//Processing non-user messages in your window

//To have a custom processing of messages <= WM_USER you should use SetWindowLongPtr from the Windows unit. It will return the address of the current WndProc, so you can just have your  

//Example:

//By intercepting the WM_NCHITTEST message you can avoid dragging the window. 


var
  PrevWndProc: WNDPROC;
...

//----------------------------------------------------------------------------------------------

function WndCallback(Ahwnd: HWND; uMsg: UINT; wParam: WParam; lParam: LParam):LRESULT; stdcall;
begin
  if uMsg=WM_INPUT then
  begin
	// do stuff
  end;
  result:= CallWindowProc(PrevWndProc,Ahwnd, uMsg, WParam, LParam);
end;
//------------------------------------------------------------------------------------------------

//install our message handler
procedure TForm1.FormCreate(Sender: TObject);
begin
  PrevWndProc:=Windows.WNDPROC(SetWindowLongPtr(Self.Handle,GWL_WNDPROC,PtrUint(@WndCallback)));
end;
//------------------------------------------------------------------------------------------------