Singularity/Library/PackageCache/com.unity.render-pipelines.universal@12.1.11/Documentation~/renderer-features/how-to-fullscreen-blit-in-xr-spi.md

# How to perform a full screen blit in Single Pass Instanced rendering in XR

The example on this page describes how to create a custom Renderer Feature that performs a full screen blit in Single Pass Instanced rendering in XR.

## Example overview

This example implements the following solution:

* A [custom Renderer Feature](https://docs.unity3d.com/Packages/com.unity.render-pipelines.universal@12.0/api/UnityEngine.Rendering.Universal.ScriptableRendererFeature.html) calls a custom [Render Pass](https://docs.unity3d.com/Packages/com.unity.render-pipelines.universal@12.0/api/UnityEngine.Rendering.Universal.ScriptableRenderPass.html).

* The [Render Pass](https://docs.unity3d.com/Packages/com.unity.render-pipelines.universal@12.0/api/UnityEngine.Rendering.Universal.ScriptableRenderPass.html) blits the Opaque Texture to the the [Camera color target](https://docs.unity3d.com/Packages/com.unity.render-pipelines.universal@7.0/api/UnityEngine.Rendering.Universal.ScriptableRenderer.html#UnityEngine_Rendering_Universal_ScriptableRenderer_cameraColorTarget) for the current renderer. The render pass uses the command buffer to draw a full screen mesh for both eyes.

The example includes [the shader](#shader) that performs the GPU side of the rendering. The shader samples the color buffer using XR sampler macros.

## Prerequisites

This example requires the following:

* The **Scriptable Render Pipeline Settings** property refers to a URP asset (**Project Settings** > **Graphics** > **Scriptable Render Pipeline Settings**).

## <a name="example-objects"></a>Create example Scene and GameObjects

To follow the steps in this example, create a new Scene with the following GameObjects:

1. Create a Cube. Ensure that the Cube is clearly visible from the main Camera.

    ![](../Images/how-to/blit-xr/example-scene.png)

Now you have the Scene necessary to follow the steps in this example.

## Example implementation

This section assumes that you created a Scene as described in section [Create example Scene and GameObjects](#example-objects).

Follow these steps to create a [custom Renderer Feature](https://docs.unity3d.com/Packages/com.unity.render-pipelines.universal@12.0/api/UnityEngine.Rendering.Universal.ScriptableRendererFeature.html) with a custom [Render Pass](https://docs.unity3d.com/Packages/com.unity.render-pipelines.universal@12.0/api/UnityEngine.Rendering.Universal.ScriptableRenderPass.html).

1. Create a new C# script. Call it `ColorBlitRendererFeature.cs`. This script implements the custom Renderer Feature.

    ```C#
    using UnityEngine;
    using UnityEngine.Rendering;
    using UnityEngine.Rendering.Universal;

    internal class ColorBlitRendererFeature : ScriptableRendererFeature
    {
        public Shader m_Shader;
        public float m_Intensity;

        Material m_Material;

        ColorBlitPass m_RenderPass = null;

        public override void AddRenderPasses(ScriptableRenderer renderer, ref RenderingData renderingData)
        {
            if (renderingData.cameraData.cameraType == CameraType.Game)
            {
                //Calling ConfigureInput with the ScriptableRenderPassInput.Color argument ensures that the opaque texture is available to the Render Pass
                m_RenderPass.ConfigureInput(ScriptableRenderPassInput.Color);
                m_RenderPass.SetTarget(renderer.cameraColorTarget, m_Intensity);
                renderer.EnqueuePass(m_RenderPass);
            }
        }

        public override void Create()
        {
            if (m_Shader != null)
                m_Material = new Material(m_Shader);

            m_RenderPass = new ColorBlitPass(m_Material);
        }

        protected override void Dispose(bool disposing)
        {
            CoreUtils.Destroy(m_Material);
        }
    }
    ```

2. Create a new C# script. Call it `ColorBlitPass.cs`. This script implements the custom Render Pass that performs the custom blit draw call.

    This Render Pass uses the `cmd.DrawMesh` method to draw a full-screen quad and perform the blit operation.

    > **NOTE:** Do not use the `cmd.Blit` method in URP XR projects because that method has compatibility issues with the URP XR integration. Using `cmd.Blit` might implicitly enable or disable XR shader keywords, which breaks XR SPI rendering.

    ```C#
    using UnityEngine;
    using UnityEngine.Rendering;
    using UnityEngine.Rendering.Universal;

    internal class ColorBlitPass : ScriptableRenderPass
    {
        ProfilingSampler m_ProfilingSampler = new ProfilingSampler("ColorBlit");
        Material m_Material;
        RenderTargetIdentifier m_CameraColorTarget;
        float m_Intensity;

        public ColorBlitPass(Material material)
        {
            m_Material = material;
            renderPassEvent = RenderPassEvent.BeforeRenderingPostProcessing;
        }

        public void SetTarget(RenderTargetIdentifier colorHandle, float intensity)
        {
            m_CameraColorTarget = colorHandle;
            m_Intensity = intensity;
        }

        public override void OnCameraSetup(CommandBuffer cmd, ref RenderingData renderingData)
        {
            ConfigureTarget(new RenderTargetIdentifier(m_CameraColorTarget, 0, CubemapFace.Unknown, -1));
        }

        public override void Execute(ScriptableRenderContext context, ref RenderingData renderingData)
        {
            var camera = renderingData.cameraData.camera;
            if (camera.cameraType != CameraType.Game)
                return;

            if (m_Material == null)
                return;

            CommandBuffer cmd = CommandBufferPool.Get();
            using (new ProfilingScope(cmd, m_ProfilingSampler))
            {
                m_Material.SetFloat("_Intensity", m_Intensity);
                cmd.SetRenderTarget(new RenderTargetIdentifier(m_CameraColorTarget, 0, CubemapFace.Unknown, -1));
                //The RenderingUtils.fullscreenMesh argument specifies that the mesh to draw is a quad.
                cmd.DrawMesh(RenderingUtils.fullscreenMesh, Matrix4x4.identity, m_Material);
            }
            context.ExecuteCommandBuffer(cmd);
            cmd.Clear();

            CommandBufferPool.Release(cmd);
        }
    }
    ```

3. <a name="shader"></a>Create the shader that performs the blit operation. Call the shader file `ColorBlit.shader`. The vertex function outputs the full-screen quad position. The fragment function samples the color buffer and returns the `color * float4(0, _Intensity, 0, 1)` value to the render target.

    ```hlsl
    Shader "ColorBlit"
    {
            SubShader
        {
            Tags { "RenderType"="Opaque" "RenderPipeline" = "UniversalPipeline"}
            LOD 100
            ZWrite Off Cull Off
            Pass
            {
                Name "ColorBlitPass"

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

                struct Attributes
                {
                    float4 positionHCS   : POSITION;
                    float2 uv           : TEXCOORD0;
                    UNITY_VERTEX_INPUT_INSTANCE_ID
                };

                struct Varyings
                {
                    float4  positionCS  : SV_POSITION;
                    float2  uv          : TEXCOORD0;
                    UNITY_VERTEX_OUTPUT_STEREO
                };

                Varyings vert(Attributes input)
                {
                    Varyings output;
                    UNITY_SETUP_INSTANCE_ID(input);
                    UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(output);

                    // Note: The pass is setup with a mesh already in clip
                    // space, that's why, it's enough to just output vertex
                    // positions
                    output.positionCS = float4(input.positionHCS.xyz, 1.0);

                    #if UNITY_UV_STARTS_AT_TOP
                    output.positionCS.y *= -1;
                    #endif

                    output.uv = input.uv;
                    return output;
                }

                TEXTURE2D_X(_CameraOpaqueTexture);
                SAMPLER(sampler_CameraOpaqueTexture);

                float _Intensity;

                half4 frag (Varyings input) : SV_Target
                {
                    UNITY_SETUP_STEREO_EYE_INDEX_POST_VERTEX(input);
                    float4 color = SAMPLE_TEXTURE2D_X(_CameraOpaqueTexture, sampler_CameraOpaqueTexture, input.uv);
                    return color * float4(0, _Intensity, 0, 1);
                }
                ENDHLSL
            }
        }
    }
    ```

4. Add the `ColorBlitRendererFeature` to the Universal Renderer asset.

    ![Add Renderer Feature](../Images/how-to/blit-xr/add-renderer-feature.png)

    For information on how to add a Renderer Feature, see the page [How to add a Renderer Feature to a Renderer](../urp-renderer-feature-how-to-add.md).

    For this example, set the Intensity property to 1.5.

5. To visualize the example, configure the project to use XR SDK. [Add the MockHMD XR Plugin to the project](https://docs.unity3d.com/Packages/com.unity.xr.mock-hmd@latest/index.html). Set the **Render Mode** property to **Single Pass Instanced**.

    ![Configure MockHMD](../Images/how-to/blit-xr/xr-plugin-mockhmd.png)

    Unity shows the following views:

    ![Final Scene and Game views](../Images/how-to/blit-xr/final-scene-and-game-view.png)

6. Enter the Play mode. Unity shows the color buffer.

    ![Final Play mode view](../Images/how-to/blit-xr/final-play-mode-view.png)

The example is complete.