how to wrap map at edges?

[porjo]

Not a bug, just a question: how would I modify the mercator example (http://bl.ocks.org/4132797) such that the map wraps around when panning left or right (like Google do with their map)?

[jasondavies]

This is quite simple to do, but requires a small modification to the tile plugin so that tiles with negative x-coordinates are not excluded. Rather than include such tiles (which could cause broken images in existing examples), perhaps the best solution would be a new option, wrap([x, y]), where x and y are booleans indicating wrapping in either direction? Most commonly wrap([true, false]) would be used for maps.

Note that only tiles with negative coordinates are currently excluded. The MapBox examples seem to have grey tiles for positive tile coordinates outside the quadtree, but not for negative coordinates. It might be worth excluding these positive tiles too for consistency, since we currently have grey on the positive edges and white on the negative edges.

Alternatively we could remove the exclusion of tiles with negative coordinates. But this would force everyone to filter the resulting tiles to ensure they don't produce broken images, and although the code for wrapping is quite simple, it would be even simpler to have an API for such a common scenario.

[jasondavies]

Hmm, my wrap(…) idea doesn’t work because we still need to generate the negative tiles so that they can be positioned correctly. The wrapping should occur when generating the URLs. Here is an example of wrapping, where I’ve removed the 0-clamp from the tile plugin.

[jasondavies]

Maybe tile.overflow, indicating whether tiles outside the quadtree should be generated in either direction? The default could be [false, false] for backwards compatibility.

[jasondavies]

Possible implementation in #101.