Allow sharing the same plugin among multiple tile sets

[xawill]

Description

Opening a dedicated issue following early discussion in #1264.

Currently, trying to register the same plugin to multiple tile sets throws an error, but this could be beneficial to support sharing the same plugin between multiple tile sets. Imagine the following use case:

I have a quantized mesh terrain I overlay with aerial imagery using the ImageOverlayPlugin. I also overlay the same aerial imagery over another tileset of 3d buildings (to have realistic roof textures). Currently we have to use two ImageOverlayPlugins doing exactly the same thing and thus loading the same aerial imagery twice.

I tried to just remove the error thrown here and using the same ImageOverlayPlugin as described above mostly works out of the box! The only issue I noticed is in case one of the two tile sets is disposed, then the textures are of course disposed in the other tile set (full black material).

Is there also something to consider in case of sharing the same plugin between tile sets with heterogeneous errorTarget?

Probably there are other issues I didn't encountered

Solution

• remove the thrown error saying that "A plugin can only be registered to a single tile set"
• maintain in the plugin a list of tile sets it is registered for and only dispose tiles when all the tile sets are disposed
• address other issues I didn't think of :) (easier said than done, of course)

Alternatives

status quo (inefficient duplicated usage of ressources)

Additional context

No response

[gkjohnson]

I tried to just remove the error thrown here and using the same ImageOverlayPlugin as described above mostly works out of the box!

Simply removing that check will break most of the plugins, unfortunately - most plugins register require knowledge of the attached tiles renderer (attaching events, caching data related to the tiles, etc). So removing this would mean updating all the plugins to be resilient to multiple tiles renderers and track the local data associated with each, etc. Generally it's more work and complexity than I think is worth it. Most plugins are fairly light in their instantiation, anyway.

The "ImageOverlayPlugin" is a unique case, though. But I think that's better addressed by adjusting that plugin to not completely dispose of an overlays texture set when unregistering it and instead just unlocking the necessary texture keys. Then the same overlay could be used on multiple tile sets (though they'd still have to share the same opacity / color settings):

const xyzOverlay = new XYZTilesOverlay( { /* ... */ } );
tileset1.registerPlugin( new ImageOverlayPlugin( { overlays: [ xyzOverlay ] } ) );
tileset2.registerPlugin( new ImageOverlayPlugin( { overlays: [ xyzOverlay ] } ) );