendererData))] -->
public class CustomOverlayRenderPass : ScriptableRenderPass
{
  
}

  5. Add the properties Material passMaterial and RTHandle passOverlayTexture to the render pass, as shown below.

    [SupportedOnRenderer(typeof(UniversalRendererData))] -->
public class CustomOverlayRenderPass : ScriptableRenderPass
{
    Material passMaterial;
    RTHandle overlayTextureHandle;
}

  6. Create a constructor method that takes a material as a parameter and assigns it to passMaterial. This method also creates the profiling sampler for the render pass and sets it to run at the AfterRenderingPostProcessing event.

    public CustomOverlayRenderPass(Material material)
{
    passMaterial = material;
    profilingSampler = new ProfilingSampler(nameof(CustomOverlayRenderPass));

    renderPassEvent = RenderPassEvent.AfterRenderingPostProcessing;
}

  7. Add a Setup method for the render pass. Use this method and parameter to create an RTHandle from the overlay texture as shown below. The use of an RTHandle allows the RenderPass API to interact with the overlay render textureA special type of Texture that is created and updated at runtime. To use them, first create a new Render Texture and designate one of your Cameras to render into it. Then you can use the Render Texture in a Material just like a regular Texture. More info
    See in Glossary    .

    public void Setup(Texture overlayTex)
{
    if (overlayTextureHandle != overlayTex)
    {
        overlayTextureHandle?.Release();
        overlayTextureHandle = RTHandles.Alloc(overlayTex);
    }
}

  8. Implement the Dispose method to release the overlay texture when the render pass is destroyed.

    public void Dispose()
{
    overlayTextureHandle?.Release();
}

  9. Create two structs, one named CopyData, and another named PassData, which contain the properties shown below. These structs hold key properties URP needs to implement the render pass.

    struct CopyData
{
    public TextureHandle source;
}

struct PassData
{
    public TextureHandle source;
    public TextureHandle overlayTexture;
    public TextureHandle internalLut;
    public Vector4 lutParams;
    public Material material;
}

  10. Add the RecordRenderGraph method as shown below.

    public override void RecordRenderGraph(RenderGraph renderGraph, ContextContainer frameData)
{

}

Implement the RecordRenderGraph method

Add the code from the following steps within the RecordRenderGraph method of the CustomOverlayRenderPass class.

  1. Get the post-processing, resource, and camera data from the frame data.

    UniversalPostProcessingData postProcessingData = frameData.Get<UniversalPostProcessingData>();
UniversalResourceData resourceData = frameData.Get<UniversalResourceData>();
UniversalCameraData cameraData = frameData.Get<UniversalCameraData>();

  2. Get the active color texture from the resource data.

    TextureHandle activeCameraColor = resourceData.activeColorTexture;

  3. Create a texture to store the active camera color target.

    RenderTextureDescriptor colorCopyDescriptor = cameraData.cameraTargetDescriptor;
colorCopyDescriptor.depthBufferBits = (int) DepthBits.None;
TextureHandle copiedColor = UniversalRenderer.CreateRenderGraphTexture(renderGraph, colorCopyDescriptor, "_CustomCameraColorCopy", false);

  4. Create a RasterRenderPass to copy the active camera color target into the texture. The copy will be used to handle blending.

    using (var builder = renderGraph.AddRasterRenderPass<CopyData>("Custom Overlay Render Pass - Copy Camera", out var passData))
{
    passData.source = activeCameraColor;
    builder.UseTexture(passData.source, AccessFlags.Read);
    builder.SetRenderAttachment(copiedColor, 0, AccessFlags.WriteAll);

    builder.SetRenderFunc((CopyData data, RasterGraphContext context) =>
    {
        Blitter.BlitTexture(context.cmd, data.source, new Vector4(1, 1, 0, 0), 0.0f, false);
    });
}

  5. Create another RasterRenderPass to copy the overlay texture to the active camera color target with a custom material. This is the container for the rest of the code you add in this section of the guide.

    using (var builder = renderGraph.AddRasterRenderPass<PassData>("Custom Overlay Render Pass - Blit Overlay", out var passData))
{
    
}

  6. Set up the properties the render pass needs to blitA shorthand term for “bit block transfer”. A blit operation is the process of transferring blocks of data from one place in memory to another.
    See in Glossary     the overlay texture, as shown below.

    using (var builder = renderGraph.AddRasterRenderPass<PassData>("Custom Overlay Render Pass - Blit Overlay", out var passData))
{
    passData.material = passMaterial;

    builder.SetRenderAttachment(activeCameraColor, 0, AccessFlags.Write);

    passData.source = copiedColor;
    builder.UseTexture(passData.source, AccessFlags.Read);
}

  7. Import the texture into the render graph system, then set the texture as an input.

    passData.overlayTexture = renderGraph.ImportTexture(passOverlayTexture);
builder.UseTexture(passData.overlayTexture, AccessFlags.Read);

  8. Check for post-processing and HDR color grading. If the configuration is correct for HDR Output, set the internal color LUT texture HDR uses as an input, and pass its parameters to the shader.

    if (postProcessingData.gradingMode == ColorGradingMode.HighDynamicRange && cameraData.postProcessEnabled)
{
    passData.internalLut = resourceData.internalColorLut;
    builder.UseTexture(passData.internalLut, AccessFlags.Read);

    int lutHeight = postProcessingData.lutSize;
    int lutWidth = lutHeight * lutHeight;

    float postExposure = 1.0f;
    ColorAdjustments colorAdjustments = VolumeManager.instance.stack.GetComponent<ColorAdjustments>();
    if (colorAdjustments != null)
    {
        postExposure = Mathf.Pow(2.0f, colorAdjustments.postExposure.value);
    }

    passData.lutParams = new Vector4(1f / lutWidth, 1f / lutHeight, lutHeight - 1f, postExposure);
}

    Note: If post processing is disabled, the HDR color conversion will be applied after this render pass and the expected colorspace for the cameras output is the default Rec709. The code in this example uses an if statement here to prevent this render pass from altering the output of the overlay camera before HDR is applied.

  9. Set a keyword on the shader to enable tonemapping, and add a command to blit the overlay texture to the active camera color target.

    builder.SetRenderFunc((PassData data, RasterGraphContext context) =>
{
    data.material.SetTexture("_OverlayTexture", data.overlayTexture);

    bool tonemappingActive = data.internalLut.IsValid();
    CoreUtils.SetKeyword(data.material, "TONEMAPPING", tonemappingActive);
    if (tonemappingActive)
    {
        data.material.SetTexture("_InternalLut", data.internalLut);
        data.material.SetVector("_InternalLut_Params", data.lutParams);
    }
        
    Blitter.BlitTexture(context.cmd, data.source, new Vector4(1, 1, 0, 0), data.material, 0);
});

This completes the CustomOverlayRenderPass script, ready for a Scriptable Renderer Feature to add it to a renderer.

For the complete code for this section, refer to Custom overlay Render Pass code.

Create the custom overlay Scriptable Renderer Feature

To add the CustomOverlayRenderPass to a renderer, you must create a Scriptable Renderer Feature with the following steps.

  1. Create a C# script and call it CustomOverlayRendererFeature.

  2. In the script, remove the code that Unity inserted in the CustomOverlayRendererFeature class.

  3. Add the following using directives.

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

  4. Set up a new CustomOverlayRendererFeature class that inherits from the ScriptableRendererFeature class.

    public class CustomOverlayRendererFeature : ScriptableRendererFeature
{
  
}

  5. Add the following properties to contain the assets and data the render pass needs.

    public class CustomOverlayRendererFeature : ScriptableRendererFeature
{
    public Shader hdrShader;
    public RenderTexture passOverlayTexture;

    Material passMaterial;

    CustomOverlayRenderPass overlayRenderPass = null;
}

  6. Create the AddRenderPasses method, and use it to apply the overlay only in Game view and to the last camera in the camera stack.

    public override void AddRenderPasses(ScriptableRenderer renderer, ref RenderingData renderingData)
{
    if (renderingData.cameraData.cameraType != CameraType.Game || !renderingData.cameraData.resolveFinalTarget)
        return;
}

  7. After the if statement, pass the overlay texture to the overlay render pass and enqueue the render pass.

    public override void AddRenderPasses(ScriptableRenderer renderer, ref RenderingData renderingData)
{
    if (renderingData.cameraData.cameraType != CameraType.Game || !renderingData.cameraData.resolveFinalTarget)
        return;

    overlayRenderPass.Setup(passOverlayTexture);

    renderer.EnqueuePass(overlayRenderPass);
}

  8. Add the Create method and create an instance of the CustomOverlayRenderPass with a new material that uses hdrShader.

    public override void Create()
{
    passMaterial = CoreUtils.CreateEngineMaterial(hdrShader);

    overlayRenderPass = new CustomOverlayRenderPass(passMaterial);
}

  9. Implement the Dispose method to release the resources the renderer feature creates once it has applied the render pass.

    protected override void Dispose(bool disposing)
{
    CoreUtils.Destroy(passMaterial);
    overlayRenderPass.Dispose();
}

For the complete code for this section, refer to Custom overlay Scriptable Renderer Feature code.

Create the custom overlay shader

The material the CustomOverlayRendererFeature creates requires a custom shader to handle the overlay and HDR Output changes. The following steps demonstrate how to create a shader capable of this.

  1. Create a new shader and name it CustomOverlayBlit.

  2. Delete the shader code Unity generates automatically and set up the outline of the shader as shown below.

    Shader "Custom/CustomOverlayBlit"
{
    SubShader
    {
        Tags{ "RenderPipeline" = "UniversalPipeline" }

        Pass
        {
            ZWrite Off ZTest Always Blend Off Cull Off

            HLSLPROGRAM
                #pragma target 2.0
                #pragma editor_sync_compilation
                #pragma vertex Vert
                #pragma fragment Frag
                #pragma multi_compile_local_fragment _ TONEMAPPING

                #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"
                #include "Packages/com.unity.render-pipelines.core/Runtime/Utilities/Blit.hlsl"
                #include "Packages/com.unity.render-pipelines.core/ShaderLibrary/Color.hlsl"
                
                TEXTURE2D(_InternalLut);
                TEXTURE2D_X(_OverlayTexture);

                float4 _InternalLut_Params;

                #define LutParams _InternalLut_Params.xyz
                #define PostExposure _InternalLut_Params.w

            ENDHLSL
        }
    }
}

  3. Create a method with the name ApplyTonemapping and the return type half3. This method should have the following parameters: half3 input, TEXTURE2D_PARAM(lutTex, lutSampler), float3 lutParams, float exposure.

  4. In the ApplyTonemapping method, multiply input by the exposure value, then saturate the modified input.

    half3 ApplyTonemapping(half3 input, TEXTURE2D_PARAM(lutTex, lutSampler), float3 lutParams, float exposure)
{
    input *= exposure;
    float3 inputLutSpace = saturate(LinearToLogC(input));
}

  5. Apply the tonemapping changes with ApplyLut2D and return the result.

    half3 ApplyTonemapping(half3 input, TEXTURE2D_PARAM(lutTex, lutSampler), float3 lutParams, float exposure)
{
    input *= exposure;
    float3 inputLutSpace = saturate(LinearToLogC(input));
    return ApplyLut2D(TEXTURE2D_ARGS(lutTex, lutSampler), inputLutSpace, lutParams);
}

  6. Create a standard Frag method as shown below. Place this method inside the HLSLPROGRAM but after the ApplyTonemapping method.

    half4 Frag(Varyings input) : SV_Target
{

}

  7. In the Frag method, retrieve the original camera color and the overlay color.

    half4 Frag(Varyings input) : SV_Target
{
    half4 color = FragBlit(input, sampler_LinearClamp);

    half4 overlay = SAMPLE_TEXTURE2D_X(_OverlayTexture, sampler_LinearClamp, input.texcoord);
}

  8. Create an if statement to check if the shader should apply tonemapping. If the shader should apply tonemapping. use the ApplyTonemapping method to apply it to the overlay.

    half4 Frag(Varyings input) : SV_Target
{
    half4 color = FragBlit(input, sampler_LinearClamp);

    half4 overlay = SAMPLE_TEXTURE2D_X(_OverlayTexture, sampler_LinearClamp, input.texcoord);

    #if TONEMAPPING
    overlay.rgb = ApplyTonemapping(overlay.rgb, TEXTURE2D_ARGS(_InternalLut, sampler_LinearClamp), LutParams, PostExposure);
    #endif
}

  9. Blend the overlay with the original camera color and return the outcome.

    half4 Frag(Varyings input) : SV_Target
{
    half4 color = FragBlit(input, sampler_LinearClamp);

    half4 overlay = SAMPLE_TEXTURE2D_X(_OverlayTexture, sampler_LinearClamp, input.texcoord);

    #if TONEMAPPING
    overlay.rgb = ApplyTonemapping(overlay.rgb, TEXTURE2D_ARGS(_InternalLut, sampler_LinearClamp), LutParams, PostExposure);
    #endif

    color.rgb = color.rgb * (1.0 - overlay.a) + overlay.rgb * overlay.a;
    return color;
}

The shader is now complete and ready for use in the CustomOverlayRenderPass and CustomOverlayRendererFeature scriptsA piece of code that allows you to create your own Components, trigger game events, modify Component properties over time and respond to user input in any way you like. More info
See in Glossary.

To see the complete code for this section, refer to Custom overlay shader code.

Finish the custom overlay

To finish the custom overlay, you must set up the scripts you’ve created, to apply their effects to the renderers in the scene. The following steps demonstrate how to do this.

  1. Find and select the main renderer the active URP Asset uses.
  2. In the Inspector window, select Add Renderer Feature > Custom Overlay Renderer Feature to add the CustomOverlayRendererFeature script.
  3. Assign the CustomOverlayBlit shader to the Shader property of the custom overlay Scriptable Renderer Feature.
  4. Assign the OverlayRenderTexture to the Overlay Texture property of the custom overlay Scriptable Renderer Feature.

The custom overlay is now complete and should appear on top of the main camera output in Play Mode. The overlay should be tonemapped in the same way as the main camera output, with no visible difference. This should be similar to the screenshot below.

Cube in the middle of the Game view with the cube from another angle as an overlay, tonemapped to match HDR Output
Cube in the middle of the Game view with the cube from another angle as an overlay, tonemapped to match HDR Output.

Note: The end result might vary depending on the placement of the overlay camera.

Complete code samples

Custom overlay render pass code

The following is the complete code sample for the Scriptable Render Pass from the example.

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

[SupportedOnRenderer(typeof(UniversalRendererData))] -->
public class CustomOverlayRenderPass : ScriptableRenderPass
{
    Material passMaterial;
    RTHandle overlayTextureHandle;

    public CustomOverlayRenderPass(Material material)
    {
        passMaterial = material;
        profilingSampler = new ProfilingSampler(nameof(CustomOverlayRenderPass));

        // The render pass is executed after post processing, so the main camera target has been tonemapped but not the overlay texture
        renderPassEvent = RenderPassEvent.AfterRenderingPostProcessing;
    }

    public void Setup(Texture overlayTex)
    {
        //Create an RTHandle from the overlay texture, to import it into the render graph system
        if (overlayTextureHandle != overlayTex)
        {
            overlayTextureHandle?.Release();
            overlayTextureHandle = RTHandles.Alloc(overlayTex);
        }
    }

    public void Dispose()
    {
        overlayTextureHandle?.Release();
    }

    class CopyData
    {
        public TextureHandle source;
    }

    class PassData
    {
        public TextureHandle source;
        public TextureHandle overlayTexture;
        public TextureHandle internalLut;
        public Vector4 lutParams;
        public Material material;
    }
    
    public override void RecordRenderGraph(RenderGraph renderGraph, ContextContainer frameData)
    {
        UniversalPostProcessingData postProcessingData = frameData.Get<UniversalPostProcessingData>();
        UniversalResourceData resourceData = frameData.Get<UniversalResourceData>();
        UniversalCameraData cameraData = frameData.Get<UniversalCameraData>();

        TextureHandle activeCameraColor = resourceData.activeColorTexture;

        // Create a texture to copy the active camera color target into
        RenderTextureDescriptor colorCopyDescriptor = cameraData.cameraTargetDescriptor;
        colorCopyDescriptor.depthBufferBits = (int) DepthBits.None;
        TextureHandle copiedColor = UniversalRenderer.CreateRenderGraphTexture(renderGraph, colorCopyDescriptor, "_CustomCameraColorCopy", false);

        // Copy the active camera color target into the texture
        using (var builder = renderGraph.AddRasterRenderPass<CopyData>("Custom Overlay Render Pass - Copy Camera", out var passData))
        {
            passData.source = activeCameraColor;
            builder.UseTexture(passData.source, AccessFlags.Read);
            builder.SetRenderAttachment(copiedColor, 0, AccessFlags.WriteAll);

            builder.SetRenderFunc((CopyData data, RasterGraphContext context) =>
            {
                Blitter.BlitTexture(context.cmd, data.source, new Vector4(1, 1, 0, 0), 0.0f, false);
            });
        }

        using (var builder = renderGraph.AddRasterRenderPass<PassData>("Custom Overlay Render Pass - Blit Overlay", out var passData))
        {
            passData.material = passMaterial;

            builder.SetRenderAttachment(activeCameraColor, 0, AccessFlags.Write);

            passData.source = copiedColor;
            builder.UseTexture(passData.source, AccessFlags.Read);

            // Import the overlay texture that will be copied onto the camera color, and set it as an input
            passData.overlayTexture = renderGraph.ImportTexture(overlayTextureHandle);
            builder.UseTexture(passData.overlayTexture, AccessFlags.Read);

            // If post-processing is enabled on the main camera, apply the tonemapping to the overlay texture as well
            // If post processing is disabled, the HDR color conversion will be applied after this render pass and the expected colorspace for the cameras output is the default Rec709
            if (postProcessingData.gradingMode == ColorGradingMode.HighDynamicRange && cameraData.postProcessEnabled)
            {
                // Import the internal color LUT texture used for HDR color grading and tonemapping
                // This includes any HDR color conversion URP needs for the display, so the output of the camera is in the display's color gamut
                passData.internalLut = resourceData.internalColorLut;
                builder.UseTexture(passData.internalLut, AccessFlags.Read);

                // Pass LUT parameters to the shader
                int lutHeight = postProcessingData.lutSize;
                int lutWidth = lutHeight * lutHeight;

                float postExposure = 1.0f;
                ColorAdjustments colorAdjustments = VolumeManager.instance.stack.GetComponent<ColorAdjustments>();
                if (colorAdjustments != null)
                {
                    postExposure = Mathf.Pow(2.0f, colorAdjustments.postExposure.value);
                }

                passData.lutParams = new Vector4(1f / lutWidth, 1f / lutHeight, lutHeight - 1f, postExposure);
            }

            builder.SetRenderFunc((PassData data, RasterGraphContext context) =>
            {
                // Pass parameters to the shader
                data.material.SetTexture("_OverlayTexture", data.overlayTexture);

                // Set a keyword on the shader to enable tonemapping
                bool tonemappingActive = data.internalLut.IsValid();
                CoreUtils.SetKeyword(data.material, "TONEMAPPING", tonemappingActive);
                if (tonemappingActive)
                {
                    data.material.SetTexture("_InternalLut", data.internalLut);
                    data.material.SetVector("_InternalLut_Params", data.lutParams);
                }
                
                // Blit the overlay texture onto the camera color
                Blitter.BlitTexture(context.cmd, data.source, new Vector4(1, 1, 0, 0), data.material, 0);
            });
        }
    }
}

Custom overlay Scriptable Renderer Feature code

The following is the complete code sample for the Scriptable Renderer Feature from the example.

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

public class CustomOverlayRendererFeature : ScriptableRendererFeature
{
    public Shader hdrShader;
    public RenderTexture passOverlayTexture;

    Material passMaterial;

    CustomOverlayRenderPass overlayRenderPass = null;

    public override void AddRenderPasses(ScriptableRenderer renderer, ref RenderingData renderingData)
    {
        // Render the overlay onto the main camera during Game view rendering only, for the last camera in the camera stack
        if (renderingData.cameraData.cameraType != CameraType.Game || !renderingData.cameraData.resolveFinalTarget)
            return;

        // Pass the overlay texture at runtime in case it changes
        overlayRenderPass.Setup(passOverlayTexture);

        // Enqueue the render pass to be executed
        renderer.EnqueuePass(overlayRenderPass);
    }

    public override void Create()
    {
        // Create a blit material from the given shader
        passMaterial = CoreUtils.CreateEngineMaterial(hdrShader);

        // Create the render pass
        overlayRenderPass = new CustomOverlayRenderPass(passMaterial);
    }

    protected override void Dispose(bool disposing)
    {
        // Destroy the render pass resources
        CoreUtils.Destroy(passMaterial);
        overlayRenderPass.Dispose();
    }
}

Custom overlay shader code

The following is the complete code sample for the shader from the example.

Shader "Custom/CustomOverlayBlit"
{
    SubShader
    {
        Tags{ "RenderPipeline" = "UniversalPipeline" }

        Pass
        {
            ZWrite Off ZTest Always Blend Off Cull Off

            HLSLPROGRAM
                #pragma target 2.0
                #pragma editor_sync_compilation
                #pragma vertex Vert
                #pragma fragment Frag
                #pragma multi_compile_local_fragment _ TONEMAPPING

                #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"
                #include "Packages/com.unity.render-pipelines.core/Runtime/Utilities/Blit.hlsl"
                #include "Packages/com.unity.render-pipelines.core/ShaderLibrary/Color.hlsl"
                
                TEXTURE2D(_InternalLut);
                TEXTURE2D_X(_OverlayTexture);

                float4 _InternalLut_Params;

                #define LutParams _InternalLut_Params.xyz
                #define PostExposure _InternalLut_Params.w

                half3 ApplyTonemapping(half3 input, TEXTURE2D_PARAM(lutTex, lutSampler), float3 lutParams, float exposure)
                {
                    input *= exposure;
                    float3 inputLutSpace = saturate(LinearToLogC(input)); // LUT space is in LogC
                    return ApplyLut2D(TEXTURE2D_ARGS(lutTex, lutSampler), inputLutSpace, lutParams);
                }

                half4 Frag(Varyings input) : SV_Target
                {
                    // Get the original camera color
                    half4 color = FragBlit(input, sampler_LinearClamp);

                    // Get the overlay color
                    half4 overlay = SAMPLE_TEXTURE2D_X(_OverlayTexture, sampler_LinearClamp, input.texcoord);

                    // Tonemap the overlay
                    #if TONEMAPPING
                    overlay.rgb = ApplyTonemapping(overlay.rgb, TEXTURE2D_ARGS(_InternalLut, sampler_LinearClamp), LutParams, PostExposure);
                    #endif

                    // Blend overlay and color
                    color.rgb = color.rgb * (1.0 - overlay.a) + overlay.rgb * overlay.a;
                    return color;
                }

            ENDHLSL
        }
    }
}
Enable HDR Output in URP
Troubleshooting Scriptable Render Passes with HDR Output in URP
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