Re: EPS--Q&A

[Killer of Trees <lemay -at- NETCOM -dot- COM>]

In article <9312171507 -dot- AA07569 -at- sctsun9 -dot- sctcorp -dot- com> Tracey Showalter
 <tshowalt -at- sctcorp -dot- com> writes:
> Does anyone know what makes EPSF "encapsulated"? Is it special operators,
> different commands, the environment in which it is created?


Regular PostScript files have commands that map graphics and text
directly to coordinates on a page.  For example, you might have
commands in a PS file that say, effectively, "go to point x,y, and
print this text, then go to point x1,y1, and print a circle."  Its a
lot more complicated than that, but thats the general idea.

Given that assumption, it would be very difficult to place a
PostScript file within another PostScript file, because the position
of the included PS graphic on the page would be hard-coded into the file.
If you want the graphic to be cornered at 350,350, and the commands
within it say its cornered at 0, 0, then it'll stubornly print at
0,0 every time unless you hand-edit the file to be cornered where you
want to corner it.  And then heaven forbid you want to change the text
around it once you have it placed properly.  Ugh.  Its nearly as bad
as manual pasteup of graphics (no offense intended to those who LIKE
manual pasteup. :)

Encapsulated PostScript files get around this problem by never
specifying absolute coordinates in the graphic file.  Instead, they
assume that the file is cornered at 0,0, and then use relative commands
(for example: move 50 points to the right, 20 points up, and draw this text)
Most environments that create PostScript graphics assume thier graphics
are encapsulated and write thier PostScript accordingly.

When the bigger PostScript file includes an encapsulated file, it will
then include some sort of wrapper around that graphic that says "while
this graphic is being processed, the current corner (say, as in the
previous example, 350, 350) is redefined to be 0,0."  And the PS
processor happily redefines 0,0, draws the encapsulated file, and then
pops back to its original coordinate system and goes on its merry way.

> Does anyone know of a good book on PS for non-programmers? _Thinking
> in PostScript_ is programming-oriented--its examples and explanations
> relate to various programming languages and since I know nothing about
> programming languages, I'm in the dark.

Try "PostScript by Example," by Henry McGilton and Mary Campione
(Addison-Wesley, 1992).  It has the advantage of being reasonably
non-technical while still being very, very complete.

However, most people I know would argue that you don't need to know
PostScript.  I'm reasonably fluent in PostScript, and I've never
landed any jobs because of it. Most interviewers, when confronted
with it on my resume, snicker and make sarcastic comments. :)






--
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Laura Lemay                              lemay -at- netcom -dot- com
writer of trifles in shadows and blood
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