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Wrong? dependency cycles detected when using a parented object as a boid rule object (object stutters then)
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Description

System Information
Operating system: Windows-10-10.0.17763 64 Bits
Graphics card: Intel(R) UHD Graphics 630 Intel 4.5.0 - Build 26.20.100.6911

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

The Empty fails to follow the object even that it is parented to it.
(empty is the leader of boids particles)

  1. create plane, create cube, add rigid body and collision to both (floor is passive)
  2. add boid particle system to cube
  3. add empty and make child of cube
  4. make boid particles follow the leader - empty
  5. play animation

for comparison i have attached blender 2.79 blend file, and 2.80 file.
see video attached.



Details

Type
Bug

Event Timeline

Philipp Oeser (lichtwerk) triaged this task as Confirmed, Medium priority.

Can confirm.

Empty wont stutter without the Boid Rule.
We are getting a dependency cycle detected (but is is not neccessary afaict)

Dependency cycle detected:
  OBEmpty/Transform Component/TRANSFORM_INIT() depends on
  OBCube/Transform Component/TRANSFORM_FINAL() via 'Parent'
  OBCube/Transform Component/RIGIDBODY_TRANSFORM_COPY() via 'Rigidbody Sync -> Transform Final'
  SCScene/Transform Component/RIGIDBODY_SIM() via 'Rigidbody Sim Eval -> RBO Sync'
  OBCube/Geometry Component/GEOMETRY_EVAL() via 'Object Geom Eval -> Rigidbody Rebuild'
  OBCube/PointCache Component/POINT_CACHE_RESET() via 'Point Cache -> Geometry'
  OBCube/Particles Component/PARTICLE_SYSTEM_DONE() via 'Particle Point Cache'
  OBCube/Particles Component/PARTICLE_SYSTEM_EVAL(ParticleSettings) via 'PSys -> Done'
  OBEmpty/Transform Component/TRANSFORM_FINAL() via 'Boid Rule'
  OBEmpty/Transform Component/TRANSFORM_SIMULATION_INIT() via 'Simulation -> Final Transform'
  OBEmpty/Transform Component/TRANSFORM_EVAL() via 'Transform Eval -> Simulation Init'
  OBEmpty/Transform Component/TRANSFORM_PARENT() via 'Eval'
  OBEmpty/Transform Component/TRANSFORM_LOCAL() via 'ObLocal -> ObParent'
  OBEmpty/Transform Component/TRANSFORM_INIT() via 'Transform Init'
Dependency cycle detected:
  OBCube/Particles Component/PARTICLE_SYSTEM_EVAL(ParticleSettings) depends on
  OBPlane/Transform Component/TRANSFORM_FINAL() via 'Particle Collision'
  OBPlane/Transform Component/RIGIDBODY_TRANSFORM_COPY() via 'Rigidbody Sync -> Transform Final'
  SCScene/Transform Component/RIGIDBODY_SIM() via 'Rigidbody Sim Eval -> RBO Sync'
  OBCube/Geometry Component/GEOMETRY_EVAL() via 'Object Geom Eval -> Rigidbody Rebuild'
  OBCube/PointCache Component/POINT_CACHE_RESET() via 'Point Cache -> Geometry'
  OBCube/Particles Component/PARTICLE_SYSTEM_DONE() via 'Particle Point Cache'
  OBCube/Particles Component/PARTICLE_SYSTEM_EVAL(ParticleSettings) via 'PSys -> Done'

This one:
OBEmpty/Transform Component/TRANSFORM_FINAL() via 'Boid Rule' seems wrong I think [it is not the empty transform being dependent on the Boid Rule?]
Might be reading it wrong though, the relation in DepsgraphRelationBuilder::build_particle_systems
add_relation(ruleob_key, psys_key, "Boid Rule"); looks good to me...

Maybe @Sergey Sharybin (sergey) can shed some light on this?

Philipp Oeser (lichtwerk) renamed this task from Empty Parenting Glitch to Wrong? dependency cycles detected when using a parented object as a boid rule object (object stutters then).Mon, Sep 2, 3:35 PM

it is not the empty transform being dependent on the Boid Rule?

OBCube/Particles Component/PARTICLE_SYSTEM_EVAL(ParticleSettings) via 'PSys -> Done'
OBEmpty/Transform Component/TRANSFORM_FINAL() via 'Boid Rule'

Actually means OBCube/Particles Component/PARTICLE_SYSTEM_EVAL(ParticleSettings) depends on OBEmpty/Transform Component/TRANSFORM_FINAL() via Boid Rule.

Line #(i) depends on line #(i + 1).

Real issue here is that rigid body needs to know object's geometry (which is known after modifier stack evaluation), and rigid body controlling final transform of the object. Now, the particles are part of modifier stack, and they depend on final transform of the object (due to parenting), and particles needs that object to fully evaluate.

This is another variation of T58044.

Oki, thx for clearing that up