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Path: utzoo!watmath!clyde!rutgers!uwvax!puff!schumann
From: schumann@puff.UUCP
Newsgroups: comp.sys.apple
Subject: Re: IIe split screen query.
Message-ID: <487@puff.WISC.EDU>
Date: Thu, 12-Feb-87 23:02:57 EST
Article-I.D.: puff.487
Posted: Thu Feb 12 23:02:57 1987
Date-Received: Fri, 13-Feb-87 23:11:48 EST
References: <630004@ui3.UUCP> <21600001@silver> <888@ihlpm.UUCP>
Organization: U of Wisconsin CS Dept
Lines: 46

jmdavis@ihlpm.UUCP (Davis) writes:
> Just so the old folklore of the Apple doesn't die I thought I would
> mention a program by {{Bob}} Bishop   where a living room with TV
> is drawn and a man appears on the tiny TV screen and dances.  This
> program used a special timing loop to flip back to the text page
> from the graphic page so that SINGLE CHARACTERS on the text page
> could be displayed on the graphic page.
> 			Mike Davis

Wrogo, Mike!

I have studied that program in depth, and (with a little help from
Apple's book about this and other PD programs they used to give away),
I have determined that he uses a Hi Res Character generator.
I have even taken out the HRCG, and made it work with other programs.
It does not scroll the screen, which limits it, but that is a very slow
process in hi res.  The program is in Integer BASIC, with parts in
machine language (disguised in the program).

If you look at the program after it runs, you will see a POKE 54,
{something}:POKE 55,{something else}.  This makes all characters
printed go through his HRCG routine.

It is not possible to access the page switches fast enough to display
the width of a single character.  The minimum width is 1/4 (maybe
1/6) of the screen.

On the //c and maybe //e, you can get an interrupt every screen
refresh.  So you can wait a while then flip pages, therby making the
border between graphic and text (or lores and hires) anywhere
VERTICALLY on the screen you like. (But disk accesses disable
interrupts).  This may absorb quite a bit of cpu time...

Interrupt, wait 1/200 second, flip switch, RTI.  This could be as
much as 3% of clock cycles if there is a lot of overhead, such as
a //c with ProDOS (both have interrupt handlers).

An HRCG would slow down throughput, but not computation time, and
the screen flipper is tricky to write, anyway.

I hope this starts some discussion......

---------------
"It...  It's your hand Buckaroo." -- Akita

Chris Schumann			schumann@puff.wisc.edu