Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cwjcc!gatech!mcnc!kk
From: kk@mcnc.org (Krzysztof Kozminski)
Newsgroups: comp.sys.mac.programmer
Subject: Usefulness of off-screen ports (was: turning on a pixel)
Message-ID: <1357@speedy.mcnc.org>
Date: 25 Aug 89 12:31:51 GMT
References: <6294@hubcap.clemson.edu> <227700031@uxa.cso.uiuc.edu> <30894@ucbvax.BERKELEY.EDU>
Reply-To: kk@mcnc.org.UUCP (Krzysztof Kozminski)
Organization: Microelectronics Center of NC; RTP, NC
Lines: 23

In article <30894@ucbvax.BERKELEY.EDU> oster@dewey.soe.berkeley.edu.UUCP (David Phillip Oster) writes:
>Conclusion: directly bit-twiddle an off-screen bitmap, then call CopyBits
>to display it for you. It will save you much present pain, and still more
>future pain.

One more thing it may do is to speed up the screen refresh times.  From
my experiments, drawing rectangles and line segments into a bitmap that
has rectangular clipRgn and visRgn is ~30% faster than doing the same
drawing into a bitmap with either of these regions composed of two
abutting rectangles (as you're likely to have if your window has its
corner overlapped by another window).

In one case, I managed to get 60-fold speedup of drawing (yup, that's
sixty) by drawing into off-screen pixmap (with my own routines - no
QD calls since I knew I did not have to clip anything and needed
a nonstandard color merging mode) and then CopyBiting it.

Summary: Off-screen bitmaps are great!

KK
-- 
Kris Kozminski   kk@mcnc.org
"The party was a masquerade; the guests were all wearing their faces."