 
       @debug 'layers', @layers
 
-    farthestLayer: -> _.findWhere @layers, { zIndex: 1 }
-    nearestLayer: -> _.findWhere @layers, { zIndex: @topZIndex }
+    # Helpers
+    # -------
+
+    _farthestLayer: -> _.findWhere @layers, { zIndex: 1 }
+    _nearestLayer: -> _.findWhere @layers, { zIndex: @topZIndex }
 
   _.extend Background::, Helpers.DebugMixin
 


      @_initDebugMixin()

    addImages: (nameTemplate, topZIndex, bottomZIndex = 1) ->
      @topZIndex = topZIndex
      for zIndex in [bottomZIndex..topZIndex]

      # @group.y = -(@group.height - @group.game.height)

      # Set vertical scroll factor and offset.
      nearest = @_nearestLayer()
      farthest = @_farthestLayer()
      for layer in @layers
        {image, zIndex} = layer
        # Factor in z-index exponentially and constrain.
