Allow Android Rotation Gesture to continue after second Pointer Lift and Land (#3057)

## Description

On iOS Rotation Gesture is not getting finished/cancelled when one of
two Pointers lifts up, allowing the Gesture to continue when a new
second Pointer arrives

On Android this behaviour differs – Rotation Gesture finishes whenever
one of two Pointers lifts up, requiring to land 2 completely new
Pointers in order to utilise Rotation Gesture again

I understand that this may be closer to default Android Gesture
Recogniser Behaviour, but find it unexpected and inconvenient

Thus in this PR I’m adding Ability to tell Rotation Gesture Builder to
enable iOS-like Behaviour, which allows Gesture Pause/Remain when second
Pointer lifts/lands

Additionally, I added some local toggleable Logs, which I find useful
for Debugging, but I’m not sure if it aligns with this Repo Style Guide
(or could noticeably reduce Performance) – please notify me, if it’s
prohibited


I think this Change may be usable for Gesture Handler Users, thus trying
to push it to the Gesture Handler (not only my own Fork) and looking
forward to any Feedback regarding both Code – Implementation/Naming
and/or local Style Guide – and Docs, which I might’ve misaligned with

Attached Gifs display what I mean (first one shows current Behaviour,
second one – with new Modifier)

<img
src="https://github.com/user-attachments/assets/ef87aa99-db12-42a5-a5ef-1fed4b11f8ac"
width="260"/>

<img
src="https://github.com/user-attachments/assets/a8337925-e1e9-4862-a5ed-b3b5cd5dde31"
width="260"/>


## Test plan
1. Use `RotationGesture` without new Modifier
(`secondPointerLiftFinishesGesture(value: boolean)`) and see if it works
as expected (as before – Gesture finishes when one of two key Pointers
is lifted)
2. Use `RotationGesture` with new Modifier
(`secondPointerLiftFinishesGesture(value: boolean)`) and see if it works
as expected (Gesture doesn't finish when second Pointer is lifted and
continues when second Pointer is landed again)

Author: DmitriyGalyanov

android/src/main/java/com/swmansion/gesturehandler/core/RotationGestureDetector.kt

@@ -57,6 +57,14 @@ class RotationGestureDetector(private val gestureListener: OnRotationGestureList
     currentTime = event.eventTime
     val firstPointerIndex = event.findPointerIndex(pointerIds[0])
     val secondPointerIndex = event.findPointerIndex(pointerIds[1])
+
+    if (
+      firstPointerIndex == MotionEvent.INVALID_POINTER_ID ||
+      secondPointerIndex == MotionEvent.INVALID_POINTER_ID
+    ) {
+      return
+    }
+
     val firstPtX = event.getX(firstPointerIndex)
     val firstPtY = event.getY(firstPointerIndex)
     val secondPtX = event.getX(secondPointerIndex)
@@ -68,6 +76,9 @@ class RotationGestureDetector(private val gestureListener: OnRotationGestureList
 
     // Angle diff should be positive when rotating in clockwise direction
     val angle = -atan2(vectorY.toDouble(), vectorX.toDouble())
+
+    tryUnpause(angle)
+
     rotation = if (previousAngle.isNaN()) {
       0.0
     } else previousAngle - angle
@@ -85,8 +96,29 @@ class RotationGestureDetector(private val gestureListener: OnRotationGestureList
     }
   }
 
+  /**
+   * Gesture pauses when second Pointer lifts
+   *
+   * Then Detector waits for a new second Pointer to arrive to continue Handling
+   * (last Pointer Lifting finishes the Gesture)
+   *
+   * @see tryPause
+   * @see tryUnpause
+   */
+  private var isPaused = false
+  private fun tryPause() {
+    if (isPaused) return
+    isPaused = true
+  }
+  private fun tryUnpause(eventAngle: Double) {
+    if (!isPaused) return
+    previousAngle = eventAngle
+    isPaused = false
+  }
+
   private fun finish() {
     if (isInProgress) {
+      isPaused = false
       isInProgress = false
       gestureListener?.onRotationEnd(this)
     }
@@ -99,33 +131,33 @@ class RotationGestureDetector(private val gestureListener: OnRotationGestureList
         pointerIds[0] = event.getPointerId(event.actionIndex)
         pointerIds[1] = MotionEvent.INVALID_POINTER_ID
       }
-      MotionEvent.ACTION_POINTER_DOWN -> if (!isInProgress) {
-        pointerIds[1] = event.getPointerId(event.actionIndex)
-        isInProgress = true
-        previousTime = event.eventTime
-        previousAngle = Double.NaN
-        updateCurrent(event)
-        gestureListener?.onRotationBegin(this)
+      MotionEvent.ACTION_POINTER_DOWN -> {
+        if (!isInProgress || isPaused) {
+          pointerIds[1] = event.getPointerId(event.actionIndex)
+          updateCurrent(event)
+        }
+        if (!isInProgress) {
+          isInProgress = true
+          previousTime = event.eventTime
+          previousAngle = Double.NaN
+          gestureListener?.onRotationBegin(this)
+        }
       }
       MotionEvent.ACTION_MOVE -> if (isInProgress) {
         updateCurrent(event)
-        gestureListener?.onRotation(this)
+        if (!isPaused) {
+          gestureListener?.onRotation(this)
+        }
       }
-      MotionEvent.ACTION_POINTER_UP -> {
+      MotionEvent.ACTION_POINTER_UP -> if (isInProgress) {
         val pointerId = event.getPointerId(event.actionIndex)
-
-        // All key pointers are up
-        if (!isInProgress && pointerId == pointerIds[0]) {
-          gestureListener?.onRotationEnd(this)
-        }
-
-        // One of the key pointers is up
-        if (isInProgress && pointerIds.contains(pointerId)) {
-          if (pointerId == pointerIds[0]) {
-            pointerIds[0] = pointerIds[1]
-          }
+        if (pointerId == pointerIds[0]) {
+          pointerIds[0] = pointerIds[1]
+          pointerIds[1] = MotionEvent.INVALID_POINTER_ID
+          tryPause()
+        } else if (pointerId == pointerIds[1]) {
           pointerIds[1] = MotionEvent.INVALID_POINTER_ID
-          isInProgress = false
+          tryPause()
         }
       }
       MotionEvent.ACTION_UP -> finish()