Loading http://www.nihilogic.dk/labs/canvas_sheet/HTML5_Canvas_Cheat_Sheet.pdf

if (!this._focusEventsAllowed) {
      return;
    }
    super.focusin(event);
    this.enableEditMode();
  }
  /**
   * onpointerdown callback for the canvas we're drawing on.
   * @param {PointerEvent} event
   */
  canvasPointerdown(event) {