Volume fog behaves differently depending on timeline selection

[JoachimArt]

I have a underwater scene/animation and I have been racking my brain as of why the frames sometimes looks different when rendered. But I have now found out that if you have a volumetric fog (I have animated the density over time) if have selected frame 500 and then render frame 500, it looks different than if I have selected frame 0 and choose to render frame 500. Therefore its difficult to tweak the animation in VFB, because what you see on that exact frame is different from how it will look when rendered as a sequence from frame 0.

[Aram Avetisyan]

Hi,

Do I understand correctly: in case of volumetric fog (is it Global volume material in Render settings > Scene, or an object with CoronaVolumeMtl), if the active keyframe in main UI is X but you do a production rendering of Y-th frame (by setting a custom range or frames in Render Settings > Common tab?) that the result is not that same as having the active keyframe in the main UI and the actually rendered frame both an Y or X?

If any keyframe is being rendering (production or IR) that exact keyframe should look all the same regardless of the active keyframe. So if you are able to solidly reproduce this, please attach a simple scene with the animated volume fog, so we can have a look.

[JoachimArt]

Hi, yes you are correct, that is the bug.
Here is a stripped down scene with no textures where you can see the bug. I have included the last frame of the animation rendered with active frame being 0 and the active frame being the last, you can clearly see the two images are looking different.
Download the files here: https://www.dropbox.com/t/qDKSRV6KISodj0sf

[Aram Avetisyan]

Hi,

Thanks for the scene.
I was able to reproduce the issue and it is definitely not expected. My guess is that frame rendering does not take into consideration the animation (at least for volumetrics animation).

This is reported now.

(Internal ID=1293019934)

[JoachimArt]

thanks glad to hear the bug is reported and will be fixed. Just to inform you, I tried deleting the animation of the fog settings, the bug is still there nonetheless and the frames end up different, so I think it must be something else. Maybe something is initiated in the beginning so if you start rendering far into an animation it will not include it - because from what I see, it becomes correct based on the settings only IF you start rendering when timeline is set to start at 0 - the fog loses its environmental affect when starting at the end of the anim, from what I can guess.