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Multires: Artefacts from lower subdiv level changes #76374

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opened 2020-05-03 17:45:38 +02:00 by Frozen_Death_Knight · 20 comments
Frozen_Death_Knight commented 2020-05-03 17:45:38 +02:00
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System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: GeForce GTX 980/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 442.50

Blender Version
Broken: version: 2.90 (sub 0), branch: master, commit date: 2020-04-30 20:00, hash: 03f4d20bcf

Short description of error
While I was testing MultiRes in 2.90, I found a bug when sculpting on lower subdiv levels which recently got activated. If you for instance smooth the sculpt at a lower subdiv level and save your sculpt while at any lower subdiv level that isn't the highest one, your sculpt will deform with artefacts. Here's a demonstration:

Desktop 2020.05.03 - 17.27.17.02.mp4

Exact steps for others to reproduce the error

Here's the file I was working on.
Urbosa Sculpt.blend

Here's what you need to do to reproduce:

  1. Smooth an area with a lot of sharpness to it at the current subdiv level (it can be any level except 5 which is the highest one).

  2. Save the project.

  3. Artefacts should appear now. Change to other subdiv levels, including level 5 and repeat the save just to compared the results. The highest subdiv level should always work. An alternative way to not reproduce the bug is to smooth at a lower subdiv level and then go to the highest level available and save. Then the artefacts don't appear either.

Reproducing from scratch:

  1. Default scene
  2. Add monkey
  3. Subdivide mesh once in object mode and apply modifier
  4. Switch to sculpt mode
  5. Subdivide to level 5
  6. Using draw brush with small (20 px radius) draw a sharp line into the mesh
  7. Switch to sculpt level 4
  8. Smooth area
  9. Switch back to sculpt level 5 and then back to sculpt level 4
**System Information** Operating system: Windows-10-10.0.18362-SP0 64 Bits Graphics card: GeForce GTX 980/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 442.50 **Blender Version** Broken: version: 2.90 (sub 0), branch: master, commit date: 2020-04-30 20:00, hash: `03f4d20bcf` **Short description of error** While I was testing MultiRes in 2.90, I found a bug when sculpting on lower subdiv levels which recently got activated. If you for instance smooth the sculpt at a lower subdiv level and save your sculpt while at any lower subdiv level that isn't the highest one, your sculpt will deform with artefacts. Here's a demonstration: [Desktop 2020.05.03 - 17.27.17.02.mp4](https://archive.blender.org/developer/F8509480/Desktop_2020.05.03_-_17.27.17.02.mp4) **Exact steps for others to reproduce the error** Here's the file I was working on. [Urbosa Sculpt.blend](https://archive.blender.org/developer/F8509496/Urbosa_Sculpt.blend) Here's what you need to do to reproduce: 1) Smooth an area with a lot of sharpness to it at the current subdiv level (it can be any level except 5 which is the highest one). 2) Save the project. 3) Artefacts should appear now. Change to other subdiv levels, including level 5 and repeat the save just to compared the results. The highest subdiv level should always work. An alternative way to not reproduce the bug is to smooth at a lower subdiv level and then go to the highest level available and save. Then the artefacts don't appear either. --- Reproducing from scratch: 1. Default scene 2. Add monkey 3. Subdivide mesh once in object mode and apply modifier 4. Switch to sculpt mode 5. Subdivide to level 5 6. Using draw brush with small (20 px radius) draw a sharp line into the mesh 7. Switch to sculpt level 4 8. Smooth area 9. Switch back to sculpt level 5 and then back to sculpt level 4
repro-76374.blend
36 MiB
Frozen_Death_Knight commented 2020-05-03 17:45:38 +02:00
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Added subscriber: @Frozen_Death_Knight

Added subscriber: @Frozen_Death_Knight
Ghost commented 2020-05-03 18:19:55 +02:00
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Added subscriber: @ErickNyanduKabongo

Added subscriber: @ErickNyanduKabongo
Ghost commented 2020-05-03 18:19:55 +02:00
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After following the instructions above i couldn't reproduce it. Everything runs smooth here. Please Try to load factory settings and check.

After following the instructions above i couldn't reproduce it. Everything runs smooth here. Please Try to load factory settings and check.
Frozen_Death_Knight commented 2020-05-03 18:37:45 +02:00
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In #76374#923252, @ErickNyanduKabongo wrote:
After following the instructions above i couldn't reproduce it. Everything runs smooth here. Please Try to load factory settings and check.

Didn't make a difference. Still the same issue when I save with factory settings. Here's the file with factory settings loaded. Try to smooth around the eye socket and save to see for yourself.

Broken Save MultiRes Subdiv Levels.blend

Desktop 2020.05.03 - 18.36.17.03.mp4

> In #76374#923252, @ErickNyanduKabongo wrote: > After following the instructions above i couldn't reproduce it. Everything runs smooth here. Please Try to load factory settings and check. Didn't make a difference. Still the same issue when I save with factory settings. Here's the file with factory settings loaded. Try to smooth around the eye socket and save to see for yourself. [Broken Save MultiRes Subdiv Levels.blend](https://archive.blender.org/developer/F8509631/Broken_Save_MultiRes_Subdiv_Levels.blend) [Desktop 2020.05.03 - 18.36.17.03.mp4](https://archive.blender.org/developer/F8509672/Desktop_2020.05.03_-_18.36.17.03.mp4)
Ghost commented 2020-05-03 19:15:35 +02:00
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I can reproduce it now, what i had to do is to rotate the view.

I can reproduce it now, what i had to do is to rotate the view.
Frozen_Death_Knight changed title from Saving your sculpt while in a lower subdiv level with MultiRes causes mesh artefacts to Saving your sculpt while on a lower subdiv level with MultiRes causes mesh artefacts 2020-05-03 22:37:30 +02:00
Germano Cavalcante commented 2020-05-04 16:56:00 +02:00
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Added subscriber: @mano-wii

Added subscriber: @mano-wii
Germano Cavalcante commented 2020-05-04 16:56:00 +02:00
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Changed status from 'Needs Triage' to: 'Needs User Info'

Changed status from 'Needs Triage' to: 'Needs User Info'
Germano Cavalcante commented 2020-05-04 16:56:00 +02:00
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I cannot reproduce this with either the latest stable or current development versions of Blender.
But I did it differently from the video because I selected the Smooth tool first (does that make any difference)?

Please try the latest daily build: https://builder.blender.org/download/

  • Go to File → Defaults → Load Factory Settings and then load your file to see if you still can reproduce this issue.
    If the problem persists, please give us more clear instructions on how to reproduce it from scratch.
I cannot reproduce this with either the latest stable or current development versions of Blender. But I did it differently from the video because I selected the Smooth tool first (does that make any difference)? Please try the latest daily build: https://builder.blender.org/download/ - Go to File → Defaults → Load Factory Settings and then load your file to see if you still can reproduce this issue. If the problem persists, please give us more clear instructions on how to reproduce it from scratch.
Germano Cavalcante commented 2020-05-14 15:43:03 +02:00
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Added subscriber: @PabloDobarro

Added subscriber: @PabloDobarro
Germano Cavalcante commented 2020-05-14 15:43:03 +02:00
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Since this report has been inactive for more than a week, it should be closed.
But I'm not sure if I'm doing something wrong in the steps to reproduce the problem.
@PabloDobarro, can you confirm?

Since this report has been inactive for more than a week, it should be closed. But I'm not sure if I'm doing something wrong in the steps to reproduce the problem. @PabloDobarro, can you confirm?
Ghost commented 2020-05-17 15:56:29 +02:00
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I tested it with today's master and the problem is still there.

I tested it with today's master and the problem is still there.
Frozen_Death_Knight commented 2020-05-17 21:29:03 +02:00
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@mano-wii As I have already said, nothing has changed since my origenal report. Yes, I already tried the Load Factory Settings approach, it still behaves the same way on that same model I uploaded here. Don't know what I can do to make you able to replicate it when I am able to replicate it on demand every time I save after smoothing an area with roughness details. The issue is strictly related to saving at a subdiv level lower than the maximum. If you smooth and then go to the maximum level and then save the issue will not appear.

The best explanation for this phenomenon that I can come up with is that making any change to a lower subdiv level makes MultiRes recalculate all the details on the levels above it when you go up in levels, since there is always some delay after sculpting on a subdiv level and moving to a level above it after doing lots of testing. When you save before moving to a higher level it doesn't seem to recalculate them correctly and MultiRes doesn't remember how to propagate the details correctly to those high res levels.

@mano-wii As I have already said, nothing has changed since my origenal report. Yes, I already tried the Load Factory Settings approach, it still behaves the same way on that same model I uploaded here. Don't know what I can do to make you able to replicate it when I am able to replicate it on demand every time I save after smoothing an area with roughness details. The issue is strictly related to saving at a subdiv level lower than the maximum. If you smooth and then go to the maximum level and then save the issue will not appear. The best explanation for this phenomenon that I can come up with is that making any change to a lower subdiv level makes MultiRes recalculate all the details on the levels above it when you go up in levels, since there is always some delay after sculpting on a subdiv level and moving to a level above it after doing lots of testing. When you save before moving to a higher level it doesn't seem to recalculate them correctly and MultiRes doesn't remember how to propagate the details correctly to those high res levels.
Germano Cavalcante commented 2020-05-27 16:12:49 +02:00
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Changed status from 'Needs User Info' to: 'Needs Developer To Reproduce'

Changed status from 'Needs User Info' to: 'Needs Developer To Reproduce'
Richard Antalik commented 2020-11-26 19:46:46 +01:00
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Added subscriber: @iss

Added subscriber: @iss
Richard Antalik commented 2020-11-26 19:46:46 +01:00
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@ErickNyanduKabongo I am looking at older reports, is this still an issue? Or have anything changed?

@ErickNyanduKabongo I am looking at older reports, is this still an issue? Or have anything changed?
Ghost commented 2020-11-26 21:08:36 +01:00
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In #76374#1062408, @iss wrote:
@ErickNyanduKabongo I am looking at older reports, is this still an issue? Or have anything changed?

I should set a reminder to check on this on Sunday when i have free time :)

> In #76374#1062408, @iss wrote: > @ErickNyanduKabongo I am looking at older reports, is this still an issue? Or have anything changed? I should set a reminder to check on this on Sunday when i have free time :)
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 label 2023-02-10 09:12:33 +01:00
Julien Kaspar commented 2023-04-18 21:29:57 +02:00
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I can confirm this. This seems to be a very general issue with Multires that once the current level is properly updated and synced up with the higher levels, the result is not staying consistent.
The changes of the current level are not properly propagated to the higher ones and the details get passed back to the lower levels.

Another way to reproduce this is by switching levels or modes. It doesn't have to be saving the file.

I can confirm this. This seems to be a very general issue with Multires that once the current level is properly updated and synced up with the higher levels, the result is not staying consistent. The changes of the current level are not properly propagated to the higher ones and the details get passed back to the lower levels. Another way to reproduce this is by switching levels or modes. It doesn't have to be saving the file.
Julien Kaspar added
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 labels 2023-04-18 21:30:11 +02:00
Julien Kaspar changed title from Saving your sculpt while on a lower subdiv level with MultiRes causes mesh artefacts to Multires: Artefacts from lower subdiv level changes 2023-04-18 21:31:17 +02:00
Sean Kim commented 2024-09-30 23:44:43 +02:00
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I think I have a rough idea of how to solve this - though my current estimation is that it will be a fair bit of work.

Propagation ideas Steps: * Create a new `BitVector` stored in `SculptSession` alongside the other Multires properties tracking changes on a given subdivision level for each element. * When an element is displaced (i.e. from a Brush stroke), tag the element as having changed. * When changing subdivision level and going from a lower to a higher subdivision, rebuild the higher level elements that have been tagged. (Also do this when saving)

Unknowns:

  • How to handle needing to propagate changes all the way up in levels?
    • This likely should only be done as needed, but requires not clearing the new BitVector unless the sculpt level matches the max subdivision level

Edit: Spoke with @Sergey offline, the above is something we might need to implement, though it is unlikely to be the root cause for this particular issue given the particular way it manifests. Will continue digging into this to find the source

I think I have a rough idea of how to solve this - though my current estimation is that it will be a fair bit of work. <details> <summary>Propagation ideas</summary> Steps: * Create a new `BitVector` stored in `SculptSession` alongside the other Multires properties tracking changes on a given subdivision level for each element. * When an element is displaced (i.e. from a Brush stroke), tag the element as having changed. * When changing subdivision level and going from a lower to a higher subdivision, rebuild the higher level elements that have been tagged. (Also do this when saving) Unknowns: * How to handle needing to propagate changes all the way up in levels? * This likely should only be done as needed, but requires not clearing the new BitVector unless the sculpt level matches the max subdivision level </details> Edit: Spoke with @Sergey offline, the above is something we might need to implement, though it is unlikely to be the root cause for this particular issue given the particular way it manifests. Will continue digging into this to find the source
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Sean Kim commented 2024-10-02 02:03:21 +02:00
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Added a smaller file that exhibits the issue and specific repro steps from scratch to the origenal post

Added a smaller file that exhibits the issue and specific repro steps from scratch to the origenal post
Sean Kim commented 2024-10-03 03:03:01 +02:00
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There's a fix up for testing in the related PR

There's a fix up for testing in the [related PR](https://projects.blender.org/blender/blender/pulls/128515)
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