How to load obj models with group information

[Sunwinds]

Hi All, I am trying to use the ObjLoader.js to load OBJ pre-segmented models. Each segment is tagged as a group in the OBJ file.
But the current ObjLoader.js seems not so capable to read group information.
What I want is loading a mesh and coloring different segments with different colors.

[mrdoob]

Can you share an example obj?

[Sunwinds]

Sure, how to send you the file?

[mrdoob]

Dropbox and share link?

[Sunwinds]

https://www.dropbox.com/s/00hl3c2hq7ok57d/Bicycle.obj
Here you go.

[mrdoob]

Thanks for the model.

I guess we should create objects instead of trying to put everything into a single geometry...

[mrdoob]

After closer inspection. What's the difference between o and g?
OBJLoader handles o as different objects, but ignores g

[bhouston]

I think there is a pretty complete specification of obj here:

http://en.wikipedia.org/wiki/Wavefront_.obj_file

In the "Referencing Materials" section here:

http://en.wikipedia.org/wiki/Wavefront_.obj_file#Referencing_materials

They describe "g" as being a reference to a polygon material group.

[bhouston]

Basically I guess g (material groups) should be mapped to different materialIds within the same mesh?

[mrdoob]

Oh, ugh... Uhm, I've mixed things up then... 437b0a9

[mrdoob]

I'll give another go tomorrow, I'm currently annoyed with the file format :)

[mrdoob]

I'm not sure how to translate obj to threejs.
This is what I'm thinking:

usemtl = material name/type to be *instantiated* in subsequent o and g
o = start new Mesh
g =  materialID

I'm not sure if that's the most accurate representation of what the data is supposed to be.

[Sunwinds]

http://www.fileformat.info/format/wavefrontobj/egff.htm
I do not think g is for material ID

[mrdoob]

Right. But we don't have the concept of polygon groups in three.js
As far as I understand, you want to change the color (thus material) of those groups, but you wouldn't want to change the position/rotation/scale of such groups. Right?

[Sunwinds]

Yes, that's it