Add a fastReplace option to TileLayerOptions.

[pento]

Based on this comment, this PR adds a fastReplace option to TileLayerOptions.

The purpose of this option is to force tiles to be removed as soon as their replacement tile is ready, skipping tileFadeIn* options, as well as the hardcoded delay in _tileReady().

Screenshots

These screenshots are based on this config: the top layer (the place names) uses transparent tiles.

Before

Note how different zoom levels of the top layer are visible at the same time while zooming.

After

It no longer shows multiple zoom levels at the same time, though there is sometimes a small flicker where no tile is visible at all, even after the tiles have been cached. I'm happy to make adjustments if there's a way to avoid this, but otherwise, I think this is an improvement.

[ibrierley]

Haven't had chance to test yet, but my main test would be how it acts on pinch/zoom. The old flutter_map flickered a lot due to the problem, so I think it may be a step back if that is impacted, but there again, if it's just an option and clearly marked that it may cause flicker, I guess it feels ok.

I did some testing with this stuff a while back and it felt like you had to have at least one of..
Fading old image in.
Displaying old image and having 2 overlayed for a very short period.
A possible flash during transition.

[pento]

Thanks for the feedback, @ibrierley! You're right, there is noticeable flickering when using pinch-to-zoom, particuarly when the layer is not yet cached: the GIF below shows this when zooming in, then the flickering does become less noticeable when zooming back out again.

I've updated the option documentation to note this caveat.

[github-actions]

This PR is stale because it has been open 45 days with no activity. Remove stale label or comment or this will be closed in 10 days.

[pento]

I've rebased this PR, I'm still using this change in my own fork, but I'd love if it could be merged here, instead. 🙂

[github-actions]

This PR is stale because it has been open 45 days with no activity. Remove stale label or comment or this will be closed in 10 days.

[pento]

Okay stalebot.

[kengu]

LGTM

[kengu]

@pento Thanks for the contribution!