Batch selections should not preview single-element non-splats

[jleibs]

Although it's not easy to do with our APIs at the moment, it's theoretically possible to log a non-splatted element with a single instance-key.

For example, a future API that allows us to log colors directly:

rr.log_points("points", [[1,2],[3,4]], instance_keys=[1, 2])
rr.log_colors("points", [RED], instance_keys=[2])

In this case, color is not a splat, but if you hover on the batch of points in the UI, it will display as if RED applies to the whole batch rather than only applying to the 2nd point.

[teh-cmc]

This should be irrelevant now that splats are handled in independent rows? @jleibs

[jleibs]

This should be irrelevant now that splats are handled in independent rows? @jleibs

Nope, still an issue. This snippet is actually runnable:

import rerun as rr

rr.init("point_test", spawn=True)
rr.log_points("points", positions=[[1, 2], [3, 4]], identifiers=[1, 2])
rr.log_points("points", positions=None, colors=[[255, 0, 0]], identifiers=[2])

Produces this data UI:

The selection UI makes it look like all the points should be red, but since the 2nd log-value is not a splat, only the second point is actualy red (which is correct)

I think the issue is basically here, where we should explicitly check for a splat instead of a length of 1.
https://github.com/rerun-io/rerun/blob/jleibs/tensor_view_without_classic/crates/re_viewer/src/ui/data_ui/component.rs#L52

[teh-cmc]

Should be fixed by #1619 #1893