Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!asuvax!ncar!tank!eecae!netnews.upenn.edu!vax1.cc.lehigh.edu!vlsi3b15!batman!nicholaA
From: nicholaA@batman.moravian.EDU (Andy Nicholas)
Newsgroups: comp.sys.apple
Subject: Re: Problems for a new IIGS owner (II)
Summary: It doesn't _really_ draw
Message-ID: <649@batman.moravian.EDU>
Date: 22 Nov 89 10:49:28 GMT
References: <1137@godot.radonc.unc.edu> <113300158@uxa.cso.uiuc.edu>
Organization: Moravian College, Bethlehem, PA
Lines: 36

In article <113300158@uxa.cso.uiuc.edu>, krb20699@uxa.cso.uiuc.edu writes:

>      There is, in fact, a demo out that draws on the frame, with animation,
> 16 levels of color, flicker-free, fast, and in sync with the main screen,
> all in SHR mode.  It is definitely possible to 'draw' on the frame in many
> colors and animate.  BUT, because the GS does not directly support it, it's
> a real hard thing to program.
>      By the way, the demo I'm talking about is the _ACS Demo_ mentioned on
> this feed awhile back.

Uh, not really.  The only way that you can change the border color is to
momentarily change the border color register (bits 0-3 of $00/C022).  If you
leave the color in the background color register set at a certain value
(a certain color in other words) for at least 1/60th of a second, that
color will show up on the screen.  This would only work if you wanted to make
the entire line of background a certain color.

Alternately, you could watch the Mega II register, HORCNT, to see when the
value changes to being in the border.  The only problem with try to do that is
that horcnt (at $00/C02F) changes it's values to cycle through $00,$40,$41,
$42,...,$7E,$7F,$00,$40,$41.. and so on.. every 980 nanoseconds with the
active video time being 40 one microsecond clock cycles starting with
$58 and ending with $7F.  All you'd have to do is see when the video register
is in the border area of a single side and then change the border color.
The main problem with this is that it happens rather fast...

> 							Ken.

If I missed something, let me know.

andy

-- 
Andy Nicholas             GEnie, AM-Online: shrinkit
Box 435, Moravian College       CompuServe: 70771,2615
Bethlehem, PA  18018              InterNET: shrinkit@moravian.edu