Microsoft KB Archive/156696

{|
 * width="100%"|

BUG: EMF Playback into DC Causes Memory Leak in GDI

 * }

Q156696

-

The information in this article applies to:


 * Microsoft Win32 Software Development Kit (SDK), on platform(s):
 * the operating system: Microsoft Windows 95
 * the operating system: Microsoft Windows 98

-

SYMPTOMS
In Windows 95 and Windows 98, when calling PlayEnhMetaFile with a non-NULL clipping region selected into the DC, GDI fails to free a copy of the clipping region it creates, thereby causing a memory leak. This leaked resource is a system resource and will not be freed when the application exits.

CAUSE
When RestoreDC is called, it copies the hMetaRgn value in the saved block over the hMetaRgn value in the hDC. If the value in the save block is NULL and the value in the hDC is not, the only reference to that region is lost and the region is not freed. Instead, RestoreDC should check for the above case and free the region.

When PlayEnhMetaFile is called, it calls the following functions: SaveDC, SetMetaRgn, play EMF records, and RestoreDC. This creates the hMetaRgn if there is a clipping region in the hDC, and then fails to release it.

RESOLUTION
To work around this problem, render the Enhanced Metafile (EMF) unclipped to a bitmap, and BitBlt the image to the screen.

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

Steps to Reproduce Problem

 * 1) Take the GEN32 sample application and add code to open an .EMF and play it on the screen 10,000 times, each time with a region selected into the DC:
 * 2) Use any utility to watch the GDI Resources.
 * 3) Start the modified Gen32 created in step 1. Load the enhanced metafile and draw it 10,000 times. Notice that the gdi resources go down considerably.

Additional query words: 4.00 kbdsi

Keywords : kbnokeyword kbSDKWin32 kbDSupport

Issue type :

Technology : kbWin32SDKSearch kbAudDeveloper kbSDKSearch kbWin32sSearch