handleWidgetKeydown(ev) {

    if (ev.ctrlKey) { // ctrl key is hold down
      ev.preventDefault();

      if (ev.keyCode === 70) { // f
        ev.preventDefault();

        const focusButtonStateTRef = `${this.widgetPopupsPath}/focus`;
        utils.setText(focusButtonStateTRef, utils.getText(focusButtonStateTRef) ? '' : '1');

        // note: it is ok to focus the graph right after this,
        // if the focus button is activated it will steal the focus anyway

      } else {

        return;

      }

    } else if (ev.keyCode === 120) { // F9
      ev.preventDefault();
      this.toggleEnlargedMode('halfscreen');

    } else if (ev.keyCode === 121) { // F10
      ev.preventDefault();
      this.toggleEnlargedMode('fullscreen');

    } else if (ev.keyCode === 27) { // ESC
      ev.preventDefault();

      utils.deleteByPrefix(this.widgetPopupsPath);

    } else {
      return;
    }

    this.canvas.focus();

  }
Called when the user click on the canvas with the right
mouse button. A context menu is opened.