Issues with particle systems and SubSurf modifier #40523

New Issue

Daniel F. R. Gordillo · 2014-06-06T16:30:44+02:00

2014-06-06 16:30:44 +02:00

System Information
Linux Mint Debian Edition, AMD Phenom II X6 1090T, Nvidia 460 GTX, 8Gb RAM.

Blender Version
Broken: 2.71 testbuild 2
Worked: (optional)

Short description of error
Weight edit & mix modifiers give strange results, affecting other particle systems than the specified in the modifier settings.

Exact steps for others to reproduce the error
There's 2 files with the same object, particle systems and materials, and 3 vertex groups: hair.normal, hair and beard. The only thing that changes, is the Weight Modifier (MIX - EDIT)

Open mods_hair-weight-edit.blend, go to Modifiers tab and disable the Weight edit modifier. We have Suzanne as intended to look: Big hair and big beard. Enabling the modifier edits the hair vertex group, but affects the beard vertex group/particle system as well. Also, THE GLOBAL INFLUENCE SETTING DOESN'T SEEM TO DO ANYTHING in this modifier.
Open mods_hair-weight-mix.blend. The same occurs, the modifier affects other vertex groups/particle systems aside from the ones defined in the settings (beard in this case) Global Influence seems to be working fine in this modifier, but only with the defined groups. The beard stays deformed.

mods_hair-weight-edit.blend

mods_hair-weight-mix.blend

**System Information** Linux Mint Debian Edition, AMD Phenom II X6 1090T, Nvidia 460 GTX, 8Gb RAM. **Blender Version** Broken: 2.71 testbuild 2 Worked: (optional) **Short description of error** Weight edit & mix modifiers give strange results, affecting other particle systems than the specified in the modifier settings. **Exact steps for others to reproduce the error** There's 2 files with the same object, particle systems and materials, and 3 vertex groups: hair.normal, hair and beard. The only thing that changes, is the Weight Modifier (MIX - EDIT) 1. Open mods_hair-weight-edit.blend, go to Modifiers tab and disable the Weight edit modifier. We have Suzanne as intended to look: Big hair and big beard. Enabling the modifier edits the hair vertex group, but affects the beard vertex group/particle system as well. Also, THE GLOBAL INFLUENCE SETTING DOESN'T SEEM TO DO ANYTHING in this modifier. 2. Open mods_hair-weight-mix.blend. The same occurs, the modifier affects other vertex groups/particle systems aside from the ones defined in the settings (beard in this case) Global Influence seems to be working fine in this modifier, but only with the defined groups. The beard stays deformed. [mods_hair-weight-edit.blend](https://archive.blender.org/developer/F92862/mods_hair-weight-edit.blend) [mods_hair-weight-mix.blend](https://archive.blender.org/developer/F92863/mods_hair-weight-mix.blend)

Daniel F. R. Gordillo commented

2014-06-06 16:30:44 +02:00

Changed status to: 'Open'

Daniel F. R. Gordillo commented

2014-06-06 16:30:44 +02:00

Added subscriber: @DGordillo

Bastien Montagne commented

2014-06-09 15:57:00 +02:00

Added subscriber: @mont29

Bastien Montagne commented

2014-06-09 15:57:00 +02:00

I don’t think weight modifiers are the issue here (at least, enabling 'show weight' options seems to give expected results). However, when I disable the subsurf modifier, everything seems OK, and when I re-enable it I even get worse results (unless I switch emission of the particles from Volume to Vertex…). All this seems rather mysterious to me.

Btw, with your Edit Weight modifier, you are only using the “remove vertices from group” feature, Global Influence can have no effect here, it only works on weights editing itself, not on add/remove!

I don’t think weight modifiers are the issue here (at least, enabling 'show weight' options seems to give expected results). However, when I disable the subsurf modifier, everything seems OK, and when I re-enable it I even get worse results (unless I switch emission of the particles from Volume to Vertex…). All this seems rather mysterious to me. Btw, with your Edit Weight modifier, you are only using the “remove vertices from group” feature, Global Influence can have no effect here, it only works on weights editing itself, not on add/remove!

Bastien Montagne changed title from ~~Weight mix and edit modifiers affect other particle systems~~ to Issues with particle systems and SubSurf modifier

2014-06-09 15:57:53 +02:00

Bastien Montagne commented

2014-06-09 15:57:53 +02:00

Added subscriber: @LukasTonne

Fazekas Laszlo commented

2014-06-09 20:56:00 +02:00

Added subscriber: @totoro-4

Fazekas Laszlo commented

2014-06-09 20:56:00 +02:00

mods_hair-weight-edit.blend: I've removed all the beards and hairs and just checked the 'beard' vertex group in the weight paint mode. If the Subsurf modifier is enabled, the VertexWeightEdit modifier has influence on the 'beard' vertex group too, but only on the new subdivision vertices from the Subsurf.

But if I switch off or apply the Subsurf, everything is normal. I think it could be something with the origindex again...

mods_hair-weight-edit.blend: I've removed all the beards and hairs and just checked the 'beard' vertex group in the weight paint mode. If the Subsurf modifier is enabled, the VertexWeightEdit modifier has influence on the 'beard' vertex group too, but only on the new subdivision vertices from the Subsurf. But if I switch off or apply the Subsurf, everything is normal. I think it could be something with the origindex again...

Fazekas Laszlo commented

2014-06-10 16:58:44 +02:00

Open this file. It's the default cube with a subsurf modifier and a vertex group. In weight paint mode, you can see the additional vertices has interpolated color only (purple between red and blue). Maybe it's okay, you can see only the colors for the "real" vertices from the mesh. It's good for weight painting. But if you add a modifier after the subsurf (mirror for example), these vertices become "real" and gets the right color (ie. green) just like when you apply the subsurf modifier.

Maybe this is normal and has nothing with the effect on particles. But it is an evidence that the resulting group weight data structure can be both "interpolated" (origindex...) or "real" after the subsurf modifier. Maybe the particle system just cannot handle one of these correctly.

vertexgroups.blend

Open this file. It's the default cube with a subsurf modifier and a vertex group. In weight paint mode, you can see the additional vertices has interpolated color only (purple between red and blue). Maybe it's okay, you can see only the colors for the "real" vertices from the mesh. It's good for weight painting. But if you add a modifier after the subsurf (mirror for example), these vertices become "real" and gets the right color (ie. green) just like when you apply the subsurf modifier. Maybe this is normal and has nothing with the effect on particles. But it is an evidence that the resulting group weight data structure can be both "interpolated" (origindex...) or "real" after the subsurf modifier. Maybe the particle system just cannot handle one of these correctly. [vertexgroups.blend](https://archive.blender.org/developer/F93766/vertexgroups.blend)

Fazekas Laszlo commented

2014-06-10 17:21:58 +02:00

It seems the applied ("real") version is the wrong one... It's strange. Load this file, press the apply button on the subsurf modifier and try to explain what you see...
vertexgroup2.blend

It seems the applied ("real") version is the wrong one... It's strange. Load this file, press the apply button on the subsurf modifier and try to explain what you see... [vertexgroup2.blend](https://archive.blender.org/developer/F93770/vertexgroup2.blend)

Fazekas Laszlo commented

2014-06-11 22:47:33 +02:00

So, now I think the particle system needs a PSYS_RECALC_RESET flag to trigger a recalculation here. The program detects some changes in the deformVerts() function of modifiers/intern/MOD_particlesystem.c. But it sets the flag only if the number of vertices/edges/faces has changed (for example if the subdivision level changed). It seems there are cases when the number of mesh elements are not changed, only their structure (order of elements, referenced customdata?). An example if you apply the subsurf modifier.

When I forced the program to set always the PSYS_RECALC_RESET in deformVerts(), the bug disappeared IMHO. But this is a brute force solution and causes a lot of redundant recalculations in the particle system - so we need something smarter...

EDIT: no, actually the original bug (weight edit modifying the wrong vertex group) is still there.

So, now I think the particle system needs a PSYS_RECALC_RESET flag to trigger a recalculation here. The program detects some changes in the deformVerts() function of modifiers/intern/MOD_particlesystem.c. But it sets the flag only if the number of vertices/edges/faces has changed (for example if the subdivision level changed). It seems there are cases when the number of mesh elements are not changed, only their structure (order of elements, referenced customdata?). An example if you apply the subsurf modifier. When I forced the program to set always the PSYS_RECALC_RESET in deformVerts(), the bug disappeared IMHO. But this is a brute force solution and causes a lot of redundant recalculations in the particle system - so we need something smarter... EDIT: no, actually the original bug (weight edit modifying the wrong vertex group) is still there.

Fazekas Laszlo commented

2014-06-12 20:28:26 +02:00

I've found something, maybe related. I've checked the psys_cache_vgroup() calls in blenkernel/particle.c and blenkernel/particle_system.c . It seems all vertex groups caches are filled in particle.c together, except the PSYS_VG_DENSITY (it's in particle_system.c). When I played with the settings of the subsurf and the weight modifier, I've noticed that sometimes only the code part in particle.c called after a change so perhaps the PSYS_VG_DENSITY related things are not refreshed (but of course, perhaps nothing else refreshed, only the caches). By the way, since you already refreshing these caches, a comparison between the old and the new contents could trigger a deeper recalculation here.

Lukas Tönne was assigned by Sergey Sharybin

2014-08-12 10:40:00 +02:00

Sergey Sharybin commented

2014-08-12 10:40:00 +02:00

Added subscriber: @Sergey

Sergey Sharybin commented

2014-08-12 10:40:00 +02:00

Lukas, mind checking whether it's a regression and if it's not triaging as a todo?

Bastien Montagne commented

2014-08-15 10:15:59 +02:00

@LukasTonne, really think issue is in particles, see this file: hair_subsurf_apply.blend (with no vgroup at all), apply subsurf modifier… Sounds like some updating issue?

Also, using particles on e.g. a solidify modifier is just impossible (do particles depend on orco? if yes, it could be a missing flag in solidify modifier specifying it does not supports orco? We used to have some modifiers not working after others…).

Back to org file in this report, now disabling and re-enabling subsurf (once weightvg modifier is enabled) seems to fixes everything… :/

@totoro-4 Your two files show a glitch in 'preview' behavior of modifiers - fixed in master (b22831e5ce).

@LukasTonne, really think issue is in particles, see this file: [hair_subsurf_apply.blend](https://archive.blender.org/developer/F103858/hair_subsurf_apply.blend) (with no vgroup at all), apply subsurf modifier… Sounds like some updating issue? Also, using particles on e.g. a solidify modifier is just impossible (do particles depend on orco? if yes, it could be a missing flag in solidify modifier specifying it does not supports orco? We used to have some modifiers not working after others…). Back to org file in this report, now disabling and re-enabling subsurf (once weightvg modifier is enabled) seems to fixes everything… :/ @totoro-4 Your two files show a glitch in 'preview' behavior of modifiers - fixed in master (b22831e5ce).

Bastien Montagne commented

2014-08-20 17:42:46 +02:00

Changed status from 'Open' to: 'Archived'

Bastien Montagne closed this issue

2014-08-20 17:42:46 +02:00

Bastien Montagne commented

2014-08-20 17:42:46 +02:00

In fact, this issue is exactly the same as #37544 - just enable Use Modifier Stack in particles’ Emission panel, and it works as expected!

So archiving, for same reason as #37544:

A brand new hair system is in development (which means non-deadly issues in current one are very unlikely to be tackled), and we have a workaround for that issue…

In fact, this issue is exactly the same as #37544 - just enable `Use Modifier Stack` in particles’ `Emission` panel, and it works as expected! So archiving, for same reason as #37544: > A brand new hair system is in development (which means non-deadly issues in current one are very unlikely to be tackled), and we have a workaround for that issue…

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Issues with particle systems and SubSurf modifier #40523