Path: utzoo!attcan!telly!lethe!yunexus!ists!helios.physics.utoronto.ca!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!elroy.jpl.nasa.gov!jarthur!nntp-server.caltech.edu!toddpw
From: toddpw@nntp-server.caltech.edu (Todd P. Whitesel)
Newsgroups: comp.sys.apple2
Subject: Re: fast screen updates on the GS
Message-ID: <1991Feb22.052544.2267@nntp-server.caltech.edu>
Date: 22 Feb 91 05:25:44 GMT
References: <2556@kluge.fiu.edu>
Organization: California Institute of Technology, Pasadena
Lines: 44

acmfiu@serss0.fiu.edu (ACMFIU) writes:

>thinking that QuickDraw would "know" that it is NOT the same address as
>the screen ($e12000) and thus not add the extra overhead for writing directly
>to the screen.

What overhead? There is no overhead for writing directly to the screen other
than the slow writes to the $e1 buffer; they aren't the primary time waster,
however.

There IS a lot of overhead for drawing things that have to be clipped, which
is where people seem to be having problems. QuickDraw's region processing
is beastly slow, and since the window manager uses it extensively to draw
overlapping windows, accelerators become an attractive option.

Quickdraw itself doesn't care where the pixel map is, except for the cursor
routines and such. What you need to do is create an offscreen grafport
(do this with OpenPort and SetPortLoc) and draw your stuff into the offscreen
grafport. When you want to update your window, use PaintPixels or PPToPort.

Correct me if I'm wrong, but you want to reduce the number of times you
have to draw the objects you're displaying in the window. The method I
just described allows you to keep an offscreen image and issue a single call
to update your window, which is what I believe you are looking for.

>It seems that QuickDraw is not "smart" enough to figure this out. What in
>the world is so darn hard about making an off-screen GrafPort?

Nothing. On off-screen GrafPort is any GrafPort whose LocInfo field has been
replaced or modified -- I've studied the QD chapter and the tech notes
about it, and I think I'm beginning to understand what all is going on.
There's a tech note that will probably help you a lot -- I'll put it up on
tybalt.caltech.edu in pub/apple2/transfer; mail me if you don't have FTP.

> Maybe I don't fully understand QuickDraw because the manuals don't seem too
>enlightening to me.

There weren't too enlightening to me either. IIgs technote 80, QuickDraw II
Clipping, explains quite a bit and makes sense of the toolcalls you mentioned.
It's on tybalt now, and will be in pub/apple2/transfer by the time you read
this.

Todd Whitesel
toddpw @ tybalt.caltech.edu


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