Path: utzoo!mnetor!uunet!husc6!endor!stew
From: stew@endor.harvard.edu (Stew Rubenstein)
Newsgroups: comp.sys.mac.programmer
Subject: Re: MF compatibility using both screen buffers
Message-ID: <4261@husc6.harvard.edu>
Date: 21 Mar 88 01:47:34 GMT
References: <2145@polya.STANFORD.EDU> <7669@apple.Apple.Com> <2155@polya.STANFORD.EDU>
Sender: news@husc6.harvard.edu
Reply-To: stew@endor.UUCP (Stew Rubenstein)
Organization: Aiken Computation Lab Harvard, Cambridge, MA
Lines: 25

In article <2155@polya.STANFORD.EDU> rwilson@polya.UUCP (Randy Wilson) writes:
>>Note that this is only a problem on MacPlus and SE; the page flipping on the
>>MacII is done differently (since you have to access the video driver on the
>>card directly).
>
>Luckily, the speed of the MacII makes page flipping unnecessary.  I have
>time to draw in an offscreen bitmap and CopyBits it into a window,
>making compatibility much easier.  Just for interest's sake, is there a
>second page on the MacII, and how would one get at it?

You can't CopyBits a full-window 4-bit-deep PixMap onto the screen in
less than the refresh time, so if you don't want annoying artifacts,
you have to page-flip.  It is possible; it is done with Control calls
to the video driver.  See the "Cards and Drivers" book for details.  I
don't have mine in front of me, but a fully loaded Apple video card
has 512Kb, and there are 640*480 = 300K pixels.  Therefore, there is
enough memory for 1 8-bit page, 3 4-bit pages, 6 2-bit pages, or 13
1-bit pages.  Other video boards ought to support the same control
calls, but I haven't tested them.


Stew Rubenstein
Cambridge Scientific Computing, Inc.
UUCPnet:    seismo!harvard!rubenstein            CompuServe: 76525,421
Internet:   rubenstein@harvard.harvard.edu       MCIMail:    CSC