Problems loading .obj with groups.

[prominentdetail]

I have a user reporting a problem with their ability to import .obj file to babylon.js
https://steamcommunity.com/app/1244040/discussions/0/3280321332558564130/

I believe this is a bug in babylon.js

If you check the obj specifications: http://paulbourke.net/dataformats/obj/

usemtl material_name

Specifies the material name for the element following it. Once a
material is assigned, it cannot be turned off; it can only be
changed.

So my understanding is that it shouldn't have to respecify the material to use for each group if it is already specified.

Here are test files to confirm the bug:
babylonGroups.zip

If you drag the files into the babylon.js sandbox, you can see that one of the groups does not have the material set:
https://sandbox.babylonjs.com/

In comparison, other programs load everything just fine because they can parse the data correctly.

[deltakosh]

Hello! as mentioned in the GIthub issue template please open the discussion in the forum first :)

[prominentdetail]

I don't have an account on the babylon.js forum, and I don't use babylon. But since I have a github account, I chose to report the issue here since this issue is easily validated. Babylon.js is parsing .obj files incorrectly based on the specification of the .obj format. A user reported the issue to me, so I made the extra effort to report the issue to the babylon.js and supply a reproducable example. It wouldn't take much effort to check it yourself and see that the material isn't being assigned to the group.

If you read this: http://paulbourke.net/dataformats/obj/
You can see it reference what they call an "element." A single face would be one element.

Elements

o point (p)
o line (l)
o face (f)
o curve (curv)
o 2D curve (curv2)
o surface (surf)

It also states what "usemtl" does:

usemtl material_name

Polygonal and free-form geometry statement.

Specifies the material name for the element following it. Once a
material is assigned, it cannot be turned off; it can only be
changed.

material_name is the name of the material. If a material name is
not specified, a white material is used.

In this case, it states that it sets the material for the element following it. Even though the word element is singular in this case, does that mean that you must specify the material for each and every face? Obviously not.
"usemtl" specifies the material for the elements. Groups are not classified as elements, so a group shouldn't influence what elements a material gets assigned to.

Take a look at how other programs handle it, and you can also confirm these statements.

[deltakosh]

Pinging @sebavan for follow up

[sebavan]

On it :-)