computeVertexNormals doen't work correctly with mesh loaded using OBJ Loader

[slavielle]

Description of the problem

I'm using computeVertexNormals on mesh from OBJ and VRML Loader in order to have a smooth shading applied.

It works with VRML Loader but it don't using OBJ Loader with exactly the same mesh.

You can see how normal looks like in the 2 cases :

VRML is smooth shaded and normals (even if inside the mesh) are mingled for one given vertex.
OBJ mesh normals are diverging for one given vertex and consequently mesh is not smooth shaded.

The question is ... why ?

One difference I have noticed is loaded mesh use geometry in VRML case and BufferGeometry in OBJ case.

Thanks in advance for answers

Three.js version

• Dev
• [x ] r74
• ...

Browser

• All of them
• Chrome
• Firefox
• Internet Explorer

OS

• [] All of them
• Windows
• Linux
• Android
• IOS

Hardware Requirements (graphics card, VR Device, ...)

[WestLangley]

OBJLoader returns non-indexed BufferGeometry (a.k.a., triangle soup), which does not share vertices, so the computed vertex normals will be face-orthogonal.

BTW, even if vertices are shared, if you call computeVertexNormals(), you have to be careful not to share vertices on hard edges. So your cone example will be a bit tricky. You must duplicate vertices at the tip of the cone, for example. It would be better to specify proper normals in your model.

@mrdoob Should OBJLoader return indexed BufferGeometry, instead?

Related: #7201

[slavielle]

Thanks for the answer

I guessed it was something like that.... (BufferGeometry which does not share vertices), but it looks like a problem to me: In the OBJ format, vertices are described as shared (indexed), so the loaded mesh doesn’t fit the geometry described in the OBJ file somehow. Using non-indexed BufferGeometry doesn’t allow using computeVertexNormals + smooth shading on loaded geometries ... a bit inconvenient. Besides having different behaviors on mesh depending on the file format (VRML/OBJ) is a bit weird.

I don’t have a good grasp about what using indexed or non-indexed BufferGeometry involves deep indside three js/WebGL. It should make sense for some reason ... but in worse case, couldn't we have it as an option for loaders?

Thanks to point me out the "crease angle" problem ... should be great to have this in computeVertexNormals method as a parameter ;) but it's not the point.

Thanks a lot

[mrdoob]

@mrdoob Should OBJLoader return indexed BufferGeometry, instead?

The reason it doesn't return indexed is because the obj format doesn't map well to indexed. In obj, vertices, normals and colors don't share the same index.

[WestLangley]

In obj, vertices, normals and colors don't share the same index.

Ah, yes.

[slavielle]

Thanks for the answer,

I see what you mean about different indexes ...

Example of a face in my OBJ:

f 6/9/13 5/7/13 14/1/13

with vertex-index/texture-uv-index/normal-index for every vertex of the described face...for example for texture in indexed BufferGeometry, you must have one uv indexed value corresponding to one indexed vertex and that not necessary the case in OBJ format, i'm i right ?

a few questions :

• is this problem is the same for normals in indexed BufferGeometry (one indexed normal for one indexed vertex)
• for uv maps is this limitation due to three.js or WebGL ?

For UV maps, it looks like a defect to me : I don't understand why all faces sharing a vertex should refer to the same point in uv map.

[mrdoob]

It's a limitation of WebGL.

[slavielle]

Ok, So it makes sense to me now ... but :) ... destroying vertices index information when loading OBJ seems to still a problem.

In fact, back to the issue, that means you could never have a smooth shading on OBJ using computeVertexNormals nor any computed method : If normals are not correctly set in the OBJ file, its over right ?

vertices Index information shouldn't be kept somewhere ?

[WestLangley]

As I said,

It would be better to specify proper normals in your model.

[slavielle]

yeah in a perfect world, it would :)

[mrdoob]

You could compute the normals in Blender and re-export.

[slavielle]

Ok i'll do that, thanks