Inject a render pass via scripting

Unity raises a beginCameraRendering event before it renders each active Camera in every frame. If a Camera is inactive (for example, if the Camera component checkbox is cleared on a Camera GameObject), Unity does not raise a beginCameraRendering event for this Camera.

When you subscribe a method to this event, you can execute custom logic before Unity renders the Camera. Examples of custom logic include rendering extra Cameras to Render Textures, and using those Textures for effects like planar reflections or surveillance camera views.

Other events in the RenderPipelineManager class provide more ways to customize URP. You can also use the principles described in this article with those events.

Use the RenderPipelineManager API

1. Subscribe a method to one of the events in the RenderPipelineManager class.

2. In the subscribed method, use the EnqueuePass method of a ScriptableRenderer instance to inject a custom render pass into the URP frame rendering.

Example code:

public class EnqueuePass : MonoBehaviour
{
    [SerializeField] private BlurSettings settings;    
    private BlurRenderPass blurRenderPass;

    private void OnEnable()
    {
        ...
        blurRenderPass = new BlurRenderPass(settings);
        // Subscribe the OnBeginCamera method to the beginCameraRendering event.
        RenderPipelineManager.beginCameraRendering += OnBeginCamera;
    }

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

    private void OnBeginCamera(ScriptableRenderContext context, Camera cam)
    {
        ...
        // Use the EnqueuePass method to inject a custom render pass
        cam.GetUniversalAdditionalCameraData()
            .scriptableRenderer.EnqueuePass(blurRenderPass);
    }
}

Example

This example demonstrates how to subscribe a method to the beginCameraRendering event.

To follow the steps in this example, create a new Unity project using the Universal Project Template

1. In the scene, create a Cube. Name it Example Cube.

2. In your Project, create a C# script. Call it URPCallbackExample.

3. Copy and paste the following code into the script.

   using UnityEngine;
   using UnityEngine.Rendering;
   
   public class URPCallbackExample : MonoBehaviour
   {
       // Unity calls this method automatically when it enables this component
       private void OnEnable()
       {
           // Add WriteLogMessage as a delegate of the RenderPipelineManager.beginCameraRendering event
           RenderPipelineManager.beginCameraRendering += WriteLogMessage;
       }
   
       // Unity calls this method automatically when it disables this component
       private void OnDisable()
       {
           // Remove WriteLogMessage as a delegate of the  RenderPipelineManager.beginCameraRendering event
           RenderPipelineManager.beginCameraRendering -= WriteLogMessage;
       }
   
       // When this method is a delegate of RenderPipeline.beginCameraRendering event, Unity calls this method every time it raises the beginCameraRendering event
       void WriteLogMessage(ScriptableRenderContext context, Camera camera)
       {
           // Write text to the console
           Debug.Log($"Beginning rendering the camera: {camera.name}");
       }
   }
   

   Note: When you subscribe to an event, your handler method (in this example, WriteLogMessage) must accept the parameters defined in the event delegate. In this example, the event delegate is RenderPipeline.BeginCameraRendering, which expects the following parameters: <ScriptableRenderContext, Camera>.

4. Attach the URPCallbackExample script to Example Cube.

5. Select Play. Unity prints the message from the script in the Console window each time Unity raises the beginCameraRendering event.

   

6. To raise a call to the OnDisable() method: In the Play mode, select Example Cube and clear the checkbox next to the script component title. Unity unsubscribes WriteLogMessage from the RenderPipelineManager.beginCameraRendering event and stops printing the message in the Console window.