diag3

function TPAFromBoxDiagonal(bx: TBox; startCorner: Integer): TPointArray;
var
  x, y, z, l, j, r, w, h, e, o, s, n: Integer;
  c: TPoint;
begin
  l := pp_BoxSize(bx);
  SetLength(Result, l);
  if (l > 0) then
  begin
    s := startCorner;
    pp_EnsureRange(s, 0, 3);
    pp_BoxDimensions(bx, w, h);
    z := ((bx.X1 + h) - 1);
    if ((s = 1) or (s = 4)) then
      c := Point(bx.X2, bx.Y1)
    else
      c := Point(bx.X1, bx.Y1);
    r := 0;
    e := 0;
    o := 0;
    j := 0;
    n := -1;
    case s of
      0: // TOP-LEFT
      repeat
        if (c.X > z) then
          e := (c.X - z);
        if (c.X > bx.X2) then
          o := (c.X - bx.X2);
        y := (bx.Y1 + o);
        for x := (c.X - o) downto (bx.X1 + e) do
        begin
          Result[r] := Point(x, y);
          if (y < bx.Y2) then
            y := (y + 1);
          r := (r + 1);
        end;
        c.X := (c.X + 1);
      until (c.X > (bx.X2 + h));
      1: // TOP-RIGHT
      repeat
        if (c.X < bx.X1) then
          o := (o + 1);
        y := (bx.Y1 + o);
        for x := (c.X + o) to (bx.X2 - e) do
        begin
          Result[r] := Point(x, y);
          if (y < bx.Y2) then
            y := (y + 1);
          r := (r + 1);
        end;
        c.X := (c.X - 1);
        if ((bx.X2 - c.X) > (h - 1)) then
          e := (e + 1);
      until (r >= l);
      2: // BOTTOM-LEFT
      repeat
        if (c.X > bx.X2) then
          o := (c.X - bx.X2);
        if (c.X > z) then
          e := (c.X - z)
        else
          n := (n + 1);
        y := (bx.Y2 - n);
        for x := (bx.X1 + e) to (c.X - o) do
        begin
          Result[r] := Point(x, y);
          if (y < bx.Y2) then
            y := (y + 1);
          r := (r + 1);
        end;
        c.X := (c.X + 1);
      until (c.X > (bx.X2 + h));
      3: // BOTTOM-RIGHT
      repeat
        if (c.X < (bx.X2 - h)) then
          o := (o + 1);
        y := (bx.Y2 - o);
        for x := (c.X + o) to (bx.X2 - e) do
        begin
          Result[r] := Point(x, y);
          if (y > bx.Y2) then
            y := (y + 1);
          r := (r + 1);
        end;
        c.X := (c.X - 1);
        if ((bx.X2 - c.X) > (h - 1)) then
          e := (e + 1);
      until (r >= l);
    end;
  end;
end;