I’m working on a cinematic using the Path Tracer in Unreal, and we’ve been getting some strange flickering issues on certain textuPath Tracer Problemres. The bug shows up more clearly when the camera moves, and sometimes the textures pop in at low resolution or seem to “recalculate” every few frames.
It also happens when the character is behind glass: the texture looks broken or low-res, and then instantly switches back to full quality as soon as the camera crosses the glass plane.
We’ve got some experienced people on the team looking into it, and we’ve tested all the usual suspects for this kind of issue, but nothing seems to have any effect so far.
Important detail: This only happens during render.
In the viewport and sequencer preview, everything looks fine. Only when render the problem appears
It’s exclusive to Path Tracer.
Do you guys have any idea what could be causing this?
Is it related to virtual texture streaming, raytracing translucency priority, or something like that?
How much ram do you have in your video card ? Could it happen because in the viewport you use a lower resolution but at render you use a higher resolution ?
What would happen if you would use a lower resolution at render ? - maybe similar to the viewport resolution. do you still have the errors ?
What if you would use a much higher resolution at render ? Would you get even more errors ?
I’m using a 4090, so the machine is actually quite powerful — which is exactly why this issue surprises me.
The glitch only happens during render — everything behaves normally in the viewport.
We’ve already tested changing resolutions, resizing textures, and all the usual suspects for this kind of error, but nothing seems to fix it.
What we have in the scene is a character with a Houdini-simmed hair (it’s actually a tentacle-like structure, kind of like an octopus), cached and imported — and a monitor playing a video file in sync.
These are really the only two elements that are somewhat “outside” the scope of a standard render setup. Everything else is pretty straightforward.
I think there might be a few issues here at different spots, I may not have some definitive answers, but can start poking at some different things.
For your blurry textures issues. this could be related to virtual texture streaming. We’ve written a few articles about this that you could explore.
Also, if you’re not doing it already you can try setting up prewarmup frame for your shots in MRQ or Sequencer. (We don’t have an article write up for preroll in sequencer yet.)
If you are using a workflow that uses subsequences, you can define preroll frames for that. The short bullet point setup for this is:
In your subsequence right-click on your camera cuts track and choose evaluate for pre-roll.
In your parent sequence choose that cut, go to properties, and set pre roll frames to send a signal to the streaming system to start streaming in your texture. (Maybe start with 5-10 frame)
