srecord noeq G22_RegionToSSIs(IImageRegion region) {

  Color color;

  L<SSI> ssis;

  new L<GrowingSSI> growingSSIs;

  class GrowingSSI {

    settable int y1;

    new ShortBuffer data;

    int y2() { ret y1+l(data)/2; }

    SSI finish() {

      ret new SSI(y1, y2()).data(data.toArray())

        .color(color);

    }

  }

  L<SSI> get() {

    if (region == null) null;

    color = region.color();

    ssis = new L;

    Rect r = region.bounds();

    int x1 = r.x1(), y1 = r.y1(), y2 = r.y2(), h = y2-y1, w = r.w;

    for (int y = y1; y < y2; y++) {

      reMutable y;

      L<IntRange> streaks = genericStreaks(w, x -> region.contains(x1+x, y));

      // finish SSIs

      while (longerThan(growingSSIs, streaks))

        ssis.add(popLast(growingSSIs).finish());

      // now we know that l(growingSSIs) <= l(streaks)

      // start new SSIs

      for (int i = l(growingSSIs); i < l(streaks); i++)

        growingSSIs.add(new GrowingSSI().y1(y));

      // continue SSIs

      for (ssi, range : unpair zipTwoLists(growingSSIs, streaks)) {

        ssi.data.add(toShort_enforce(x1+range.start));

        ssi.data.add(toShort_enforce(x1+range.end));

      }

    }

    for (ssi : cloneAndClear(growingSSIs))

      ssis.add(ssi.finish());

    ret ssis;

  }

}