{==============================================================================]
  Explanation: Set minimum / maximum size to bx.
               size.X1 = min. X1, size.Y1 = min. Y1, size.X2 = max. X2, size.Y2 = max. Y2
               Returns true if constraints were set to bx.
[==============================================================================}
function SetBoxConstraints(var bx: TBox; size: TBox): Boolean;
var
  tmp: TBox;
begin
  if ((size.X1 <= size.X2) and (size.Y1 <= size.Y2)) then
  begin
    tmp := TBox(bx);
    if (bx.X1 < size.X1) then
      bx.X1 := Integer(size.X1);
    if (bx.X1 > size.X2) then
      bx.X1 := Integer(size.X2);
    if (bx.Y1 < size.Y1) then
      bx.Y1 := Integer(size.Y1);
    if (bx.Y1 > size.Y2) then
      bx.Y1 := Integer(size.Y2);
    if (bx.X2 > size.X2) then
      bx.X2 := Integer(size.X2);
    if (bx.X2 < size.X1) then
      bx.X2 := Integer(size.X1);
    if (bx.Y2 > size.Y2) then
      bx.Y2 := Integer(size.Y2);
    if (bx.Y2 < size.Y1) then
      bx.Y2 := Integer(size.Y1);
    Result := ((bx.X1 <> tmp.X1) or (bx.Y1 <> tmp.Y1) or (bx.X2 <> tmp.X2) or (bx.Y2 <> tmp.Y2));
  end else
    Result := False;
end;

var
  b: TBox;

begin
  b := IntToBox(100, 100, 400, 400);
  if SetBoxConstraints(b, IntToBox(250, 250, 500, 500)) then
    WriteLn(b);
  b := IntToBox(100, 100, 400, 400);
  if SetBoxConstraints(b, IntToBox(0, 0, 300, 300)) then
    WriteLn(b);
end.