BUG: Graphics Operations Consume GDI Memory

• Microsoft Windows Software Development Kit (SDK) for Windows version 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 Microsoft Windows version 3.1. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

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:
   Arc, Chord, Ellipse, Pie, Rectangle, RoundRect

   Region functions:
   CreateEllipticRgn, CreateEllipiticRgnIndirect, CreateRoundRectRgn

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);