Add an option for disabling interim tiles

When displaying a tile, if that tile is not loaded yet, OpenLayers assumes that it is pertinent to display an “interim tile”, that is a tile that has the same tile coordinates as the parent tile but with a different key – different PARAMS for a WMS source. The relevant code is here.

That behavior is appropriate for some use-cases, as in the wmts-dimensions example. But it is not for other use-cases. For example think about the case of a WMS source where the LAYERS and FILTER params change based on user selections. In that case when the user unselects a layer in the UI you don’t want to show “old” tiles. I am seeing very disturbing artifacts in an OL application because of interim tiles.

So I think it would make sense to add a useInterimTiles option to the tile sources. That option would default to true, but users would be able to set it to false for cases where “interim tiles” do not make sense.

Note that the issue I describe here is completely different from https://github.com/openlayers/openlayers/issues/5251. With “interim tiles” the latter refers to parent tiles at lower resolutions, while this issue refers to tiles with the same x/y/z but with different keys/params.

What do you think?

[elemoine]

@elemoine If you can, I’d suggest using v6, currently at 6.0.0-beta.5. We’ll be releasing 6.0 final very soon.

Yep, maybe. The application I am working on (with others) is about to be released, so I guess it’s not a good time for updating it to using 6.0.0-beta.5.

Your fix above makes sense though. If you want, you can create a pull request against the v5.3.x branch, from which we can release v5.3.2.

Cool. I’ll do that then. I can also provide an example demonstrating the problem.

[ahocevar]

@elemoine If you can, I’d suggest using v6, currently at 6.0.0-beta.5. We’ll be releasing 6.0 final very soon.

Your fix above makes sense though. If you want, you can create a pull request against the v5.3.x branch, from which we can release v5.3.2.