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Branched path tracing with high samples sometimes causes CUDA error
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Description

System Information
Operating system: Win10 1903
Graphics card: GTX 1080ti * 2

Blender Version
Broken: 2.83.5

Short description of error
Using branched path tracing mode with high samples, the render starts but finishes really quick and results a transparent image.
But using path tracing mode with the same amount of samples (or even more) , it works fine.
Using branched path tracing mode with a fairly low samples can still work.
It has noting to do with the resolution of the image. I changed the resolution to 1280*720 and it still crashed.




It happens on certain project, not all. I tested with many of my blender projects. Most of them can be rendered successfully, but my recent project.

Exact steps for others to reproduce the error
Switch to branched path tracing mode and bump the samples really high.

Event Timeline

Brecht Van Lommel (brecht) claimed this task.

This is a known limitation of branch path tracing on the GPU, it can time out because the path takes too long to compute. For now this is not considered a bug, solving it will require a different rendering algorithm.

Does this happen on CPU only as well? Are you sure you need 500AA samples? Apart from that BPT is kind of broken since 2.8 as MIS on lamps just introduces a lot of noise. Still unsolved unfortunately.

This is a known limitation of branch path tracing on the GPU, it can time out because the path takes too long to compute. For now this is not considered a bug, solving it will require a different rendering algorithm.

Thank you for replying.