EVERYTHING YOU EVER WANTED TO KNOW ABOUT GDOS (AND MORE)
by Douglas N. Wheeler
WHAT IS GDOS?
GDOS is an extension to GEM which adds new capabilities to
your ST. GDOS is available with many commercial Atari programs,
as well as to registered Atari developers ($500 if it is to be
distributed with a product, free if it is not going to be
distributed).
The three primary new capabilities are:
1. The ability to use multiple fonts in various point sizes
on the screen, printer, and other output devices.
2. Allows the creation of metafiles, which are standardized
files intended to be usable by many different applications. This
allows files created in one program to be used in another.
3. Support for various output devices with resolutions up
to 32,767 x 32,767 (including emulation of this resolution on the
screen). This allows graphics to be printed at the highest
resolution of the output device.
HOW TO USE GDOS
In theory, using GDOS is as simple as putting GDOS.PRG in
your AUTO folder and booting the computer. In practice, though,
a series of conditions must be met. The most important of these
conditions is that there must be a valid ASSIGN.SYS file present
in the root directory of the boot disk.
The following is a typical ASSIGN.SYS file.
As you can see, I have divided the file into distinct
groups. The first line of the ASSIGN.SYS file is used to tell
GDOS where the fonts and device drivers are located. This line
must always start with PATH= which is followed by a pathname of
up to 64 characters locating the fonts and drivers.
Following the path identifying line is the list of device
drivers and their associated fonts. Each group is composed of
four parts. First if a number representing the type of device:
The Atari STs have four built-in device drivers, they are:
01 Default screen (used when an application doesn't care
about the screen resolution)
02 Low resolution screen
03 Medium resolution screen
04 High resolution screen
Immediately following the device number may be a "load flag"
of either "p" or "r". A "p" indicates that the device driver is
"p"ermanent and does not need to be loaded by GDOS. Because the
ST has it's screen drivers built into ROM, there will be a "p"
after devices 01-04. An "r" indicates that the device driver
should be kept "r"esident, causing GDOS to load the device driver
immediately and hold it in memory. If a load flag is not
present, GDOS will only load the device driver when an
application opens (accesses) that device.
After the device number and load flag is the filename of the
device driver as it appears in the disk directory. In the case
of ROM-resident drivers, the filename is only a place-holder (but
must be present). Keep in mind that the device driver must be in
the folder specified in the path line.
On the lines following those three items is a list of fonts
associated with that device (again, these are the filenames as
they appear in the indicated path of the disk).
You may have noticed a few lines with semicolons (;) in
them. GDOS will treat any text on a line to the right of a
semicolon as a comment and will ignore it.
Some ASSIGN.SYS files have a device 00 (00p SCREEN.SYS).
This can help prevent incompatibilities between GDOS and some
older (pre-GDOS) programs. On the other hand, including it can
cause other problems. It is suggested you leave it out unless
absolutely necessary.
EDITING/CREATING ASSIGN.SYS
Now, why would you want to change your ASSIGN.SYS file?
Well, if you have just one program which uses GDOS, and you are
happy with the fonts you have, then there is no reason to change
it. But, now that GDOS is beginning to be used more on the ST,
many of us are acquiring a collection of GDOS applications and
fonts. By editing or creating a new ASSIGN.SYS, you could create
a "universal" ASSIGN.SYS and font/driver folder to be used with
all of these programs!
Luckily, the ASSIGN.SYS file is a standard text (ASCII) file
which may be edited with most text editors and word processors.
The only requirement is that the file does not contain any
formatting codes. This can usually be accomplished in a word
processor by turning document mode off, or selecting "Save as
text" (check your word processor manual for exact instructions
for doing this). If you are using a text editor, such as
MicroEmacs or Tempus, there shouldn't be any special saving
techniques.
Starting at the top, the first thing you may want to change
is the PATH= line at the beginning of the ASSIGN.SYS file. By
changing this line, you can put your fonts and printer drivers on
another disk or hard drive partition (instead of your boot disk).
If you are using floppies, keep in mind that this directory
(folder) must be present when an application accesses any of the
GDOS devices. Also, to speed booting, this directory should be
present when GDOS is loaded.
Below is a list of my recommended configurations based on
what arrangement of disk drives is being used.
One floppy drive:
Boot disk (drive A) with:
AUTO folder containing GDOS.PRG
GDOS.SYS folder containing the fonts and drivers
ASSIGN.SYS with PATH=A:\GDOS.SYS
Any GDOS application(s) (you may wish to create
separate boot disks for each GDOS
application)
Two floppy drives:
Boot disk (drive A) with:
AUTO folder containing GDOS.PRG
ASSIGN.SYS with PATH=B:\GDOS.SYS
Font/driver disk (drive B) with:
GDOS.SYS folder containing fonts and drivers
Application disk (drive A after booting GDOS) with:
Any GDOS application(s) (you may wish to create
separate application disks for each GDOS
application)
Hard drive (booting from floppy):
Boot disk (drive A) with:
AUTO folder containing hard drive boot program and
GDOS.PRG
ASSIGN.SYS with PATH=C:\GDOS.SYS
Hard drive partition C with:
GDOS.SYS folder containing fonts and drivers
Any hard drive partition with:
Any GDOS application(s) (may be on any partition)
Hard drive (autobooting):
Hard drive partition C with:
AUTO folder containing GDOS.PRG
GDOS.SYS folder containing fonts and drivers
ASSIGN.SYS with PATH=C:\GDOS.SYS
Any hard drive partition with:
Any GDOS application(s) (may be on any partition)
Of course, these are only suggestions, and other
configurations may be better for different applications.
Hopefully you should now be able to create other set-ups without
too much difficulty. There are a few "musts" that have to be
observed:
1. GDOS.PRG must be in the AUTO folder of the boot disk.
2. ASSIGN.SYS must be in the root directory of the boot
disk.
3. The PATH= line in the ASSIGN.SYS file must contain the
complete pathname of the folder containing the fonts and drivers
(GDOS.SYS is Atari's current name for this folder--previously,
Atari called it GEMSYS. You may, of course, choose any name you
like).
4. The fonts and drivers must be in the right place when
an application tries to open a device.
Adding a new device driver or new fonts is very simple. All
you have to do is put the device driver and/or fonts in the
correct folder (as defined by PATH=) then add the filenames to
the ASSIGN.SYS file.
A BIT ABOUT FONTS
One question about GDOS fonts that people ask is, "when are
the fonts loaded?" Many people are under the impression that all
the fonts are loaded when GDOS is initially loaded. This is not
true (and cannot be done). An "r" load flag in the ASSIGN.SYS
file will cause GDOS to load only the device driver, not the
fonts. Fonts are loaded only after an application opens a device
and asks for the fonts to be loaded. At that time, GDOS will
attempt to load all the fonts for that device. If there is an
error (can't find the find, not enough memory, etc.) GDOS will
skip over that font and continue with the next one. When an
application is through with the fonts, it can "unload" the fonts
to free up that memory.
Another fact that many people don't understand is that the
font filename is irrelevant to GDOS. Each font has a "header"
consisting of various parameters, some of these are: point size,
font name, and a font ID which is used to identify fonts of the
same type (i.e. all swiss fonts have the same ID). Another thing
to note is that GDOS does not handle line spacing, this is
handled by the application regardless of the actual size of a
given font. Some programs use the point size to determine line
spacing, and others use the actual height of the font (yes, the
point size can be set different from the actual size).
For those of you creating your own fonts (with GEMFED,
FONTZ!, or any other way), you must assign a unique font ID (from
0 to 32,767) to each of your fonts, and all font of the same type
(i.e. Times), but of different size, must have the same ID. You
should also note that some GDOS applications can only use fonts
with an ID between 0 and 255. Because of this, it is advisable
to keep your font IDs in that range.
Another thing you must know when creating your own fonts, is
the resolution of the devices you are creating the fonts for.
The following is a list of most of the currently available
devices and their resolution.
Low resolution screen 45 x 45 (horizontal dpi x vertical
dpi)
Medium resolution screen 91 x 45
High resolution screen 91 x 91
9-pin dot-matrix printer 120 x 144
24-pin printer 180 x 180 or 360 x 360 (NEC P-series only)
Laser printer 150 x 150 (some) or 300 x 300
(dpi figures for the screen are approximate)
As you can see, most of these devices have square (round)
pixels. This allows for sideways printing using the same fonts
as for vertical (normal) printing. A notable exception to this
is with the 9-pin dot-matrix printers, which will distort
characters when printing them sideways. Different drivers handle
this differently, they either ignore the fact (and print
distorted characters sideways), or they print the left and right
sides of a horizontal page on two separate vertical pages, which
must then be taped together. The first method is the easier (and
faster) of the two, but the second method will produce correct
characters, and the taping isn't too bad if you are going to
photocopy the final product.
It would be possible to create separate fonts for sideways
printing. but so far this has not been done. Also, some Epson
printers have a 144 x 144 dpi mode (double plotter mode) which
could be utilized. This would not only allow non-distorted
sideways printing, but offers slight higher resolution in the
horizontal axis.
FONT FILENAMES
As I stated earlier, font filenames are not used by GDOS.
To us humans, though, consistent filenames can greatly simplify
things. With the official release of GDOS (late 1987), Atari
adopted a standardized way of naming font files. Here I will
explain Atari's idea and add a few extensions.
A font filename like ATSS10EP.FNT may look meaningless to
someone who doesn't know how the filename was derived, but is, in
fact, very functional.
The first and second characters (AT) indicates the
creator/distributor of the font (in this case Atari). Atari has
suggested that these characters be "AT" for all fonts used on the
Atari; this seems meaningless to me, as I don't have any fonts
for any other computers on my ST disks (why would I?). I feel
these two characters can be put to better use to specify the
creator or distributor of the font.
The third and fourth characters (SS) identify the typestyle
(in this case sans serif). These should be unique to a
particular rendition of a typeface.
The fifth and sixth characters (10) specify the point size
of the font. This should be the point size as printed on the
device the font was designed for, not the pixel height. Also,
sizes less than 10 should have a leading zero (i.e. 06) to
maintain the overall structure.
The seventh and eighth characters (EP) specify the device
for which the font was designed (in this case the Epson 9-pin
driver). If there are no seventh and eighth characters, the font
is assumed to be for the high-resolution screen.
The filename extender on all fonts will be .FNT.
Although not many companies/individuals have produced GDOS
fonts for the ST (yet), I recommend that all font filenames
follow this convention to avoid confusion. I also suggest a few
standard identifiers:
Typestyles:
SS - Sans Serif (Atari's Swiss)
TR - Times Roman (Atari's Dutch)
TP - Typewriter (Atari)
DB - Dingbats (Timeworks' Bullets)*
DL - Drury Lane (Timeworks)*
MA - Madison (Timeworks)*
RK - Rockface (Timeworks)*
RA - Ravinia (Timeworks)*
CL - Camelot (Neocept)*
Device:
(none) - Monochrome graphics (high/low resolution screen)
CG - Color graphics (medium resolution screen)
EP - Epson 9-pin dot-matrix printer (120 x 144)
SP - Star NB-15 24-pin dot-matrix printer (180 x 180)
LB - Atari SMM804 9-pin dot-matrix printer (120 x 144)
LS - Standard laser printer (300 x 300)
MF - Metafile
MG - Monochrome graphics (high/low resolution)*
NC - NEC P-series 24-pin dot-matrix printer (360 x 360)*
LL - Low resolution laser printer (150 x 150)*
LQ - Epson LQ-series 24-pin printers (180 x 180)*
* indicates unofficial representations which I suggest in an
effort to standardize font filenames, and to simplify the whole
matter.
In many cases, the creator/distributor is not important, in
which case the first four characters can be used for the
typestyle. You will also notice that I have listed typestyles
from various companies, I have done this because I recommend that
you rename all of the font you currently have to match the above
conventions, this will save you a lot of confusion in the future
when you may have ten times as many fonts. One thing to note if
you create a master ASSIGN.SYS file, is that although the
Timeworks Swiss and Dutch fonts are different from Atari's, they
use the same font IDs. GDOS could get very confused if you have
two fonts with the same ID and point size. My personal
recommendation is to replace Timeworks' Swiss and Dutch fonts in
the 10, 12, 18, and 24 point sizes with the ones from Atari, as I
feel these are much more professional and true to the original
Helvetica and Times Roman typefaces.
Because the font filename convention has changed since GDOS
was first made available, it is helpful to know the old format
(which is still being used in many cases). The old font
filenames were laid out as follows:
cccrttpp.FNT
ccc - Creator/distributor (for screen fonts, i.e. MIG =
Migraph) or Device (for other fonts, i.e. EPS = Epson 9-pin
printer)
r - Resolution (i.e. L = low res, H=high res)
tt - Typeface (i.e. SS = sans serif, as above)
pp - Point size (as above)
METAFILES
Metafiles are theoretically ideal graphics files (keeping in
mind that text is represented graphically) which can be exchanged
between different GDOS applications. Metafiles are those files
with a .GEM extender. Metafiles are "ideal" in the respect that
they are resolution independent. They are simply instructions
for the computer to recreate a page on any output device at that
device's highest resolution. This is accomplished by storing
commands for drawing lines, circles, rectangles, text, etc.,
unlike most picture files (.NEO, PI?, etc.) which store the dots
making up an image.
Unfortunately, the metafile standard is not being used
consistently yet. This results in programs not being able to
read metafiles created by another application. In most cases,
the fault lies with the program trying to load the metafile, not
the creator. Many different parameters may be present in the
header of a metafile, but only a few of these are required.
Many applications expect (and need) some of the optional
parameters to be present to properly represent the image. As
such, they have difficulty loading files which don't have these
parameters. Currently Easy-Draw (version 2.3) is the most
capable of the available GDOS applications, and can read just
about any metafile.
Some of the more recent GDOS applications are allowing the
use of GEM image files (those ending in .IMG). These are
bit-mapped images similar to those created by the various ST
paint programs (but without the screen size and resolution
limitations). As is the case with other paint files, these
images may be jagged or blocky when printed on a high resolution
device.
A very important fact about images in metafiles is that the
metafile does not actually contain a copy of the image. The
metafile only contains the filename of the image on disk. This
means that you must not remove the disk containing an image while
the metafile is being printed, and every time you print that
metafile, the image must be in the same disk (or you will have to
change your file). If GDOS can't find the image, it will just
skip over it. Be warned.
For all you programmers, currently some programs (such as
OUTPUT.PRG and OUTPRINT.PRG) have difficulty handling metafiles
with large coordinates. Try to keep the coordinate space as
small as possible while still maintaining enough for good output
quality.
MISCELLANEOUS COMMENTS
If you are using the Timeworks Desktop Publisher ST (TDTP),
you must run the FONTWID.APP program each time you modify the
ASSIGN.SYS file. Another important fact is that the relative
widths of the Timeworks fonts are not the same for different
devices. What this means is that if you create a document with
TDTP installed for use with an Epson 9-pin printer, then load the
file into TDTP installed for use with a laser printer, the text
will be re-flowed. This may result in different page breaks,
lost text, extra white space, etc. The best solution to this
problem is to create the document with a TDTP installed for the
device which will create the final copy. Another idea is to use
Atari's fonts (if you have them--they are not public domain), as
the relative sizes between devices is very close (there still may
be a few differences, but can be fixed readily).
It should also be noted that Timeworks' ASSIGN.SYS files is
a mess. Apparently they list all the fonts they have available
for all their device drivers in one ASSIGN.SYS file. I suggest
you create your own based on the information presented here.
For those of you who have seen a lot of DEGAS Elite GDOS
fonts floating around, don't get too excited. For those to print
properly (even blocky), you must have matching printer fonts for
the screen fonts. GEMFED or FONTZ! greatly simplify this
process, but if you intend to create a complete set of fonts in
four or five sizes, you will have a lot of work ahead of you.
Anyone creating fonts for the general public (either
commercial or public domain), try to remember that not everyone
is using the same kind of monitor or printer you are. If at all
possible, create fonts for all the devices I have listed above.
For those of you creating fonts with FONTZ!, you should be
aware that scaling fonts may change the aspect ratio of the
characters. I'll say it again: Creating high quality fonts is a
lot of work. Period.
One thing I didn't mention are metafile fonts. These are
not really fonts, but merely width tables designed to keep
correct character spacing in a file when used with different GDOS
applications. They are rarely used and, in most cases, can be
eliminated without any loss of quality.
Because GDOS has gone through many revisions, there is some
confusion over which is the latest. When GDOS is loaded, a
message is displayed on the screen saying it is installed, and
the version number. The original GDOS displayed "GEMVDI
Installed". After that, it switched to "GDOS Version 1.x
Installed". The most common were 1.1, 1.2, 1.3, 1.5, and 1.8.
The newest revisions of GDOS display "GDOS RELEASE 1.x
Installed", with 1.1 being the newest (1.0 is still widely used).
As you can see, it is very important to read the boot-up message
when determining which revision you are using. Also, as a
sidenote, if you can't get RELEASE 1.0 or 1.1, you should try to
avoid Version 1.8, which had some problems.
To prevent problems with some of the device drivers
available, fonts should be listed in the ASSIGN.SYS file in
ascending order by font ID. Some device drivers will not find
fonts which are listed out of ID order.
Some of the GDOS fonts available have the entire ST
character set defined, including greek, hebrew, and other
character (most are unused by the average person). As you might
imagine, these take up space, usually, more than 50% of the font
file! So, if you're running out of memory (especially with a
Mega ST2 and SLM804), you can use FONTZ! to strip out the upper
characters. Do this by setting the upper ASCII value to 127.
Many people who have seen printouts of GDOS text have
complained that the text is blocky. This blockiness is usually
the result of font scaling. If a device driver does not have a
font available in the requested size, it will use the next
smaller size, or it may double the size of a smaller font. It it
uses the next smaller size, the text will look strange, because
it will have the spacing of the requested size, with the
character size of the actually used size. When doubling a
smaller font, blockiness will occur, and even then, the requested
size may not be obtained. The best solution to this problem is
to be aware of what size fonts are available, and only use those
in your files.
Currently there are rumors of a future version of GDOS which
supports scalable outline (or vector) fonts. It's important to
realize that GDOS does not create the characters. The device
drivers are responsible for creating the actual characters, and
could be rewritten to support outline fonts without any (or very
minor) changes to GDOS.
Ever since GDOS was released for the ST, people have been
complaining, saying that GDOS was supposed to be included with
the ST. While Atari may have planned that originally, I don't
believe Atari ever stated publicly that GDOS was to be included.
Keep in mind that much of the early ST documentation was based on
the IBM version of GEM, and reflects DRI's handling of GDOS, not
Atari's.
Also, at this time, Atari has no plans to incorporate GDOS
into the TOS ROMs.
GLOSSARY
Aspect Ratio - The relation of width to height. Maintaining
a constant aspect ratio ensures the same proportions regardless
of size.
Device (Graphics Device) - Anything used to create some form
of output, usually on a video screen or printed on paper or film.
Device Driver - A computer program used to control a device
as specified by a "master" application.
Font - A typeface of a given style and point size.
GDOS - Graphics Device Operating System; an extension to the
Atari ST's operating system allowing for the use of various fonts
and graphics devices.
GEM - Graphics Environment Manager; the portion of the ST's
operating system which is responsible for most of the visual
aspects of the ST.
Header - A portion of a file (usually at the beginning)
containing various parameters describing the file.
Line Spacing - The distance between successive line of text,
usually measured in points.
Parameter - A number or other symbol used to represent a
given attribute (dimension, color, direction, size, mode, etc.)
Pixel - Picture element; a single dot, usually one of many
used to create a complete image on a video screen or printed on
paper or film.
Point - A typographical unit of measure; approximately
1/72".
COPYRIGHTS, TRADEMARKS, ETC.
This document is copyright 1988 by Douglas N. Wheeler, all
rights reserved.
This document may be reproduced for non-commercial use
without further permission. For commercial reproduction, please
contact the author.
Any questions or comments about this document can be
directed to:
Douglas N. Wheeler
PSC 3 Box 6096
Travis AFB, CA 94535
(707) 437-3786
GEnie address D.N.WHEELER.
This document mentions several commercial/copyrighted
products. In each case, it is to be understood that the names
are trademarks of their respective companies and are used here
only as references. I am in no way connected, either through
employment or otherwise, to any of these companies.
I cannot be held responsible for any damages resulting from
the use or misuse of the information contained in this document.
This document was created for the purpose of providing
information, it is up to the reader to accept responsibility for
the results of the use of this information.
I'd like to thank Paul Mazurek, from Migraph, for his
comments and suggestions for this document.
