a simplified code example of how Discord's Android app selectively allows child views of OverlappingPanelsLayout to handle their own horizontal scrolls

PanelsHorizontalScrollingInChildViews.kt

class PanelsChildGestureRegionObserver : View.OnLayoutChangeListener {
  ...
  override fun onLayoutChange(
    view: View?,
    left: Int,
    top: Int,
    right: Int,
    bottom: Int,
    oldLeft: Int,
    oldTop: Int,
    oldRight: Int,
    oldBottom: Int
  ) {
    if (view != null) {
      val coordinates = intArrayOf(0, 0)
      view.getLocationOnScreen(coordinates)
      val x = coordinates[0]
      val y = coordinates[1]
      val absoluteLeft = x + left
      val absoluteTop = y + top
      val absoluteRight = x + right
      val absoluteBottom = y + bottom
      viewIdToGestureRegionMap[view.id] = Rect(
        absoluteLeft,
        absoluteTop,
        absoluteRight,
        absoluteBottom
      )
      publishGestureRegionsUpdate()
    }
  }


  private fun publishGestureRegionsUpdate() {
    val gestureRegions = viewIdToGestureRegionMap.values.toList()
    gestureRegionsListeners.forEach { gestureRegionsListener ->
      gestureRegionsListener.onGestureRegionsUpdate(gestureRegions)
    }
  }
}

class ChatInputFragment: Fragment() {
  private val container: View by bindView(R.id.chat_input_container)
  override fun onViewCreated(
    view: View,
    savedInstanceState: Bundle?
  ) {
    super.onViewCreated(view, savedInstanceState)
    // Provider.get() returns a lazily instantiated
    // activity-scoped singleton.
    container.addOnLayoutChangeListener(
      PanelsChildGestureRegionObserver.Provider.get()
    )
  }
}

class PanelsFragment: Fragment(),
  PanelsChildGestureRegionObserver.GestureRegionsListener {
  private val panels: OverlappingPanelsLayout by bindView(R.id.overlapping_panels)
  ...
  override fun onGestureRegionsUpdate(gestureRegions: List<Rect>) {
    panels.setChildGestureRegions(gestureRegions)
  }
}