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.

 1 case WM_NCCALCSIZE:
 2   {
 3   lRet = 0;
 4   const int cxBorder = 2;
 5   const int cyBorder = 2;
 6   InflateRect((LPRECT)lParam, -cxBorder, -cyBorder);
 7   }
 8 
 9 case WM_NCCALCSIZE: 
10   {
11   LPNCCALCSIZE_PARAMS pncc = (LPNCCALCSIZE_PARAMS)lParam;
12   //pncc->rgrc[0] is the new rectangle
13   //pncc->rgrc[1] is the old rectangle
14   //pncc->rgrc[2] is the client rectangle
15 
16   lRet = DefWindowProc (hwnd, WM_NCCALCSIZE, wParam, lParam);
17   pncc->rgrc[0].top += ExtraCaptionHeight;
18   }

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