BUG: Graphics Operations Consume GDI Memory

ID: Q98058

3.10 WINDOWS kbprg kbbuglist

The information in this article applies to:

Microsoft Windows Software Development Kit (SDK) 3.1

SYMPTOMS

In the Microsoft Windows graphical operating environment, when a device driver has rectangle capabilities (such as the 8514/a display driver) and an application draws many large graphic objects, memory in the GDI data segment is lost. Eventually, GDI runs out of memory and Windows crashes.

CAUSE

GDI allocates a block of memory and then checks to see whether the device has rectangle capabilities. If the device does have rectangle capabilities, GDI calls into the device to let it do the drawing and does not free the allocated memory.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article.

MORE INFORMATION

If the device does not have rectangle capabilities (for example, the standard VGA display driver), GDI performs the drawing and frees the memory. If an application is consuming GDI resources, run the application on a machine with a VGA display. If GDI resources are not being consumed on a VGA, then it is quite likely that the application has encountered this bug.

Under certain circumstances, the following Windows application programming interfaces (APIs) may encounter this problem:


   Drawing functions:
   <B>Arc</B>, <B>Chord</B>, <B>Ellipse</B>, <B>Pie</B>, <B>Rectangle</B>, <B>RoundRect</B>


   Region functions:
   <B>CreateEllipticRgn</B>, <B>CreateEllipiticRgnIndirect</B>, <B>CreateRoundRectRgn</B>

Third-party display-driver developers can avoid the GDI bug by not claiming rectangle capabilities in the display driver. Just do not set the PC_RECTANGLE bit in the dpPolygonals member of GDIINFO, and then rebuild the driver.

Applications developers can use several approaches to avoid the problem code. One approach is to create a memory device context (DC) and use it instead of the display DC in the GDI functions. When complete, BitBlt the memory DC to the screen DC. When using a compatible memory DC, the bug is avoided because GDI performs the drawing instead of the driver.

The following code fragment demonstrates this approach:


   hMemDC = CreateCompatibleDC(hDC);
   hBitmap = CreateCompatibleBitmap(hDC, width, height);
   hOldBitmap = SelectObject(hMemDC, hBitmap);
   PatBlt(hMemDC, 0, 0, width, height, WHITENESS);
   /***

   Use hMemDC in all the GDI functions
   .
   .
   .

   ***/ 

   BitBlt(hDC, 0, 0, width, height, hMemDC, 0, 0, SRCCOPY);
   SelectObject(hMemDC, hOldBitmap);
   DeleteObject(hBitmap);
   DeleteDC(hMemDC);

The functions PatBlt, MoveTo/LineTo, Polyline, and FillRect are safe alternatives to the drawing functions.

Additional query words: buglist3.10 3.10 8514.DRV 8514 VGA.DRV

Keywords : kbSDKWin16
Version : WINDOWS:3.1
Platform : WINDOWS
Issue type : kbbug