Just a post I thought may be useful, I was getting frustrated with lack of detailed info on how the UV border vertices get smoothed in different apps

-- NOTE 1 --

I’ve attached some images comparing Mudbox, Maya and Modo. It uses the standard Mudbox tree, it is a closed mesh. 

Mudbox has been set to subdivide a-la Mudbox 2009 mode with smooth UVs set to ON
Maya used the standard smooth node with smooth UVs on.
Modo uses the pSubs, smooth UVs

From what I can see:

All three apps smooth the 3D mesh identically in 3d space.

Modo pSubs seems to interpolate the UV borders in relation to what the mesh actually looks like in 3D, and has the least distortion of all three if you paint and bake a texture. From what I gather, it uses the ‘true’ pixar subd library.

Mudbox appears to smooth out boundary UVs whose vertex has an edge valencey of 5 and above, yet ‘suck-in’ boundary UVs of edge valency 3. A little weird IMHO

Maya smooths the whole border, there are no options for pinning corners.

All 3 apps, from what I can gather, use catmull clark UV smoothing interpolation, yet all three do different things to the UV boundaries.

....Mudbox does not match Modo in any way at all from what I can see…

-- NOTE 2--

The ‘default’ new way to smooth UV borders in Mudbox was introduced during Mudbox 2010, this essentially preserves the border completely linearly, smoothing internal UVs.  It matches a mode that Maya can have (preserve border), matches a mode pixar introduced for renderman during prman 14/15 , and what zBrush does by default.

Thats good in principal, but...from what I understand, Modo 501 doesn’t support this mode, and more importantly, baked textures will have ‘distortion’ due to the texture approaching the linear UV border, this can be a pain when painting the map or fixing it in photoshop.

There is also the potential for the smoothed internal UVs to smooth very closely and sometimes even overlap the linear border, especially if your base mesh is pretty low

Some would argue that the UVs need to interpolate and truly represent what the mesh looks like in 3D, to avoid all potential texture distortion. I’d agree

Anyone have any thoughts? Maybe Mudbox dev team can reply to shed any light on what the variable MUDBOX2009_SUBDIVIDE_SMOOTH_UV actually is doing to UVs ?

many thanks

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Hi,

This is a great post! I’m a modo user myself and can’t get Mudbox to work with modo at all. I can get displacements from Mud to render at all. Do you have any tips for setting the two applications so that Mudbox displacement and textures can be rendered in modo?

Thanks!

Wes

Wes McDermott | 3D Artist | Author
http://the3dninja.com
http://the3dninja.com/blog

x_gunslinger, what version of Mudbox are you using for these tests?  I can’t reproduce those results in 2012.

Edit: I take that back.  I’m seeing the same results in 2012, as well, with 2009 smoothing turned on.

Great post Gunslinger, thanks.

I have always been a little confused about the UV smoothing thing. I presume that if you are smoothing either the borders and/or internally, that you must always use the highest subdivision UVs to paint on (or as reference in Photoshop) otherwise your textures will not align correctly with the UVs?

Our renderer smooths UVs internally but preserves the border if the model is tagged to be a subdivision surface if you use any renderer to smooth your model you should be fully aware of how it will interpolate the UVs, so it’s always best to try to paint and bake onto a model that emulates what it wil do at render time.

Mudbox docs says it does this by default, smooth internal but keep border, BUT seems to pull in the border UVs corners wherever it finds a vertex on a UV border connected to two edges and one face . This means we can’t use the subdivision method in Mudbox as much as we’d like, and rely on pre subdividing our base mesh into the ‘correct’ UV space to do a ray cast bake onto. see my earlier images above for this weird little behaviour on these types of verts.

All my tests were 2011.5 on windows

Mudbox 2012 windows, no ENV variables set, using tree geometry from lvl0.
All smooth/ subdivide options on for under Mesh > Subdivide

Please see attached images, highlighting areas where border vertices do not stay on the border when subdividing

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isnt max doing the same..?

http://www.linkedin.com/pub/christoph-schaedl/6/558/73b

I wouldn’t know if Max does it, but prman, Maya and Arnold’s options will truly preserve every border UV

tried it in maya… and the border edges are also moving…
but in a different way… strange..

http://www.linkedin.com/pub/christoph-schaedl/6/558/73b

x_gunslinger, I’ve logged a bug.  That corner shouldn’t be moving.  Thanks for your persistence with this matter.

I did a couple of tests with Mudbox 2010 smoothing with modo 501 pSubs and Maya Catmull-clark. I overlay-ed the the smoothed/divided Mudbox UVs over the smoothed UV version in both modo and Mudbox. I noticed that the smoothed UVs from modo 501 pSubs and Maya 2012 match Mudbox with no issues. However, when comparing the subdivided UVs from all three programs, the base(non-subdivided) UV positions are shifted in position from the subdivided UVs as gunslinger reported.

Is the issue being reported a matter of the base UVs not matching the subdivided UVs? I just wanted to make sure I was on the same page as from what I’ve seen, the subdivided UVs are matching in the programs I use.

Here are the screen shots. These images show the smoothed subdivided UVs from Mudbox over the smoothed subdivided UVs from both modo and Maya. The first image is from Maya.

Thanks,

Wes

Wes McDermott | 3D Artist | Author
http://the3dninja.com
http://the3dninja.com/blog

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