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From: jrv@demon.siemens.com (James R Vallino)
Newsgroups: comp.windows.ms.programmer
Subject: Does a window know when it is being overwritten?
Message-ID: <59847@siemens.siemens.com>
Date: 1 May 91 22:09:14 GMT
Sender: news@siemens.siemens.com
Reply-To: jrv@demon.siemens.com
Organization: Siemens Corporate Research, Inc.
Lines: 27

Continuing to persue my previous problem with an image processing task under
Windows, I have a much more Windows specific question.

Does a window know when it is being overwritten?  The potential exists
whenever the input focus is lost.  The focus will be lost whenever another
application is brought up on top of my client area.  This is also true when
my application brings up a dialog box.  For drop down menus and child windows
I don't think that is true.  I have control over when the child window will
appear.  I don't recall any message sent just before a menu is dropped.  The
basic problem is that before anyone overwrites part of my client display
memory, I have to save the pixels which will be overwritten.  I don't have
another copy of the pixel data.  It has been generated by a coprocessor on
the display card running some algorithms on my image data.  I could keep a
shadow copy of the data in extra memory on the display card.  But I will
still not know if it is OK for the display coprocessor to write the data to
the diplay area if I don't know that I own all of the pixels in my client
area.

I think I'm going to have to bag the idea of using Windows without adding
more cost to my display board to get some extra hardware support.

Thanks!
--
Jim Vallino	Siemens Corporate Research, Inc., Princeton, NJ
jrv@demon.siemens.com
princeton!siemens!demon!jrv
(609) 734-3331