Hi Toni,
Antonio Bleile wrote:
> Hi,
>
> I can't find documentation about how normals are
> indexed/referenced in OpenSG. I'd like to know
> how I can specify per vertex normals and
> per face normals!
>
> I use something like this to create a mesh:
>
> osg::beginEditCP(n_geom_core);
> n_geom_core->setTypes (type); // GL_TRIANGLES
> n_geom_core->setLengths (lens);
> n_geom_core->setIndices (indices);
> n_geom_core->setPositions(pnts);
> n_geom_core->setMaterial(cmat);
> n_geom_core->setNormals(norms); // per vertex?
> osg::endEditCP(n_geom_core);
OpenSG doesn't really have face normals, or any face-based attributes for that
matter. Which is partially because of the unclear definition of what a face is
in connected primitives like strips and fans, and partially because OpenGL
doesn't have them, which means to support them you have to either do copy magic
or fall back to immediate mode and drop performance. So by default all
attributes, including normals, are vertex-based.
To do face normals you have to use multi-indexed geometry (which is immediate
mode and slow anyway), and have the same normal index for all three vertices.
calcFaceNormals does that for you, is you really need them.
A simpler workaround is to use flat shading on the pieces that you want flat.
That won't work well with shaders, but for normal OpenGL stuff it should work
just fine.
Hope it helps
Dirk
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