(EmberGen)Upscaling causes different smoke durations. (Confirmed)

Hello. I’m playing with the new beta version and I’m experiencing some framerate dependency issues (at least it looks like that). I narrowed down the issue in my particular case to the smoke dissipation parameter, and it seems like it acts differently on low fps. Basically I get more smoke when the framerate is low. It disappears slower, so the end result looks different depending on the framerate. If thats the case, I would assume that other parameters that are determined in seconds are affected too, but I haven’t confirmed this.

Excuse me. Whats up with this?

Hmm, I’m not sure how this can be the case. The simulation parameters like dissipation should not depend on any real time, but on the simulation time step, which should be fixed regardless of whether it’s able to simulate it fast or slow. If you have a preset for a “fast” and “slow” case that you think showcases the effect you’re observing I’d love to take a look to see what’s going on.

Hello. I uploaded a test file here:

Observe that the smoke fully disappears by the end of the loop when upscaling is set to none, and there is a considerable amount of smoke left when upscaling is enabled, so the fps is lower.

@KristofLovas that’s just the nature of upscaling and has nothing to do with the framerate. Upscaling gives you more detail, more detail means more smoke, more smoke means longer decay times, more smoke & detail means less frame rate.

Nothing here indicates a frame rate dependency bug. :slight_smile:

Also your repro test file was just the default scene to my knowledge.

Maybe im misunderstanding the functionality of upscaling then. I thought it should give more detail but not more quantity.

Also I don’t know how is that the basic scene. I added a couple of things to it. Collision, force, animated parameters, and a different shader.

Ok then lets parse it differently, this still don’t seem to be correct to me because lets say you set up some sim working on normal res so its fast. You enable upscale and you get different look, not the same look with more detail. Is this the intended behavior?

I understand that if the error is not what I thought it would be.
I tested this in the burnout template and I get similar results. Without upres, the smoke fully disappears by around frame 420, and there is still (not very little) smoke at that frame when I have upres enabled.
Images attached.

These pictures are showing roughly the same frame and one has upscale and smoke left, while the another doesn’t have neither.

I see what you’re seeing now. I was checking frame 360 of the burnout preset and it’s definitely different in terms of smoke density. I don’t think it’s related to dissipation or framerate at all, but it’s possibly much more nuanced.

Our current upscaling technique isn’t a post-processing technique, instead it actually uses a higher resolution texture for the advection quantities (density, temperature, etc) while the velocity keeps the lower resolution, while also keeping a low resolution copy of to make sure things like weight and buyancy is as consistent as can be for the low resolution and upscaled simulations.

It would be expected for the upscaled version to give subtly different results in terms of concentrations (due to small variations during advection accumulating over time), but the underlying velocity field should be the same, so we’d expect the movement to be consistent. This might be what’s happening here.

This is definitely something to look into more deeply though, and perhaps analyze more rigorously, so thanks for bringing it up.

Hope that makes sense.

I see. Thanks for looking into this. The thread title should be changed to something related to upscale I guess. I don’t seem to be able to change it anymore.