async tile loading while playing movie

[will-moore]

When a movie is playing, the T index updates without waiting for tiles to load, with the tiles loading asynchronously.
This means that the tiles update at different rates, showing some tiles at different time-points than others while the movie is playing.
When the movie stops playing, all tiles catch up to display the final T-index.
An example is at https://idr.openmicroscopy.org/webclient/img_detail/4007802/

NB: the old 'webgateway' viewer doesn't suffer from this issue with images under 3k x 3k since it doesn't tile them (Also it waits for each plane to load before updating T-index, so the rate of movie depends on speed of loading data).
https://idr.openmicroscopy.org/webgateway/img_detail/4007802/

There are various options for addressing this:

• Wait for all tiles to load before incrementing T-index.
  • Pros: this would work for truly "big" images
  • Cons: Needs investigation into how tricky/reliable the code is for this. We need to be sure we can reliably tell when the last visible tile has loaded and change the movie playing logic to wait for this event
• For images like the one above where the image is not a "big" image, we could load a plane at a time instead of loading tiles.
  • Pros: Relatively easy to fix.
  • Cons: Wouldn't fix the issue for "big" images that are movies (don't know how common such images are?)

cc @francesw @sbesson

[francesw]

Feedback from submitter:

I think if you waited for all the tiles to load before incrementing the user might be sitting there a while, but since you only browse on a plane-by-plane basis then it might be faster/less noticeable to the user to just load a plane at a time – same implementation idea as MaMuT, only load what it is you actually want to look at when you’re looking at it.