Win32 Plus Extra Height of Caption Bar

you set the size of the non-client area by handling the WM_NCCALCSIZE message. But don't do this unless you plan to do all of the non-client drawing as well by handling WM_NCPAINT

Edit: here are two code fragments, one that handles WM_NCCALCSIZE and provides a simple n pixel border, and another than adds some extra pixels after DefWindowProc has done the default handling.

 case WM_NCCALCSIZE:
   {
   lRet = ;
   const int cxBorder = ;
   const int cyBorder = ;
   InflateRect((LPRECT)lParam, -cxBorder, -cyBorder);
   }

 case WM_NCCALCSIZE:
   {
   LPNCCALCSIZE_PARAMS pncc = (LPNCCALCSIZE_PARAMS)lParam;
   //pncc->rgrc[0] is the new rectangle
   //pncc->rgrc[1] is the old rectangle
   //pncc->rgrc[2] is the client rectangle

   lRet = DefWindowProc (hwnd, WM_NCCALCSIZE, wParam, lParam);
   pncc->rgrc[].top += ExtraCaptionHeight;
   }

You can learn a lot by passing WM_NCCALCSIZE to DefWindowProc and looking at the values of the NCCALCSIZEPARAM before and after.