MASH instance caching not working

[adrian_wyer]

i have a plane crash i'm animating, and i have setup a MASH network with dynamics to throw debris out of the plane.

When i hit play the sim it works fine, when i write a cache using the MASH cache creator it plays through the timeline and the instances are visible and appear to be behaving as expected.

But when i try and play back the cached sim, i get the following error;

// Error: MASH_TRASH_inPositionPPCache7 (Cache File): `S:/PROJECTS/J588_C5Planes/Databases/SHOTS/KEGWOR/INCD/KEGWOR_INCD/data/MASH_TRASH_inPositionPP` may have an invalid cache description or invalid, missing or empty cache file.

you can see that the instances are working on some frames, then just disappear on others

I've tried deleteing the caches, manually from disk too, i've rebuilt the scene about 8 times today, and am running out of time

we render in redshift, so i have to use instances to render correctly (also have other mash setups that use proxies)

was expecting to get this rendering this weekend, but looks like that is scuppered...

any ideas how i can force the cache to work... i'm assuming it's writing incomplete frames during the initial solve

if only Bifrost supported redshift proxies 😞

[sepu6]

I would try to use the repro and save it as an .abc instead. That cache option on Mash is not very reliable. 

[adrian_wyer]

yeah i tried that, unfortunately shader info isn't saved, so where i'm instancing a bunch of different objects, all with their own redshift shaders, the abc comes back in with a lambert...

looking into a bifrost-> maya particles using HeydoubleU plugin so i can render in redshift... works so far apart from collision size variation (as you saw on the other thread)

[adrian_wyer]

did have a thought... i was using the bullet dynamics in MASH.... 

I am  keying my distribute node value to increase the number of 'instances' over time

having just experimented with the bulletfrost plugin for bifrost, it mentions that you can't change the number of objects in the simulation dynamically, ie you need all the objects to be there on frame 1... wonder if this is an issue with the mash bullet implementation/caching?

although Ian has a demo where he does just that;  https://www.youtube.com/watch?v=QXio_nuKGMs

however he's NOT caching the sim

[adrian_wyer · Accepted solution]

for what it's worth, after some testing, it appears that the culprit was the changing instance count/bullet interaction

if i start the shot with all the instances emitted on frame 1, caching seems to behave

in case anyone else stumbles down this road