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Particle system, Hair, unwanted recalculations
Confirmed, NormalPublicBUG


System Information
Operating system: Windows-7-6.1.7601-SP1 64 Bits
Graphics card: GeForce GTX 660 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 456.71

Blender Version
Broken: version: 2.83.9, branch: boneMaster_283, commit date: 2020-11-17 11:33, hash: rB6bd7c877fbb3
Worked: (newest version of Blender that worked as expected)

Short description of error
Object with hair system rotates slowly when it is not instanced. So I suppose, that something racalculates again and again with each movement.

Exact steps for others to reproduce the error

  • Open attached file
  • Unhide any of the collections
  • Compare the speed to rotate the object with the instance.

The greater the number of child particles, the more evident the problem

Event Timeline

I can't reproduce this on 2.93.0 Alpha, branch: master, commit date: 2021-02-02 10:10, hash: rBd19aaad0bce1 nor on 2.83.12.

@Vyacheslav (hitrpr) Indeed, increasing the displayed amount of the children makes the impact noticeable on my machine (15fps with 100 children vs 25+fps with the instance).

Now the problem is that it seems like the performance for this case was not better in the past (2.83.12 gets about 11fps for me). If it was always slower, then this is just a limitation, not a regression.

@Falk David (filedescriptor) Yep, it was like this in the past, but what the reason and what calculated? Is it so necessary for object transforms?
May be there is the area for improvement, not just limitation.

Germano Cavalcante (mano-wii) changed the task status from Needs Triage to Confirmed.Thu, Feb 4, 10:02 PM
Germano Cavalcante (mano-wii) updated the task description. (Show Details)
Germano Cavalcante (mano-wii) changed the subtype of this task from "Report" to "Bug".

I can confirm the problem.
I'm also not sure what causes the recalculation.