Re: [Assimp-discussions] aiProcess_GenNormals question

[Giuseppe B. <el...@gm...>]

As already David Nadlinger mentioned, it's like that because of the
real-time 3d graphics, where unfortunately you can't have normal and color
per triangle/face.

More specifically, the vertex shader in the graphic pipeline expects always
data for each vertex attribute.

For example, here, you need position, normal and color:

https://github.com/g-truc/ogl-samples/blob/b856b8ca236e1b46d40cf514784a25d3eaec5f4f/data/gl-430/buffer-uniform.vert#L17-L19

then each vertex has to come with a position, a normal and a color data
(vec*) inside your gpu buffer objects.

This is the norm unless very specific cases.


Giuseppe

2017-05-30 12:49 GMT+02:00 David Rivkin, PhD <dav...@sc...>:

> Why does aiProcess_GenNormals (option to Importer::ReadFile()) generating
> a list of Normals for each vertex when there should be just 1 per Face, and
> hence the array of mNormals should be equal to the aiMesh.mNumFaces, not
> aiMesh.mNumVertices?  The normal should be both a aiVector3Dand a Real
> scaler (offset typically referred to as 'w' in code for Omega) as well.
>
> In fact, the documentation is very confusing stating "aiVector3D
> <http://www.assimp.org/lib_html/vector3_8h.html#a47f446977120a9ca7d868353aad70b09>*
> aiMesh::mNormals
> Vertex normals
>
> The array contains normalized vectors, NULL if not present. The array is
> mNumVertices in size...."  This should be Face Normals.
>
> I would consider this a bug.
> --
> Thank you,
> Prof. David Rivkin, PhD
> President & Chief Scientist
> SciEssence Intl.
>
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