Hair dynamics don't work with smooth shading #71460

New Issue

Joao Morgado · 2019-11-09T20:24:19+01:00

Joao Morgado commented

2019-11-09 20:24:19 +01:00

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: eefd806afc
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.]

**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: `eefd806afc` 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.]

Joao Morgado commented

2019-11-09 20:24:19 +01:00

Added subscriber: @MrJoMo

Philipp Oeser commented

2019-11-11 13:15:04 +01:00

Added subscriber: @lichtwerk

Philipp Oeser commented

2019-11-11 13:15:04 +01:00

Cannot reproduce here, see
#71460.blend

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

Cannot reproduce here, see [#71460.blend](https://archive.blender.org/developer/F8031333/T71460.blend) Do you see the issue in above file as well? If not, please attach you file here...

Garry R. Osgood commented

2019-11-11 17:01:41 +01:00

Added subscriber: @grosgood

Garry R. Osgood commented

2019-11-11 17:01:41 +01:00

Looks like #68681. I could not reproduce that bug because I have only AMD cards around here; the issue with #68681 and possibly this incident seems particular to NVIDIA cards.
[Edit]
Just tried it with @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.

Looks like #68681. I could not reproduce that bug because I have only AMD cards around here; the issue with #68681 and possibly this incident seems particular to NVIDIA cards. [Edit] Just tried it with @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 commented

2019-11-15 04:27:51 +01:00

In #71460#808994, @lichtwerk wrote:
Cannot reproduce here, see
#71460.blend

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.

Blender 2019-11-14 22-20-13.mp4

> In #71460#808994, @lichtwerk wrote: > Cannot reproduce here, see > [#71460.blend](https://archive.blender.org/developer/F8031333/T71460.blend) > > 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. [Blender 2019-11-14 22-20-13.mp4](https://archive.blender.org/developer/F8084281/Blender_2019-11-14_22-20-13.mp4)

Joao Morgado commented

2019-11-16 22:15:30 +01:00

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.

Philipp Oeser commented

2019-11-28 10:58:58 +01:00

Thx all for getting back, it really looks like the same roots as #68681 (Hair Dynamics: simulation doesn't work depending on smooth/flat shaded surfaces (and nvidia gpus?)), will merge these reports...

Philipp Oeser commented

2019-11-28 10:59:05 +01:00

Closed as duplicate of #68681

Philipp Oeser closed this issue

2019-11-28 10:59:05 +01:00

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Hair dynamics don't work with smooth shading #71460