Apply visual colors

[stephane-caron]

If I understand correctly, visual materials are currently read and written but not rendered. Loading e.g. the Upkie URDF we get the dark "ninja" version:

Trimesh can render materials so getting them to yourdfpy is a matter of plugging the right info. Here is for instance a draft PR to do so (opening the issue here to keep track):

Is there an interest to render colors (eventually materials) in yourdfpy?

[clemense]

Oh, that's great, thanks! What do you think is missing to make this a non-draft PR?

[stephane-caron]

Well I hacked the call to apply_visual_color(geom, v) at the first spot I found where it worked, so first I wanted your feedback on whether it makes sense within the overall code 😃

There are three aspects to materials from the URDF reference that a visualizer would eventually need to handle: color, texture and named material.

If it makes sense, we could go for it this way:

• Color: this PR
• Named materials: subsequent PR (probably more involved, with updates to Robot and _parse_robot)
• Texture: later (not part of my current use cases but likely useful to others)

[stephane-caron]

And #15 adds support for named materials, so now the Upkie model renders as:

Moving the remaining point on textures to #16 so that we can let the PR close this issue.