Loading too many tiles after #1014

After landing #1014 @johnsusi and I have noticed that it’s now loading more tiles than it needs. Beforehand (in my experience) it loads the highest level that covers the entire image with a single tile and then progresses upward from there. Now it does that but also progresses downward, loading every single level down to level 0. In @johnsusi’s case he had immediateRender on, so it’s even more dramatic that it’s loading everything (instead of just the top level it needed).

Obviously we don’t want to be loading these unnecessary tiles. One approach would be to roll back #1014, but I think it’s actually the right step forward, and it’s just uncovered an existing flaw in our logic, so I propose we leave the patch and seek to fix this new issue.

One theory: When we go through looking for the next tile to load perhaps we don’t have a “don’t bother” threshold. Now with #1014 we keep looking for next tiles to load more aggressively, so we need to institute that threshold. It should be based on the knowledge that the tiles needed to cover the scene are already in process somehow.

Note that if a high level tile fails to load, we should then fall back to loading a tile below it to cover that space. Perhaps our current code treats “this tile is currently being loaded” as a load failure.

@johnsusi says he’ll dig into it, and perhaps @CaptainCodeman can be of help as well.

[harukizaemon]

@iangilman Ahh. In this case it was four tiles, yes and then it began loading the next higher level of resolution. So long as that’s normal, all good. Thank you!

[iangilman]

@harukizaemon That may be perfectly normal… if level 10 is the largest level that’s contained in a single tile, OSD would open that first, but then continue onto level 11 for higher resolution.

What we’re concerned about here is if it then starts going back down the levels and opening 9, 8, etc.