Many ST owners who have managed to attach their
computer to a colour monitor should by now have obtained a free copy
of the Atari 'public domain' low resolution graphics design program,
Neochrome. If not, stop reading this article, call your dealer and
demand a copy NOW, it's excellent, probably better than anything
you've used before ... and it's free!
A large proportion of those who have obtained
Neochrome are also likely to have purchased a copy of Degas - a
multimode graphics design program by Batteries Included. The many
features of Degas include a first class font designer, very useable
zoom, user designed fills and extensive shape drawing commands. Both
programs are far better than anything possible on 8 bit machines,
but both have their own individual benefits and weaknesses, and
sadly there is a fundamental difference between the format of each
program's saved screen that does not allow any compatibility between
the two.
The DEGAS disk does contain a conversion program
to enable Neo-Chrome screens to be converted to a DEGAS format, but
there is no comparable program to allow conversion in the opposite
direction. It is this conversion that has proved far more useful to
the writer, for instance in producing a graphic outline and any text
content using the full screen, zoom and text facilities of DEGAS,
then convert and paint with Neo-Chrome making full use of that
program's ease of colour selection with dynamic colour scrolling.
Close investigation of the two screen formats
revealed the information shown in the accompanying boxes and it was
then decided to write the short conversion program listed here, in
ST BASIC since this is the only language that is universally
available to ST users at all levels.
The utility as listed is a very bare bones program
with plenty of scope for expansion and improvement by readers, but
which will also work perfectly well without any alteration. When the
program is running don't move the mouse or it will show itself on
the newly converted screen. Also remember that there is no error
checking on filenames of the pictures to be converted, so make sure
that you don't overwrite you original screen.
When running the program, you are asked for the file name of the
DEGAS screen to be converted. Make sure it has the extension 'PI1'
and when you are asked for the file name for the converted screen to
be saved under, it should have the extension 'NEO'. Any colours
selected from DEGAS (though remember it is far easier to select
colours with NeoChrome!) are maintained throughout the conversion,
but for safety's sake it is always best to carry out any conversions
on a copy of your original screen. This program will, of course,
only work with screens saved in the Low Resolution mode of DEGAS but
the actual program can be typed and run in monochrome if it proves
more convenient.
Type in the BASIC program listing and remember to
save it before running. It is also advisable to have a disk
available containing your DEGAS screen and more than 33,000 bytes
free.
NEOCHROME SCREENS
These are always 32,128 bytes long. 32,000 bytes
are the actual screen RAM of the picture and the other 128 bytes
contain information about the colour rotation pointers and colours.
These bytes are at the head of the screen file and are best
considered in terms of 16 bit words.
| Words 0 to 1 |
colour rotation pointers(?) |
| Words 2 to 7 |
colours
in the form of $abcd where
a =
0 (always)
b = 0 to 7 (red level)
c = 0 to 7 (green level)
d = 0 to 7 (blue level)
(0070
=green, 0777 = white) - if this sounds familiar, think about
the Control Panel! |
| Words 18 to 23 |
form a null file name of 8
spaces, a dot and three further spaces i.e. 2020 2020 2020
2020 2E20 2020) |
| Word 24 |
$801E (haven't a clue on this
one?) |
| Words 25 to 63 0000 |
(likewise) |
| Finally 32,000 bytes
of picture information follow. |
DEGAS SCREENS
These are always 32,034 bytes long. 32,000 bytes
are the actual screen RAM of the picture and the other 34 bytes
contain information about the mode and colours. These bytes are at
the head of the screen file and again are best considered in terms
of 16 bit words.
| Word 0
|
mode,
0000 1 = Low resolution (.P11)
0001 = Medium resolution (.P12)
0002
= High resolution (.P13) |
| Words 1 to 16 |
define
colours, these are in the form of $abcd where
a = 0 (always)
b = 0 to 7 (red level)
c = 0 to 7 (green level)
d =
0 to 7 (blue level) |
| Finally 32,000 bytes
of picture information follow. |
List of \DEGNEO.BAS
10
openw 2
20 fullw 2
30 clearw 2
40 print "Converting from DEGAS to NEOCHROME."
50
print
60 input "Please enter file to be converted..",ip$
70 input "Please enter the new filename..",op#
80 bload ip$,&h7805e
90 for n%=1 to 16
100 word%=peek(&h7805e+2*n%)
110
poke &h78002+2*n%,word%
120
next n%
130 poke &h78000,0
140 poke &h78002,0
150 poke &h78024,&h2O20
160
poke &h78026,&h2020
170
poke &h78028,&h2020
180
poke &h7802a,&h2020
190
poke &h7802c,&h2e20
200
poke &h7802e,&h2020
210
poke &h78030,&h801e
220
for n%=1 to 39
230 poke &h78030+2*n%,&h0000
240 next n%
250
bsave op$,&h780OO,32128
260
clearw 2
270
end
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