Change Pinch Gesture Handler Behavior to transition to END state after one finger is taken off screen and one left

Description

After testing PinchGestureHandler in react-native-gallery-toolkit I found that on the real device Pinch gesture is active even though we have only a single finger on the screen. This breaks my focal point logic which is working as expected on Android.

Screenshots

As soon as I release one finger - it jumps because now the focal point is not the point between fingers, but that single finger location.

But it should just transition to state “END” instead.

Steps To Reproduce

1. Run pinch example
2. Add log to onGestureEvent of PinchHandler

onGestureEvent={(evt) => console.log(evt.nativeEvent.numberOfFingers)}

1. Do the pinch then release one finger and move it
2. See that it fires even with 1 finger pressed after wi

Expected behavior

The gesture should be in the state “end” as soon as the user releases one finger – just like on Android

Actual behavior

The gesture remains active even when the user released one finger

Snack or minimal code example

Run the example app

Package versions

• React: 16.13.1
• React Native: 0.63.3
• React Native Gesture Handler: 1.8.0

[nhannah]

@terrysahaidak please consider the opposite as currently smooth 1->2->1->2 finger movement on iOS seems to function better than Android. I have just spent a good amount of time on this issue and can give a bit more insight after looking at the Android implementation. Currently Android gets a start event with 1 finger pressing, this start event is missing info for focal, etc. Then until a second finger is applied no active events are fired, once a second finger is applied active events come in again until less than 2 fingers remain, GestureHandler then fires the end event, but as a finger still remains I believe MotionEvents from ScaleGestureDetector still arrive and are discarded. This means that at best with a Pan and Pinch Handler on Android you can pan, then pinch, then pan, i.e. 1->2->1 fingers. You cannot return to 2 finger use. I have implemented this using reanimated 2 alongside the iOS version where the pinch handler takes over indefinitely after it starts and it seems to me as the pinch handler on iOS is almost a pass through to UIPinchGestureRecognizer it is the preferable way; but either way matching the interaction would be the key preference here.

[nhannah]

@iqqmuT You can take a look at my implementation of pinch to zoom here: https://github.com/GetStream/stream-chat-react-native/blob/92f891e42ec2c881d357ffc1a759fc8c26edf727/src/components/ImageGallery/ImageGallery.tsx . Overall for a smooth experience the iOS functionality makes more sense and is a 1:1 representation of the native handler as I noted previously. You can easily deal with the change in the number of touches detected, but with Android ending the gesture tracking you are not given a choice of how you want to deal with one finger being removed. Therefore the iOS implementation adds flexibility and utility.