private
  { Private declarations }
  AnchorX, AnchorY,
  CurX, CurY: Integer;
  Bounding: Boolean;
 end;
 implementation
 procedure TForm1.FormMouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
 begin
  AnchorX := X;
  CurX := X;
  AnchorY := Y;
  CurY := Y;
  Bounding := True;
 end;
 procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
 begin
  if Bounding then
  begin
  Canvas.Pen.Mode := pmNot;
  Canvas.Pen.Width := 2;
  Canvas.Brush.Style := bsClear;
  Canvas.Rectangle(AnchorX, AnchorY, CurX, CurY);
  CurX := X;
  CurY := Y;
  Canvas.Rectangle(AnchorX, AnchorY, CurX, CurY);
  end;
 end;
 procedure TForm1.FormMouseUp(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
 begin
  if Bounding then
  begin
  Bounding := False;
  Canvas.Pen.Mode := pmNot;
  Canvas.Brush.Style := bsClear;
  Canvas.Rectangle(AnchorX, AnchorY, CurX, CurY);
  end;
 end;