[Bf-committers] Blender tangent space calculation

[Morten Mikkelsen]

Don't forget to look in do_multires_bake() in object_bake.c
It shows you how to add the tangent layer:

float *pvtangent= NULL;

// create tangent vectors if not already created
if(CustomData_get_layer_index(&dm->faceData, CD_TANGENT) == -1)
	DM_add_tangent_layer(dm);

// get pointer to the already generated tangents
pvtangent= DM_get_face_data_layer(dm, CD_TANGENT);





On Thu, Nov 17, 2011 at 8:49 AM, Eugene Minov <minov.eug at gmail.com> wrote:

> >
> > >The proper way to get the tangent layer can be seen in:
> > >
> > >
>
> https://svn.blender.org/svnroot/bf-blender/trunk/blender/source/blender/editors/object/object_bake.c
> >
>
> Okay, I've found a 'multiresbake_get_normal' function for correct normals
> calculation.
> I also looked into 'DM_add_tangent_layer' function in:
>
> https://svn.blender.org/svnroot/bf-blender/trunk/blender/source/blender/blenkernel/intern/DerivedMesh.c
> According to it, the tangent layer is filling by tangents when created. So
> I do
> need only to access and welding them and normals?
> That's good if so.
>
> Today I had time to try understand how RNA's works.
> And I almost create and test python interface with collections for faces
> and
> indexed vertices with normals and tangents in it.
> Hopefully soon I'll start welding.
>
> >
> > >If you need a free ultra simple welder there's one here -->
> > >http://jbit.net/~sparky/academic/welder/
> > >You specify how many floats you have per vertex and it will weld for
> you.
> >
>
> Okay, good one, I think I'll use it :)
>
> Thanks!
>
> On Wed, Nov 16, 2011 at 8:43 PM, Morten Mikkelsen <mikkelsen7 at gmail.com
> >wrote:
>
> > Sorry for confusing you here but I think I found a better reference for
> you
> > since
> > you'll be needing the tangents too and you are not supposed to be
> building
> > them yourself.
> >
> > The proper way to get the tangent layer can be seen in:
> >
> >
> >
> https://svn.blender.org/svnroot/bf-blender/trunk/blender/source/blender/editors/object/object_bake.c
> >
> > do_multires_bake()
> >
> > These are being fetched after the line:
> >
> > float *pvtangent= NULL;
> >
> >
> > These are then read in the function flush_pixel() including the normal
> > which is fetched from there using multiresbake_get_normal()
> > which as you can see looks a lot like the GetNormal() function
> > I pointed you to in DerivedMesh.c.
> > Anyway, definitely use this file as your reference. I should have shown
> you
> > this one from the beginning.
> >
> > If you need a free ultra simple welder there's one here -->
> > http://jbit.net/~sparky/academic/welder/
> > You specify how many floats you have per vertex and it will weld for you.
> >
> >
> >
> > On Wed, Nov 16, 2011 at 5:32 AM, Eugene Minov <minov.eug at gmail.com>
> wrote:
> >
> > > >
> > > > >If you can get hold of the dm
> > > > >(DerivedMesh)
> > > > >on the c side of things then I can show you how to get the correct
> > > normals
> > > > >and tangents
> > > > >and even help you get them welded should you want this.
> > > >
> > >
> > > Ok! Sounds good to me :)
> > >
> > > So right now I in progress of checkout latest svn sources and compile
> > > blender. (had problems with net)
> > > Then first of I'll try to create test version of python/C interface.
> I've
> > > not decided yet what names I'll use for it.
> > > And finally will be trying to implement it looking in DerivedMesh.c,
> > > I think that it's realy are a good example.
> > >
> > > If or when I have a problem, I'll be glad to use your help :)
> > > Many thanks for your kind cooperation!
> > >
> > >
> > >
> > > On Tue, Nov 15, 2011 at 10:41 PM, Morten Mikkelsen <
> mikkelsen7 at gmail.com
> > > >wrote:
> > >
> > > > I don't know anything about Python but if you can get hold of the dm
> > > > (DerivedMesh)
> > > > on the c side of things then I can show you how to get the correct
> > > normals
> > > > and tangents
> > > > and even help you get them welded should you want this.
> > > >
> > > >
> > > >
> > > >
> > > > On Tue, Nov 15, 2011 at 10:43 AM, Eugene Minov <minov.eug at gmail.com>
> > > > wrote:
> > > >
> > > > > Yes, I absolutely agree, hard faces obviously must be exported in
> the
> > > > same
> > > > > way how they seen in render.
> > > > > I think they can welds along with tangents.
> > > > >
> > > > > On Tue, Nov 15, 2011 at 9:01 PM, Morten Mikkelsen <
> > > mikkelsen7 at gmail.com
> > > > > >wrote:
> > > > >
> > > > > > There is no point in doing this unless you export the correct
> > > tangents
> > > > > and
> > > > > > normals. That is the ones
> > > > > > that were used to bake the normal map.
> > > > > >
> > > > > > I realize it blows that there is no API function to get the
> render
> > > > > normal.
> > > > > > So what you have to do is produce it yourself
> > > > > > like is done in
> > > > > > DerivedMesh.c<
> > > > > >
> > > > >
> > > >
> > >
> >
> https://svn.blender.org/svnroot/bf-blender/trunk/blender/source/blender/blenkernel/intern/DerivedMesh.c
> > > > > > >
> > > > > > and
> > > > > > many other places as well.
> > > > > > An example in this file is the static function GetNormal() which
> is
> > > > used
> > > > > as
> > > > > >  a call-back function by mikktspace.c
> > > > > > and you can see how it uses the averaged normal if the face is
> set
> > to
> > > > > > smooth and it uses
> > > > > > the face normal which it calculates itself if the face is set to
> > > flat.
> > > > > >
> > > > > > If you are going to make an api to export tangents I for one
> cannot
> > > > > > emphasize enough
> > > > > > that I prefer an all or nothing solution. Either do it right or
> > don't
> > > > do
> > > > > it
> > > > > > at all.
> > > > > > The last thing we need is to introduce a new tangent space
> standard
> > > > > within
> > > > > > blender.
> > > > > > Either export the correct basis that was used for baking (this
> > > includes
> > > > > the
> > > > > > normal)
> > > > > > or don't try to do it at all.
> > > > > > _______________________________________________
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