Make double-tapping on make zoom in by a factor of 2 on iOS

[1ec5]

In WebKit on iOS, double-tapping the map zooms in by a very small amount, probably a factor of 1.1. Double-tapping should zoom in by a factor of 2, for consistency with double-clicks in desktop browsers and double-taps in the Mapbox iOS SDK.

Reproduced in v0.19.1 in Safari on iOS 9.3.

/cc @lucaswoj

[kristfal]

I think this may be a bug. It was working as intended (zooming by a factor of 2) before – but now, you'll need to double-tap and hold on the last tap for the map movement to continue zooming by a factor of 2.

[mgd722]

Any workaround for this? Still a thing in Chrome on iOS using v0.36.0

[aparajita]

I put some logging in all of the event handlers, and this is what happens on iOS Safari when I double-tap:

double click handler
map touchend
drag pan touchend
drag pan up
map mousemove
drag rotate down
drag pan down
map mousedown (this calls map.stop(), killing the zoom)
map mouseup
drag pan mouseup
drag pan up
map click
zoomend

When I commented out the map.stop() call in the map mousedown handler, the zoom worked correctly.

Some policy decisions have to be made by the maintainers. Currently, any zoom or pan can be canceled by a click. The simplest solution would be to set a flag in the double click handler that the map mousedown handler checks, and if the flag is set, the map mousedown handler doesn't call map.stop(). It may be preferable to ignore the mousedown completely during a zoom, so that user map event listeners don't get the mousedown.

Thoughts?