Getting some NaN in path_tracing sample

[Hurleyworks]

I'm getting some NaN in optix_pathtracing_kernels.cu line 201 RGB colorResult = (1 - curWeight) prevColorResult + curWeight contribution;

I add these lines after line 201 to color the NaN pixels super red

 RGB colorResult = (1 - curWeight) * prevColorResult + curWeight * contribution;
 if (isnan(colorResult.r) || isnan(colorResult.g) || isnan(colorResult.b))
 {
     printf("contribution: %f, %f, %f\n", contribution.r, contribution.g, contribution.b);
     colorResult = RGB(make_float3(1000000.0f, 0.0f, 0.0f)); // super red
 }

And here is the output after rendering for a few minutes. Do you know what the problem might be? It is still so hard to debug OptiX. It seems it gets harder and harder with each new release.

[shocker-0x15]

Typical NaN in a renderer comes from something in BRDF (e.g. acos(x), |x| > 1), invalid reference frame, etc). Could you check first if your input mesh is valid, particularly like tangent vectors?

[Hurleyworks]

Thanks for the quick reply. I simplified down to a single triangle and checked the tangents and they seem correct. I was using the SimplePBRMaterial and have tried LambertMaterial too and there are NaN's with both.

I am only using environment texture for lighting. Here is my command line -cam-pos -0.753442 0.140257 -0.056083 -cam-yaw 75 -name tester -obj E:/common_content/obj/triangle.obj 0.0551 trad -brightness 1.0 -env-texture C:/Users/Steve/Downloads/resting_place_4k.exr -inst tester -begin-pos 0.362 0.329 -2.0 -begin-pitch -90 -begin-yaw 150 -end-pos -0.719 0.329 -0.442 -end-pitch -90 -end-yaw 30

[shocker-0x15]

An environment texture can be another NaN source and my light sampling code possibly misses a proper corner case handling. I'll try to see on my side as well.

[shocker-0x15]

The cause was IBL importance sampling. It rarely samples theta == 0 and this makes PDF value infinity and leads to NaN in the end. Could you try the following fix?

diff --git a/path_tracing/path_tracing_shared.h b/path_tracing/path_tracing_shared.h
index a01c582..4ab033c 100644
--- a/path_tracing/path_tracing_shared.h
+++ b/path_tracing/path_tracing_shared.h
@@ -231,6 +231,10 @@ CUDA_DEVICE_FUNCTION CUDA_INLINE void sampleLight(
         plp.s->envLightImportanceMap.sample(u0, u1, &u, &v, &uvPDF);
         float phi = 2 * Pi * u;
         float theta = Pi * v;
+        if (theta == 0.0f) {
+          *areaPDensity = 0.0f;
+          return;
+        }

         float posPhi = phi - plp.f->envLightRotation;
         posPhi = posPhi - floorf(posPhi / (2 * Pi)) * 2 * Pi;

[Hurleyworks]

Great. That fixes the NaN problem. Thank you very much for the quick help!

I was hoping this would fix a problem I've having with corruption during denoising but it does not unfortunately. https://forums.developer.nvidia.com/t/black-box-rendering-errors/274226/10

[shocker-0x15]

It is possibly worth using ptx instead of OptiX-IR if you are using. OptiX-IR used to make isnan() not working a while ago. https://forums.developer.nvidia.com/t/optix-7-5-debuggable-optix-ir-makes-isnan-not-working/228251/5 I'm not sure if this issue has been fixed.

[Hurleyworks]

Thanks for the suggestion. I tried it but it did not help.

On Wed, Nov 29, 2023 at 7:45 AM shocker-0x15 @.***> wrote:

It is possibly worth using ptx instead of OptiX-IR if you are using. OptiX-IR used to make isnan() not working a while ago.

https://forums.developer.nvidia.com/t/optix-7-5-debuggable-optix-ir-makes-isnan-not-working/228251/5 I'm not sure if this issue has been fixed.

— Reply to this email directly, view it on GitHub https://github.com/shocker-0x15/GfxExp/issues/13#issuecomment-1831829734, or unsubscribe https://github.com/notifications/unsubscribe-auth/AB56PP4PLHOWCCPYDGUNJ4DYG4U6PAVCNFSM6AAAAAA76WDP3SVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMYTQMZRHAZDSNZTGQ . You are receiving this because you authored the thread.Message ID: @.***>

-- -Steve http://berserko.hurleyworks.com/ http://www.hurleyworks.com

[shocker-0x15]

Unfortunate that ptx didn't help, but let me close this issue since the original question seems resolved.

[Hurleyworks]

Thanks again for the help.

If you are a ChatGPT4 user, I made a custom GPT for OptiX8 by feeding it the Programming and API Guides and pdf versions of your OptiX_Utility library. It's a lot more fun to chat with the manuals than to have to dig around them looking for answers. :) https://chat.openai.com/g/g-xuly7sb4A-optix-pathtracer-pro