   #   if referenceFrame.page != newCurrentPage || referenceFrame.atEndEdge != atEndEdge
   #     @setReferenceFrame page: newCurrentPage, atEndEdge: atEndEdge
 
-  # _queueUpdateEvent: (newReferenceFrame, previousReferenceFrame)->
-  #   @onNextReady =>
-  #     referenceFrame = @getReferenceFrame()
-  #     @queueEvent "scrollUpdate",
-  #       previousReferenceFrame:previousReferenceFrame
-  #       referenceFrame:       referenceFrame
-  #       focusedPage:          referenceFrame.page
-  #       currentGeometry:      @getCurrentGeometry()
-  #       pagesBeforeBaseline:  @getPagesBeforeBaseline()
-  #       pagesAfterBaseline:   @getPagesAfterBaseline()
-
   # _sizeChanged: (newSize, oldSize) ->
   #   @_queueUpdateEvent()
   #   super

      else
        child._translateLocationXY 0, offsetDelta for child in inFlowChildren

    @_updateTracking mainCoordinate, inFlowChildren, mainChildrenSize, mainElementSizeForChildren, mainChildrenAlignedOffset + offsetDelta

  _updateTracking: (mainCoordinate, inFlowChildren, mainChildrenSize, mainElementSizeForChildren, mainChildrenOffset) ->
    {_scrollPosition, _tracking, _track} = @getPendingState()


  # ######################################
  @getter
    isVertical:                -> @_childrenLayout == "column"

    numChildrenOnScreen: ->
      {isVertical, windowSize} = @
      numChildrenOnScreen = 0

      for child in @children when child.inFlow
        if isVertical
          pos = child.getCurrentLocationY false, point0
          size = child.getCurrentSize().y
        else
          pos = child.getCurrentLocationX false, point0
          size = child.getCurrentSize().x
        numChildrenOnScreen++ if pos < windowSize && pos + size > 0

      numChildrenOnScreen

  #   atEnd:                     -> @_atEnd
  #   atStart:                   -> @_atStart
  #   inMiddle:                  -> !@_atEnd && !@_atStart
