Fix robot model artist for Blender

[gonzalocasas]

What type of change is this?

• Bug fix in a backwards-compatible manner.
• New feature in a backwards-compatible manner.
• Breaking change: bug fix or new feature that involve incompatible API changes.
• Other (e.g. doc update, configuration, etc)

Checklist

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• I added a line to the CHANGELOG.md file in the Unreleased section under the most fitting heading (e.g. Added, Changed, Removed).
• I ran all tests on my computer and it's all green (i.e. invoke test).
• I ran lint on my computer and there are no errors (i.e. invoke lint).
• I added new functions/classes and made them available on a second-level import, e.g. compas.datastructures.Mesh.
• I have added tests that prove my fix is effective or that my feature works.
• I have added necessary documentation (if appropriate)

[gonzalocasas]

This is a pretty annoying bug, so, after review ok and merge, I would suggest to create a 1.9.2 release asap.

[beverlylytle]

review, ok and ...

[gonzalocasas]

@beverlylytle added one more fix: clear() should do the hide_set magic, instead of deleting the objects

[beverlylytle]

I'm not sure that that's true. In the base BlenderArtist we have

    def clear(self) -> None:
        """Delete all objects created by the artist."""
        compas_blender.delete_objects(self.collection.objects)

[gonzalocasas]

I'm not sure that that's true. In the base BlenderArtist we have

    def clear(self) -> None:
        """Delete all objects created by the artist."""
        compas_blender.delete_objects(self.collection.objects)

yes, and that indeed will delete the objects, but it's not what the robot model artist expects.. I dont recall why, but I remember this was changed long ago for hiding instead of deleting (it was an external contribution).

[beverlylytle]

I recall that the instantiation of the artist resulted in the drawing of all the collision and visual geometries, without calling draw*. So that was changed... the create method creates all the geometries and then hides them. Then draw* would unhide them. but it feels weird that delete would have different behaviors for different artists. maybe there should be hide_* methods.

[tomvanmele]

fwiw, i agree with @beverlylytle that the behaviour should be consistent. however, it is not clear to me what the use case for hide/show would be. is this to not have to redraw some of the meshes in between different calls to a script?

[beverlylytle]

for a robot model, it would be nice to toggle whether you are looking at the collision geometries or the visual geometries, without all the computational effort of reading and parsing the URDF holding all the geometric data. that would be the use case of hid/show.

[gonzalocasas]

alright, changed the artist to really delete when calling clear and added a bit of code to ensure the thing recreates geometry when needed.

[tomvanmele]

for a robot model, it would be nice to toggle whether you are looking at the collision geometries or the visual geometries, without all the computational effort of reading and parsing the URDF holding all the geometric data. that would be the use case of hid/show.

fair enough, but i guess this toggling would only be possible in an interactive scenario or in gh, no?