static <A> PatchworkImage<A> mergePatchworkImagesVertically(L<PatchworkImage<A>> images, O... _) {
  if (empty(images)) null;
  optPar int spacing = imageMergeSpacing();
  int h = intSum(mapMethod h(images))+(l(images)-1)*spacing;
  int w = intMax(mapMethod w(images));
  PatchworkImage<A> out = new(w, h);
  int y = 0;
  for (img : images) {
    int x = (w-img.w())/2;
    for (patch : img.patches)
      out.addPatch(patch.image,
        x+patch.bounds.x, y+patch.bounds.y, patch.userValue);
    y += img.h() + spacing;
  }
  ret out;
}