Author: Rafael Cotta

I've been trying to create a MDI form without those annoying scrollbars when a 
child form is moved outside main form area and I couldn't find an easy way. Setting 
the scrollbars to visible := false won't work! 
So, I found an example on a newsgroup... yeah! Here I show how to do it.

Answer:

It's a two step proccess. 

Step one : put the code below inside the OnCreate event of the main form. 

1   if ClientHandle <> 0 then
2   begin
3     if (not (GetWindowLong(ClientHandle, GWL_USERDATA) <> 0)) then
4     begin
5       SetWindowLong(
6         ClientHandle,
7         GWL_USERDATA,
8         SetWindowLong(ClientHandle, GWL_WNDPROC, integer
9         (@ClientWindowProc))
10        );
11    end;
12  end;


Step two: Put this standalone function inside the unit that contains the main form, 
before the OnCreate event (once OnCreate references to this function). 
13  
14  function ClientWindowProc(wnd: HWND; msg: Cardinal; wparam, lparam: Integer): 
15  Integer;
16    stdcall;
17  var
18    f: Pointer;
19  begin
20    f := Pointer(GetWindowLong(wnd, GWL_USERDATA));
21    case msg of
22      WM_NCCALCSIZE:
23        begin
24          if (
25            GetWindowLong(wnd, GWL_STYLE) and
26            (WS_HSCROLL or WS_VSCROLL)) <> 0 then
27            SetWindowLong(
28              wnd,
29              GWL_STYLE,
30              GetWindowLong(wnd, GWL_STYLE) and not
31              (WS_HSCROLL or WS_VSCROLL)
32              );
33        end;
34    end;
35    Result := CallWindowProc(f, wnd, msg, wparam, lparam);
36  end;


That's it!!! 

The code was originally posted by Peter Below in a newsgroup (borland.public.delphi.objectpascal). I've made some little changes.