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bake hair dynamics issues
Confirmed, NormalPublicKNOWN ISSUE


System Information
Operating system: wind 10
Graphics card: gtx 1070

Blender Version
Broken: blender-2.80-79f67acccb36-win64
Worked: idk

unable to bake hair dynamics. i click the button but nothing happens. in particle edit mode particle hair still looks as if it was not simulated.

Event Timeline

Jacques Lucke (JacquesLucke) lowered the priority of this task from 90 to 30.Mar 25 2019, 1:41 PM

I can't reproduce the issue in my simple test.
Please provide an as-simple-as-possible .blend file that shows the issue.

here i made a simple uv sphere, i made hair particle, i click bake, i try switch to perticle edit and it crashes blender. you can open this blend and try switch to particle edit, it will crash it

Jacques Lucke (JacquesLucke) raised the priority of this task from 30 to 50.Mar 25 2019, 3:25 PM

this is the same thing, except, before bake i enabled disk cache. now it does not crash with switching to particle edit, but particles are not visible in particle edit.

dev369 (dev369) renamed this task from bake hair dynamics doesnt do anything to bake hair dynamics issues.Mar 25 2019, 3:38 PM

should this not be at least high priority and be fixed for release of 2.8? hair dynamics is pretty important feature id say, currently i still cant get it to work its been a while. i mean, without hair dynamics we are severely limited to what we do by hand and rigging..

On entering particle editmode in crash.blend I am getting :
`BLI_assert failed: /blender/source/blender/draw/intern/draw_cache_impl_particles.c:1519, particle_batch_cache_ensure_edit_pos_and_seg(), at '!"Hairs are not in edit mode!"'`
This I have definitely seen in other reports, will dig these up...

Looks like a duplicate of T59583, no?

I am not too familiar with the hair system, but may I ask what particle editing after caching dynamics is actually there for?
(is this used for cache editing like for cloth -- to fix penetrations?)
I can see 2.79b and 2.79 branch being able to do this, but even there it seems pretty much broken, at least for me the hair cache paths look nothing like the actual hair (when in particle edit mode...)
@Robert Guetzkow (rjg) (the reporter of T59583) also mentioned in his report:

I'm not sure when or why you'd actually want to do that, but it shouldn't cause a crash...

The issue with not seeing the particles in particle editmode (no particles in particle edit.blend) might stem from the issue that these caches sometimes cannot be generated correctly (see reports like T62563: Hair Dynamics: cannot generate a valid particle cache)

@Philipp Oeser (lichtwerk)

... might stem from the issue that these caches sometimes cannot be generated correctly (see reports like T62563: Hair Dynamics: cannot generate a valid particle cache)

This might narrow your search scope. T62563 is grounded in a memory management tactic adopted for the rendering depsgraph, which, since November 2018, is deleted after use on every frame. The need to do that arises from the large memory consumption of the rendering depsgraph contending for the equally large memory requirements of the renderer, observed in some of the fairly immense scenes found in the Spring production. Unfortunately, hair dynamics code examines particle system state across multiple frames, and gets confused when the cleaning up of the rendering depsgraph also cleans up the cow'ed object and related particle system buffers. There are some text files which I wrote attached to that bug report which goes into gory details.
That issue doesn't figure in this bug, I don't think, because the depsgraph for the viewport has an indefinite lifetime; the disappearance of a depsgraph does not drive this bug in the manner that it does for T62563.
Per the User Guide particle editing by and large depends on a pre-existing in-memory baked cache: baking to disk does not support particle editing. The cache also needs to be frame-to-frame coherent. An in-memory cache with dropped or trashed frames can give rise to all kinds of interesting behavior but the issue would be difficult to notice until the particle system loads the queer data and tries to manipulate it. I suspect (but have not proved) the case of corruption after cache generation from time to time, making bugs of this type transient in nature. That's as far as I come with this. Thank you for your work in - at least - bringing some order to the bug reports surrounding the dark secrets of the particle and hair system.

Richard Antalik (ISS) changed the subtype of this task from "Report" to "Known Issue".