PostScript Print
Volume Number: 2
Issue Number: 6
Column Tag: PostScript Printing
Place PostScript in MacWrite Documents 
By Mike Schuster, Adobe Systems, MacTutor Contributing Editor
Embed PostScript in Fonts and Pictures
When a Macintosh application prints to Apple's LaserWriter printer, the
Printing Manager converts the sequence of QuickDraw operations that the application
used to image the document on the screen into a PostScript® program that describes the
appearance of the document on printed pages. The Printing Manager then transmits this
program to the LaserWriter, which contains a PostScript interpreter bundled with a
xerographic marking engine. The interpreter executes the page description and
produces output on the attached output device.
The PostScript language itself was designed by Adobe Systems, Inc. to be a
high-level, device independent page description language with powerful text and
graphics capabilities. PostScript includes operators to outline or fill any arbitrary
graphical shape constructed from straight lines, arcs, and cubic polynomical curves; to
treat any shape as a clipping path to crop any other graphics; and to render text and
sampled images of arbitrary resolution at any size or angle on the page.
Quickdraw versus PostScript
Normally, PostScript programs are generated automatically by the Printing
Manager when the application's client selects the Print command. Let us briefly review
how this is done. On the Mac, all drawing is done through the quickdraw routines. On the
Laser, all drawing is done through PostScript. Hence quickdraw calls must be converted
to the closest PostScript equivalent. Quickdraw is designed so that all the quickdraw
routines reduce down to a dozen or so standard drawing routines. This lets an
application designer write his own quickdraw routines by replacing these primary
routines or "quickdraw verbs" with his own. The Print Manager converts each of these
quickdraw verbs to a call on a PostScript procedure, which closely emulates the
quickdraw action using PostScript primitives. The definition of that procedure is
contained in Laserprep, which is downloaded into the Laserwriter. The PostScript
procedures defined in the Laserprep file in effect re-define the quickdraw verbs in
terms of PostScript commands. When you use the command-F key to produce a
PostScript file, the Print Manager generates a file of procedure calls into this
Laserprep file. So you couldn't use this PostScript file without the Laserprep file being
downloaded into the Laserwriter first. Thus in normal printing, the Mac quickdraw
environment is completely translated to a PostScript environment automatically
through the actions of the Printing Manager and Laserprep. This automatic conversion
is very useful, since neither the application's user nor its designer need to understand
or worry about the details and concerns of the PostScript environment.
There are several situations, however, when it would be useful to type or paste
raw PostScript commands directly into a document, so that the images generated by the
commands are integrated on the printed page along with the rest of the document. The
reason for this is that neither QuickDraw nor current applications are capable of
imaging the full repetoir of PostScript graphics on the screen. Hence, many of the
LaserWriter's powerful capabilities remain relatively unexplored and unexploited, at
least when using MacWrite, MacDraw and MacPaint. And since the Laserwriter costs
some $4800, it would be nice to be able to use all of it's capabilities!
But there is lots of good news on the horizon. Apple's new Printing Manager,
version 3.1, contains several useful facilities for including PostScript in a document.
Apple is madly documenting its capabilities. As a preview, we'll look at what you can do
with them.
The “PostScript Escape” Font
The new Printing Manager treats any text in the font named “PostScript Escape”
as PostScript commands and sends the text straight through to the LaserWriter. When
the Print Manager sees text displayed in the PostScript Escape font, that text is not
converted into a Laserprep text drawing call, but simply inserted into the rest of the
PostScript file. In this way, pure postscript is included in this file of Laserprep calls
and executed directly by the laserwriter.
Any font may be used as the "PostScript Escape" font, but consider this example
using the font I've created (available on source code disk #9 from the MacTutor mail
order store). Here is an example. First, type the following PostScript program into the
middle of a MacWrite document:
gsave initgraphics
/Times-BoldItalic findfont 27 scalefont setfont
/rays
{ 0 1.5 179
{ gsave rotate 0 0 moveto 108 0 lineto stroke grestore } for
} def
300 400 translate .25 setlinewidth
newpath 0 0 moveto (StarLines) true charpath clip
newpath 54 -15 translate rays
grestore
Then hilight the whole paragraph, and select my PostScript Escape font from
MacWrite's Font menu. The paragraph will disappear! Now print the document. The
effects of the embeded postscript will appear in the LaserWriter printout.
Invisible Fonts
Whats going on? First, my PostScript Escape font is invisible! Using Apple's
ResEdit, I made a copy of the Times 12 point font and called it PostScript Escape. Then I
erased all of the black bits in the entire font and set the width of each letter to zero.
Then I reduced the ascent and descent so that the font is only 1 point tall. Finally, I
pasted the font into my System file. You can do the same thing to create this font if you
don't want to wait to get it on a source code disk.
Why bother with an invisible font? If the PostScript Escape font was visible,
then any PostScript set in it would leave blank areas on the printed page, since
MacWrite assumes that the text will be printed as it appears on the screen. Since only
the graphic objects that the PostScript produces are visible on the printed page, we
have no choice but to make it invisible, otherwise we would loose screen- page fidelity.
How does one edit invisible text? Easy, just select something that includes the
PostScript and change the whole thing to Times, for example. Edit the PostScript, make
it invisible again, and print.
PostScript Considerations
When you imbed normal postscript in MacWrite, your postscript image will
come out upside down. This is because the coordinate reference system for quickdraw
and postscript are opposite. You fix this by adding in front of the postscript two calls:
gsave initgraphics
now add your postscript stuff
grestore
This has the effect of saving the Print Managers coordinate system, initializes
the default postscript coordinate system, then it draws the postscript, and finally
restores the print manager's coordinate system. In PostScript, (0,0) is at the bottom
of the page, while in quickdraw (0,0) is at the top of the page. In our example above we
have added these commands so the PostScript has the same orientation as the rest of the
Macwrite file.
Another problem is placement. Paste the postscript at the bottom of the page, so
the Macwrite stuff does not overwrite the postscript image. Or if you estimate where
your figure should be placed on the page, you can leave space in the Macwrite document
for the figure, and place your postscript stuff in the blank box, but remember you have
to set your postscript coordinates in your postscript commands to match that box area.
The Print Manager doesn't tell you where it is on the page!
Pagemaker Doesn't Work!
Pagemaker does not use the default Print Manager routines, which makes calls on
Laserprep. Rather it calls it's own RAM based Print Manager in Pagemaker which
makes calls on Aldusprep, and this Pagemaker Print Manager does not know about this
PostScript escape routine so it will be treated like a regular text font, and hence there
still is no way to imbed PostScript into your Pagemaker layout! Pagemaker is supposed
to be updating their product to support these new print manager functions sometime
this summer. They will add a PostScript place command to place PostScript text files in
a manner similar to placing a MacWrite file. A quickdraw picture feature will allow the
quickdraw picture to represent the postscript stuff and make placement on the page as
easy as placing a MacDraw figure. If they can pull this off in a timely manner, it will
greatly increase the sophistication level of Pagemaker in the marketplace.
Get a copy of PostScript Language Reference Manual and PostScript Language
Tutorial and Cookbook, by Adobe Systems and published by Addison-Wesley and use this
technique to try out some of the examples.
PostScript in Pictures
The new Printing Manager also has some goodies for those of you who use
QuickDraw pictures. Try embedding the following C code into a picture or place them
between a PrOpenPage and a PrClosePage in your printing loop:
C Code Example
open picture(@rect);
fillrect(@rect, white);
PicComment(190, 0, 0l); /* Begin PostScript mode */
/* Send following Quickdraw text as PostScript */
PicComment(194, 0, 0l); /* this is postscript escape font */
DrawText("/pgsave initgraphics");
DrawText("\p/Times-BoldItalic findfont 27 scalefont setfont");
DrawText("\p/rays");
... /* add postscript commands */
DrawText("\pgrestore");
PicComment(191, 0, 0l); /* End PostScript mode */
close picture;
Print Manager Bug
The fillrect simply draws a white rectangle to get around a bug in the print
manager which causes it to think this is a blank page unless it sees at least one
quickdraw drawing command. The white rectangle on white obviously won't do anything
we can see, but it will force the Print Manager to then show our postscript stuff rather
than a blank page.
These PicComment calls are intercepted by the Printing Manager. Comments
190 and 191 bracket the PostScript, and comment 194 tells the Printing Manger that
the following text is set in the PostScript Escape font, so the Printing Manager simply
forwards all of the text to the Laserwriter.
The Parkhurst Picture
What else does the Printing Manager do? A while back Bill Parkhurst, author of
the T/Maker's ClickArt Effects package, argued that each QuickDraw Picture should
have two forks - a QuickDraw fork and a PostScript fork. When such a picture is
drawn on the screen or printed on the ImageWriter, only the QuickDraw fork is used.
When it is printed on a PostScript printer, only the PostScript is used. You get the best
of both worlds, good looking printed documents and good screen approximations without
the need for a PostScript interpreter resident on the Macintosh. Apparently, version
3.1 has some support for the Parkhurst Picture, but details have yet to be documented,
and there is some doubt whether the implementation will work in the current version.
It is not known if Apple is planning to support this untested code features.
Downloadable font problems: With this implementation of PostScript escape, a
needed downloaded font will not be donwloaded unless the font is used in the regular
quickdraw portion of the file.
Laserwriter Plus RAM memory problems: One of the great mysteries is why
Apple did not increase the RAM memory in the Laserwriter Plus so that downloadable
fonts could be supported. As it is now, only one small font can be downloaded at a time
due to the fact that only about 50K of RAM is left. Application programs could be
designed to get around this problem by imaging the page one font at a time, rather than
composing all the page at once. The page should be reorganzied by the application by
font, so that each font component is sent only once to the printer. An ascii postscript
file sort program that sorts the postscript by font and sends it to the printer in the
sorted order, using one font at a time on a page basis would be a great utility program.
It also would be great to design this abilitiy into existing page makeup software.
Another fix is to use the note operator which allows drawing in a smaller area on the
page in one of three page sizes: letter, note and legal. Using note size, the RAM previously
allocated for the whole page area is now smaller by 100K, which can be used by fonts so
up to 4 downloadable fonts can be supported, but you have to use the note operator in
your own postscript file. The Print Manager uses the note operator automatically. The
Page Setup allows you select between note size (7.7 by 10.2 on a page 8.5 by 11) and
legal size (6.7 by 13 on an 8.5 by 14 inch page). Letter size (8 by 11 on a 8.5 by 11
inch page is not supported by the Print Manager, which is why you can't print to the
edge of the page. The note operator can select letter size in a custom postscript file
however. Aldus prep does not use the note operator. Because there is not enough RAM
memory in the Laserwriter Plus or the Laserwriter, you can't have both a full size page
and downloadable fonts.
Referenced by (2):