Make double-tap-drag work like it does in Google Maps

[1ec5]

When I showed #1292 to @heyitsgarrett, the first thing he tried was a double-tap-drag gesture that allows you to zoom the map in and out with one finger. MKMapView doesn’t support this gesture, but Google Maps does. To my surprise, so does MGLMapView, apparently as a side effect of #1296. Unfortunately, our behavior isn’t quite the same as Google’s, and the differences are unintuitive:

• We only recognize the gesture if you double-tap, hold, then drag vertically – Google Maps doesn’t require a hold
• Dragging upwards zooms in while dragging downwards zooms out – the opposite of Google Maps

[friedbunny]

Hrm, I seem to recall reading that this intentionally added by @incanus. Either way, I like the feature but it does lack discoverability (e.g., I had no idea Google Maps had this). Agree that the additional hold is unnecessary from a usability standpoint, Goog's feels good to me

[ajashton]

it does lack discoverability

On the Android side of things this is more common/known I think. Nearly all Google apps have it as an alternate gesture to pinch-zooming (photos, email, chrome, docs).

[1ec5]

Yes, this is a Googleism – a handy one, because you can zoom out with one finger. I was surprised to see it half-work in here; we should either recognize it the way Google Maps users expect or not support it at all.

[1ec5]

Hrm, I seem to recall reading that this intentionally added by @incanus.

Indeed, it was implemented as a UILongPressGestureRecognizer requiring one tap and a quarter-second hold in cutting-room-floor/mapbox-gl-cocoa@86e9aad. We could nix or reduce the required hold duration, though that might introduce ambiguity with other gesture recognizers.

[incanus]

Yeah, I carried this over from our iOS SDK: mapbox/DEPRECATED-mapbox-ios-sdk#184

I think a long press gesture which requires two taps should be fine. We can nix the delay. We don't otherwise use the double-tap so I don't think it will interfere or will be easily resolved. It'll still be a long press, though, because combining a tap and a drag is tricky otherwise.

[incanus]

To be clear, we have enough relatively major gesture tuning going on (#1296, #1292) that we should probably wait on this until b2.

[ljbade]

Making a note that any improvements to touch handling on iOS should also be eventually ported to Android in the big clean up needed in #553

[friedbunny]

Fixed back in #2153.

[heyitsgarrett]

😄

[1ec5]

Apparently MapKit in iOS 11 introduces a quick-zoom gesture that zooms in while dragging upwards, like how we implemented it originally but unlike Google Maps and our current implementation. Call it natural zooming, if you will. 🤷‍♂️