How can I manually tell the TileLayerOptions to load and paint a tile?

[JaffaKetchup]

Discussed in #963

^{Originally posted by JaffaKetchup July 5, 2021}
I need to do this as I'm implementing a way to remove grey tiles, but I can't change the base code in flutter_map. See JaffaKetchup/flutter_map_tile_caching#12.

My existing code:

@override
ImageProvider getImage(Coords<num> coords, TileLayerOptions options) {
    // `preloadSurroundings` is a boolean dictating whether the grey tiles should be attempted to be removed
    if (preloadSurroundings) {
      for (double x = coords.x - 6; x < coords.x + 6; x++) {
        for (double y = coords.y - 6; y < coords.y + 6; y++) {
          /*_CachedTileImageProvider(
            getTileUrl(Coords<num>(x, y)..z = coords.z, options),
            Coords<num>(coords.x, coords.y)..z = coords.z,
            cacheName: cacheName,
          );*/
         // How can I manually load AND PAINT the image above
        }
      }
    }
    return _CachedTileImageProvider(
      getTileUrl(coords, options),
      Coords<num>(coords.x, coords.y)..z = coords.z,
      cacheName: cacheName,
    );
  }

[ibrierley]

Isn't this just the same issue as 963?

[JaffaKetchup]

Yeah, I can close it if you want (as duplicate), but it was to attract attention because no-one had answered, so I wasn't sure if anybody had actually seen it, or no-body knew. That's why it has a 'Discussed in' header.

[ibrierley]

The issue also confuses me, as typically grey tiles are just transparent tiles that aren't available yet aren't they...so what's actually trying to be achieved ?

[JaffaKetchup]

Yeah, sorry, should've clarified. This is for my plugin that handles caching.

A user wanted to preload a whole area after it had been downloaded (JaffaKetchup/flutter_map_tile_caching#12) to totally avoid the grey tiles (which still appeared even if the tile was cached/downloaded already because of the time to lookup, fetch from the caching database and paint).

I suggested that preloading a whole area would be unnecessary and could cause extreme performance issues (if 20000 tiles (currently max number of cached tiles allowed) were shown, the map would be incredibly laggy), so the idea is to automatically get the nearest tiles in each direction before the user scrolls there.

Therefore I need to paint a tile before it actually becomes visible, the topic of this issue/discussion.

[ibrierley]

I've certainly played with preloading tiles (iirc I preloaded an extra tile the user was panning to). But I had to edit the tile layer code myself around the tileRange.min.y for loop (which looks partially what you are trying already)...Only thing I can think of is to have your own tile_layer code (or have it as part of the plugin), but maybe that's an issue.

Just thinking though (taking a quick scan of the plugin), do you need to use a database, why not just use a file cache ? (just wondering if that's faster to get around the problem another way).

[JaffaKetchup]

Yeah, I hoped I wouldn't have to edit the code in this package.
The main reason I can't use files is that the plugin was originally created by someone else using sqflite, so instead of changing it completely, I've just stuck with it. It also allows better queries etc.. Rewriting for that now would be a huge refactoring and at the moment, I just don't particularly want to do that.

[JaffaKetchup]

Actually, I've reconsidered. Perhaps using a file method would be better. I can still find some code from one of my previous attempts at #798, so @ibrierley, do you think using a file method would be quicker?

[ibrierley]

I suspect it "may" be :D, I've been using await DefaultCacheManager().putFile() await DefaultCacheManager().getFileFromCache() with https://pub.dev/packages/flutter_cache_manager as its felt relatively straightforward to implement (there's also await DefaultCacheManager().getSingleFile(url) which I'm using);

…

On Sat, Jul 10, 2021 at 9:22 AM Luka S ***@***.***> wrote: Actually, I've reconsidered. Perhaps using a file method would be better. I can still find some code from one of my previous attempts at #798 <#798>, so @ibrierley <https://github.com/ibrierley>, do you think using a file method would be quicker? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#966 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AA5YN5K5YNU3VIDRAGWK42LTW77L3ANCNFSM5ADBWIFA> .

[JaffaKetchup]

That package looks good at first glimpse, but this worries me:

By default the cached files are stored in the temporary directory of the app. This means the OS can delete the files any time.

Information about the files is stored in a database using sqflite on Android, iOS and macOs, or in a plain JSON file on other platforms. The file name of the database is the key of the cacheManager, that's why that has to be unique.

I need to not store in app cache, because the OS deleting map tiles could have bad consequences (extreme example: hiker downloads an area, without the hiker knowing, the OS deletes it, the hiker gets stuck on a mountain with no signal). I also need to have multiple caching spaces to keep a functionality I recently added. This may be solvable if I specify where else to put it?

And surely by using a database, it won't make a difference to the time again.

Although this package has nice features built-in like having an expiry, I may have to use network_to_file_image, and make that expiry functionality another way using metadata of some sorts?

But yeah, I probably will have a go with this, to see if it is indeed faster. Hopefully, it'll cut down on my library's size as well (less code). I'll try the package you mentioned first, but I feel I may need to use that other library instead. Thanks for the suggestion!

However, in the event that neither of these two options is faster, I'll still need to do the original purpose of this issue, so I'm leaving this issue open for that.

[JaffaKetchup]

I've done the basics required, and unfortunately, I can't see that much of a difference. I'll still have to do this, but a way might be to make the map bigger than normal, so it overflows the visible area?

[JaffaKetchup]

Ok, so that doesn't work very well either.

So the question still stands, 'How can I manually tell the TileLayerOptions to load and paint a tile?'

[JaffaKetchup]

Hi there,
Does anyone else have any ideas, or I'll close this for now?
Thanks.

[ibrierley]

Tbh, given the sluggish turnaround of changes here anyway, I'd probably go with a custom plugin alternate tile provider.