UV coordinates ignored by MeshOBJLoader

[ScheiklP]

Problem

When passing an .obj file and texture .png to OglModel, they are correctly loaded and mapped.

visual_node.addObject(
        "OglModel",
        filename="mesh.obj",
        texturename="texture.png",
)

For the MeshOBJLoader the UV coordinates are ignored.

loader = visual_node.addObject(
        "MeshOBJLoader",
        filename="mesh.obj",
        handleSeams=True,
)

visual_node.addObject(
        "OglModel",
        texcoords=loader.texcoords,
        texturename="texture.png",
)

---

Environment

Context

• System: Ubuntu 20.04
• Version of SOFA: master branch at commit 06899d4
• State: Install directory

[ScheiklP]

Did some more digging.

In the code above texcoords=loader.texcoords, is not valid, because the loader did not actually read any data yet.

Changing it to

loader = visual_node.addObject(
        "MeshOBJLoader",
        filename="mesh.obj",
        handleSeams=True,
)

loader.init()

visual_node.addObject(
        "OglModel",
        texcoords=loader.texcoords,
        texturename="texture.png",
)

fixed the issue. Is this still valid behavior?

[epernod]

yes you need to use handleSeams = true if you want to use the vertices buffer + texcoords.
But this mode can't be used as input of a mechanical mesh because some vertices are duplicated for the UV coordinates.

[ScheiklP]

handleSeams = True was set in both cases. The main problem was that the loader was not initialized.
It worked best (also without the init) when passing the LinkPath, and not the data container itself.
So I guess this is more a thing of having example code than a bug.

Where would be the best place to document an example like this?

loader = visual_node.addObject(
        "MeshOBJLoader",
        filename="mesh.obj",
)

visual_node.addObject(
        "OglModel",
        texcoords=loader.texcoords.getLinkPath(),
        texturename="texture.png",
)

[damienmarchal]

Hi @ScheiklP

Thanks for reporting and you are right in your conclusion (it is because that the object does not need to be initialize when created in python).

Actually getting rid of the need to init the data is a long standing issue: see sofa-framework/SofaPython3#173

This PR is probably the place to have future discussion on that topic and I close the issue,