fix: prevent negative left-shift when using negative zoomOffset

[monsieurtanuki]

Fixed the case where zoomOffset is negative.
Couldn't test it properly, e.g. with Retina Tile Layer example.

{Edit] I did manage to reproduce the bug though, by forcing zoomOffset to -1.

[JaffaKetchup]

This doesn't look like it works quite right :(

[monsieurtanuki]

This doesn't look like it works quite right :(

Ah, everything's got to be perfect with you! 😉

That said, as explained I couldn't see how to test the code, more specifically cases with a zoomOffset different from 0. Any suggestion?

[JaffaKetchup]

To be fair, I don't know necessarily what I would expect to see with a negative zoom offset - maybe that screenshot is what it's supposed to be? I'll have a look at what it looked like on an older version.

[JaffaKetchup]

Maybe this is working correctly. Using this code to test:

TileLayer(
      zoomOffset: -1,
      minNativeZoom: 1,
      maxNativeZoom: 18,
      urlTemplate: 'https://tile.openstreetmap.org/{z}/{x}/{y}.png',
      userAgentPackageName: 'dev.fleaflet.flutter_map.example',
      tileProvider: NetworkTileProvider(httpClient: httpClient),
    );

I think yesterday I tested without a minNativeZoom, which would obviously cause problems. Nevermind!

Ah, everything's got to be perfect with you! 😉

Sorry, you're right 😅

[JaffaKetchup]

I think this works correctly. Will try to ask original reporter to test, but seems to be OK. Thanks and apologies :)

[mash-g]

Hi, thanks for the fix. When do changes reach pub.dev?

[JaffaKetchup]

Hey @mash-g, I'd be interested to know if this actually fixes an issue you have - I guess a negative offset is more common than I expected 😂

But in answer, we have no fixed release schedule. Likely this one will be waiting for a little bit unless there's another more critical fix soon - I would like to release them faster, but it requires coordination from the rest of the maintainer team, so it's usually not too quick.

I'll open a PR for the release, but have to wait for a review before it can be merged and released.

[mash-g]

Hey @JaffaKetchup,

I re-confirmed that with flutter_map v8.2.1, the app generates a "Invalid argument(s): -1" exception which is resolved when the app is linked with the latest version from the main branch. Interestingly, the exception doesn't seem to occur while the map is zoomed in to street level, but becomes guaranteed as the map is zoomed out to country level.

Stack for above exception:

#0      int._shlFromInteger (dart:core-patch/integers.dart:86:42)
integers.dart:86
#1      int.<< (dart:core-patch/integers.dart:117:49)
integers.dart:117
#2      TileCoordinatesResolver.get (package:flutter_map/src/layer/tile_layer/tile_coordinates.dart:83:22)
tile_coordinates.dart:8

In this case, the tile provider API that the app is using sends 512x512 px tiles. As per docs, the app is setting zoomOffset=-((512/256) - 1) in the TileLayer which may have been contributing to this error.

Thanks!