There is no difference between "keep corners" and "all" under "UV Smooth" #83470
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Reference: blender/blender#83470
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System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: GeForce GTX 1660 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 456.38
Blender Version
Broken: version: 2.92.0 Alpha, branch: master, commit date: 2020-12-05 13:56, hash:
52a6c4f34dWorked: (newest version of Blender that worked as expected)
Short description of error
There is no difference between "keep corners" and "all" under "UV Smooth", the corners are supposed to be linked to the texture, but here the corners are not linked to the texture."All" should be unlinked from the textures. This will cause problems with the corner mappings, see attachment.
This model I imported into c4d and maya, also using "keep corners" under "UV Smooth" , they don't have this problem after subdividing, which leads to a problem that my models from other software need to be adjusted again in the position of the edges of the uv or mapping to handle correctly, which is very cumbersome.
Exact steps for others to reproduce the error
1.Select Model
2.Adding a subdivision surface modifier
3.subdivision surface modifier > advanced > uv smooth > keep corners
uv.blend
Added subscriber: @Dayar
Added subscriber: @APEC
Can you provide screens how it should be?
This is what it looks like in c4d.
This comment was removed by @APEC
Yes, it seems do some unwanted stretches here
It better to go here for further discussion
https://devtalk.blender.org/t/subdivision-surface-in-blender-2-8-behave-different-compared-to-maya-and-zbrush/12248/29
UV is the same, the subdivision is also Catmull Clark
The result is the same, with distortion at the top and sides.
Yes, I got it, already made a message on the devtalk forum. Nice catch by the way!
Thank you.
(Forgive me for my poor English.)
I have one more question, when I tested some more features recently, I found that blender's 'Bevel Modifier' offered an 'Arc' in the 'Miter Outer' option, which I found to be very useful.
When working with such models, c4d users usually use the first method, while blender users can use the second method to make the process easier.
But it still requires an additional step, if there are too many in the model, which would require many cuts with the knife tool.
It may be a bit greedy to say this, but I'd like to make a suggestion, and that is, coud you please help us connect this line after you 'Arc' it, or provide an additional option under 'Arc' to connect or not, so that we quad modelers can save some more modeling time.
The model file is as follows ：
Sharp vs Arc.blend
I'm just a simple user as you.
Last request it's not for bug reporting thread. Moderators relocate you to such kind of resources like
https://blender.community/c/rightclickselect/
https://devtalk.blender.org/c/other-topics/usability/16
My suggestion is delete request message and duplicate it on resources above to keep this bug report clear as possible.
Haha, I see. I don't know much about it. Thank you.
Added subscriber: @ostry
Opensubdiv does not know topology of uv map, only mesh. So corners created by placing seams on continous mesh are not seen as corners by opensubdiv.
Added subscribers: @Sergey, @mano-wii
I can confirm that only the vertex uvs that are connected to only 1 face are kept in place.
Perhaps this option should affect all boundary vertices?
This does appear to be a bug, but this same behavior was seen in the old toggle
"subdivide UVs".This feature has been improved in
517f58be, it may need developer evaluation.I also think it's not SDS patch's fault cos it exist in older blender versions (2.83).
As I mentioned on devtalk thread
"if mesh “closed” then unwrapped UV corners would be sharp, if mesh “opened” and some UV vertices have more then 2 edges, then this corners would be smooth, if UV vertex have only 2 edges then this corner would be sharp." - it's a correct behavior in my opinion.
Do we need to create new task not related to Sub-D Patch?
Because this issue will be a huge loss for users who use paint on SDS in Blender and then use other soft for SDS.
Just look at this (its 2.90 without SDS patch)
It seems that UV use it's own SDS modifier and do not respect geometry in 3D.
I can assure you that this does not happen in the other two major programs that I use with the OpenSubDiv (Catmull-Clark Sub-D).
OpenSubdiv is used for UVs interpolation. The behavior is explained in https://graphics.pixar.com/opensubdiv/docs/subdivision_surfaces.html#face-varying-data-and-topology (see the
Face-varying Interpolation Rulessection).If the behavior in Blender is different from what is described then it is a bug, otherwise is more of a possible improvement.
It behave different, so it's a bug since 2.8, I have no 2.79 can't test it.
I can provide UVs after sds applied from other 3d apps I used
https://devtalk.blender.org/t/subdivision-surface-in-blender-2-8-behave-different-compared-to-maya-and-zbrush/12248/45?u=apec
Added subscriber: @brecht
2.8 definitely behaves different from 2.79, as there is no UV smoothing strategy in OpenSubdiv which matches 2.79 exactly.
The current "Keep Corners" actually means "UVs are smoothed, corners on discontinuous boundary are kept sharp".
Not sure what default strategy in other software, but you need something like "Smooth, keep corners+junctions+concave" or "UVs are smoothed, boundaries are kept sharp". We would need expose those settings though.
@brecht, I remember we've been looking into non-confusing set of options to be exposed. Think it's time to re-evaluate the decision. Anything against P1883 ?
Also seems that boundary smoothing options might need more clarification (we can do it separately).
Here is comparison Blender (blue) and other (red).
UV Smooth - Keep Corners
Original other app pixar sds (for some other comparison cases).
Options for selecting UV behavior only mislead users, if its Pixar SDS, there is only one UV behavior, and only one Mesh behavior in 3d View.
@Sergey, rather than exposing all these options, maybe we should just make "Keep Corners" behave like
SUBSURF_UV_SMOOTH_PRESERVE_CORNERS_AND_JUNCTIONSorSUBSURF_UV_SMOOTH_PRESERVE_CORNERS_JUNCTIONS_AND_CONCAVE?I find all these options quite confusing, to me it seems like there is a correct solution that gives minimal distortion, and all these different options probably exist for legacy reasons.
@brecht , To me it seems that both
FVAR_LINEAR_CORNERS_PLUS1andFVAR_LINEAR_CORNERS_PLUS2(which is what we callSUBSURF_UV_SMOOTH_PRESERVE_CORNERS_AND_JUNCTIONSandSUBSURF_UV_SMOOTH_PRESERVE_CORNERS_JUNCTIONS_AND_CONCAVE, because it's way more interesting to inverse meaning of variables to keep brain sharp when reading specs ;) are there for legacy of software.In theory it sounds good and such to have a single option, but then I'm not sure how to quantify which of the suggested ones is the way to go.
Another thing which I'm not sure how big of a deal here yet, is that it seems like some of the confusion is coming here from other software using some weird default in settings. Or, maybe, users are picking weird setting and then expect Blender to behave the same when importing models. So from fully supported interoperability it makes sense to support all interpolation rules (maybe hide obscure ones unless "advanced" options are shown).
Sorry for disturbing but where I can test this D10111 patch?
Changed status from 'Needs Triage' to: 'Resolved'