# The way dragging should work is that you start in the yellow *adj

  # widget*, wherever it is, but your drag is moving the *target*. The

  # adj will travel around too, but it may do extra moves to not bump

  # into stuff or to get out from under your finger.

  constructor: (@config) ->

    # config has:

    #   getTarget -> vec2 of current target position

    #   getSuggestedTargetOffset -> vec2 pixel offset from target

    #   emptyBox -> true if you want no value display

    # updated later by layout algoritm

class window.AdjustableFloatObservable extends Adjustable

  constructor: (@config) ->

    # config also has:

    #   observable -> ko.observable we will read and write

    #   getValueForPos(pos) -> what should we set to if the user

    #                          moves target to this coord?

  _getValue: () ->

    @config.observable()

  continueDrag: (pos) ->

    # pos is vec2 of pixels relative to the drag start.

    #   graph

    #   subj

    #   pred

    #   ctx

    #   getTargetPosForValue(value) -> getTarget result for value

    #   getValueForPos

    if not @config.ctx?

      throw new Error("missing ctx")

    @config.graph.runHandler(@_syncValue.bind(@), "adj sync #{@config.subj}")

  _syncValue: () ->

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

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

                              @config.graph.LiteralRoundedFloat(newValue),

                              @config.ctx)

class window.AdjustableFade extends Adjustable

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

    @config = {

      getSuggestedTargetOffset: -> offset

      getTarget: @getTarget.bind(@)

      ctx: ctx

    }

  getTarget: ->

    mid = @note.worldPts[@i0].x(.5).add(@note.worldPts[@i1].x(.5))

    $V([@note.zoomInX(mid.e(1)), @yForV(mid.e(2))])

  _getValue: ->