Add Ellipsoids archetype.

[kpreid]

What

Implement an Ellipsoids archetype and visualizer. This may be used to render ellipsoids, or spheres where Points3D is unsuitable because the actual boundary in space is significant. It is intended as a first step towards completing #1361, by adding ellipsoids and by sketching out a general mechanism for rendering procedurally-generated shapes, which will be reusable for cylinders and anything which needs many vertices to render.

The archetype, extensions, etc. are largely forked off of Boxes3d.

Unfinished parts / future work:

• Currently, the spheres are always drawn as wireframes (with an automatically chosen mesh subdivision level). We will want to also support solid rendering (i.e. triangles in place of lines), but many use cases for spheres might want them to be transparent, which isn't yet properly supported in 3D space views (Draw order & (order independent) transparency #702), so I chose wireframe as the first version.

• Currently, all of the wireframe lines are piped through the LineDrawableBuilder every frame. Instead, they should be drawn as instanced meshes; that will require implementing a new renderer that invokes the existing line shader with the different data layout. However, this current implementation should not be worse than if the user were to create a similar number of lines directly.

• The sphere mesh needs a choice of subdivision level. Currently, it is automatically derived from the size of the sphere in the scene, which may be inappropriate depending on the scale of scene units or the specific application. I'd like feedback on the best way to handle this. Just add another component, perhaps kind of like the Radius component?

• I‘m not sure what the best way to handle the (future) errors in generating meshes is. Should it return a SpaceViewSystemExecutionError (which hides unrelated data), just draw nothing and continue (which could lead to silent missing data), or something else?

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
• I've included a screenshot or gif (if applicable)
• I have tested the web demo (if applicable):
  • Using examples from latest main build: rerun.io/viewer
  • Using full set of examples from nightly build: rerun.io/viewer
• The PR title and labels are set such as to maximize their usefulness for the next release's CHANGELOG
• If applicable, add a new check to the release checklist!
• If have noted any breaking changes to the log API in CHANGELOG.md and the migration guide

• PR Build Summary
• Recent benchmark results
• Wasm size tracking

To run all checks from main, comment on the PR with @rerun-bot full-check.

[emilk]

Needs screenshot and instructions on how to test!

[kpreid]

Needs screenshot and instructions on how to test!

I've added a screenshot to the PR description. One is still needed in the archetype docs, but I assume I don't actually have permissions to run upload_image.py to create one. Also, the comments there suggest a 16:9 aspect ratio, but the example I created looks a little silly that way, and the existing archetype doc screenshots aren't 16:9 — should I stick to that, or do what looks good?

For testing, cargo run --bin snippets -- ellipsoid_batch should do.

[kpreid]

What pull request labels are appropriate to satisfy the labels check? Should it be labeled with all three APIs since it touches all of them? What about the rendering aspect? Is that re_viewer since that's the closest dependent of re_space_view_spatial?

[emilk]

This looks great to me!

[emilk]

The snippets test is failing:

> pixi run -e py docs/snippets/compare_snippet_output.py archetypes/ellipsoid_batch
…
Traceback (most recent call last):
  File "/Users/emilk/code/rerun/rerun/docs/snippets/all/archetypes/ellipsoid_batch.py", line 12, in <module>
    rr.Ellipsoids(
    ^^^^^^^^^^^^^
AttributeError: module 'rerun' has no attribute 'Ellipsoids'

EDIT: fixed.

[kpreid]

The remaining unchecked checkbox says to test in the web viewer, but following the links says “pr/6853 is not a valid web viewer version”. Should I continue regardless? Does that need to be authorized?

[emilk]

Sadly our CI for contributors doesn't build a web viewer. You can test it locally with pixi run rerun-web… but it should be fine. Let's merge this and fix anything that pops up later :)