Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!ucbvax!dewey.soe.berkeley.edu!oster
From: oster@dewey.soe.berkeley.edu (David Phillip Oster)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Alternate screen buffer ... How?
Message-ID: <29681@ucbvax.BERKELEY.EDU>
Date: 15 Jun 89 02:30:38 GMT
References: <8042@cc.nu.oz> <4656@ucdavis.ucdavis.edu>
Sender: usenet@ucbvax.BERKELEY.EDU
Reply-To: oster@dewey.soe.berkeley.edu.UUCP (David Phillip Oster)
Organization: School of Education, UC-Berkeley
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In article <4656@ucdavis.ucdavis.edu> heberlei@iris.ucdavis.edu (Todd) writes:
>	* what it is
You point the video controller at a different block or RAM on the MacPlus,
and earlier machines. Newer machines, particularly MacII and up don't have
one.
>	* where to find info on it
The Segment Loader chapter of the phone book addition of inside macintosh
tells how to issue a Launch system call to get it.
>	* maybe a short piece of code showing how to use it
Since it is not compatible with the RAM Cache, System 7 and future, nor
with newer Macintoshes, it seems like a WOMBAT:
Waste Of Money Brains And Time.
>[I currently draw in an offscreen buffer and CopyBits onto the screen]
This is already about the best you can do, espically as some of the newer
video boards on the Mac II have such large video memory that they have to
flip the system into 32-bit mode during the CopyBits, then flip it back to
24-bit afterward. This means the base address stored in the PixMap isn't
even valid in 24-bit mode, so you can't just decode the data structures
and twiddle the screen bits directly.