Troubleshooting Scriptable Render Passes with HDR Output in URP

High Dynamic Range (HDR) Output changes the inputs to your scriptable render pass when it applies tone mapping and color space conversions. These changes can cause your scriptable render pass to produce incorrect results. This means that when you use HDRhigh dynamic range
See in Glossary Output and a scriptable render pass that happens in or after the AfterRenderingPostProcessing injection point, you need to account for the changes HDR Output makes. This also applies when you want to add overlays during or after 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, such as UI(User Interface) Allows a user to interact with your application. Unity currently supports three UI systems. More info
See in Glossary or output from other camerasA 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, because you need to work with the color gamut that results from HDR Output. To make a scriptable render pass work with the changes HDR Output makes, you must manually perform tone mapping and convert color space in a script.

However, if you add your scriptable render pass at or before the BeforeRenderingPostProcessing injection point, you don’t need to make any changes for compatibility with HDR Output. This is because Unity executes your scriptable render pass before it renders the HDR Output.

Note: You can avoid this problem when you use a camera stack to render camera output before Unity performs tone mapping. Unity then applies HDR Output processing to the last camera in the stack. To learn how to set up a camera stack, refer to Camera stacking.

Tone map and convert color space in a script

To make a scriptable render pass pass work with the changes HDR Output makes to color space and dynamic range, use the SetupHDROutput function to apply tone mapping and color space conversion to the material the scriptable render pass alters:

Open the C# script which contains the Scriptable Render Pass you wish to use with HDR Output.

Add a method with the name SetupHDROutput to the Render Pass class.

The following script gives an example of how to use the SetupHDROutput function:

class CustomFullScreenRenderPass : ScriptableRenderPass
{
    // Leave your existing Render Pass code here

    static void SetupHDROutput(ref CameraData cameraData, Material material)
    {
        // This is where most HDR related code is added
    }
}

Add an if statement to check whether HDR Output is active and if the camera has post-processing enabled. If either condition is not met, disable the HDR Output shaderA program that runs on the GPU. More info
See in Glossary keywords to reduce resource usage.

static void SetupHDROutput(ref CameraData cameraData, Material material)
{
    // If post processing is enabled, color grading has already applied tone mapping
    // As a result the input here will be in the display colorspace (Rec2020, P3, etc) and in nits
    if (cameraData.isHDROutputActive && cameraData.postProcessEnabled)
    {

    }
    else
    {
        // If HDR output is disabled, disable HDR output-related keywords
        // If post processing is disabled, the final pass will do the color conversion so there is
        // no need to account for HDR Output
        material.DisableKeyword(HDROutputUtils.ShaderKeywords.HDR_INPUT);
    }
}

Create variables to retrieve and store the luminance information from the display as shown below.

if (cameraData.isHDROutputActive && cameraData.postProcessEnabled)
{
    // Get luminance information from the display, these define the dynamic range of the display.
    float minNits = cameraData.hdrDisplayInformation.minToneMapLuminance;
    float maxNits = cameraData.hdrDisplayInformation.maxToneMapLuminance;
    float paperWhite = cameraData.hdrDisplayInformation.paperWhiteNits;
}
else
{
    // If HDR output is disabled, disable HDR output-related keywords
    // If post processing is disabled, the final pass will do the color conversion so there is
    // no need to account for HDR Output
    material.DisableKeyword(HDROutputUtils.ShaderKeywords.HDR_INPUT);
}

Retrieve the tonemappingThe process of remapping HDR values of an image into a range suitable to be displayed on screen. More info
See in Glossary component from the Volume Manager.

if (cameraData.isHDROutputActive && cameraData.postProcessEnabled)
{
    var tonemapping = VolumeManager.instance.stack.GetComponent<Tonemapping>();

    // Get luminance information from the display, these define the dynamic range of the display.
    float minNits = cameraData.hdrDisplayInformation.minToneMapLuminance;
    float maxNits = cameraData.hdrDisplayInformation.maxToneMapLuminance;
    float paperWhite = cameraData.hdrDisplayInformation.paperWhiteNits;
}

Add another if statement to check whether a tonemapping component is present. If a tonemapping component is found, this can override the luminance data from the display.

if (cameraData.isHDROutputActive && cameraData.postProcessEnabled)
{
    var tonemapping = VolumeManager.instance.stack.GetComponent<Tonemapping>();

    // Get luminance information from the display, these define the dynamic range of the display.
    float minNits = cameraData.hdrDisplayInformation.minToneMapLuminance;
    float maxNits = cameraData.hdrDisplayInformation.maxToneMapLuminance;
    float paperWhite = cameraData.hdrDisplayInformation.paperWhiteNits;

    if (tonemapping != null)
    {
        // Tone mapping post process can override the luminance retrieved from the display
        if (!tonemapping.detectPaperWhite.value)
        {
            paperWhite = tonemapping.paperWhite.value;
        }
        if (!tonemapping.detectBrightnessLimits.value)
        {
            minNits = tonemapping.minNits.value;
            maxNits = tonemapping.maxNits.value;
        }
    }
}

Set the luminance properties of the material with the luminance data from the display and tonemapping.

if (cameraData.isHDROutputActive && cameraData.postProcessEnabled)
{
    var tonemapping = VolumeManager.instance.stack.GetComponent<Tonemapping>();

    // Get luminance information from the display, these define the dynamic range of the display.
    float minNits = cameraData.hdrDisplayInformation.minToneMapLuminance;
    float maxNits = cameraData.hdrDisplayInformation.maxToneMapLuminance;
    float paperWhite = cameraData.hdrDisplayInformation.paperWhiteNits;

    if (tonemapping != null)
    {
        // Tone mapping post process can override the luminance retrieved from the display
        if (!tonemapping.detectPaperWhite.value)
        {
            paperWhite = tonemapping.paperWhite.value;
        }
        if (!tonemapping.detectBrightnessLimits.value)
        {
            minNits = tonemapping.minNits.value;
            maxNits = tonemapping.maxNits.value;
        }
    }

    // Pass luminance data to the material, use these to interpret the range of values the
    // input will be in.
    material.SetFloat("_MinNits", minNits);
    material.SetFloat("_MaxNits", maxNits);
    material.SetFloat("_PaperWhite", paperWhite);
}

Retrieve the color gamut of the current color space and pass it to the material.

// Pass luminance data to the material, use these to interpret the range of values the
// input will be in.
material.SetFloat("_MinNits", minNits);
material.SetFloat("_MaxNits", maxNits);
material.SetFloat("_PaperWhite", paperWhite);

// Pass the color gamut data to the material (colorspace and transfer function).
HDROutputUtils.GetColorSpaceForGamut(cameraData.hdrDisplayColorGamut, out int colorspaceValue);
material.SetInteger("_HDRColorspace", colorspaceValue);

Enable the HDR Output shader keywords.

// Pass the color gamut data to the material (colorspace and transfer function).
HDROutputUtils.GetColorSpaceForGamut(cameraData.hdrDisplayColorGamut, out int colorspaceValue);
material.SetInteger("_HDRColorspace", colorspaceValue);

// Enable HDR shader keywords
material.EnableKeyword(HDROutputUtils.ShaderKeywords.HDR_INPUT);

Call the SetupHDROutput method in your Execute() function to ensure that HDR Output is accounted for whenever this Scriptable Render Pass is in use.

Complete Script Example

The following is the complete code from the example:

class CustomFullScreenRenderPass : ScriptableRenderPass
{
    // Leave your existing Render Pass code here

    static void SetupHDROutput(ref CameraData cameraData, Material material)
    {
        // If post processing is enabled, color grading has already applied tone mapping
        // As a result the input here will be in the display colorspace (Rec2020, P3, etc) and in nits
        if (cameraData.isHDROutputActive && cameraData.postProcessEnabled)
        {
            var tonemapping = VolumeManager.instance.stack.GetComponent<Tonemapping>();

            // Get luminance information from the display, these define the dynamic range of the display.
            float minNits = cameraData.hdrDisplayInformation.minToneMapLuminance;
            float maxNits = cameraData.hdrDisplayInformation.maxToneMapLuminance;
            float paperWhite = cameraData.hdrDisplayInformation.paperWhiteNits;

            if (tonemapping != null)
            {
                // Tone mapping post process can override the luminance retrieved from the display
                if (!tonemapping.detectPaperWhite.value)
                {
                    paperWhite = tonemapping.paperWhite.value;
                }
                if (!tonemapping.detectBrightnessLimits.value)
                {
                    minNits = tonemapping.minNits.value;
                    maxNits = tonemapping.maxNits.value;
                }
            }

            // Pass luminance data to the material, use these to interpret the range of values the
            // input will be in.
            material.SetFloat("_MinNits", minNits);
            material.SetFloat("_MaxNits", maxNits);
            material.SetFloat("_PaperWhite", paperWhite);

            // Pass the color gamut data to the material (colorspace and transfer function).
            HDROutputUtils.GetColorSpaceForGamut(cameraData.hdrDisplayColorGamut, out int colorspaceValue);
            material.SetInteger("_HDRColorspace", colorspaceValue);

            // Enable HDR shader keywords
            material.EnableKeyword(HDROutputUtils.ShaderKeywords.HDR_INPUT);
        }
        else
        {
            // If HDR output is disabled, disable HDR output-related keywords
            // If post processing is disabled, the final pass will do the color conversion so there is
            // no need to account for HDR Output
            material.DisableKeyword(HDROutputUtils.ShaderKeywords.HDR_INPUT);
        }
    }
}

Implement an HDR Output compatible custom overlay in URP

Graphics performance and profiling

Unity Manual

Troubleshooting Scriptable Render Passes with HDR Output in URP

Tone map and convert color space in a script

Complete Script Example