procedure TPanel.WMNCHitTest(var Msg: TWMNCHitTest);
begin
  inherited;
  if (Msg.Result = HTCLIENT)
      and PtInRect(Rect(Self.Width - 10, Self.Height - 10, Self.Width, Self.Height), ScreenToClient(Point(Msg.XPos, Msg.YPos)))
        and (((Self as TControl).Name = 'Panel3') or ((TControl(Self).Name = 'Panel1')))then
    Msg.Result := HTBOTTOMRIGHT;
end;

procedure TSizeablePanel.Paint;
var
  EdgeMarg: Integer;
begin
  inherited Paint;
  with Canvas do
  begin
    Pen.Style:= psSolid;
    Pen.Width:= 1;
    Pen.Color:= clGray;
    EdgeMarg:= 3;
    MoveTo(Self.ClientWidth - 6,Self.ClientHeight - EdgeMarg);
    LineTo(Self.ClientWidth - EdgeMarg,Self.ClientHeight - 6);
    MoveTo(Self.ClientWidth - 9,Self.ClientHeight - EdgeMarg);
    LineTo(Self.ClientWidth - EdgeMarg,Self.ClientHeight - 9);
    MoveTo(Self.ClientWidth - 12,Self.ClientHeight - EdgeMarg);
    LineTo(Self.ClientWidth - EdgeMarg,Self.ClientHeight - 12);
  end;
end; 

procedure TSizeablePanel.MouseMove(Shift: TShiftState; X, Y: Integer);
begin
  Self.DisableAutoSizing;

  if (GetCaptureControl = Self) and FResize then
    begin
      if (X >= MaxConstrX) and (Y >= MaxConstrY)
        then Self.SetBounds(Self.Left, Self.Top, MaxConstrX, MaxConstrY)
        else if (X >= MaxConstrX)
          then Self.SetBounds(Self.Left, Self.Top, MaxConstrX, y + Fdy)
          else if (Y >= MaxConstrY)
            then Self.SetBounds(Self.Left, Self.Top, x + Fdx, MaxConstrY)
            else if (X <= MinConstrX) and (Y <= MinConstrY)
              then Self.SetBounds(Self.Left, Self.Top, MinConstrX, MinConstrY)
              else if (X <= MinConstrX)
                then Self.SetBounds(Self.Left, Self.Top, MinConstrX, y + Fdy)
                else if (Y <= MinConstrY)
                  then Self.SetBounds(Self.Left, Self.Top, x + Fdx, MinConstrY)
                  else  Self.SetBounds(Self.Left, Self.Top, x + Fdx, y + Fdy);
    end;

  Self.EnableAutoSizing;

if (x > Self.ClientWidth - sizeGripSize) and (y > Self.ClientHeight - sizeGripSize)
  then
    Self.Cursor := crSizeNWSE
  else
    Self.Cursor:= crDefault;
end;   

procedure TForm1.FormCreate(Sender: TObject);
begin
  FPnl := TSizeablePanel.Create(Self);

  with FPnl do
  begin
    Parent := Self;
    Left := 10;
    Top := 10;
    Color:= clMoneyGreen;
    Caption := FPnl.ClassName;
  end;
end;

procedure TForm1.FormResize(Sender: TObject);
begin
  FPnl.MaxConstrX:= Self.ClientWidth - 50;
  FPnl.MaxConstrY:= Self.ClientHeight - 50;
end; 

  if (GetCaptureControl = Self) and FResize then
    begin
      if (X >= MaxConstrX) and (Y >= MaxConstrY)
        then Self.SetBounds(Self.Left, Self.Top, MaxConstrX, MaxConstrY)
        else if (X >= MaxConstrX)
          then Self.SetBounds(Self.Left, Self.Top, MaxConstrX, y + Fdy)
          else if (Y >= MaxConstrY)
            then Self.SetBounds(Self.Left, Self.Top, x + Fdx, MaxConstrY)
            else  Self.SetBounds(Self.Left, Self.Top, x + Fdx, y + Fdy);

      Self.Invalidate;
    end;

  //Note:
  //Msg.wParam = 0  - pressed "Cancel" button
  //Msg.wParam = 1  - pressed "Save" button

  if Assigned(FPnl) then
    case Msg.wParam of
      0:begin
          if FPnl.IsUseCloseQuery //use of the CloseQuery dialog
            and FPnl.MemoPnl.Modified then
              if Application.MessageBox(PChar(QueryWarningMessage),PChar(QuertWarningCaption), MB_ICONINFORMATION + MB_YESNO) = IDYES
                then
                  {$IFDEF UNIX}
                  edtText.Text:= UTF8StringReplace(FPnl.MemoPnl.Text,#10,'~', [rfReplaceAll]);
                  {$ELSE}
                  edtText.Text:= UTF8StringReplace(FPnl.MemoPnl.Text,#13#10,'~',[rfReplaceAll]);
                  {$ENDIF}
        end;
      1:begin
          {$IFDEF UNIX}
          edtText.Text:= UTF8StringReplace(FPnl.MemoPnl.Text,#10,'~', [rfReplaceAll]);
          {$ELSE}
          edtText.Text:= UTF8StringReplace(FPnl.MemoPnl.Text,#13#10,'~',[rfReplaceAll]);
          {$ENDIF}
        end;
    end;

  FreeAndNil(FPnl);