Bug Fullscreen blit raises a Null Reference Exception when using Blitter API on a 2D project

A null reference exception is raised every time when using the Blitter API to copy from one render target to another in Universal Render Pipeline when a 2D render pipeline asset is in use.
(This is when using blit without specifying a material override - it appears one of the core materials is not being correctly created for 2D projects).

Below is a minimal test case illustrating the bug. Note that this code is reproducing almost verbatim an example from the URP documentation:

https://docs.unity3d.com/Packages/c...renderer-features/how-to-fullscreen-blit.html

2022.3.1f1

SomeBlitRendererFeature

Code (CSharp):

1. using UnityEngine;
2. using UnityEngine.Rendering.Universal;
3.  
4. internal class SomeBlitRendererFeature : ScriptableRendererFeature
5. {
6.     public Shader m_Shader;
7.     public float m_Intensity;
8.  
9.     SomeBlitPass m_RenderPass = null;
10.  
11.     public override void AddRenderPasses(ScriptableRenderer renderer,
12.                                     ref RenderingData renderingData)
13.     {
14.         if (renderingData.cameraData.cameraType == CameraType.Game)
15.             renderer.EnqueuePass(m_RenderPass);
16.     }
17.  
18.     public override void SetupRenderPasses(ScriptableRenderer renderer,
19.                                         in RenderingData renderingData)
20.     {
21.         if (renderingData.cameraData.cameraType == CameraType.Game)
22.         {
23.             // Calling ConfigureInput with the ScriptableRenderPassInput.Color argument
24.             // ensures that the opaque texture is available to the Render Pass.
25.             m_RenderPass.ConfigureInput(ScriptableRenderPassInput.Color);
26.             m_RenderPass.SetTarget(renderer.cameraColorTargetHandle);
27.         }
28.     }
29.  
30.     public override void Create()
31.     {
32.         m_RenderPass = new SomeBlitPass();
33.     }
34.  
35.     protected override void Dispose(bool disposing)
36.     {
37.     }
38. }

SomeBlitPass

Code (CSharp):

1. using UnityEngine;
2. using UnityEngine.Rendering;
3. using UnityEngine.Rendering.Universal;
4.  
5. internal class SomeBlitPass : ScriptableRenderPass
6. {
7.     ProfilingSampler m_ProfilingSampler = new ProfilingSampler("TestingBlit");
8.     RTHandle m_CameraColorTarget;
9.  
10.     public SomeBlitPass()
11.     {
12.         renderPassEvent = RenderPassEvent.BeforeRenderingPostProcessing;
13.     }
14.  
15.     public void SetTarget(RTHandle colorHandle)
16.     {
17.         m_CameraColorTarget = colorHandle;
18.     }
19.  
20.     public override void OnCameraSetup(CommandBuffer cmd, ref RenderingData renderingData)
21.     {
22.         ConfigureTarget(m_CameraColorTarget);
23.     }
24.  
25.     public override void Execute(ScriptableRenderContext context, ref RenderingData renderingData)
26.     {
27.         var cameraData = renderingData.cameraData;
28.         if (cameraData.camera.cameraType != CameraType.Game)
29.             return;
30.  
31.         CommandBuffer cmd = CommandBufferPool.Get();
32.         using (new ProfilingScope(cmd, m_ProfilingSampler))
33.         {
34.             Blitter.BlitCameraTexture(cmd, m_CameraColorTarget, m_CameraColorTarget);
35.         }
36.         context.ExecuteCommandBuffer(cmd);
37.         cmd.Clear();
38.  
39.         CommandBufferPool.Release(cmd);
40.     }
41. }

Add the feature to a 2D renderer and it will throw the null reference exception:

Code (csharp):

1. ArgumentNullException: Value cannot be null.
2. Parameter name: material

The erroneous code in URP comes from the call to BlitTexture, which invokes GetBlitMaterial(TextureXR.dimension) and gets a null return.

Code (CSharp):

1.  
2. BlitTexture(cmd, source, scaleBias, GetBlitMaterial(TextureXR.dimension), bilinear ? 1 : 0);
3.  

 

Reported as IN-45287

 

Hi ManueleB,

Thank you for your reply, more details below.

It's not possible to check the frame debugger with this, as Unity fails to even draw the frame debugger UI:

I was aware of this last bit and my original code where I found this bug does not do this, I wanted to make it as close as possible to the example in the documentation for simplicity. Fair point though! I've updated the example code to blit from screen to a temporary buffer and back, but the same error still occurs.

I'm surprised by this, there's no mention of these requirements in the documentation and it works absolutely fine on 3D URP since about version 7 or so. What method are we supposed to use to get the camera target? There's even renderingData.cameraData.renderer.cameraColorTargetHandle exposed, which was updated when the RTHandle API went live - maybe I am misunderstanding you?

Cheers!

Code (CSharp):

1. using UnityEngine;
2. using UnityEngine.Rendering;
3. using UnityEngine.Rendering.Universal;
4.  
5. internal class SomeBlitPass : ScriptableRenderPass
6. {
7.     ProfilingSampler m_ProfilingSampler = new ProfilingSampler("TestingBlit");
8.     RTHandle m_CameraColorTarget;
9.     RTHandle _temp;
10.  
11.     public SomeBlitPass()
12.     {
13.         renderPassEvent = RenderPassEvent.BeforeRenderingPostProcessing;
14.     }
15.  
16.     public override void Configure(CommandBuffer cmd, RenderTextureDescriptor cameraTextureDescriptor)
17.     {
18.         RenderingUtils.ReAllocateIfNeeded(ref _temp, cameraTextureDescriptor, name: "blit_test_target");
19.     }
20.  
21.     public void SetTarget(RTHandle colorHandle)
22.     {
23.         m_CameraColorTarget = colorHandle;
24.     }
25.  
26.     public override void OnCameraSetup(CommandBuffer cmd, ref RenderingData renderingData)
27.     {
28.         ConfigureTarget(m_CameraColorTarget);
29.     }
30.  
31.     public override void Execute(ScriptableRenderContext context, ref RenderingData renderingData)
32.     {
33.         var cameraData = renderingData.cameraData;
34.         if (cameraData.camera.cameraType != CameraType.Game)
35.             return;
36.  
37.         CommandBuffer cmd = CommandBufferPool.Get();
38.         using (new ProfilingScope(cmd, m_ProfilingSampler))
39.         {
40.             Blitter.BlitCameraTexture(cmd, m_CameraColorTarget, _temp);
41.             Blitter.BlitCameraTexture(cmd, _temp, m_CameraColorTarget);
42.         }
43.         context.ExecuteCommandBuffer(cmd);
44.         cmd.Clear();
45.  
46.         CommandBufferPool.Release(cmd);
47.     }
48.  
49.     public void Dispose()
50.     {
51.         _temp?.Release();
52.     }
53. }

Code (CSharp):

1. using UnityEngine;
2. using UnityEngine.Rendering.Universal;
3.  
4. internal class SomeBlitRendererFeature : ScriptableRendererFeature
5. {
6.     public Shader m_Shader;
7.     public float m_Intensity;
8.  
9.     SomeBlitPass m_RenderPass = null;
10.  
11.     public override void AddRenderPasses(ScriptableRenderer renderer,
12.                                     ref RenderingData renderingData)
13.     {
14.         if (renderingData.cameraData.cameraType == CameraType.Game)
15.             renderer.EnqueuePass(m_RenderPass);
16.     }
17.  
18.     public override void SetupRenderPasses(ScriptableRenderer renderer,
19.                                         in RenderingData renderingData)
20.     {
21.         if (renderingData.cameraData.cameraType == CameraType.Game)
22.         {
23.             // Calling ConfigureInput with the ScriptableRenderPassInput.Color argument
24.             // ensures that the opaque texture is available to the Render Pass.
25.             m_RenderPass.ConfigureInput(ScriptableRenderPassInput.Color);
26.             m_RenderPass.SetTarget(renderer.cameraColorTargetHandle);
27.         }
28.     }
29.  
30.     public override void Create()
31.     {
32.         m_RenderPass = new SomeBlitPass();
33.     }
34.  
35.     protected override void Dispose(bool disposing)
36.     {
37.         base.Dispose(disposing);
38.         if (disposing)
39.         {
40.             m_RenderPass.Dispose();
41.         }
42.     }
43. }

 

Anyway, the camera target bit is unrelated to the original bug - the blit error still occurs if I attempt to blit between two temporary targets:

Code (CSharp):

1. using UnityEngine;
2. using UnityEngine.Rendering;
3. using UnityEngine.Rendering.Universal;
4.  
5. internal class SomeBlitPass : ScriptableRenderPass
6. {
7.     ProfilingSampler m_ProfilingSampler = new ProfilingSampler("TestingBlit");
8.     RTHandle _temp;
9.     RTHandle _temp2;
10.  
11.     public SomeBlitPass()
12.     {
13.         renderPassEvent = RenderPassEvent.BeforeRenderingPostProcessing;
14.     }
15.  
16.     public override void Configure(CommandBuffer cmd, RenderTextureDescriptor cameraTextureDescriptor)
17.     {
18.         RenderingUtils.ReAllocateIfNeeded(ref _temp, cameraTextureDescriptor, name: "blit_test_target");
19.         RenderingUtils.ReAllocateIfNeeded(ref _temp2, cameraTextureDescriptor, name: "blit_test_target2");
20.     }
21.  
22.     public override void Execute(ScriptableRenderContext context, ref RenderingData renderingData)
23.     {
24.         var cameraData = renderingData.cameraData;
25.         if (cameraData.camera.cameraType != CameraType.Game)
26.             return;
27.  
28.         CommandBuffer cmd = CommandBufferPool.Get();
29.         using (new ProfilingScope(cmd, m_ProfilingSampler))
30.         {
31.             Blitter.BlitCameraTexture(cmd, _temp, _temp2);
32.         }
33.         context.ExecuteCommandBuffer(cmd);
34.         cmd.Clear();
35.  
36.         CommandBufferPool.Release(cmd);
37.     }
38.  
39.     public void Dispose()
40.     {
41.         _temp?.Release();
42.         _temp2.Release();
43.     }
44. }

 

Thanks for your reply, that was my guess aswell. Now that the old Blit functionality has been removed though it means the replacement doesn't cover all the previous use cases until fixed, which is unfortunate!

The workaround to create and initialise my own blit material works but that removes many of the advantages of having the API in the first place. Do you know if this will be accepted on the tracker?

Cheers

 

Hi Manuelle,

The associated bug report IN-45287 was just closed as 'Not Qualified' by the QA Team. Is a fix still in progress?

Cheers,
Elliot

 

@ManueleB any updates on this? I am also running into this issue which prevents me from updating Unity to the latest LTS version.

 

Thanks kennyy, appreciate it!