docs: function DirectorTouchScreen () {
      DirectorTouchScreen.superclass.constructor.call(this)
  
      // Hardcode some viewport sizes for iOS devices
      var ua = window.navigator.userAgent
      if (ua.match(/(iPhone|iPod)/)) {
          this.viewportSize = { portrait:  new geo.Size(320, 416)
                              , landscape: new geo.Size(480, 268)
                              }
      } else if (ua.match(/(iPad)/)) {
          this.viewportSize = { portrait:  new geo.Size(768, 928)
                              , landscape: new geo.Size(1024, 672)
                              }
      }
  }