var
DefaultWndProc: WNDPROC;
function WndCallback(AHWND: HWND; uMsg: UINT; wParam: WParam; lParam: LParam):LRESULT; stdcall;
var
LRect: TRect;
begin
if uMsg = WM_NCCALCSIZE then
DoWhatEverYouWant
else
Result := CallWindowProc(DefaultWndProc, AHWND, uMsg, WParam, LParam);
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
DefaultWndProc := Windows.WNDPROC(SetWindowLongPtr(Handle, GWL_WNDPROC, PtrInt(@WndCallback)));
end;