Can I write my own ISource without forking mapbox-gl-js?

[dzfranklin]

mapbox-gl-js version: 3.6.0

Question

My ultimate goal is to render epsg:27700 tiles as a mapbox-gl layer.

OpenLayers provides a function that essentially takes a tile source and a target tile extents and projection and returns a canvas of the target tile reprojected from source tile(s).

I could implement this as a custom layer but I think it fits much better as an ISource. I want to write something like your RasterTileSource except the loadTile function would also do reprojection.

If I wrote a custom layer I think I would need to figure out things like when to load or abort loading tiles based on map interactions whereas if I could write an ISource your existing code would handle all that.

The documentation for ISource hints at this being possible: "The Source interface must be implemented by each source type, including "core" types like vector, raster, or video) and all custom, third-party types". However, I can't figure out how to do this in practice.

• style.addSource constructs the source via a static map of source type to implementation in ISource
• ISource (recursively through Evented) contains a bunch of internal logic so I would want to have my class extend it rather than rewrite all the code needed to conform to the interface. But it isn't exported so I can't access it from an external project.

This makes me think I would have to fork mapbox-gl-js and make a few trivial changes to get a custom ISource to work. Is there a better way to do this?

Links to related documentation

• The internal docs of ISource (mentioned above):

  mapbox-gl-js/src/source/source.ts

  Line 70 in 7f10517

  export interface ISource extends Evented<SourceEvents> {

• https://docs.mapbox.com/style-spec/reference/sources/

[dzfranklin]

For other who run into this you can do this with maplibre via addProtocol