getBoundsZoom behave differently depending on the zoom level you currently are.

[rphlo]

Here is illustration of issue.

https://jsfiddle.net/kjpe1ys5/1/

I believe the use of mapBoundsToContainerBounds in getBoundsZoom is the root cause of this issue.

[rphlo]

L.Map::mapBoundsToContainerBounds makes call to L.Map::latLngToContainerPoint which is rounding values is the problem.

[Raruto]

For those interested in learning more, I'll try to expand the concept explained by https://github.com/Raruto/leaflet-rotate/issues/25#issuecomment-1434397860

Offending code

var bounds = [[60.81123, 25.71632], [60.81028, 25.73166], [60.7997, 25.72892], [60.80061, 25.71362]];

// 1. draw a small rectangle on map
L.rectangle(bounds).addTo(map);

// 2. set a zoom level really far away from that bounds
map.setZoom(0, {animate: false});

// 3. trigger the bug
map.fitBounds(bounds, { animate: false });

// 4. run it once more to make it work properly
// map.fitBounds(bounds, { animate: false });

NB the { animate: false } parameter is optional, it's just for copy-pasting all above code into the browser console (otherwise you may not see the bug).

The actual final problem is due to the fact that when zoom = 0 the following calculation:

map.mapBoundsToContainerBounds(L.latLngBounds(bounds)).getSize();

returns an incorrect value: { x: 0, y: 0 }, which results in an infinite zoom level calculation (ref: L.Map::getScaleZoom) after the first map.fitbounds call:

...

map.setZoom(0, {animate: false});

map.fitBounds(bounds, { animate: false });
console.log(map.getZoom()); // zoom = 24 (ie. map maxZoom level == Infinity)

map.fitBounds(bounds, { animate: false });
console.log(map.getZoom()); // zoom = 13

Below the same portion of code that causes the above bug within L.Map::getBoundsZoom:

https://github.com/Raruto/leaflet-rotate/blob/16d7b3568df12a607ca2de298151636271e0e118/src/map/Map.js#L418-L436

👋 Raruto