Question Raytraced Ambient Occlusion ghosting

Hey, RTAO denoiser rely on accumulation to be able to have a nice result at a fraction of the cost, meaning the RTAO result of a specific frame depends on the previous frames as well.
So when you are switching meshes, RTAO still uses the result of the previous meshes and take a few frames to converge to the correct result with this new mesh.
What needs to be done is basically telling HDRP to discard the history when that happens, there's no API or simple way to do that but one thing you can do is when switching meshes, you can disable the denoiser, and then re-enable it on the next frame, that way, history will be discarded. you will get a "snap", but you won't see any ghosting in theory.
Here's a snippet of how that could work:

Code (CSharp):

1.  
2. using UnityEngine.Rendering;
3. using UnityEngine.Rendering.HighDefinition;
4. public class ToggleObject : MonoBehaviour
5. {
6.     public Volume m_Volume;
7.  
8.     // Update is called once per frame
9.     void Update()
10.     {
11.         VolumeProfile profile = m_Volume.sharedProfile;
12.         if (!profile.TryGet<ScreenSpaceAmbientOcclusion>(out var ssao))
13.         {
14.             ssao = profile.Add<ScreenSpaceAmbientOcclusion>(false);
15.         }
16.    
17.         // Re-enable AO denoiser if set to false
18.         if(!ssao.denoise) ssao.denoise = true;
19.    
20.         // Toggling between meshes
21.         if(Input.GetKeyDown(KeyCode.T))
22.         {
23.             ssao.denoise = false;
24.         }
25.     }
26. }
27.  

Hope that helps!

 

Clearly not a priority right now, but that's not out of the question.
There's already some mechanism to discard history automatically when the occluder or the receiver of AO is moving too fast (to avoid having too much ghosting) !

Also, I just realized there's already functions on the HDCamera class to enable / disable accumulation but they are currently not public API, they are internal to HDRP (could still be accesible via an ASMDEF wrapper), but that mean just setting those function to public would make it even easier for users to disable accumulation (on any effect) when needed, like this:

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. using UnityEngine.Rendering;
6. using UnityEngine.Rendering.HighDefinition;
7.  
8. public class ToggleObject : MonoBehaviour
9. {
10.     public Camera camera;
11.     HDCamera hdCamera;
12.     // public Volume m_Volume;
13.     // Start is called before the first frame update
14.     void Start()
15.     {
16.         hdcamera = HDCamera.GetOrCreate(camera);
17.     }
18.  
19.     // Update is called once per frame
20.     void Update()
21.     {
22.  
23.         // Re-enable accumulation on camera if set to false
24.         if(!hdCamera.ActiveRayTracingAccumulation()) hdCamera.SetRayTracingAccumulation(true);
25.      
26.         // Toggling between meshes
27.         if(Input.GetKeyDown(KeyCode.T))
28.         {
29.             hdCamera.SetRayTracingAccumulation(false);
30.         }
31.     }
32. }
33.  

I'll see what can be done, thanks for the post !