[Bf-committers] Opensubdiv and catmull-clark again

Fri Nov 6 07:03:08 CET 2015

Hi Sergey!

I wasn't suggesting the latest OSD should have been rushed into 2.76. But
definitely for the next update. I've upgraded Blender to OSD 3.0.3 locally
and it fixes GLSL compute for both AMD and Intel on Windows. Adaptive
subdivision doesn't seem to work on Intel chips -- on Windows or Mac --
even with Pixar's example programs. No crash or errors; the surface just
doesn't appear on screen. Non-adaptive works fine.

How soon can we bump the libs to 3.0.3? I have a few changes to the
Blender-OSD glue. Can those go into master or would you prefer a new branch
for the stuff I'll be working on?

No ideas yet for the normals but I will investigate. As you know we're
moving to GLSL 1.5 soon so rewriting is going to happen anyway.

Mike Erwin
musician, naturalist, pixel pusher, hacker extraordinaire

On Thu, Nov 5, 2015 at 11:22 PM, Sergey Sharybin <sergey.vfx at gmail.com>
wrote:

> Yury,
>
> For the original mail: OpenSubdiv and Blender original CCGSubSurf are using
> different approaches to the patch topology construction, but both of them
> technically are Catmull-Clark subdivisions. There's no correct or wrong
> crease here, it's just different and behaves better in one situation or
> another. We'll switch to OpenSubdiv completely once all the issues are
> solved.
>
> For the followup mail: you're pointing out all the TODOs and limitations
> mentioned in the original release page [1]. Don't see much reason to
> discuss them here, we'll need to work on this still. With a project size of
> OpenSubdiv and the tight release schedule we had so far you can't really
> have everything to be ideally supported from the first commit. It'll all
> come eventually.
>
> Mike,
>
> GLSL Compute is disabled for AMD devices because original OSD library we
> used for the 2.76-rc1 had a bug on AMD hardware. It was fixed later at rc2
> or rc3 from the OpenSubdiv side, but we can't bump library versions at the
> RC stage (bumping it will mean we're allowing to use hardware which was
> known to be buggy without too much tests done first).
>
> For the shading, here's the bug report [2]. I didn't find a way to evaluate
> limit surface on the GPU when using non-adaptive subdivisions and i didn't
> really heard back from Pixar about how it could be done. Wold need to ask
> the guys again. But OpenSubdiv 3.0 is quite fresh so far and perhaps
> non-adaptive case is not high priority for them yet.
>
> Perhaps we can do some other trickery to get better normals, but that'd
> requite having tessellation control and evaluation shaders which was quite
> hard to do with current OpenGL state we've got. It didn't quite work for me
> when trying to sue it as an #extension for glsl 1.3 and mumping glsl to 1.4
> and higher would mean re-writting all the existing shaders (due to removed
> of loads of deprecated stuff in it, i.e. gl_Normal). Maybe you can have
> some other ideas here tho.
>
> [1]
> http://wiki.blender.org/index.php/Dev:Ref/Release_Notes/2.76/OpenSubdiv
> [2] https://developer.blender.org/T45707
>
>
>
> On Thu, Nov 5, 2015 at 10:02 PM, Mike Erwin <significant.bit at gmail.com>
> wrote:
>
> > Hi guys,
> > I'm actively working on OpenSubdiv, especially getting it running on more
> > systems (Intel gfx on Windows, Mac). GLSL compute works on the latest
> > version of OSD (official Blender release doesn't use this yet). Similar
> > performance to Transform Feedback. The other problems you mention... yep
> > those are still problems.
> >
> > Thanks for pointing out #2 -- I knew it looked odd but didn't make the
> > connection to low-poly normals. Can you give a link to the bug tracker?
> >
> > From my understanding, OpenSubdiv will become *the* subsurf
> implementation
> > in Blender, and the old system will go away. But first we need to fix
> these
> > problems.
> >
> > Mike Erwin
> > musician, naturalist, pixel pusher, hacker extraordinaire
> >
> > On Thu, Nov 5, 2015 at 7:52 AM, Yury Baranov <cucumberer at gmail.com>
> wrote:
> >
> > > Opensubdiv is unusable ATM in fact. Problems are:
> > > 1. Unable to apply Subsurf with OSD enabled. Result is identical to
> > Subsurf
> > > without OSD check.
> > > 2. Shading is wrong (bug is in the bugtracker already). OSD takes
> normals
> > > for shading from lowpoly instead of computing new normals.
> > > 3. No UV subdivision.
> > > 4. GLSL Compute is not working for me.
> > > OK, the feature is too new and too raw to use it in production. But OSD
> > is
> > > based on Catmull-Clark algo, which is already used in the Subsurf
> > modifier,
> > > OSD is just speeding mesh calculation up. The problem is, OSD and
> > > Catmull-Clark subdiv models look different, it not supposed to happen
> > IMHO.
> > >
> > > 2015-11-05 15:33 GMT+03:00 Nahuel Belich <casillapforos at yahoo.com.ar>:
> > >
> > > > intersting, in that case, as a modeler i would prefer the open subv
> > > > result, however i didnt model that much using it, the performance its
> > > much
> > > > much better, but the shading its "weird" or not accurate on most
> cases.
> > > . .
> > > >  i need to test it more to shape an opinion
> > > > PasteAll.org - opensubdiv.jpg
> > > > |   |
> > > > |   |   |   |   |   |
> > > > | PasteAll.org - opensubdiv.jpgPasteAll.org - opensubdiv.jpg
> > > > opensubdiv.jpg ~0.11mb..ish. 916 px. 1335 px. |< << hi PasteAll.org
> is
> > > > brought to you by the monkeys of GraphicAll.org -  |
> > > > |  |
> > > > | Ver en www.pasteall.org | Vista previa por Yahoo |
> > > > |  |
> > > > |   |
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >      El Jueves, 5 de noviembre, 2015 5:09:30, Yury Baranov <
> > > > cucumberer at gmail.com> escribió:
> > > >
> > > >
> > > >  Hi. I just mentioned that Blender's subdivision surface is acting a
> > > little
> > > > bit different than opensubdiv. It's noticable when using creases on
> > > > geometry like this: http://puu.sh/la3Xw/3c06b8b687.png
> > > > Blender's catmull-clark subdivs: http://puu.sh/la3ZJ/a5f8ce2ddf.png
> > > > Opensubdiv: http://puu.sh/la40E/529b72bec5.png
> > > >
> > > > Looks like Blender's Catmull-Clark subdivs are not Catmull-Clark
> > > subdivs...
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>
>
> --
> With best regards, Sergey Sharybin
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