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Date: 2 Jun 89 14:28:54 GMT
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Date: 02 June 1989, 11:16:40 MES
From: Julian F. Reschke         (0251) 861 241       ONM07    at DMSWWU1A
To:   info-ata at score

I've received a lot of questions about my program BigScreen.

The program originally was published in "ST-Magazin", issue 11/1988
-- but is nevertheless free. I'll try to summarize the most
important points in this article using my broken english...


-----
Usage
-----

BigScreen HAS to be placed into the AUTO-folder. It can be
configured by holding down Control, Shift, Alternate or
CapsLock during startup. Using '+', '-', '*' and '/', you
can change the desired screen resolution (BigScreen displays
the setting for the three resolutions). Press any other key
to continue. SPACE continues without saving the new configuration,
RETURN does it (the new settings are saved directly into the
program file -- no parameter file, no installation program!).

Error messages:

"BigScreen not installed"
BigScreen was not installed, because you have selected the
standard ST-resolution.

"Configuration saved..."
BigScreen has saved the new settings.

"BigScreen installed..."
BigScreen did install without errors.

"File \auto\bigscrn.prg not found."
BigScreen couldn't find the program file to save the new
settings.

"Can't write to program file."
BigScreen wasn't able to write the new settings into the
program file.

"[trying to fix problems with old TOS versions...]"
When using TOS-versions <1.4, BigScreen allocates a safety
buffer to prevent crashes caused by the addressing bugs
in the line-a-routines. Ignore (see tech. information)!

-------------------------
What to do with BigScreen
-------------------------

BigScreen is fine for using properly programmed GEM-applications
on larger screens -- especially if the window updating is slow
(use larger windows...). But it's main purpose is to help
programmers to write proper GEM-applications without having
to buy a SM 194/MatScreen/Moniterm.


--------------------
The name of the game
--------------------

BigScreen patches some negative line-a-variables when the AES
does his v_opnwk()-call. These variables are documented in
S.A.L.A.D. (and in my book 'Atari ST Profibuch', Sybex Germany).

When using a 'normal' horizontal resolution (ie 640 in High- and Med-
Rez and 320 in Low-Rez), scrolling is done directly by the hardware
(via the screen base register).

When using a wider screen, BigScreen allocates a 'virtual'
screen and copies it during VB into the physical screen
memory (nice example for the difference between physbase
and logbase!!!). I've tried to do my best, but in this
mode BigScreen will slow down the machine significantly.

The horizontal resolution can only be changed in steps of
16 Bytes, because the BIOS relies on BYTES_PER_LINE to be
a multiple of 16 (Leonard promised to fix this in the final
release of TOS 1.4).

Problems with older TOS-versions: The line-a-routines of TOS 1.0
can't handle screens bigger than 32768 Bytes, so BigScreen will
not be of any use on this obsolete OS-version. In TOS 1.2,
there is still a problem -- the sprite functions (used for the
mouse-pointer) use short-adressing. I've solved this
problem by pirating the routine from TOS 1.4, which works well.

All pointers are changed using the XBRA-protocol, which is very
popular in Germany. It's an extension of an older idea of
Moshe Braner (it's documented in the Profibuch and some german
computer magazines).

When using BigScreen, there is naturally no point using
ALT-HELP to print the screen. Instead, I've inserted
a function that *tries* to save the screen image as IMG-file
on the boot drive (monochrome only). However, doing Gemdos-calls
from the VBI isn't save, so I guarantee for nothing.

The actual version is 1.1.


---------------
Copyright notes
---------------

BigScreen is free, as long it is NOT used commercially. However,
I'd be happy to get applications developed with the help of
BigScreen (and I REQUEST commercial sofware developers to send
a copy of the finished program), other donations and -- suggestions.

Here's my snail mail address:

Julian F. Reschke
Contributing editor of 'ST-Magazin'
Hensenstrasse 142
D-4400 Muenster
F.R.G.

   Tel.: 0251/861241
Mailbox: Maus Muenster, 0251/80386