Microsoft KB Archive/150611

= Qvision 2000 and Matrox Mga Ultima Cause Access Violation =

Article ID: 150611

Article Last Modified on 11/1/2006

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APPLIES TO


 * Microsoft Windows NT Workstation 4.0 Developer Edition
 * Microsoft Windows NT Server 3.5
 * Microsoft Windows NT Server 3.51

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This article was previously published under Q150611





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 violation in ntdll.dll at 0x77fa02ad with exception 0xc0000037.

This error is only known to occur using the Mga.sys driver. There may be other drivers that also produce this error.

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 

HANDLE mainFrame; extern LRESULT WINAPI DrawProc (HWND, UINT, WPARAM, LPARM);

int APIENTRY WinMain (HMODULE hModule, HINSTANCE hNULL, PSTR cmdLine,    int cmdShow) { MSG msg; WNDCLASS wc;

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); } }

LRESULT WINAPI DrawProc (HWND hwnd, UINT msg, WPARM mp1, LPARAM mp2) { PAINTSTRUCT ps;

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)); }

Keywords: KB150611

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