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Q151921: PRB: LoadBitmap GPFaults on Compressed Bitmaps in Windows 3.1

Article: Q151921
Product(s): Microsoft Windows Software Development Kit
Version(s): WINDOWS:3.1
Operating System(s): 
Keyword(s): kbOSWin310 _IK kbSDKWin16
Last Modified: 16-JUL-1999

3.10
WINDOWS
kbgraphic kbprb

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The information in this article applies to:

- Microsoft Windows Software Development Kit (SDK) 3.1 
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SYMPTOMS
========

Calling LoadBitmap from an application causes a General Protection Fault (GP)
Fault when attempting to load a compressed bitmap.

CAUSE
=====

There is a problem with the way the Windows 3.x standard VGA driver handles
compressed bitmaps. When a bitmap is saved as compressed, non-VGA drivers tend
to leave the biClrUsed member of the BITMAPINFOHEADER at zero. This behavior
causes the VGA driver to GPF as it tries to load the bitmap because the VGA
driver attempts to decode the color table as though it were RLE encoded data.
This can easily lead to running off the end of the data.

RESOLUTION
==========

One work around would be to use uncompressed bitmaps. However, if compression is
absolutely necessary, another way would be to save the bitmap compressed using
the VGA driver so the biClrUsed member of the BITMAPINFOHEADER structure is
properly set to the number of colors in the color table. Every other driver that
then attempts to load the bitmap should be able to do so successfully.

STATUS
======

This behavior is by design.

MORE INFORMATION
================

Applications typically save images in compressed format in order to save space.
This behavior can be accomplished in Microsoft Visual C++ version 1.52 by
loading the bitmap in App Studio, selecting the Resource.Properties menu item
and checking the "Save Compressed" checkbox.

Additional query words: 3.10

======================================================================
Keywords          : kbOSWin310 _IK kbSDKWin16 
Technology        : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK310
Version           : WINDOWS:3.1
Issue type        : kbprb

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