Cant set particles[0].hair_keys[-1].co = Vector((0,0,3)) #60930

New Issue

Jose Conseco · 2019-01-27T21:25:06+01:00

Jose Conseco commented

2019-01-27 21:25:06 +01:00

There is no way in blender 2.8 to write hair_key- [x].co to hair particle system.
Simple blend file with one particle hair and script:

bpy.context.active_object.particle_systems.active.particles- [x].hair_keys[-1].co = Vector((0,0,3))

HairKey_Set.blend

Works ok in blender 2.79. I tried to write hair_key.co to depsgraph evaluated object, but it would not work too.

There is no way in blender 2.8 to write hair_key- [x].co to hair particle system. Simple blend file with one particle hair and script: > bpy.context.active_object.particle_systems.active.particles- [x].hair_keys[-1].co = Vector((0,0,3)) [HairKey_Set.blend](https://archive.blender.org/developer/F6424528/HairKey_Set.blend) Works ok in blender 2.79. I tried to write hair_key.co to depsgraph evaluated object, but it would not work too.

Jose Conseco commented

2019-01-27 21:25:06 +01:00

Added subscriber: @JoseConseco

Joshua Worth commented

2019-01-28 02:32:04 +01:00

Added subscriber: @YoklJO

Joshua Worth commented

2019-01-28 02:32:04 +01:00

I haven't worked on Blender's source before, and found this ticket which seemed debuggable.
I found the culprit, which is in rna_ParticleHairKey_location_object_info of rna_particle.c.
In this check: if (psmd && psmd->mesh_final && psmd->psys) {, mesh_final is null, so it never finds the ParticleHairKey instance to modify. I don't really know what mesh_final is for, but I noticed that it isn't used anywhere in the function, so changing that if statement to: if (psmd && psmd->psys) { makes the problem in this ticket's description go away. I have no idea if this will cause other problems, because maybe it's important to check that mesh_final is not null.

I haven't worked on Blender's source before, and found this ticket which seemed debuggable. I found the culprit, which is in `rna_ParticleHairKey_location_object_info` of `rna_particle.c`. In this check: `if (psmd && psmd->mesh_final && psmd->psys) {`, `mesh_final` is null, so it never finds the `ParticleHairKey` instance to modify. I don't really know what mesh_final is for, but I noticed that it isn't used anywhere in the function, so changing that if statement to: `if (psmd && psmd->psys) {` makes the problem in this ticket's description go away. I have no idea if this will cause other problems, because maybe it's important to check that `mesh_final` is not null.

Sergey Sharybin was assigned by Sebastian Parborg

2019-01-29 10:51:23 +01:00

Rhett Jackson commented

2019-03-19 07:55:36 +01:00

Added subscriber: @Jandals

Rhett Jackson commented

2019-03-19 08:03:34 +01:00

I have run into this same problem writing to hair_key- [x].co and I've also noticed that it's not just the ParticleHairKey that can't be found. When I try to access it, the Particle instance can't be found either.

If I'm looking for

C.object.particle_systems[0].particles[0].hair_key[0].co

reading from

C.object.particle_systems[0].particles[0]

also fails, which used to work in 2.79.

I have run into this same problem writing to hair_key- [x].co and I've also noticed that it's not just the ParticleHairKey that can't be found. When I try to access it, the Particle instance can't be found either. If I'm looking for ``` C.object.particle_systems[0].particles[0].hair_key[0].co ``` reading from ``` C.object.particle_systems[0].particles[0] ``` also fails, which used to work in 2.79.

Alexander Meißner commented

2019-04-14 10:21:09 +02:00

Added subscriber: @Lichtso

Alexander Meißner commented

2019-04-14 10:21:09 +02:00

The problem goes far deeper:
Depsgraph copies every object and all their parts including ParticleSystemModifierData.
The copy of ParticleSystemModifierData is used in deformVerts and gets a mesh_final assigned.
However, the rna_ParticleHairKey_location_object_info looks in the original object for the ParticleSystemModifierData and that one never gets a mesh_final.
rna_ParticleHairKey_location_object_info also does a linear search over all hairs for every access to a HairKey which is extremely inefficient.

Thus, rna_ParticleHairKey_location_object_info is fundamentally broken in two ways: Its performance and it can never output a ParticleData pointer.
As the comment in the source code says, a fix would be storing all needed pointers like ParticleSystemModifierData and ParticleData in the ParticleHairKey pointerRNA.
Here an example of how the pointers of copies look like:

direct_link_modifiers psmd=0x7fbd0577d528

deg_expand_copy_on_write_datablock id_orig=0x7fbd062dde08 id_cow=0x7fbd06426c08 id_cow_recalc=0x2087
BKE_object_copy_data ob_dst=0x7fbd06426c08 ob_src=0x7fbd062dde08
initData psmd=0x7fbd05a134d8
copyData dst_psmd=0x7fbd05a134d8 src_psmd=0x7fbd0577d528
deformVerts psmd=0x7fbd05a134d8 psmd->mesh_final=0x7fbd0624d008

deg_expand_copy_on_write_datablock id_orig=0x7fbcfef17408 id_cow=0x7fbd0630ec08 id_cow_recalc=0xffffff83
freeData psmd=0x7fbd05a134d8
deg_expand_copy_on_write_datablock id_orig=0x7fbd062dde08 id_cow=0x7fbd06426c08 id_cow_recalc=0x2002
BKE_object_copy_data ob_dst=0x7fbd06426c08 ob_src=0x7fbd062dde08
initData psmd=0x7fbd05a008f8
copyData dst_psmd=0x7fbd05a008f8 src_psmd=0x7fbd0577d528
deformVerts psmd=0x7fbd05a008f8 psmd->mesh_final=0x7fbd001dc208

rna_ParticleHairKey_location_object_info ptr=0x11d1db198 hkey=0x7fbd057a79f8 ob=0x7fbd062dde08
    psmd=0x7fbd0577d528 psmd->mesh_final=0x0 psmd->psys=0x7fbd057333b8
rna_ParticleHairKey_location_object_set ptr=0x11d1db198 psmd=0x0 pa=0x0

Note: The mesh_final is necessary because blender stores all HairKeys relative to their emitter mesh surface if the PSYS_HAIR_DYNAMICS flag is not set. See the use of psys_mat_hair_to_object in rna_ParticleHairKey_location_object_get and rna_ParticleHairKey_location_object_set.

The problem goes far deeper: Depsgraph copies every object and all their parts including ParticleSystemModifierData. The copy of ParticleSystemModifierData is used in deformVerts and gets a mesh_final assigned. However, the rna_ParticleHairKey_location_object_info looks in the original object for the ParticleSystemModifierData and that one never gets a mesh_final. rna_ParticleHairKey_location_object_info also does a linear search over all hairs for every access to a HairKey which is extremely inefficient. Thus, rna_ParticleHairKey_location_object_info is fundamentally broken in two ways: Its performance and it can never output a ParticleData pointer. As the comment in the source code says, a fix would be storing all needed pointers like ParticleSystemModifierData and ParticleData in the ParticleHairKey pointerRNA. Here an example of how the pointers of copies look like: ``` direct_link_modifiers psmd=0x7fbd0577d528 deg_expand_copy_on_write_datablock id_orig=0x7fbd062dde08 id_cow=0x7fbd06426c08 id_cow_recalc=0x2087 BKE_object_copy_data ob_dst=0x7fbd06426c08 ob_src=0x7fbd062dde08 initData psmd=0x7fbd05a134d8 copyData dst_psmd=0x7fbd05a134d8 src_psmd=0x7fbd0577d528 deformVerts psmd=0x7fbd05a134d8 psmd->mesh_final=0x7fbd0624d008 deg_expand_copy_on_write_datablock id_orig=0x7fbcfef17408 id_cow=0x7fbd0630ec08 id_cow_recalc=0xffffff83 freeData psmd=0x7fbd05a134d8 deg_expand_copy_on_write_datablock id_orig=0x7fbd062dde08 id_cow=0x7fbd06426c08 id_cow_recalc=0x2002 BKE_object_copy_data ob_dst=0x7fbd06426c08 ob_src=0x7fbd062dde08 initData psmd=0x7fbd05a008f8 copyData dst_psmd=0x7fbd05a008f8 src_psmd=0x7fbd0577d528 deformVerts psmd=0x7fbd05a008f8 psmd->mesh_final=0x7fbd001dc208 rna_ParticleHairKey_location_object_info ptr=0x11d1db198 hkey=0x7fbd057a79f8 ob=0x7fbd062dde08 psmd=0x7fbd0577d528 psmd->mesh_final=0x0 psmd->psys=0x7fbd057333b8 rna_ParticleHairKey_location_object_set ptr=0x11d1db198 psmd=0x0 pa=0x0 ``` Note: The mesh_final is necessary because blender stores all HairKeys relative to their emitter mesh surface if the PSYS_HAIR_DYNAMICS flag is not set. See the use of psys_mat_hair_to_object in rna_ParticleHairKey_location_object_get and rna_ParticleHairKey_location_object_set.

Jose Conseco commented

2019-05-18 13:03:19 +02:00

Changed status from 'Open' to: 'Resolved'

Jose Conseco closed this issue

2019-05-18 13:03:19 +02:00

Jose Conseco commented

2019-05-18 13:03:19 +02:00

After new depsgraph changes I tried to set particle hair keys co again, and got it working. Sollution:

obj = bpy.context.active_object
depsgraph = bpy.context.evaluated_depsgraph_get()
object_eval = obj.evaluated_get(depsgraph)
object_eval.particle_systems.active.particles[0].hair_keys[-1].co = Vector((0,0,3))

Then tab into particle editmode, and out. I should update hair position. Not sure if there is better way (without tab)

After new depsgraph changes I tried to set particle hair keys co again, and got it working. Sollution: ``` obj = bpy.context.active_object depsgraph = bpy.context.evaluated_depsgraph_get() object_eval = obj.evaluated_get(depsgraph) object_eval.particle_systems.active.particles[0].hair_keys[-1].co = Vector((0,0,3)) ``` Then tab into particle editmode, and out. I should update hair position. Not sure if there is better way (without tab)

Alexander Meißner commented

2019-05-22 18:20:55 +02:00

Does not work for me it seems.
It does not matter how much I switch between object, particle and edit modes.

And others still have the same problem:
https://blender.stackexchange.com/questions/134532/blender-2-8-dynamically-set-particle-locations-via-python

Does not work for me it seems. It does not matter how much I switch between object, particle and edit modes. And others still have the same problem: https://blender.stackexchange.com/questions/134532/blender-2-8-dynamically-set-particle-locations-via-python

Joshua Worth commented

2019-05-22 19:08:34 +02:00

@JoseConseco That seems more like a work-around to the actual problem. If the original problem is still there, then this ticket should not be set to Resolved.

Jose Conseco commented

2019-05-22 19:11:29 +02:00

But this seems to work ok. There is other problem preventing writing to hair positions: https://developer.blender.org/T64805.
Try adding cache manualy, then solution mentioned 2 posts above will work.

But this seems to work ok. There is other problem preventing writing to hair positions: https://developer.blender.org/T64805. Try adding cache manualy, then solution mentioned 2 posts above will work.

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Cant set particles[0].hair_keys[-1].co = Vector((0,0,3)) #60930