Method mousewheel

js/src/PanZoom.ts:215–223

()

  }

  mousewheel() {
    if (this.model.get('allow_zoom')) {
      const event = d3GetEvent();
      event.preventDefault();
      const delta = event.deltaY * -1;
      const mouse_pos = this.mousePos();
      this._zoom(mouse_pos, delta);
    }
  }

  _zoom(mouse_pos, delta) {
    if (delta) {