_pointerToPositionObject(pointer) {
    const canvasPos = this.canvas.DOMtoCanvas(pointer);
    return {
      left: canvasPos.x - 1,
      top: canvasPos.y + 1,
      right: canvasPos.x + 1,
      bottom: canvasPos.y - 1,
    };
  }
Return a position object in canvasspace from a single point in screenspace
@param {{x: number, y: number}} pointer
@returns {{left: number, top: number, right: number, bottom: number}}
@private