Track tails (or trails) in annotator view

[subdavis]

Keywords: trails, tails

Is your feature request related to a problem? If so, Please describe.
For certain kinds of annotation tasks, like creating and modifying fish tracks, the ability to look at trail lines is useful. Ability to see gaps in the track, etc.

Describe the solution you'd like
See the trails in the annotator. Maybe just fixed number of frames (forward or backward)?

Additional context
This is complicated and expensive to generate on the client. Research will need to happen about whether this happens server side or client side.

[waxlamp]

@subdavis, by "trails" you mean the head/tail data for the last N frames, is that right?

Does the Mongo storage make this easier? More generally, what makes it hard to generate the trails for a given frame?

[subdavis]

No, this has nothing to do with persistence. This is a client side feature.

It's hard because it makes the runtime complexity bigger. to render a frame, we've put a huge amount of effort into making lookup-geometry-by-frame-number a very fast operation. There's a red/black tree and everything. The result is that, even with hundreds of tracks on screen, each track only does one lookup to render.

Now, to show a tail, you need to do N lookups for previous and future states for every single track. You can sora pre-computed some of this server-side, but since this is an editor, it's like server-side-rendering: you hydrate client state and then expect it to change as the user does stuff.

That's why I made this difficulty:hard.