public Iterable<TileCoord> getFilledTiles() {
    return filledRanges == null ? Collections.emptyList() :
      () -> filledRanges.entrySet().stream()
        .<TileCoord>mapMulti((entry, next) -> {
          int x = entry.getKey();
          for (int y : entry.getValue()) {
            if (extents.test(x, y)) {
              TileCoord coord = TileCoord.ofXYZ(x, y, z);
              if (!tileContents.containsKey(coord)) {
                next.accept(coord);
              }
            }
          }
        }).iterator();
  }
Returns an iterator over the coordinates of every tile that is completely filled within this polygon at this zoom
level, ordered by x ascending, y ascending.
planetiler-core/src/main/java/com/onthegomap/planetiler/render/TiledGeometry.java