Allow zoom levels beyond 21 on Android

[1ec5]

#4417 capped the maximum zoom level at 21 to work around #4416, #4272, and #4168. Of these issues, #4416 was fixed in #4508, #4168 was Android-specific, and it isn’t clear whether the root cause behind #4272 was ever fixed. This ticket tracks allowing zoom levels greater than 21 again.

/cc @jfirebaugh @ansis

[ansis]

There is a another limit at z25.5. We store zoom levels in the symbol buffers in a single byte to the tenth of a decimal place. This makes the max possible value 255/10 = 25.5. This could be changed by using more bits but I don't think we have any reason to support zooms > 25.5

[1ec5]

#4417 decreased MapboxConstants.MAXIMUM_ZOOM (on Android) and mbgl::util::MAX_ZOOM (across all platforms) from 25.5 down to 21.0. Yet I see no trace of the latter change in the commit histories in include/mbgl/util/constants.hpp or src/mbgl/util/constants.cpp on master. mbgl::util::MAX_ZOOM is still 25.5.

#7306 decreased MapboxConstants.MAXIMUM_ZOOM further to 20.0 without explanation. @tobrun, do you recall why you did this?

[jfirebaugh]

Looks like the change to constants.cpp in #4417 conflicted with ee651d7 during the merge of the release branch to master, and the latter won.

[Etienne-io]

It's becoming critical on our side to be able to zoom at least to 22 (better to 23)

Are you planing something for this issue ?

[1ec5]

On iOS as of 40e4755, I’m able to set the maximumZoomLevel to 25.5 and pinch out to 23.90 (in the D.C. area) before the map gets stuck:

[1ec5]

Tracking the hang on iOS in #9359. If you hide the scale bar, it should go further without any problems.