Q180330: PRB: InvalidateRect() Yields Empty Update Region on Win95/98/Me

Article: Q180330
Product(s): Microsoft C Compiler
Version(s): 5.0,6.0
Operating System(s): 
Keyword(s): kbGDI kbMFC KbUIDesign kbVC500 kbVC600 kbOSWin95 kbOSWin98 kbWndw kbGrpDSMFCATL
Last Modified: 20-OCT-2001

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The information in this article applies to:

- The Microsoft Foundation Classes (MFC), used with:
   - Microsoft Visual C++, 32-bit Enterprise Edition, versions 5.0, 6.0 
   - Microsoft Visual C++, 32-bit Professional Edition, versions 5.0, 6.0 
   - Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
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SYMPTOMS
========

The Win32 InvalidateRect() function, or the MFC function with the same name,
does not invalidate any region on Microsoft Windows 95, Windows 98, or Windows
Millennium Edition (Me), even though the function's return value is nonzero. A
call to GetUpdateRect() afterwards returns a null rectangle, as well as a return
value of zero. The same code works correctly on Microsoft Windows NT 4.0 and
Windows 2000.

CAUSE
=====

InvalidateRect(), or the MFC function that wraps it, behaves differently
depending on whether you use it on Windows 95, Windows 98, Windows Me, Windows
NT 4.0, or Windows 2000. On Windows NT 4.0 and Windows 2000, InvalidateRect()
will accept a pointer to a non- normalized RECT and invalidate a region as if
the RECT were normalized. Windows 95, Windows 98, and Windows Me require that
the RECT be normalized to use it successfully with InvalidateRect().

RESOLUTION
==========

You can normalize the RECT yourself, or use the MFC function
CRect::NormalizeRect() on the RECT whose pointer you are passing to
InvalidateRect(). To normalize a RECT, you must compare the top and bottom
values, and swap them if the top is greater than the bottom. In addition, you
must swap the left and right values if the left is greater than the right.

STATUS
======

Microsoft is researching this problem and will post new information here in the
Microsoft Knowledge Base as it becomes available.

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

A non-normalized rectangle can often be produced unintentionally if you use
mapping modes other than MM_TEXT. MM_HIENGLISH, MM_LOENGLISH, MM_HIMETRIC,
MM_LOMETRIC, and MM_TWIPS cause the y-axis to have the reverse direction of that
for the default mapping mode (MM_TEXT). This can result in non- normalized
RECTs. In addition, you can set up the two "custom" mapping modes (MM_ISOTROPIC
and MM_ANISOTROPIC) so that either the y-axis or x- axis, or both, are reversed
from that in MM_TEXT. You can produce non- normalized RECTs by using functions
such as LPtoDP or DPtoLP when using a mapping mode other than the default.

Please also note that InvalidateRect uses client area device coordinates, not
logical coordinates. This is by design.

Additional query words: Invalid Update

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Keywords          : kbGDI kbMFC KbUIDesign kbVC500 kbVC600 kbOSWin95 kbOSWin98 kbWndw kbGrpDSMFCATL 
Technology        : kbAudDeveloper kbMFC
Version           : :5.0,6.0
Issue type        : kbprb

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