CMEMDC.EXE Memory Bitmap for Scrolling in CScrollV
ID: Q151856
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The information in this article applies to:
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The Microsoft Foundation Classes (MFC), used with:
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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. Click the file names below to download the files:
Cmemdc.exe
For more information about how to download files from the Microsoft
Download Center, please visit the Download Center at the following Web
address
http://www.microsoft.com/downloads/search.asp
and then click How to use the Microsoft Download Center.
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 kbsample kbnokeyword kbDocView kbMFC kbVC
Version : winnt:4.0,4.1
Platform : winnt
Issue type :