This example uses the WinUpdateWindow call to send a WM_PAINT message to a window procedure.

#define INCL_WINWINDOWMGR
#include <OS2.H>
#define WM_USERDEF WM_USER + 1
main()
{

}
static MRESULT ClientWindowProc( HWND hwnd, USHORT msg, MPARAM mp1, MPARAM mp2 )
{
 switch(msg)
 {
  case WM_PAINT:
  break;
  case WM_USERDEF:
   WinUpdateWindow(hwnd);
 }
}