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Unable to read back in external baked physics cache
Closed, DuplicatePublicKNOWN ISSUE


System Information
Operating system: Windows-10-10.0.18362 64 Bits
Graphics card: GeForce GTX 1080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 416.34

Blender Version
Broken: version: 2.80 (sub 75), branch: master, commit date: 2019-07-29 14:47, hash: rBf6cb5f54494e
Worked: (optional)

Short description of error
When baking a simple physics particle cache to file, it appears to bake correctly, but then when attempting to read it back in it either reports as no valid file found, or only identifies 1 or 2 points instead of hundreds. Sample file with bake attached,

Exact steps for others to reproduce the error
[Please describe the exact steps needed to reproduce the issue]
[Based on the default startup or an attached .blend file (as simple as possible)]

Event Timeline

Philipp Oeser (lichtwerk) lowered the priority of this task from 90 to High.Sep 2 2019, 11:30 AM

Can confirm.
Even though particles are under complete rewrite atm, this looks pretty bad to me.
I dare setting this to High prio, @Brecht Van Lommel (brecht) correct me if I am wrong.
Or does EOL mean we are shipping unusable versions until the new stuff is in place? (we could, just asking...)

I did some digging, and it turns out that ptcache_read() reads the correct number of points. It's ptcache_particle_read() that's rejecting the points because psys->totpart is set to a low number (i.e. to the number of points you're seeing). Somehow it's not getting the total number of points from the pointcache. This could be due to the fact that the info file (i.e. the bphys file for frame 0) isn't written to disk, but I'm too unfamiliar with how the code is supposed to work.

A test with 2.79 shows that this issue was already there in 2.79 (and possibly earlier). AFAIK this means that it won't be fixed any more.

PS: Un-checking the 'External Cache' checkbox erases all cache files without any notification, if they happen to be in the same directory as Blender would store them when baking, so it's a dangerous thing to touch.

Brecht Van Lommel (brecht) lowered the priority of this task from High to Low.

This is not high priority especially if it happens in 2.79 and with particles being end of life.

That means it's low priority, someone might fix it but we won't prioritize it.

Sorry, my bad, I thought I checked and this was working in 2.79, but apparently it isnt...

Brecht Van Lommel (brecht) changed the subtype of this task from "Report" to "Known Issue".Jan 27 2020, 11:43 AM

From my testing in T68436: External Particle Cache Playback Is Broken (2.8), the bphys file for frame zero was actually written... So my tests were working in 2.79...
But these two reports are the same, will merge T68436 here.

OK, will merge the other way around