KnowledgeBase Archive

An Archive of Early Microsoft KnowledgeBase Articles

View on GitHub

Q151856: CMEMDC.EXE Memory Bitmap for Scrolling in CScrollV

Article: Q151856
Product(s): Microsoft C Compiler
Version(s): winnt:4.0,4.1
Operating System(s): 
Keyword(s): kbfile kbDocView kbMFC kbVC kbGrpDSMFCATL
Last Modified: 06-MAY-2001

-------------------------------------------------------------------------------
The information in this article applies to:

- The Microsoft Foundation Classes (MFC), used with:
   - Microsoft Visual C++, 32-bit Editions, versions 4.0, 4.1 
-------------------------------------------------------------------------------

SUMMARY
=======

Scrolling a complex image in a CScrollView can be very slow and jerky since
OnDraw() is called for every WM_VSCROLL and WM_HSCROLL message. While only part
of the window is invalidated and redrawn, the whole painting code gets called
every time.

This CMemDC sample demonstrates drawing to a memory bitmap instead of the screen.
The complex, time-consuming drawing code only needs to be performed when the
image changes and in OnInitialUpdate(). During OnPaint(), the only work that
needs to be done is a simple BitBlt from the memory bitmap to the screen.

The sample code draws a complex pattern on its client area. A menu option toggle
allows the user to see the speed difference between using and not using the
offscreen bitmap. Printing and print preview are supported through the normal
printing code, and do not use the memory bitmap.

While CMemDC is a 32-bit sample, the same technique can be used in 16-bit MFC
applications.
The following files are available for download from the Microsoft Download
Center:

Cmemdc.exe

For additional information about how to download Microsoft Support files, click
the article number below to view the article in the Microsoft Knowledge Base:

  Q119591 How to Obtain Microsoft Support Files from Online Services

Microsoft used the most current virus detection software available on the date of
posting to scan this file for viruses. Once posted, the file is housed on secure
servers that prevent any unauthorized changes to the file.


NOTE: Use the -d option when running CMEMDC.EXE to decompress the file and
recreate the proper directory structure.

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

This sample is a MFC implementation of the Windows SDK sample, MemDC. For more
information, please see the following article in the Microsoft Knowledge Base:

  Q130805 SAMPLE: Drawing to a Memory Bitmap for Faster Performance

Additional query words: 4.00 4.10

======================================================================
Keywords          : kbfile kbDocView kbMFC kbVC kbGrpDSMFCATL 
Technology        : kbAudDeveloper kbMFC
Version           : winnt:4.0,4.1

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.