Qvision 2000 and Matrox Mga Ultima Cause Access Violation

The information in this article applies to:

• Microsoft Windows NT Workstation versions 3.5 and 3.51
• Microsoft Windows NT Server versions 3.5 and 3.51

SUMMARY

This article outlines a special programming case that causes an access violation when running the Qvision 2000 or Matrox Mga Ultima Video cards. These cards use the Mga.sys video driver.

The problem is caused by making some bad graphics calls. (These are shown in a program included in the More Information section below.) The problem causes the following error message to be returned by NT 3.51:

   access violates in ntdll.dll at 0x77fa02ad with exception 0xc0000037.

The programming problem is produced by calling BeginPath and Endpath with no points defined (no LineTo definitions) and calling StrokeAndFillPath (really the FillPath is the problem).

Once this has been done there is a problem with the hdc. The failure will show up when MoveToEx is called (after the previous calls have messed up the device context - hdc).

MORE INFORMATION

Here is a simple sample program that produces the error:

#include <windows.h>

int APIENTRY WinMain (HMODULE hModule, HINSTANCE hNULL, PSTR cmdLine,
     int cmdShow)

        memset (&wc, 0, sizeof (WNDCLASS));
        wc.lpszClassName = "MAIN";
        wc.hbrBackground = (void * ) (COLOR_WINDOW +1);
        wc.style = CS_VREDRAW | CS_HREDRAW;
        wc.lpfnWndProc = DrawProc;
        if  (!RegisterClass (&wc)) exit (-1);
        if  ( (mainFrame = CreateWindow ("MAIN", "Mca Test",
             WS_OVERLAPPEDWINDOW, 0, 0, 300, 200, NULL,
              NULL, 0, NULL) ) == NULL)
           return (FALSE);
        ShowWindow (mainFrame, SW_SHOW);

        While (GetMessage (&msg, NULL, 0, 0) )
        {
            TranslateMessage (&msg);
            DispatchMessage(&msg);
        }
}

   switch (msg)
   {
   case  WM_CLOSE:
        DestroyWindow (mainFrame);
        return (0);
   case WM_DESTROY:
        PostQuitMessage (0);
        return (0);
   case WM_PAINT:
        BeginPaint (hwnd, &ps);
        BeginPath  (ps.hdc);
        EndPath (ps.hdc);
        StrokeAndFillPath (ps.hdc); // Fillpath is the problem here
                                    // since nothing has been drawn
        BeginPath (ps.hdc);
        MoveToEx (ps.hdc, 50, 50, NULL); //This is the failure point
        LineTo (ps.hdc, 100, 100);
        LineTo (ps.hdc, 150,  150);
        EndPath (ps.hdc);
        StrokeAndFillPath (ps.hdc);
        MoveToEx (ps.hdc, 300, 300, NULL);
        EndPaint (hwnd, &ps);
        return (0);
    }
    return (DefWindowProc (hwnd, msg, mp1, mp2));