Shared collision detection between different sources

[mourner]

Currently if you add multiple sources to the map, collisions will be handled independently in each source, because source tiles are parsed independently. This makes it impossible for example to add GeoJSON labels and POIs that play nicely with OSM labels & POIs. The style defines how to make them play nice, but it's not reflected in the rendering.

Not sure how to approach this though — should we parse all labels & POIs separately and do it in one pass for all sources if a source is added/removed? This will affect performance a lot though. Should we just not handle this issue? Then the only way to use GeoJSON nicely will be to blend it in the VT source.

@ansis @kkaefer @edenh

[kkaefer]

When moving this to a tile-only-level rather than a source/tile level, we are also going to face a few other issues: What happens when you are zooming in, you retain the parent tile and show one (but not all) child tiles that are within the retained parent tile? Do we "knock out" labels placed in the parent tile?

[mourner]

@kkaefer don't we have the same issue currently within one source?

[kkaefer]

Yes, but this is currently handled. This ticket is about sharing the collision detection between different sources. This gets a little trickier since you can enable/disable sources.

[mourner]

Closing in favor of #1042