Maniphest T71460

Hair dynamics don't work with smooth shading
Closed, Duplicate
Actions

Assigned To
None
Authored By
Joao Morgado (MrJomo)
Nov 9 2019, 8:24 PM
Tags
  • BF Blender
  • Physics
Subscribers
Garry R. Osgood (grosgood)
Joao Morgado (MrJomo)
Philipp Oeser (lichtwerk)

Description

System Information
Operating system: Windows-10-10.0.18362 64 Bits
Graphics card: GeForce RTX 2070 SUPER/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 431.86

Blender Version
Broken: version: 2.81 (sub 16), branch: master, commit date: 2019-11-07 20:33, hash: rBeefd806afc15
Worked: Not sure

Short description of error
Hair dynamics on an animated object work fine if the object is flat shaded, but break when enabling smooth shading. The error looks like the root of the hairs move with the obejct but the rest of the hair stays in place.

Exact steps for others to reproduce the error

Start new scene
Select default cube
Add particle system and set it to hair
Enable "Hair Dynamics" in the particle settings
Animate the cube moving in any direction.
Play animation.

[At this point everything should work as intended. Cube will move and hair will dynamically follow along.]

Right click on cube and select "Shade smooth"
Play animation again

[Now the hair dynamics don't work and hairs appear to stretch as the root stay attached to the cube and the rest of the hairs stay in place.]

Related Objects

Event Timeline

Joao Morgado (MrJomo) created this task.Nov 9 2019, 8:24 PM
Philipp Oeser (lichtwerk) lowered the priority of this task from 90 to 30.Nov 11 2019, 1:15 PM
Philipp Oeser (lichtwerk) added a project: Physics.
Philipp Oeser (lichtwerk) added a subscriber: Philipp Oeser (lichtwerk).

Cannot reproduce here, see

T71460.blend548 KBDownload

Do you see the issue in above file as well?
If not, please attach you file here...

Garry R. Osgood (grosgood) added a subscriber: Garry R. Osgood (grosgood).EditedNov 11 2019, 5:01 PM

Looks like T68681. I could not reproduce that bug because I have only AMD cards around here; the issue with T68681 and possibly this incident seems particular to NVIDIA cards.
[Edit]
Just tried it with @Philipp Oeser (lichtwerk) 's test file. Did not reproduce it; animation is correct with both smooth and flat shading. Suspect this is an NVIDIA specific issue; have only AMD cards here.

Joao Morgado (MrJomo) added a comment.EditedNov 15 2019, 4:27 AM
In T71460#808994, @Philipp Oeser (lichtwerk) wrote:

Cannot reproduce here, see

T71460.blend548 KBDownload

Do you see the issue in above file as well?
If not, please attach you file here...

Hi Philipp. I do see the issue on this file. Attached is a video of opening the file and testing playback both with smooth shading and with flat shading. As you can see, smooth shading breaks the hair simulation.

Joao Morgado (MrJomo) added a comment.Nov 16 2019, 10:15 PM

Further testing appears to show that adjusting the number of particles fixes the problem. So for example, if instead of the default 1000, I change it to 999 or 1001, the the dynamics work again.

Dalai Felinto (dfelinto) raised the priority of this task from 30 to 90.Nov 26 2019, 11:15 PM
Philipp Oeser (lichtwerk) added a comment.Nov 28 2019, 10:58 AM

Thx all for getting back, it really looks like the same roots as T68681: Hair Dynamics: simulation doesn't work depending on smooth/flat shaded surfaces (and nvidia gpus?), will merge these reports...

Philipp Oeser (lichtwerk) closed this task as a duplicate of T68681: Hair Dynamics: simulation doesn't work depending on smooth/flat shaded surfaces (and nvidia gpus?).Nov 28 2019, 10:59 AM