scope regionBorder_innerPoints.

static Pt[] #directions = {

  pt(1, 0), pt(0, 1), pt(-1, 0), pt(0, -1) // r, d, l, u

};

static L<Pt> regionBorder_innerPoints(BWImage_FastRegions regions, int iRegion) {

  new PtBuffer out;

  Pt p = regions.samplePixel(iRegion);

  int x = p.x, y = p.y;

  // move up until we're at the edge of the region

  // probably we don't actually need to do this because of the way

  // the image was scanned, but we'll do it anyway

  while (y > 0 && regions.inRegion(iRegion, x, y-1))

    y--;

  // found our first border pixel with background above

  int dir = 3; // direction up

  // remember first point

  int firstX = x, firstY = y;

  int safety = regions.size();

  loop: do {

    out.add(x, y);

    for (int turn = 3; turn <= 6; turn++) { // try left, straight, right, back

      int newDir = (dir+turn) & 3;

      Pt d = directions[newDir];

      int x2 = x+d.x, y2 = y+d.y;

      if (regions.inRegion(x2, y2, iRegion)) {

        x = x2; y = y2; dir = newDir;

        continue loop;

      }

    }

    // if we get here, the region is just 1 pixel (so we're done)

    break;

  } while ((x != firstX || y != firstY) && --safety >= 0);

  ret out;

}