constructor: (@config) ->

    # config also has:

    #   graph

    #   subj

    #   pred

    #   ctx

    #   getTargetPosForValue(value) -> getTarget result for value

    #   getValueForPos

    super()

    @ctor2()

    if not @config.ctx?

      throw new Error("missing ctx")

    @config.graph.runHandler(@_syncValue.bind(@),

  _syncValue: () ->

    @_currentValue = @config.graph.floatValue(@config.subj, @config.pred)

    @_onChange() if @_onChange

  _getValue: () ->

    # this is a big speedup- callers use _getValue about 4x as much as

    # the graph changes and graph.floatValue is slow

    @_currentValue

  getTarget: () ->

    @config.getTargetPosForValue(@_getValue())

    # only works on one subscription at a time

    throw new Error('multi subscribe not implemented') if @_onChange

    @_onChange = onChange

  continueDrag: (pos) ->

    # pos is vec2 of pixels relative to the drag start

    super(pos)

    newValue = @config.getValueForPos(@_editorCoordinates())

    @config.graph.patchObject(@config.subj, @config.pred,

                              @config.graph.LiteralRoundedFloat(newValue),

                              @config.ctx)

class window.AdjustableFade extends Adjustable

  constructor: (@yForV, @zoomInX, @i0, @i1, @note, offset, ctx) ->

    super()

    @config = {

      getSuggestedTargetOffset: -> offset

      getTarget: @getTarget.bind(@)

      ctx: ctx

    }

    @ctor2()

  getTarget: ->

      if adj

        ev.stopPropagation()

        @currentDrag = {start: start, adj: adj}

        adj.startDrag()

  onMove: (ev) ->

    pos = @_mousePos(ev)

    if @currentDrag

      @hoveringNear = null

      @currentDrag.cur = pos

      @currentDrag.adj.continueDrag(

        @currentDrag.cur.subtract(@currentDrag.start))

    else

      near = @_adjAtPoint(pos)

      if @hoveringNear != near

        @hoveringNear = near

        @redraw()

  onUp: (ev) ->

    return unless @currentDrag

    @currentDrag.adj.endDrag()

    @currentDrag = null

  _setAdjuster: (adjId, makeAdjustable) ->

    # callers register/unregister the Adjustables they want us to make

    # adjuster elements for. Caller invents adjId.  makeAdjustable is

    # a function returning the Adjustable or it is null to clear any

    # adjusters with this id.

        delete @adjs[adjId]

    @redraw()

    window.debug_adjsCount = Object.keys(@adjs).length

  updateAllCoords: ->

    @redraw()

  _adjAtPoint: (pt) ->

    nearest = @qt.find(pt.e(1), pt.e(2))

    if not nearest? or nearest.distanceFrom(pt) > maxDist

      return null

      @_traceBorder(params.screenPts, 12, 0x888888)

    if params.selected

      @_traceBorder(params.screenPts, 6, 0xff2900)

    shape = new PIXI.Polygon(params.screenPts)

    @graphics.beginFill(@_noteColor(params.effect), .313)

    @graphics.drawShape(shape)

    @graphics.endFill()

    @_traceBorder(params.screenPts, 2, 0xffd900)

    @_addMouseBindings()

  update: ->

    if not @parentElem.isActiveNote(@uri)

      # stale redraw call

      return

    if @worldPts

      @brickLayout.setNoteSpan(@, @worldPts[0].e(1),

                               @worldPts[@worldPts.length - 1].e(1))

    params = @_planDrawing()

    @worldPts = params.worldPts