Multires modifier data (CD_MDISPS) can remain on a (once shared) mesh, bloats filesize, adding a new multires modifer will already have its levels then #88144
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Reference: blender/blender#88144
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System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: GeForce GTX 960/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 457.09
Blender Version
Broken: version: 2.93.0 Beta, branch: master, commit date: 2021-05-08 06:10, hash:
a9eea6d9dcShort description of error
When adding multires and press subdivide, a single press adds 3 levels at once and gives the result in the picture
The left part is obtained after applying the mirror modifier
Exact steps for others to reproduce the error
Add multiresolution and press subdivide bug.blend
If the modifier is removed and re-added, the bug disappears
Found a way to reproduce this:
Object Data Propertiesnote: this behavior does not occur if one removes the Multires modifier from the Default Cube object prior to deletion in step 4
So opposed to any other modifier (afaict), Multires seems to store info in mesh that is kept around.
It does get removed from the mesh when the modifier gets removed, but it does not get removed from the (possibly shared) mesh when the object gets deleted.
Upon further inspection, these are stored in a
CD_MDISPScustom data layer on the mesh.Now when
ob->datais changed (step - [x]), or when a new modifer is added, the levels of the modifer will be made matching (seeBKE_mesh_assign_object&BKE_modifiers_test_object&multiresModifier_set_levels_from_disps)This can also be observed when for example a second multires modifier is added on top of an existing mutires modifier (levels will also be made matching).
Now I assume that in the end this has its reasons (and it might very well turn out to not be a bug), but will leave up to module devs to decide.
(I think it would be reasonable to remove CD_MDISPS initially when adding a new multires modifier?)
Added subscriber: @cfnjrey
#98249 was marked as duplicate of this issue
Added subscriber: @badbunny_uk
Not sure if this is what I should do here (tell me if this isn't helpful and I won't do it again!) but I confirm this issue in 2.92.
Also two other observations:
Added subscriber: @filedescriptor
@badbunny_uk Confirming an issue is always a good thing (if it has not been confirmed yet), so thank you.
Added subscriber: @PratikPB2123
Changed status from 'Needs Triage' to: 'Needs User Info'
Can confirm with the attached file but unable to reproduce from scratch.
@cfnjrey , did you apply some extra modifiers before adding Multiresolution in the list?
Mirror only
The model originally also had solidify and maybe bevel, but these were not applied
Changed status from 'Needs User Info' to: 'Needs Triage'
Added subscriber: @lichtwerk
Changed status from 'Needs Triage' to: 'Needs Developer To Reproduce'
Found a way to reproduce this:
Object Data Propertiesnote: this behavior does not occur if one removes the Multires modifier from the Default Cube object prior to deletion in step 4
So opposed to any other modifier (afaict), Multires seems to store info in mesh that is kept around.
It does get removed from the mesh when the modifier gets removed, but it does not get removed from the (possibly shared) mesh when the object gets deleted.
Upon further inspection, these are stored in a
CD_MDISPScustom data layer on the mesh.Now when
ob->datais changed (step - [x]), or when a new modifer is added, the levels of the modifer will be made matching (seeBKE_mesh_assign_object&BKE_modifiers_test_object&multiresModifier_set_levels_from_disps)This can also be observed when for example a second multires modifier is added on top of an existing mutires modifier (levels will also be made matching).
Now I assume that in the end this has its reasons (and it might very well turn out to not be a bug), but will leave up to module devs to decide.
(I think it would be reasonable to remove CD_MDISPS initially when adding a new multires modifier?)
multiresolution odd workto Multires modifier data (CD_MDISPS) can remain on a (once shared) mesh, adding a new multires modifer will already have its levels thenAdded subscriber: @Sergey
@Sergey probably knows more.
This is a known shortcoming of the way how the CD_MDISPS is stored and used: stored on object-data level and used from object-level. Removing CD_MDISPS when modifier is added could solve some issues but will introduce others.
Changed status from 'Needs Developer To Reproduce' to: 'Archived'
This sounds like this should be closed then.
If removing CD_MDISPS when a new modifier is added will likely introduce other issues, I think this is just a shortcoming we have to live with.
@Sergey: correct me if I am wrong and there are other ways to circumvent this issue.
Changed status from 'Archived' to: 'Confirmed'
This has been reported again, see #98249 (Bloated mesh data example (multires CD_MDISPS hanging around without a multires modifier)) and actually I think we should reopen this (even if only as a Known Issue)
Multires modifier data (CD_MDISPS) can remain on a (once shared) mesh, adding a new multires modifer will already have its levels thento Multires modifier data (CD_MDISPS) can remain on a (once shared) mesh, bloats filesize, adding a new multires modifer will already have its levels thenAdded subscriber: @reed2000