`backup interval` large spike cache files render extra foam every 15 frames.

[anthonyh]

hi,

i`m using the ship wake scene as a base for more boat sims. i run the simulation and the cache files are pretty uniform sizes except exactly every 15 frames the cache doubles or more in size which means when rendered the foam/splash is much bigger on that frame. what can i do to stop that ?
using 2.2 for 2012(yes i know we`re stuck in the past but at least it`s not so full of bugs..

**edit: ok i`ve found the other thread about backup interval set at 15 frames being an issue.
do i just have to turn it off or could i get the nightly version to sort this as we`re in the middle of a job. obviously if the nightly has it`s own issues turning it off would probably be the better option ?

thanks,
anthonyh

[anthonyh]

oh, and any chance to get access to post to the other sections ?
cheers
ant

[Svetlin.Nikolov]

Hey,

You have to email support at chaosgroup dot com for forum permissions, sometimes they go missing for some reason.

As far as the 15th frame flickering - it's not the backup interval that's at fault, but probably you have motion blur enabled and you don't have velocity exported for the foam and splash - note that this is not the same as the velocity export for the grid in the Output panel. You should be able to export it from the bottom of the Foam and Splash panels and you have to simulate again then. The other option would be to turn off motion blur.

Cheers!

[anthonyh]

thanks for replying.
i didn`t have motion blur enabled so i don`t think it`s that. i tried simulating with the backup interval switched to 0 and the big cache files disappeared, i haven`t tried rerendering yet but it seems pretty coincidental that these were the exact frames that looked different and the cache file was over twice the size on each and every one. we`ll see when it renders.
i don`t have velocity exported for the splash or foam, do i need them ? just for velocity pass ?
i`ll contact chaos for permission.
thanks again.

[Svetlin.Nikolov]

I thought you meant that the foam and splash bubbles are bigger at each 15th frame when you render them

It's been discussed in other topics and in the docs site, but the thing is that at backup frames, Phoenix dumps all possible simulation data to the cache file, so one can later hit Restore and continue a simulation from that frame. This includes all particle and grid channels, some of which are not exported by default in order to save hard disk space for channels that are needed only by e.g. motion blur or particle size animation by age, etc. Setting the backup interval to 0 won't create backup frames, so if you don't need to continue a simulation from the middle, you're fine this way cache-size-wise.

Cheers!

[anthonyh]

well it`s good that setting to 0 will fix my problem but why would it render the backup/restore data ? i understand so it can restore the sim but it shouldn`t be renderable ? is this something might be fixed at some point ? or am ii missing an option not to render all the dump data ?

[Svetlin.Nikolov]

All the exported data is renderable, it's not something internal that doesn't make sense for rendering - what the backup frame does is to basically turn on export of all the possible grid channels in the Output panel and all the possible particle channels in the Foam and Splash panels too - velocities, ages, IDs, etc. These are channels that you would export if you need motion blur or playback animation, etc, but their export is off by default.

[anthonyh]

sorry, i guess i`m not understanding.
whatever sim i generate with the backup interval on it would surely make every sim render incorrectly for my needs.? i.e by rendering all the data including the backup every x frames. the only thing it`s done for me is make my animation flicker by having more data rendered on screen than i had intended every 15 frames. those cache files with backup were no use since it rendered incorrectly (visually, since every x frame now looks different to the rest of the sim). how would you use the restore feature without it making my render go wrong visually ? i can`t wrap my head around using the backup function unless you have the ability to not render the extra data it creates needed to use the restore feature.
it`s like i want 1 teapot rendered but i`m forced to have lots of teapots every 15 frames(not the best analogy i`m sure)
sorry if i`m taking up your time. my brain space might be limited..
anthony

[Svetlin.Nikolov]

The rendered sequence would flicker only in case you have a render option that needs a certain particle channel, but you don't export it.

For example, if have motion blur enabled but you didn't check velocity for export, then you would have no motion blur on the particles for 14 frames and on the 15th frame you'd finally have the motion blur rendered. But if you do export the velocity, then you'd have correct motion blur for all the frames and there won't be any difference between the backup frames and the rest render wise

[anthonyh]

ok, i understand. i`m simulating water but i only have liquid output channel enabled. i`m not rendering using motion blur so should that work ? i switched off velocity output since the cache files were way large as it is. have i done that wrong then.?

[Svetlin.Nikolov]

Nope, that's fine.