/**
   * Called when a Command object is set as the current
   * command.
   *
   * @param painter The parent SkyBrush instance this is being attached to.
   */
  onAttach( painter:SkyBrush ) {
    if ( ! this.isInAttach ) {
      this.isInAttach = true

      if ( this.shiftDown ) {
        painter.onShift( this.shiftDown )

        // call if shift is down,
        // so control is properly setup
        if ( painter.isShiftDown() ) {
          this.shiftDown.call( painter, true )
        }
      }

      this.isInAttach = false
    }
  }

  /**
   * For when a Command object is detached from SkyBrush,
   * and it is no longer set as the current command.
   *
   * @param painter The parent SkyBrush instance this is being detached from.
   */
  onDetach( painter:SkyBrush ) {
    if ( ! this.isInDetach ) {
      this.isInDetach = true

      if ( this.shiftDown ) {
        painter.removeOnShift( this.shiftDown )

        /*
         * If changing whilst shift is down,
         * we call as though it was lifte,
         * so it's like it was released.
         */
        if ( painter.isShiftDown() ) {
          this.shiftDown.call( painter, false )
        }
      }

      this.isInDetach = false
    }
  }

        onChange : n => {
          command[ field ] = n
          input.value = `${n}`

          if ( callback ) {
            callback.call( command, n, painter )
          }

          if ( isCursor ) {
            painter.refreshCursor()
          }
        }

    toggle.addEventListener( 'click', ev => {
        ev.stopPropagation()
        ev.preventDefault()
        switchOption()

        command[ field ] = option
        if ( callback ) {
          callback.call( command, option, painter )
        }

        if ( isCursor ) {
          painter.refreshCursor()
        }
    } )

      requestAnimationFrame(() => {
        let n = parseInt( input.value )

        if ( isNaN(n) ) {
          return
        }

        if ( n >= 1 ) {
          n = Math.round( n )
          input.value = `${n}`

          command[ field ] = n

          if ( callback ) {
            callback.call( command, n, painter )
          }

          if ( isCursor ) {
            painter.refreshCursor()
          }
        }
      })