[Bf-committers] Blender tangent space calculation

Tue Nov 15 01:58:50 CET 2011

You should be careful referring to them as "compliant". I understand what
you mean that they are compliant in "format".
But as is explained here -->
http://wiki.blender.org/index.php/Dev:Shading/Tangent_Space_Normal_Maps
the only way to be fully compliant is to use the exact same spaces that
were used to generate the bake.
This can also be achieved by using the referenced implementation (which is
used in Blender) because it's designed to be order-independent
and also independent of how the geometry is indexed or even indexed at all.

Being fully compliant is what allows the renderer to achieve smooth
transitions of normal fields going from one island to the next.
This is important for characters especially.

On Mon, Nov 14, 2011 at 8:34 AM, Alberto Torres <kungfoobar at gmail.com>wrote:

> In the last days I've been doing a blender->ogre material converter
> and after learning how each engine calculates the normals from tangent
> normal maps, I've found that Ogre::Mesh::buildTangentVectors builds
> the necessary vectors compatible with blender ones. It has a couple of
> options for splitting mirrored UVs and saving the polarity in the 4th
> component, just like blender's generated GLSL code expects.
>
> 2011/11/14 Eugene Minov <minov.eug at gmail.com>:
> > Hi!
> > One more question, if I may.
> > I've seen that there is a couple of the exporter programs which can
> > generate tangents to export for specific 3D engines only, like
> OgreExporter.
> >
> > So why not to simply adding possibility for generate/access a tangent
> > normals into the python api?
> > I am not saying that it very hard to generate those tangents using
> Morten's
> > implementation directly in program, but think it'll be more a..
> consistence
> > and ease way for people who building their games to properly export their
> > meshes :)
> >
> > Maybe if nobody wants, then I'd like to try implement this by some time.
> > What you guys think about this?
> >
> > Eugene
> >
> > On Mon, Nov 14, 2011 at 2:41 AM, Eugene Minov <minov.eug at gmail.com>
> wrote:
> >
> >> Oh, my bad :) I've seen that page but I'd thought this page is explains
> >> different baking modes in blender's render.
> >>
> >> Morten Mikkelsen - thank you for your great implementation! I'will learn
> >> it!
> >> M.G. Kishalmi - thanks for explanation )
> >>
> >>
> >> On Mon, Nov 14, 2011 at 1:55 AM, M.G. Kishalmi <lmg at kishalmi.net>
> wrote:
> >>
> >>> Eugene,
> >>>
> >>> the link Morten pointed you
> >>> to<
> >>>
> http://wiki.blender.org/index.php/Dev:Shading/Tangent_Space_Normal_Maps
> >>> >explains
> >>> that
> >>>  the tangent space you created your normal maps in (in blender)
> >>>  is generated by the implementation in
> >>> mikktspace.h<
> >>>
> https://svn.blender.org/svnroot/bf-blender/trunk/blender/intern/mikktspace/mikktspace.h
> >>> >and
> >>> mikktspace.c<
> >>>
> https://svn.blender.org/svnroot/bf-blender/trunk/blender/intern/mikktspace/mikktspace.c
> >>> >
> >>> .
> >>>
> >>> you might want to use those in your app (check the licence inside).
> >>>
> >>> cheers,
> >>>  lmg
> >>>
> >>>
> >>> On Sun, Nov 13, 2011 at 10:51 PM, Eugene Minov <minov.eug at gmail.com>
> >>> wrote:
> >>>
> >>> > Wow!! Thanks a lot, for pointing me to the google ;)
> >>> >
> >>> > But I afraid that maybe I've not correctly describe my problem. If
> so,
> >>> > sorry for that, because my english is still kinda weak.
> >>> > My problem not in generating a normal maps (a textures) in blender.
> Not
> >>> at
> >>> > all.
> >>> >
> >>> > My problem is that I cannot fully correct render my already generated
> >>> > normal maps in my app. Because, how I mentioned in the last mail, the
> >>> usual
> >>> > methods for this purpose (by UV coords) is not gives me desired
> results.
> >>> >
> >>> > So I wanted to ask for help with information about methods blender
> uses
> >>> for
> >>> > generating tangents.
> >>> >
> >>> > And yes, I had searched in google but unfortunately have't found
> >>> something
> >>> > helpful yet.
> >>> > If someone can point me to that kind of info, I will be very
> grateful!
> >>> >
> >>> > On Mon, Nov 14, 2011 at 12:08 AM, Morten Mikkelsen <
> >>> mikkelsen7 at gmail.com
> >>> > >wrote:
> >>> >
> >>> > > There you go buddy --> http://lmgtfy.com/?q=blender+tangent+space
> >>> > >
> >>> > >
> >>> > >
> >>> > > On Sun, Nov 13, 2011 at 8:46 AM, Eugene Minov <minov.eug at gmail.com
> >
> >>> > wrote:
> >>> > >
> >>> > > > Hi.
> >>> > > > I am sorry if I subscribe into a wrong place, I am new and I've
> not
> >>> > > > actually planned to change or to debug the blender sources yet.
> >>> > > > But I trying to write app that'll be render models with normal
> >>> mapping
> >>> > > > exported from blender, and I have a question about how exactly is
> >>> > blender
> >>> > > > calculates a tangent vectors when Unwrap operation in the editing
> >>> mode
> >>> > > > performs?
> >>> > > >
> >>> > > > Calculating tangents in my app in usual manner (using UV coords
> and
> >>> > verts
> >>> > > > positions) gives me different tangents for each face of the same
> >>> vertex
> >>> > > > indexed from, and thus crumpled normal map looking.
> >>> > > > Then by looking into blender sources (searching  by 'tangent'
> >>> keyword)
> >>> > > I've
> >>> > > > found a couple of functions with tangents calculations, like:
> >>> > > >    float axis[3] = {0.0f, 0.0f, 1.0f};
> >>> > > >    cross_v3_v3v3(tangent, normal, up);
> >>> > > >    normalize_v3(tangent);
> >>> > > >
> >>> > > > After I tried same method in my program I've gotten almost
> perfect
> >>> > > looking
> >>> > > > model, depending on what initial axis I've used.
> >>> > > > To choose, which axis to use (0, 0, 1), (0, 1, 0) or (1, 0, 0)
> for
> >>> each
> >>> > > > normal, I calculate max dot product of tangent calculated by each
> >>> axis
> >>> > > with
> >>> > > > tangent calculated from UV coords.
> >>> > > > But still it seems that in some rare vertices tangent is
> calculates
> >>> > > wrong,
> >>> > > > maybe because of wrong initial axis.
> >>> > > >
> >>> > > > So, can anyone please give me any information about tangents
> >>> > calculation
> >>> > > > formula that blender uses while generates UV coords or some
> advice
> >>> > about
> >>> > > > choosing initial axis.
> >>> > > > Thanks for help.
> >>> > > >
> >>> > > > Eugene
> >>> > > > _______________________________________________
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> >>> > > > Bf-committers at blender.org
> >>> > > > http://lists.blender.org/mailman/listinfo/bf-committers
> >>> > > >
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