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From: dseah@wpi.wpi.edu (David I Seah)
Newsgroups: comp.sys.apple
Subject: Re: Problems for a new IIGS owner (II)
Message-ID: <5659@wpi.wpi.edu>
Date: 16 Nov 89 21:16:18 GMT
References: <1137@godot.radonc.unc.edu>
Reply-To: dseah@wpi.wpi.edu (David I Seah)
Organization: Worcester Polytechnic Institute, Worcester, MA. USA
Lines: 51

In article <1137@godot.radonc.unc.edu> rosenman@godot.UUCP (Julian Rosenman) writes:
>I want to thank all of you who answered the questions under "Problems
>for a new IIGS user." However, one of the questions apparently
>confused a lot of you. I asked if the "frame" (the area that surrounds
>the text area) could be changed (i.e. written to) OTHER THAN THE
>BACKGROUND COLOR. Most of you wrote to tell me that I could change the
>color via the control panel. We all know that. Some answered that the
>frame could not be changed, that it was "cast in stone" (I assume this
>means in hardware), "cast in ROM" (does this mean that with a change
>in ROM this area might be accessible in the future?) or "requires
>tricky interrupt handeling" (does this mean that we could write into
>the frame if we were very clever?).

Oops, sorry for the misunderstanding.  I guess when I saw the subject title, I
assumed the worst :-) Anyway, let me say that as far as I know, the screen
border can not be changed to a color other than those defined in the control
panel.  The color of the background, border, and text is definable through a
(couple of?) hardware register(s) whos addresses I don't have handy at the
moment.  There are only a limited number of settings possible.  I don't know
if the colors are hardcoded into the VGC or lurking somewhere in ROM.

You can't write into "the frame", but some games have done some tricks with
it, most notably Tomahawk GS.  There is a register that contains the number of
the current scanline being written.  One could conceivably watch this register
very closely and change the border color on an arbitrary scanline.  The result
would be a two-color border split horizontally across the screen.  If you are
using Super Hires Graphics, you can also set a scanline control byte to
generate an interrupt whenever a particular scanline is drawn.  Your
interrrupt handler could change the border color.  So, you have limited
control over the border, but you would have to choose SHR colors that matched
a border color to get that glorious wide-screen effect. 

Since there is no memory associated with the border color, you wouldn't be
able to draw in the border.  My impression is that the border color is a VGC
bonus function (more exciting than blanking the edges, I suppose).  

I can feel Dave Lyons ready to clarify/correct these points with a hearty
quote from Tech Note #something 8-)

>It seems to me that part of the fun of the Apple II line is finding
>ways to make the machine do things that Apple never intended it to do.
>Writing into the frame would be in the spirit of the thing, as well as
>providing lot of extra pixels which are always in short supply.

I agree!  Like survive for ten+ years!  (a joke!  a joke!) BTW, there's this
chip called the TMS34070 Color Pallete chip which duplicates an awful lot of
the IIGS's graphics modes (it's uncanny...16/4096, even supports fill mode!). 
It uses video RAM and supports some overlaying capability.
-- 
Dave Seah | O M N I D Y N E  S Y S T E M S - M |   Internet: dseah@wpi.wpi.edu 
          |   User Friendly Killing Machines   |   America Online: AFC DaveS
   "MY GOD! I HAVE POCKETS!!! I CAN'T BELIEVE IT! I HAVE POCKETS!!" - Tick