NETB131 Programming Project
Programming language PostScript
An overview
Ilija Jovanov, F40681
Preface:
1.)History
and Special Features
2.)"Hello World" Program
3.)Fundamental Data
Types (integer, floating point, string) and
Assignment Operator
4.)Basic Control Flow
(conditional and loop statements)
5.)Functions - syntax,
writing and using functions, example
6.)Arrays - syntax,
definition, example
7.)Compilers
8.)Projects and Software in
PostScript
9.)Standard
10.) References
1.)History
and Special Features
The concepts of the PostScript language were
seeded in 1976
when John
Warnock was working at Evans & Sutherland, a famous computer
graphics company. At that time John Warnock was developing an
interpreter
for a large three-dimensional graphics database of New York
harbor. Warnock conceived the Design System language to process
the
graphics, very similar to the Forth programming language.
Concurrently,
researchers at Xerox
PARC
had developed the first laser
printer and had recognized the need for a
standard means of defining page images. In 1975-76 a team led by Bob
Sproull
developed the Press format, which was eventually used in the Xerox
Star
system to drive laser printers. But Press, a data format rather than a
language, lacked flexibility, and PARC
mounted the InterPress
effort to create a successor.In 1978
Evans and Sutherland asked Warnock
to move from the San Francisco Bay Area to their
main
headquarters in Utah,
but he was not interested in moving. He then joined Xerox
PARC
to work with Martin Newell. They
rewrote
Design System to create JaM (for "John and Martin") which was
used for VLSI design and the
investigation of
type and graphics printing. This work later evolved and expanded into
the InterPress
language.Warnock left with Chuck
Geschke and founded Adobe
Systems in December 1982. They created a
simpler language, similar to InterPress, called PostScript, which went
on the
market in 1984.
At
about this time they were visited by Steve
Jobs,
who urged them to adapt PostScript to be used as the language for
driving laser
printers.
In March of 1985,
the Apple LaserWriter
was the first printer to ship with PostScript, sparking the desktop
publishing (DTP) revolution in
the mid-1980s.
The
combination of technical merits and widespread availability made
PostScript a
language of choice for graphical output for printing applications. For
a time
an interpreter (sometimes
referred to
as a RIP -for Raster Image Processor)
for the
PostScript language was a common component of laser
printers, into the 1990s.Once the de facto
standard for electronic distribution of final
documents meant for publication, PostScript is steadily being
supplanted by one
of its own descendants, the Portable Document Format or PDF in this
area. By 2001 there
were fewer
printer models which came with support for PostScript, largely due to
the
growing competition from much cheaper non-PostScript ink jet printers
(PostScript interpreters added significantly to printer cost), and new
software-based methods to render PostScript images on the computer,
making them
suitable for any printer (PDF provided one such method). The use of a
PostScript laser printer still can, however, significantly reduce the
CPU
workload involved in printing documents, transferring the work of
rendering
PostScript images from the computer to the printer.
PostScript Level 1
The PostScript language has had two major upgrades. The first version,
known as PostScript Level 1, was introduced in 1984.
PostScript
Level 2
PostScript Level 2 was introduced in 1991, and included several
improvements: improved speed and reliability, support for in-RIP
separations, image decompression (for example, JPEG images
could be rendered by a PostScript program), support for composite
fonts,
and
the form mechanism for caching reusable content.
PostScript
3
PostScript 3 (Adobe dropped the "level" terminology in favor of
simple versioning) came at the end of 1997, and along with many new
dictionary-based versions of older operators, introduced better color
handling, and new filters (which allow in-program
compression/decompression, program chunking, and advanced
error-handling).PostScript 3 was significant in terms of replacing the
existing
proprietary color electronic prepress systems, then widely used for
magazine production, through the introduction of smooth shading
operations with up to 4096 shades of grey (rather than the 256
available in PostScript 2), as well as DeviceN, a color space that
allowed the addition of additional ink colors (called spot
colors) into composite color pages
2.)"Hello
World" Program
%!PS
/Courier findfont
20 scalefont
setfont
72 500 moveto
(Hello world!) show
showpage |
Or if the output device has a
console:
3.)Fundamental
Data Types
(integer, floating point, string) and
Assignment Operator
Numbers:
- Signed integers,
such as
123 -98 43445 0 +17
-Real numbers,
such as
-002
34.5 -3.62
123.6e10 1.0E-5
1E6 -1.
0.0
- Radix numbers,
such as
8#1777 16#FFFE 2#1000
Example:
will compute (3 + 4)
× (5 − 1)
Strings:
There
are three conventions for quoting a literal string
object:
- As literal
text, enclosed in (
and )
- As hexadecimal
data, enclosed in <
and >
- As ASCII
base-85 data, enclosed
in <~
and
~>
(LanguageLevel
2)
Example:
| (Hello,
world!) show
% Typeset "Hello, world!" |
Assignment Operator:
The language syntax uses reverse Polish notation,
which makes parentheses unnecessary, but reading a program requires
some practice, because one has to keep the layout of the stack in
mind.This program doesn't have assignment operator. Arithmetic in C:
grade = (test1 + test2 + test3 +
final ) / 4;
counter = counter + 1; |
Arithmetic in PostScript
/grade test1 test2 add test3 add
final add 4 div def
/counter counter 1 add def |
4.)Basic
Control Flow (conditional
and loop statements)
Loops:
There are three loops in postscript. The
first is the
repeat loop.
1.)The form of this loop is:
This will do op num times.
2.)Then there is the for loop with the form:
3.)The final loop is the loop with the form:
This
loop will need to have an exit statement inside of it
to terminate if not then you have an infinite loop (the best kind).
Here is an example of a repeat loop used in a procedure called harmonic:
|
/harmonic
{ /num 0 def
/current 1 def
{/num 1 current div num add def
/current current 1 add def
} repeat
num
} def
|
5.)Functions
- syntax, writing and
using functions, example
Functions:
The PostScript language includes operators and
procedures
that take arguments
off the operand stack and put their
results back on the
stack. The add operator,for example, pops two
arguments, which must be numbers, and
pushes the sumof those numbers back on the stack. add could
be
viewed as a function with twoinput values and one output
value.Similarly, the following procedure computes the
average and
the square root ofthe product of two numbers:
|
{ 2 copy add
2 div
3 1 roll mul
sqrt
}
|
6.)Arrays -
syntax, definition,
example
Arrays:
The characters [ and ] are self-delimiting tokens
that
specify the construction of an array. For example, the
program fragment:
results in the construction of an array object
containing
the integer object 123,
the literal name object abc, and the
string object xyz. Each
token within the brackets is executed in turn.
The [ and ] characters are special syntax for names that,
when executed, invoke PostScript operators that collect
objects and construct an
array containing them. Thus the example [ 123 /abc
(xyz) ] contains these five tokens:
• The name object [
• The integer object 123
• The literal name object abc
• The string object xyz
• The name object ]
7.)Compilers
-A postscript interpreter with previewers for serval systems
and many fonts.
-hp2ps is an HP-GL interpreter that is written in
Postscript. It runs mostly on the printer itself. There is a small C
program,
provided mainly to circumvent Postscript's problems with the ^C
character,
which is a prominent part of HPGL's text support. The C program is not
necessary
if the HP-GL does not contain text, or uses a different label
terminator.
8.)Projects
and Software
-
Use
in printing
-
Software:
-Epson StylusRIP
-PageMaker
-Adobe
9.)Standard
- ASCII/ISO
-
TrueType - the standard outline font
technology for both
Windows and the Macintosh
10.)References
http://en.wikipedia.org/wiki/PostScript#Use_in_printing
http://www-cdf.fnal.gov/offline/PostScript/BLUEBOOK.PDF
http://www.adobe.com/products/postscript/pdfs/PLRM.pdf
http://www.tailrecursive.org/postscript/postscript.html
http://www-cdf.fnal.gov/offline/PostScript