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From: dlyons@Apple.COM (David A. Lyons)
Newsgroups: comp.sys.apple
Subject: Re: Elementary (I assume) Window programming question
Message-ID: <38777@apple.Apple.COM>
Date: 19 Feb 90 23:15:02 GMT
References: <9002161625.AA26906@tj.tis.com>
Organization: Apple Computer Inc, Cupertino, CA
Lines: 40

In article <9002161625.AA26906@tj.tis.com> lee@TIS.COM (Theodore Lee) writes:
>In my spare time I've been browsing through the toolbox references and
>TML examples, gearing myself up for doing some *REAL* programming.
>One thought has come to mind -- is there any usual way of updating
>windows without completely regenerating them?  Suppose you have a big
>window that took a lot of calculating to fill.  [...]

Someone else posted an answer to this last week, but I don't think they
answered the question you were really asking.  I think you're looking for
a technique like this:

Do your drawing to a QuickDraw port that isn't on the screen.  When your
window needs to be updated, copy part of the image from your offscreen
grafport to the window.  This way the time-consuming generation of the
image is just done when necessary.

To create an off-screen grafport, allocate 170 bytes of memory somewhere,
call OpenPort on it, allocate enough memory for your offscreen pixelmap,
set up a LocInfo record for your offscreen pixelmap, and use SetLocInfo
to cram that LocInfo record into your port.  (You may want to do a big
EraseRect to clear your offscreen pixel map to the port's background
pattern; I don't remember whether the background pattern is initialized
to white for you with OpenPort or whether you have to set it yourself
first.)

When your window's content-draw procedure gets called, just do a
PPToPort from the offscreen pixel map to the window (which is the
current port, conveniently enough).

If you need to make changes to the window's contents, do the drawing in
the offscreen port and do an InvalRect or InvalRgn on the window to force
an update.  (Or do the same drawing over again in both ports.  Whatever.)
-- 
David A. Lyons, Apple Computer, Inc.      |   DAL Systems
Apple II Developer Technical Support      |   P.O. Box 875
America Online: Dave Lyons                |   Cupertino, CA 95015-0875
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My opinions are my own, not Apple's.