Hair density maps increases hair children amount on reopening scene file (or rendering which will get slow) #89598

New Issue

Daniel Westlund · 2021-07-02T11:24:54+02:00

Daniel Westlund commented

2021-07-02 11:24:54 +02:00

System Information
Operating system: window 10
Graphics card: 2080 Ti

blender 2.93.00

Worked: dont know when it worked

Hair density changes on reopening scene file

Open the attached file and first turn of and turn on and of interpolated children
see how the density changes. The number of children increases.
save the file and reopen it to see that its back to a lower number of children.
affects both viewport and offline render

Test File
Hair_Density_bug_01.blend

**System Information** Operating system: window 10 Graphics card: 2080 Ti **blender 2.93.00** Worked: dont know when it worked Hair density changes on reopening scene file - Open the attached file and first turn of and turn on and of interpolated children - see how the density changes. The number of children increases. - save the file and reopen it to see that its back to a lower number of children. - affects both viewport and offline render Test File [Hair_Density_bug_01.blend](https://archive.blender.org/developer/F10209562/Hair_Density_bug_01.blend)

Daniel Westlund commented

2021-07-02 11:24:54 +02:00

Added subscriber: @Dawe69

blender-admin commented

2021-07-02 11:24:54 +02:00

#89596 was marked as duplicate of this issue

Raimund Klink commented

2021-07-02 13:28:59 +02:00

Added subscriber: @Raimund58

Raimund Klink commented

2021-07-02 13:28:59 +02:00

This report does not contain all the requested information, which is required for us to investigate the issue.

Please submit a new report and carefully follow the instructions. Be sure to provide system information, Blender version, the last Blender version which worked, and a .blend file with exact steps to reproduce the problem.

A guideline for making a good bug report can be found at https://wiki.blender.org/wiki/Process/Bug_Reports

This report does not contain all the requested information, which is required for us to investigate the issue. Please submit a new report and carefully follow the instructions. Be sure to provide system information, Blender version, the last Blender version which worked, and a .blend file with exact steps to reproduce the problem. A guideline for making a good bug report can be found at https://wiki.blender.org/wiki/Process/Bug_Reports

Daniel Westlund commented

2021-07-02 14:51:04 +02:00

Just open the scene file and turn off and then on the children of the hair. you will see that when you turn it on again, the number of children will increase.
If you save and reopen the same file its back to a lower number of children again.
This is also persistent in render etc.

best/
Daniel

Just open the scene file and turn off and then on the children of the hair. you will see that when you turn it on again, the number of children will increase. If you save and reopen the same file its back to a lower number of children again. This is also persistent in render etc. best/ Daniel

Raimund Klink commented

2021-07-02 14:59:19 +02:00

You did not include a blend file...

Pratik Borhade commented

2021-07-02 15:15:21 +02:00

Changed status from 'Needs Triage' to: 'Needs User Info'

Daniel Westlund commented

2021-07-02 15:17:08 +02:00

Hair_Density_bug_01.blend

[Hair_Density_bug_01.blend](https://archive.blender.org/developer/F10209562/Hair_Density_bug_01.blend)

Daniel Westlund commented

2021-07-02 15:17:21 +02:00

Sorry!

Pratik Borhade commented

2021-07-05 10:50:33 +02:00

Changed status from 'Needs User Info' to: 'Needs Triage'

Pratik Borhade commented

2021-07-05 10:50:43 +02:00

Added subscriber: @PratikPB2123

Philipp Oeser commented

2021-07-07 10:48:24 +02:00

Added subscriber: @lichtwerk

Philipp Oeser commented

2021-07-07 10:48:24 +02:00

Changed status from 'Needs Triage' to: 'Confirmed'

Philipp Oeser commented

2021-07-07 10:48:24 +02:00

Can confirm, will have a quick look.

Daniel Westlund commented

2021-07-07 13:06:13 +02:00

I have a hunch that it is connected to my other bug report here: https://developer.blender.org/T89596 but I'm probably wrong...

Philipp Oeser self-assigned this 2021-07-07 13:19:00 +02:00

Philipp Oeser commented

2021-07-07 13:19:00 +02:00

Got a fix for this, just double-checking the reasoning behind the change...

Philipp Oeser commented

2021-07-07 15:15:33 +02:00

Hrmf, I should have not looked into this [turned into a timesink], to properly reason about particle code is... not easy.
Will post my findings tomorrow

Hrmf, I should have not looked into this [turned into a timesink], to properly reason about particle code is... not easy. Will post my findings tomorrow

Philipp Oeser commented

2021-07-08 10:09:57 +02:00

Added subscriber: @iss

Philipp Oeser removed their assignment 2021-07-09 14:08:43 +02:00

Philipp Oeser commented

2021-07-09 14:08:43 +02:00

Added subscribers: @JacquesLucke, @Sergey

Philipp Oeser commented

2021-07-09 14:08:43 +02:00

Here are my findings:

changing settings on the ParticleSettings trigger this bug (e.g. changing child_type), whereas changing settings on the ParticleSystem wont (e.g. changing child_seed)
- note here that changes on the particle system (the "working" scenario) will tag the particle system ID_RECALC_PSYS_CHILD -- the "broken" state tries it too (but on the owner ID
what happens in the "broken" scenario is that we are "loosing" more and more (on each iteration) particles tagged PARS_UNEXIST
- in system_step: initialize_all_particles will clear PARS_UNEXIST (under certain condition -- this needs a bit more investigation [from module devs probably])
- in system_step: reset_particle > init_particle_texture will set PARS_UNEXIST correctly (but this is only done for a subset -- starting from )
- this results in an ever increasing number of existing particles (psys->totpart vs psys->totunexist shifts [totpart increases, totunexist decreases]), which is wrong

related (I think) commits:

Doing this change (which will basically reset all particles) will show a working state (but the "fix" is probably the wrong thing to do):
P2243: T89598_snippet



diff --git a/source/blender/blenkernel/intern/particle_system.c b/source/blender/blenkernel/intern/particle_system.c
index 06d3daaf4d6..c82c65776d4 100644
--- a/source/blender/blenkernel/intern/particle_system.c
+++ b/source/blender/blenkernel/intern/particle_system.c
@@ -4513,7 +4513,7 @@ static void system_step(ParticleSimulationData *sim, float cfra, const bool use_
     distribute_particles(sim, part->from);
     initialize_all_particles(sim);
     /* reset only just created particles (on startframe all particles are recreated) */
-    reset_all_particles(sim, 0.0, cfra, oldtotpart);
+    reset_all_particles(sim, 0.0, cfra, 0);
     free_unexisting_particles(sim);
 
     if (psys->fluid_springs) {

Other suspicion is that RNA updates (rna_Particle_redo_child / particle_recalc) tagging goes wrong in terms of ParticleSystem vs. ParticleSettings (see very first finding).

Will step down, maybe this rings a bell immediately for @Sergey or @JacquesLucke

Here are my findings: - changing settings on the `ParticleSettings` trigger this bug (e.g. changing `child_type`), whereas changing settings on the `ParticleSystem` wont (e.g. changing `child_seed`) - note here that changes on the particle system (the "working" scenario) will tag the particle system `ID_RECALC_PSYS_CHILD` -- the "broken" state tries it too (but on the owner ID - what happens in the "broken" scenario is that we are "loosing" more and more (on each iteration) particles tagged `PARS_UNEXIST` - in `system_step`: `initialize_all_particles` will clear `PARS_UNEXIST` (under certain condition -- this needs a bit more investigation [from module devs probably]) - in `system_step`: `reset_particle` > `init_particle_texture` will set `PARS_UNEXIST` correctly (but this is only done for a subset -- starting from ) - this results in an ever increasing number of existing particles (`psys->totpart` vs `psys->totunexist` shifts [totpart increases, totunexist decreases]), which is wrong related (I think) commits: - 9b64ebc605 - dced56f - 78c491e62a - ee762ce93f Doing this change (which will basically reset **all** particles) will show a working state (but the "fix" is probably the wrong thing to do): [P2243: T89598_snippet](https://archive.blender.org/developer/P2243.txt) ``` diff --git a/source/blender/blenkernel/intern/particle_system.c b/source/blender/blenkernel/intern/particle_system.c index 06d3daaf4d6..c82c65776d4 100644 --- a/source/blender/blenkernel/intern/particle_system.c +++ b/source/blender/blenkernel/intern/particle_system.c @@ -4513,7 +4513,7 @@ static void system_step(ParticleSimulationData *sim, float cfra, const bool use_ distribute_particles(sim, part->from); initialize_all_particles(sim); /* reset only just created particles (on startframe all particles are recreated) */ - reset_all_particles(sim, 0.0, cfra, oldtotpart); + reset_all_particles(sim, 0.0, cfra, 0); free_unexisting_particles(sim); if (psys->fluid_springs) { ``` Other suspicion is that RNA updates (`rna_Particle_redo_child` / `particle_recalc`) tagging goes wrong in terms of ParticleSystem vs. ParticleSettings (see very first finding). Will step down, maybe this rings a bell immediately for @Sergey or @JacquesLucke

Philipp Oeser changed title from ~~Hair density changes on reopening scene file~~ to Hair density maps increases hair children amount on reopening scene file (or rendering which will get slow)

2021-07-23 13:39:02 +02:00

Sergey Sharybin commented

2021-09-03 16:33:00 +02:00

Doesn't really ring any bells.
The particle system is only in the maintenance mode, meaning only newly introduced issues can be fixed.

Doesn't really ring any bells. The particle system is only in the maintenance mode, meaning only newly introduced issues can be fixed.

Dalai Felinto commented

2022-05-09 15:17:32 +02:00

Added subscriber: @dfelinto

Dalai Felinto commented

2022-05-09 15:17:32 +02:00

Thanks for the report. Marking this as known issue since it depends on the old particle settings which is end of life .

Thanks for the report. Marking this as known issue since it depends on the [old particle settings which is end of life ](https://developer.blender.org/tag/nodes_physics/).

Philipp Oeser removed the

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Hair density maps increases hair children amount on reopening scene file (or rendering which will get slow) #89598