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PostScript
Startup Secrets



Don Lancaster



Most PC users go far out of their way to
blindfold themselves and tie both their
feet together when they first try to apply
PostScript. By understanding a few simple first
setup principles and some insider user secrets,
PostScript can easily become as PC-friendly
as it is on all of the other machines.



For openers, please do not ever
call PostScript a page description
language. To do so is a gross and
demeaning insult that's pretty much
comparable to referring to UNIX as a
"checkbook balancer".

Instead, PostScript is one totally
general purpose computer language
which can hold its own against any
modern contender. While it happens
to excel in dirtying up any otherwise
clean sheets of paper, you'll find that
page descriptions and page layouts
form only an inconsequential corner
of PostScript's real abilities.

As a general purpose computer
language, PostScript often ends up
strongly object-oriented, especially
in its EPS file transfer modes. There
are usually three different forms of
PostScript output, allowing you to
make markings upon sheets of thin
stuff; to return useful information for
host recording, external control, and
user interaction; or to write directly
to local or shared SCSI disk files.

PostScript is rather highly device
independent. On the input end, this
means that any old text file from any
old editor or word processor on any
old computer can be used as your
program source. On the output end,



the very same PostScript file can be
used to drive anything from a low
resolution desktop laser printer up
through the fanciest of high precision
phototypesetters. PostScript can also
be used for embroidery, sign cutting,
desktop prototyping, plotting, video
editing, engraving, CAD/CAM, FAX
interchange, image compression, or
any of a host of other emerging new
applications.

PostScript is related to Forth, as a
second cousin three times removed
and five times disowned. As such,
PostScript uses the postfix notation
(reverse Polish having no goto's); is
extensible (you can define a nearly
infinite variety of new operators as
combinations of all existing ones); is
reentrant, (any operator or proc can
call any other one to any reasonable
depth); is stack oriented (providing
for inherent self- addressing); and is
loosely typed (you do not have to rig-
idly predefine everything).

PostScript is exceptionally good at
manipulating strings and arrays. It is
strongly dictionary oriented, giving
you local and global constructs. In a
mind-boggling feature not available
in any other common language, your
dictionary entries can relate any two



of the dozens of object types, not just
key-value pairs.

PostScript does its linear graphical
transformations on the fly. Thus it is
simple for you to translate, rotate,
scale, or otherwise transform any
image to any size or any position at
any time. PostScript has built in
cubic spline capabilities that use
Bezier Curves. These can easily let you
draw smooth flowing curves given
only a sparse set of the ending and
control points. Your use of these
splines lets you create typography by
using a procedural description rather
than with a bitmap. Only a single
outline description (combined with
suitable hinting rules) is needed for
all sizes and all variations of any
user-chosen font. Unlike the hershey
bar effect of scaled bitmaps, scaled
splines will get smoother as they are
enlarged.

Sophisticated font machinery is an
inherent part of PostScript. A two-
step process is used. The first time a
character is needed, it gets built up
from a tightly compacted descript-
ion. At the same time, a bitmap copy
of the final character is usually saved
to a font cache. Repeated reuse of the
same character then can get imaged
much faster.

The latest PostScript Level II adds
some surprising new features, such
as a full FAX capability, instant and
unrestricted access to all font paths,
higher speeds, improved color seps,
strong forms and step-and-repeat
capabilities, JPEG video compression,
and bunches more.

As a general purpose computer
language, PostScript is fast and fun
to use. You could generate award



PC TECHNIQUES 67



winning output with nothing but five
minutes of instruction and a dozen
simple commands. Or you can spend
a lifetime exploring and pushing the
envelope of an incredibly powerful
new multimedia communications
tool. But be forwarned: PostScript is
extremely addictive.

You do not normally go out and
buy your own copy of the PostScript
language. Instead, the language is
built into or gets added on to most
popular laser printers. It is important
that you realize that any PostScript
speaking printer is really a general
purpose computer which executes
PostScript programs. An extremely
powerful computer with a fast and
an exceptionally clean architecture
that is lots of fun to program and use.
It is definitely not a "just dump the
text" printer. And does not become
one until such time as you or some
firmware teaches it exactly what you
want it to become.

Programming in PostScript

A PostScript program is usually
nothing more than a plain old ASCII
textfile that contains ordinary words
and numbers. PostScript programs
can be ^reinstalled as firmware or
cartridges; can be downloaded on the
fly; or can be persistently downloaded
once to remain available as long as
computer power remains turned on.
Downloading can be done via serial
ports, AppleTalk, shared SCSI comm,
Ethernet, or directly to or from a
modem, hard disk, or CD ROM.

As we will see shortly, one-way
parallel ports should definitely not be
used with PostScript under any cir-
cumstances. Ever.

There are several popular ways of
generating PostScript code. One is to
use raw PostScript to write your own
programs using your favorite word
processor or editor. This one is my
overwhelming favorite and is by far
your most powerful and the most
flexible. Raw PostScript also usually
generates by far the shortest and the
fastest-running files as well.

A second method of providing
PostScript code is to use an emulator.
An emulator is a currently running
PostScript program which accepts an
input in some other format and
converts it on the fly into suitable
PostScript commands. The popular
traditional emulators include PCL,
Diablo, Imagewriter, Epson, HPGL,



PostScript DEMANDS full two-way host comm, especially for on-screen error
messages and for host recording of returned data.

Make ABSOLUTELY CERTAIN you can run this 13-byte PostScript program...

(OK) == flush

If your comm setup, network, or print buffer does not display the OK on your host
screen, then STOP IMMEDIATELY and make your system PostScript usable.



and TEX. Most users usually outgrow
traditional emulators twelve minutes
or less into their use. ["Gee. I'd sure
like some larger drop titles, an initial
cap, proportional spreadsheet fonts,
and a box around that sidebar. . ."]

PostScript Level II adds powerful
new filter emulators. Some of these
early offerings include full FAX and
JPEG video compression.

The third method of generating
PostScript program code is to use an
applications package to write the code
for you. Obvious examples include
Ragemaker, Adobe Illustrator, Ventura
Publisher, and Aldus Freehand.

Although fast and convenient for
beginners, all of these application
packages force you to do their own
things in their own way and generate
code that is inherently slower, lots
longer, and far less flexible than by



writing your own raw PostScript.

EPS files are related to PostScript
code generators. These are simply
pretested and (hopefully) debugged
textfile program modules that have a
standard header and trailer. These
also disallow certain obscure Post-
Script operators that can cause havoc
when they get imported into another
supervisory program. EPS is short for
Encapsulated PostScript.

Setting Up Your Serial Comm

All PostScript programs demand
two-way host recordable and fully
on-screen displayable comm.

Any communication, networking,
or print buffering setup that prevents
you from immediately receiving on-
screen error messages or from your
recording any host-returned data is
severely crippling you and will surely



A FIGURE 2 - PC to LaserWriter cable options.




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68 Nov/ Dec 1991



A FIGURE 3 - PostScript serial comm initial checkout.

1 . Connect the PostScript printer to a suitable serial cable, select a 9600 comm
mode, apply power, and verify the baud rate on the test page.

2. Boot a suitable two-way comm program such as Crosstalk or ProComm.
Select 9600 baud, 8 data bits, 1 stop bit, no parity, full duplex, all filters off,
and XON/XOFF handshaking.

3. Type a single ctrl-T. A message of...

%% [status: idle]%%

should appear on your host screen. If nothing happens, your cables are not
properly crossed or your comm is not properly activated. If gibberish appears,
your baud rate or other comm parameters are wrong. If a different legible
PostScript message appears, reset the printer per the next step or otherwise
attend to the problem (e.g. add paper; replace cartridge; free a jam, etc.)

4. Reset your printer by typing a ctrl-C followed by a ctrl-T half a second or
more later. You once again should get the %% [status: idle]%% message
promptly appearing on your host screen.

DO NOT GO BEYOND THIS POINT WITHOUT YOUR PROPER ERROR
MESSAGES BEING CORRECTLY DISPLAYED ON SCREEN!

5. Reset your printer again and type the word showpage, one word and all lower
case. A page should eject. Reset your printer again and type your middle
name. An error message should appear on-screen. Reset your printer again
and run Figure one. An OK should appear on your host screen.

6 To run other PostScript code, first create and save the code to disk as a
standard ASCII textfile. Use your favorite editor or word processor. Then
transmit the code with your comm program. Try figure four as a useful
example.

7. Note that improper XON/XOFF handshaking will not affect short programs,
typically those under 5000 characters or a page and a half. Do NOT, under
any circumstances, attempt to use DTR handshaking.



return to haunt you.

Virtually all the non-IBM users of
PostScript have a SendPS or similar
program that always provides them
with a full and instant two-way re-
cordable host comm.

Figure one shows you a thirteen
byte PostScript program to verify
that you have a useful comm setup. If
you fail to get an "OK" on your host
computer screen, then you should
immediately get rid of your present
comm setup and replace it with a
decent one. The longer you wait to
do this, the more it will cost you in
time, money, and frustration.

Any one-way parallel port should
NEVER be used with PostScript!

And those printer manufacturers
that lead you to believe otherwise are
doing a severe disservice to both you
and the PC community at large.

These epsilon minuses should get
staked to their nearest anthill. Or
chopped up and fed to the cows. Or,
at the very least, spanked and sent to
bed without any supper.

Many PostScript programs (such
as figure one, that Adobe Distillery,
the GENIEVST.PS stock investment



analysis code, or countless others)
will not run at all on a one-way port.
And those programs that do run will
place you under an extreme comm
disadvantage. Even for such trivial
matters as running out of paper or
going low on toner.

On the other hand, there is a great
programming opportunity here. For
the first PC Techniques reader to come
up with an equivalant to SendPS that
provides a full two-way recordable
comm over a parallel port is certain
to run away with a very large bag of
marbles. But, until that happens, you
definitely must not use any one-way
parallel port with PostScript.

Yes, you can find printable error
trappers. These can greatly simplify
program testing and debug. And you
certainly should. Our GEnie PSRT
#196 EHANDLER.PS is one source.
But by no stretch of the imagination
is a printing error trapper a suitable
substitute for fully recordable two-
way comm and instant on-screen
error messages.

By the same token, COPYing any
PostScript program to your serial
COM1 port is one big no-no. Again,



because it flat out prevents you from
receiving all your timely and crucial
on-screen error messages and from
host recording returned data. And
also because it usually prevents the
normal PostScript XON/XOFF hand-
shaking protocol.

Serial Cables

Figure two shows you six popular
serial cables, useful for connecting
Apple LaserWriters to PC or clone
computers. On the baseline DB25 to
DB25 connector, the usual mistake
people make is forgetting to locally
jumper the auxiliary RTS and CTS
pins (4 & 5) on the IBM end. These
serial pins are an IBM anachronism
not found elsewhere.

Note that the data and optional
handshake paths are crossed in what
you IBM folks call a null modem, and
what Apple calls a printer cable.

The usual mistake when you are
connecting RS232 to the RS423 used
by DB9 or MiniDIN-8 connectors is
failing to ground the "unused" RXD+
input. Be sure to use the connections
shown. RXD is differential.

Note especially that older Apple
LaserWriters make optional use of a
RS423 DB9 connector whose pinouts
end up wildly different than the DB9
RS232 used on newer IBM or PC gear.
Neither a "straight" nor a "crossed"
DB9 cable can be used. Worse, it is
likely to cause fireworks and possible
damage at both ends.

Rather than building up a special
cable, it is usually simpler to take any
old cable and an ohmmeter and find
out what pins you really have. Then
you go to Radio Shack and pick up a
DB-25 male and a female connector
and some short jumper wires. You
then build an adaptor for one end of
your cable that makes the cable you
have into the one you really want.
Ready-to-jumper modules are also
readily available.

Your First Comm Test

A good first comm debug routine
is shown you in figure three.

Connect up the proper cable and
select the correct baud rate on your
PostScript computer. (That's that box
that wrongly has a "printer" label on
it.) Then boot a suitable full two-way
comm program such as Crosstalk,
PoComm or whatever you are using
with your modem. Initially, select
9600 baud, eight data bits, one stop



PC TECHNIQUES 69



A FIGURE 4 - Use this PostScript fractal fern as a practice file.




/problistcreate {mark /counter def probabilities {1 28 mul round cvi {transforms counter get}
repeat /counter counter 1 add def} forall counttomark 128 sub neg dup gt { [1 1 0] repeat}
{pop} ifelse] /problist exch def} bind def

/doit {problistcreate 1 1 20 {problist rand -24 bitshift get transform 2 copy moveto .001 1 rlineto}
repeat newpath numdots {problist rand -24 bitshift get transform 2 copy moveto .001 rlineto
stroke} repeat} bind def

%% /// demo - remove or alter before reuse. ///

/numdots 6000 def % increase for denser image; decrease to print faster

/transforms [ [0 .16 0] [.2 .23 -.26 .22 1.6] [-.15 .26 .28 .24 .44]
[.85 -.04 .04 .85 1.6]] def

/probabilities [ .01 .07 .07 .85] def

1 setlinecap setlinewidth 200 300 translate 30 dup scale doit showpage quit



bit, no parity, full duplex, filters off,
and XON/XOFF handshaking.

Then enter a ctrl-T. If all is well,
you should get an on-screen message
of [status: idle].

Always reset your printer before
any reuse. To do this, you do a ctrl-C
followed by a ctrl-T half a second or
more later. There is never any point in
continuing further if you cannot get
the [status:idle] message.

Next, enter the word showpage, as
one word, all lower case. A blank
page should promptly eject out of the
PostScript computer. Reset once
again. Now type your middle name.
You should get an on-screen error
message that reminds you that you
forgot to previously define your mid-
dle name as a PostScript proc.

The general procedure for running
a raw PostScript or an EPS routine is
to save all your code as a standard
ASCII textfile to disk. Then get into
your favorite comm program. Type a
[C][T] to get the [status:idle] message.
Then send your file. Any problems
should immediately appear on your
host screen.

Figure four is a practice PostScript
program. It does a fractal fern, and
can be stunningly beautiful. For your
first few passes, keep your numdots
variable in the thousands. Then raise
it as high as you want for a detailed
final hard copy.

By the way, this fern program is an
excellent PostScript clone buster. It
works just fine with genuine Adobe
PostScript but totally demolishes
most of the PS imitators, fakes, and
hanger-onners.

It is usually a good idea to defeat
your comm program local echoing.
Having to take time out to display
outgoing characters and to scroll
screens dramatically slows down all
your de-facto baud rates. Especially
at higher settings.

After your comm seems up and
working, you can next check out all
of the PostScript drivers on your
applications software to verify that
they are working properly. There is
no point in trying anything with a fancy
package before you verify that your basic
two-way recordable comm is up and
working with raw PostScript.

You can later speed your comm up
to 19200 or even 59600 baud. Details
vary with the printer, but you can
call me per the end blurb for more
help on this.



Note that any PostScript printer
setting marked 9600 is often fully
reprogrammable. Should you royally
foul things up, your setting marked
1200 is usually always 1200 baud, 8
data bits, and 1 stop bit. You could
always drop back to this setting and
then reprogram the other one.

It is normally a good idea to start
and end all of your files with a [D]
end-of-file command.

Obvious ways to divert a single
serial port for several uses include
manually replugging cables, using
an A-B switch box, or substituting a
third-party card that has multiple
serial ports.

Transparent Data Channels

Any communications setup has a
big dilemma. There has to be some
means to control the channel you are
communicating over. Do you add
extra control wires or reserve some
characters for commands?

PostScript normally uses a nearly
(but not quite) transparent sec data
channel. The reserved characters are
shown you in figure five.

As long as you send only printable
ASCII characters, you will never have
any transparency problems. The real



transparency killer is that [D]. Any
inadvertent hex $04 or "CHR$(04)"
causes an end-of-file termination of
your PostScript program. With any
XON/XOFF handshaking, the [Q]
and [S] characters are also obviously
reserved and must never be used for
any other purpose.

If you decide to use any control
characters in your raw PostScript
code or emulator, you have to make
absolutely certain they don't conflict
with the uses of figure five.

How can you handle your images,
"perfect" emulators and binary data
if some codes are restricted? There
are several popular ways. One is to
use hex-ASCII pairs. Each data value
is broken down into a high byte and
a low byte and separately sent as
printable ASCII 0-9 or A-F characters.
This always will work and is totally
transparent, but requires twice the
characters and transmits at half the
usual comm speed.

An improvement on hex pairs that
got built into Level II is known as
ASCII85. This is basically a base 85
numbering scheme that substitutes
five printable ASCII characters for
four unrestricted binary bytes. The
speed and storage penalty for a full



70 Nov/ Dec 1991



ctrl-C


Force job reset


ctrl-D


end-of-job marker


ctrl-J


Newline or linefeed


ctn-M


Carriage Return


cin- 1


Inquire printer status


ctrl-Q


XOFF stop handshake


ctrl-S


XON restart handshake


ctrl-H


Interactive backspace


ctrl-R


Interactive redisplay


ctrl-U


Interactive erase line



transparency is only 20 percent.

Yes, you could defeat PostScript's
reserved characters by creative use of
the undocumented openscc operator
in statusdict. But this is a tricky and
dangerous process. The proc format
is 9600 25 openscc.

[J] 's and Such

PostScript will do its darndest to
remain totally device independent.
But there are just enough differences
between the Mac and the IBM comm
standards that you do have to watch
out. Changes may be requied when
moving any supposedly "device in-
dependent" textfile from one system
to the other.

For instance, the Mac normally
uses only [M] carriage returns, while
IBM often uses [M][J] carriage return
and linefeed pairs. An IBM textfile
will often double space on a Mac. In
PostScript code, this often will not
matter, but within PostScript strings
or currentfile readings, results may
end up double spaced. Similarly, a
Mac textfile can appear as one single
humongous long string on an IBM
screen or disk file.

The obvious solution here is to add
or remove the [J] linefeeds during a
transfer. Many utility programs give
you an option to do just this.

Another problem character is [Z].
Many IBM file transfer programs will
fill out the end of their listing with
enough [Z] characters to come up to
an even page boundary. These same
[Z] characters can give PostScript or a
Mac fits if they are not properly
predefined. It pays to check the end
of your files for extra characters, and
then strip off any unneeded ones.

Certain older versions of the Mac
AppleTalk reception code in some
printers wrongly failed to convert
the [M] carriage returns into the [J]
PostScript newline characters. This



can cause imaging differences with
some PostScript text scanner codings.
Rewrite your text scanning code if
your AppleTalk images differently
than serial comm.

A final possible problem character
is the tab command [I] . Some systems
substitute tabs for multiple spaces
and vice versa. Any [I] routed to a
PostScript program which does not
expect it can generate errors.

Some word processors may insist
on forcing extra unwanted carriage
returns, especially at a screen line
ending or when importing or fully
formatting text. It is super important
to prevent any unintended carriage
return introductions when creating
or sending PostScript text. Especially
if those carriage returns can end up
inside PostScript strings or are pre-
sent during currentfile readings.

Type 1 Fonts

In their essential form, Adobe
Type I printer fonts are simple text
files that start out with a readable
header and then drop into a compact
eexec encoded file. Any of these files
in their "bare bones" format can be
downloaded device independently
from any host source.

Machine specific extensions are
sometimes added to Type I fonts. For
instance, a Mac Type I font will have
a data fork and a resource fork, and
may include some pre-ATM Quick-
Draw screen character bitmap info.
Thus, a Mac Type I font can't simply
be moved over and used on a PC.

There are several simple ways to
convert Mac Type I fonts into a PC
usable form.

One method requires a PostScript
printer with a local hard disk. Just
Mac download the Type I font to
disk. Then read the font back to a PC
host. Note that the only difference
between any old hard disk textfile
and a font is that the font is placed in
a /fonts/ subdirectory.

A second method needs a Mac
application swift enough to "go fish"
for host based fonts not already on
the printer. Create a short textfile
that needs the target font. Then print,
but choose either an option-F [print
ASCII file to disk] or the option-K
[print ASCII file and all the needed
persistent dictionaries to your disk].
Transfer the disk-based text file to a
PC and then strip off everything that
is not the Type I font itself.



A third method uses a shareware
program to automatically convert the
font formats for you. The GEnie PSRT
#207 UNADOBE.SIT is typical.

Going from PC to the Mac is far
simpler. Make sure your file contains
only your Type I font printer info.
Then use the Download PostScript File
option of SendPS to download your
font to the printer.

Be sure to note that their Download
PostScript Font option will expect the
Mac format font listing, while their
Download PostScript File selection
accepts an ordinary ASCII text file
from any source.

For More Help

Two essential PostScript books are
the Adobe blue book, and otherwise
known as the PostScript Tutorial and
Cookbook, and the revised red book,
which is titled the PostScript Reference
Manual II. The red book includes full
details on EPS files, Level II, and on
new Display PostScript.

LaserWriter tech info appears in
the Apple white book, also called the
LaserWriter Technical Reference.

I am also now laboring under the
delusion that my Intro to PostScript
video and my new LaserWriter Secrets
book/disk combo might be of help to
you. I carry lots of other PostScript
products by Adobe, by myself, and
by other leading authors. There is a
no-charge PostScript voice helpline
here at Synergetics which you can call
per the blurb below.

Finally, a major and PostScript-
oriented BBS is up on GEnie as PSRT.
Included are hundreds of demos,
utilities, fonts, and my power tools,
along with RTC conferences with all
major PostScript players.

You can voice call (800) 638-9636
for connect info. Your typical down-
loading charges for an average PSRT
file is around twenty-one cents. ♦



Microcomputer pioneer and guru Don
Lancaster is the author of 26 books and
countless articles. Don maintains a
no-charge technical helpline found at
(602) 428-4073, besides offering all his
own books, reprints, and his technical
services. He also has a free brochure of
his insider desktop publishing secrets
waiting for you. Your best calling times
are often 8-5 on weekdays, Mountain
Standard Time. Or you can reach Don
by way of Synergetics, at Box 809,
Thatcher, AZ 85552.



PC TECHNIQUES 71




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