Summary
I attempted to use the Path Tracer with Adaptive Sampling in UE5.4.4, and it worked correctly. However, using the exact same settings in the UE5.5.0 Preview version, Path Tracing fails to render as expected. The Unreal Engine uses progressive rendering for Path Tracing, and typically, noise in the viewport should decrease as the sample count increases over time. Currently, the rendering appears to refresh in horizontal strips from the top to the bottom of the screen, and only the result from the first sample is displayed. When the viewport is moved, the previous view does not clear but instead overlays on top of the window. The next sample image appears only in the black regions of the previous sample, and this overlay occurs with every sample iteration. Additionally, the same issue is observed when rendering using the sequencer for cinematic output.
Please select what you are reporting on:
Creative
What Type of Bug are you experiencing?
Other
Steps to Reproduce
- Use UE5.5.0 Preview to create any starter level. I used the Virtual Production project template.
- After creating the project, configure the usual settings to enable Path Tracing.
- Exit the project, then go to the project directory and edit the DefaultEngine.ini file. Under the renderersettings category, add the following line:
“r.PathTracing.Experimental=True” - Reopen the project and change the viewport mode to Path Tracing.
- Open the console and enter “r.PathTracing.AdaptiveSampling 1” and press Enter.
Expected Result
The scene should render normally, just as when Path Tracing is typically enabled. During the latter part of the rendering, the speed should increase, resulting in fewer noise artifacts as more samples are processed.
Observed Result
The rendering appears to refresh in horizontal strips from the top to the bottom of the screen. Only the first sample is displayed in the viewport, and when the viewport is moved, the previous view does not clear but instead overlays on top. The next sample image only appears in the black regions of the previous sample, and this stacking occurs with every sample iteration.
Platform(s)
Win11 23H2
NVIDIA Driver : Studio 561.09
Additional Notes
I believe Adaptive Sampling is incredibly helpful, especially under complex lighting conditions. It allows me to maintain the same image quality in areas with complex or insufficient lighting as in well-lit areas without over-sampling unnecessarily. This feature has the potential to cut my rendering time in half, significantly optimizing the workflow without compromising on visual quality.