Tile loading and resolution change

[jburel]

Due to the size of the image. Changing resolution while loading the tiles lead to a nasty blocking stage depending on the size of the images. The controls should be disabled when the tiles are loaded. That happens on dev_4_4 but more obvious on develop

[wmoore]

It's tricky to manage this via Javascript - I tried to monitor the status of tiles loading (detecting when all tiles have loaded) in ​https://github.com/will-moore/openmicroscopy/commit/f00e04dcce9b2ceced13428a8d10187250e8f59b. This works OK if none of the tiles you want have been cached by the browser. But if you've got tiles cached, then you don't get an "load" event fired when setting the tile src attribute, so the Javascript would assume that the tile hasn't loaded.

We may need to fix this issue in the Django code or lower? It's almost like you need the zoom level change to be notified and then to ignore all tile requests for other zoom levels?

[jamoore]

Moving to next FS milestone for cleanup. If this is more appropriate elsewhere, please feel free to move it.

[jburel]

Will: could you investigate that one?

[wmoore]

There's really not much we can do with the current architecture. The images are loaded simply by setting the src attribute of image tiles, and so we have no control over the loading of data. Many http requests are made at once (all the visible tiles) and I don't know that these can be cancelled after that. We also don't have a reliable way of knowing whether tiles are loading or not (so we can't disable controls during loading) because the 'load' callback on an <img> is not reliable (see previous comment & commit).

Any ideas Ola / Carlos?