function getSegments(extent) {
  return [
    [
      [extent[0], extent[1]],
      [extent[0], extent[3]],
    ],
    [
      [extent[0], extent[3]],
      [extent[2], extent[3]],
    ],
    [
      [extent[2], extent[3]],
      [extent[2], extent[1]],
    ],
    [
      [extent[2], extent[1]],
      [extent[0], extent[1]],
    ],
  ];
}
@param {import("../extent.js").Extent} extent extent
@return {Array<Array<import("../coordinate.js").Coordinate>>} extent line segments