getViewportSize_(rotation) {
    const size = this.viewportSize_;
    if (rotation) {
      const w = size[0];
      const h = size[1];
      return [
        Math.abs(w * Math.cos(rotation)) + Math.abs(h * Math.sin(rotation)),
        Math.abs(w * Math.sin(rotation)) + Math.abs(h * Math.cos(rotation)),
      ];
    }
    return size;
  }
Returns the current viewport size.
@private
@param {number} [rotation] Take into account the rotation of the viewport when giving the size
@return {import("./size.js").Size} Viewport size or `[100, 100]` when no viewport is found.