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From: info-mac@uw-beaver
Newsgroups: fa.info-mac
Subject: InvalRect()
Message-ID: <501@uw-beaver>
Date: Thu, 24-Jan-85 05:19:55 EST
Article-I.D.: uw-beave.501
Posted: Thu Jan 24 05:19:55 1985
Date-Received: Fri, 25-Jan-85 07:32:35 EST
Sender: daemon@uw-beaver
Organization: U of Washington Computer Science
Lines: 23

From: Randy Schulz <lcc.randy@UCLA-LOCUS.ARPA>

The window manager documentation states that unless the global location
paintWhite is cleared, InvalRect() or InvalRgn() -ing part of your
window should cause the invalidated rectangle to be automatically
painted white before it gets redrawn.  Though I'm sure the manual is
correct, my recent experience leads me to disbelieve this.  When I need
to move an object on the screen, I InvalRect() the area it currently
occupies.  If I do not also call EraseRect() on the same rectangle, the
old image is not erased before (or after) the newly placed one is drawn
in response to the update event.  Can I assume that I do not need to
erase any part of the screen before I draw in response to an update
event?  If so, why might it be that I don't appear to get the update
region erased automatically?  I am properly calling BeginUpdate()
before I redraw the window and EndUpdate() immediately afterwards.
Any help will be appreciated.

					Randy Schulz
					Locus Computing Corp.
					lcc!randy@ucla-cs
				  trwrb!lcc!randy
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