Double tap zoom gesture moves to quickly

[cammace]

We offer the double tap to zoom in/out on the map but currently the zooming will happen too quickly when barely dragging your finger up or down.

cc: @mapbox/android

[tobrun]

My initial idea was that this is related to screen density since the devices having this issue were mostly newer devices with a large pixel ratio. Now looking into the code I'm seeing that this is not related to the x,y value of pixels but that issue is coming from detector.getScaleFactor() that is used as part of zoomBy in the gesture shown in the OP.

My hunch is that scale factor is too large due to screen density (this value is coming from an external dependency and we would have to work around this in our code) or that the values we are feeding core are not correct (eg. negative values or spike values, in normal situations I'm seeing logs with values around 1 but when a major shift happens I'm seeing a sole value that is negative (eg -0.56) or a value that is way larger as the rest (eg. 14).

[tobrun]

Here are some sequences of scale factors provided to the SDK from our gesture detector library:

V/MapGestureDetector$ScaleGestureListener: Scale 1.0046271
V/MapGestureDetector$ScaleGestureListener: Scale 1.0089378
V/MapGestureDetector$ScaleGestureListener: Scale 1.0184126
V/MapGestureDetector$ScaleGestureListener: Scale 1.0239114
V/MapGestureDetector$ScaleGestureListener: Scale 1.046406
V/MapGestureDetector$ScaleGestureListener: Scale 1.0642886
V/MapGestureDetector$ScaleGestureListener: Scale 1.080839
V/MapGestureDetector$ScaleGestureListener: Scale 1.119591
V/MapGestureDetector$ScaleGestureListener: Scale 1.1630605
V/MapGestureDetector$ScaleGestureListener: Scale 1.250629
V/MapGestureDetector$ScaleGestureListener: Scale 0.53555655
V/MapGestureDetector$ScaleGestureListener: Scale 8.800293
V/MapGestureDetector$ScaleGestureListener: Scale 1.4822774
V/MapGestureDetector$ScaleGestureListener: Scale 1.2489731
V/MapGestureDetector$ScaleGestureListener: Scale 1.1681666
V/MapGestureDetector$ScaleGestureListener: Scale 1.1117692
V/MapGestureDetector$ScaleGestureListener: Scale 1.0839446
V/MapGestureDetector$ScaleGestureListener: Scale 1.0684125
V/MapGestureDetector$ScaleGestureListener: Scale 1.0564218
V/MapGestureDetector$ScaleGestureListener: Scale 1.0442512
V/MapGestureDetector$ScaleGestureListener: Scale 1.0412383
V/MapGestureDetector$ScaleGestureListener: Scale 1.0306668
V/MapGestureDetector$ScaleGestureListener: Scale 1.0241464
V/MapGestureDetector$ScaleGestureListener: Scale 1.0180855

or

V/MapGestureDetector$ScaleGestureListener: Scale 0.946373
V/MapGestureDetector$ScaleGestureListener: Scale 0.9367054
V/MapGestureDetector$ScaleGestureListener: Scale 0.91751075
V/MapGestureDetector$ScaleGestureListener: Scale 0.89154875
V/MapGestureDetector$ScaleGestureListener: Scale 0.8659967
V/MapGestureDetector$ScaleGestureListener: Scale 0.8338932
V/MapGestureDetector$ScaleGestureListener: Scale 0.76041627
V/MapGestureDetector$ScaleGestureListener: Scale 0.5274352
V/MapGestureDetector$ScaleGestureListener: Scale -7.3576527
V/MapGestureDetector$ScaleGestureListener: Scale 0.4487716
V/MapGestureDetector$ScaleGestureListener: Scale 0.74890393
V/MapGestureDetector$ScaleGestureListener: Scale 0.8576364
V/MapGestureDetector$ScaleGestureListener: Scale 0.90766495
V/MapGestureDetector$ScaleGestureListener: Scale 0.94259167
V/MapGestureDetector$ScaleGestureListener: Scale 0.95532775
V/MapGestureDetector$ScaleGestureListener: Scale 0.976783
V/MapGestureDetector$ScaleGestureListener: Scale 0.98298824
V/MapGestureDetector$ScaleGestureListener: Scale 0.9842705
V/MapGestureDetector$ScaleGestureListener: Scale 0.9980335
V/MapGestureDetector$ScaleGestureListener: Scale 1.0029142

I'm currently trying out the latter approach in #7514 (comment) and allowing values >0.8 and <1.2.