Category : DeskTop Publishing in the 1990's
Archive   : GS261EXE.ZIP
Filename : LANGUAGE.DOC

Copyright (C) 1989-1992 Aladdin Enterprises. All rights reserved.

This file is part of Ghostscript.

Ghostscript is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY. No author or distributor accepts responsibility
to anyone for the consequences of using it or for whether it serves any
particular purpose or works at all, unless he says so in writing. Refer
to the Ghostscript General Public License for full details.

Everyone is granted permission to copy, modify and redistribute
Ghostscript, but only under the conditions described in the Ghostscript
General Public License. A copy of this license is supposed to have been
given to you along with Ghostscript so you can know your rights and
responsibilities. It should be in a file named COPYING. Among other
things, the copyright notice and this notice must be preserved on all
copies.

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This file, language.doc, describes the Ghostscript language.

For an overview of Ghostscript and a list of the documentation files, see
README.

The Ghostscript interpreter, except as noted below, is intended to execute
properly any source program written in a language defined by reference to
the December 1990 printing of the PostScript Language Reference Manual
(Second Edition) published by Addison-Wesley (ISBN 0-201-18127-4). The
Ghostscript language includes the following elements of the PostScript
(TM) language:

- The full PostScript Level 1 language, as also defined in the
first edition of the PostScript Language Reference Manual, ISBN
0-201-10174-2, Addison-Wesley, 1985.

- The CMYK color, file system, version 25.0 language, and
miscellaneous additions listed in sections A.1.4, A.1.6, A.1.7, and
A.1.8 of the Second Edition respectively, including allowing a string
operand for the 'status' operator;

- The Display PostScript extensions listed in section A.1.3
of the Second Edition, but excluding the operators listed in section
A.1.2. These facilities are only available if the dps feature or the
level2 feature was selected at the time that Ghostscript was compiled
and linked.

- The composite font extensions listed in section A.1.5 of
the Second Edition, but not the ability to handle Type 0 fonts.
These facilities are only available if the compfont feature or the
level2 feature was selected at the time that Ghostscript was compiled
and linked.

- A subset of the other PostScript Level 2 operators and
facilities listed in section A.1.1 of the Second Edition, identified
below. These facilities are only available if the level2 feature was
selected at the time that Ghostscript was compiled and linked.

Ghostscript also includes a number of operators defined below that are not
in the PostScript language.

Stub facilities
---------------

The following operators, while provided in the current release, have only
a partial or dummy implementation.

Form and pattern operators:
execform

Graphics state operators:

currentblackgeneration, currentcolorscreen,
currenthalftonephase, currentundercolorremoval,
setblackgeneration, setcolorscreen,
sethalftonephase, setundercolorremoval,
currenthalftone, sethalftone

Interpreter parameter operators:
currentsystemparams, currentuserparams
setsystemparams, setucacheparams, setuserparams
ucachestatus

Path construction operators:
ucache

Virtual memory operators:
currentshared, scheck, setshared, setvmthreshold, shareddict,
SharedFontDirectory, vmreclaim

Miscellaneous operators:
serialnumber

Unclassified Level 2 operators
------------------------------

Ghostscript provides the following PostScript Level 2 operators
listed in section A.1.1 of the Second Edition and not listed in any
of the other A.1 sections.

File operators:
filter (all but DCTEncode/Decode)

Resource operators:
defineresource, findresource, resourceforall, resourcestatus,
undefineresource

Character and font operators:
cshow, xshow, yshow, xyshow
glyphshow
findencoding, rootfont, setcachedevice2
(WMode is supported, but composite fonts are not)

Graphics state operators:
currentcolor, currentcolorspace, setcolor, setcolorspace
(except for Indexed with procedure, true Separation, and Pattern)
currentcolorrendering, setcolorrendering

Miscellaneous operators:
languagelevel

In addition, Ghostscript supports the following Level 2 facilities:

- Use of a dictionary with the image and imagemask operators;

- Use of a string or a file as data source with the image,
imagemask, and colorimage operators.

When the Level 2 features are present, Ghostscript also supports the
following operator:

<1 or 2> .setlanguagelevel -
Set the current language level to Level 1 or Level 2.
When the language level is 1, no Level 2 facilities
are provided.

Unimplemented Level 2 facilities
--------------------------------

Ghostscript currently does not implement the following Level 2
operators and variables:
currentdevparams, setdevparams
GlobalFontDirectory
makepattern
realtime
currentpagedevice, setpagedevice
startjob

Ghostscript currently does not implement the following Level 2
facilities not enumerated above:
garbage collection
global and local VM
page devices
job control
halftone dictionaries
user names

Ghostscript-specific additions
==============================

Miscellaneous
-------------

^Z is counted as whitespace.

run can take either a string or a file as its argument. In the former
case, it uses findlibfile to open the file (searching directories as
needed). In the latter case, it just runs the file, closing it at the
end, and trapping errors just as for the string case.

Mathematical operators
----------------------

arccos
Computes the arc cosine of a number between -1 and 1.

arcsin
Computes the arc sine of a number between -1 and 1.

String operators
----------------

type1encrypt
Encrypts fromString according to the algorithm for Adobe
Type 1 fonts, writing the result into toString.
toString must be at least as long as fromString or a
rangecheck error occurs. state is the initial state of
the encryption algorithm (a 16-bit non-negative
integer); newState is the new state of the algorithm.

type1decrypt
Decrypts fromString according to the algorithm for Adobe
Type 1 fonts, writing the result into toString. Other
specifications are as for type1encrypt.

Relational operators
--------------------

max
Returns the larger of two numbers or strings.

min
Returns the smaller of two numbers or strings.

File operators
--------------

findlibfile true or false
Opens the file of the given name for reading. If the file
cannot be opened using the supplied name, searches
through directories as described in use.doc. If the
search fails, findlibfile simply pushes false on the
stack and returns, rather than causing an error.

unread -
Pushes back the last-read character onto the front of the
file. If the file is only open for writing, or if the
integer argument is not the same as the last character
read from the file, causes an ioerror error. May also
cause an ioerror if the last operation on the file was not
a reading operation.

writeppmfile -
Writes the contents of the device, which must be an image
device, onto the file, in Portable PixMap (ppm) format.
Does not close the file.

Path operators
--------------

rectappend -
rectappend -
rectappend -
Appends a rectangle or rectangles to the current path, in
the same manner as rectfill, rectclip, etc. Only
defined if the dps option is selected.

Filters
-------

Ghostscript supports all standard filters except DCTEncode and
DCTDecode. Ghostscript does not support the use of a procedure as a
data source or sink, only a file or a string. In addition,
Ghostscript supports two non-standard filters:

/eexecDecode filter
Creates a filter for decrypting data that has been
encrypted using eexec encryption as described in the
Adobe Type 1 Font Format documentation. The
seed_integer must be 55665 for proper operation.

/PFBDecode filter
Creates a filter that decodes data in .PFB format, the
usual semi-binary representation for Type 1 font files
on IBM PC and compatible systems. If hex_boolean is true,
binary packets are converted to hex; if false, binary
packets are not converted.

Miscellaneous operators
-----------------------

- currenttime
Returns the current value of a continuously-running timer,
in minutes. The initial value of this timer is undefined.

getenv true or false
Looks up a name in the shell environment. If the name is
found, returns the corresponding value and true; if the
name is not found, returns false.

makeoperator
Constructs and returns a new operator that is actually the
given procedure in disguise. The name is only used for
printing. The operator has the executable attribute.

setdebug -
If the Ghostscript interpreter was built with the DEBUG
flag set, sets or resets any subset of the debugging
flags normally controlled by -Z in the command line.
Has no effect otherwise.

- oserrno
Returns the error code for the most recent OS error.

- oserror
Returns the error string for the most recent OS error.

Device operators
----------------

copydevice
Copies a device.

getdevice
Returns a device from the set of devices known to the
system. The first device, which is default, is numbered
0. If the index is out of range, causes a rangecheck
error.

makeimagedevice
Makes a new device that accumulates an image in memory.
matrix is the initial transformation matrix: it must be
orthogonal (i.e., [a 0 0 b x y] or [0 a b 0 x y]).
palette is a string of 2^N or 3*2^N elements, specifying
how the 2^N possible pixel values will be interpreted.
Each element is interpreted as a gray value, or as RGB
values, multiplied by 255. For example, if you want
a monochrome image for which 0=white and 1=black, the
palette should be ; if you want a 3-bit deep
image with just the primary colors and their complements
(ignoring the fact that 3-bit images are not supported),
the palette might be <000000 0000ff 00ff00 00ffff
ff0000 ff00ff ffff00 ffffff>. At present, the palette
must contain exactly 2, 4, 16, or 256 entries,
and must contain an entry for black and an entry
for white; if it contains any entries that aren't black,
white, or gray, it must contain at least the six primary
colors (red, green, blue, and their complements cyan,
magenta, and yellow); aside from this, its contents are
arbitrary.
Alternatively, palette can be null. This is interpreted
as 24-bit-per-pixel color, where the four bytes of each
pixel are respectively R, G, and B.
Note that one can also make an image device (with the same
palette as an existing image device) by copying a device
using the copydevice operator.

copyscanlines
Copies one or more scan lines from an image device into a
string, starting at a given scan line in the image.
The data is in the same format as for the image
operator. Error if the device is not an image device or
if the string is too small to hold at least one complete
scan line. Always copies an integral number of scan
lines.

setdevice -
Sets the current device to the specified device. Also
resets the transformation and clipping path to the
initial values for the device.

- currentdevice
Gets the current device from the graphics state.

devicename
Gets the name of a device.

deviceinitialmatrix
Gets the initial matrix of a device, i.e., the one that
defaultmatrix would return if the device were the
current device.

getdeviceprops ...
Gets all the properties of a device. Currently defined
names and values for all devices are:
HWResolution [ ]
X and Y resolution in pixels/inch.
HWSize [ ]
X and Y size in pixels.
InitialMatrix [<6 floats>]
Initial transformation matrix.
Name
Read-only. The device name.
For printers, the following are also defined:
BufferSpace
Buffer space for band lists, if the bitmap
is too big to fit in RAM.
MaxBitmap
Maximum space for a full bitmap in RAM.
OutputFile
() means send to printer directly,
otherwise specifies the file name for
output; a %d is replaced by the page #;
on Unix systems, (|command) writes to a pipe
PageCount
Read-only. Counts the number of pages
printed on the device.

...
putdeviceprops
Sets properties of a device. May cause undefined,
typecheck, rangecheck, or limitcheck errors.

- flushpage -
On displays, flushes any buffered output, so that it
is guaranteed to show up on the screen; on printers,
has no effect.

Character operators
-------------------

.type1addpath -
.type1addpath -
Adds the description of a character to the current
path. The string argument is a scalable
description encoded in Adobe Type 1 format. This
operator, like setcharwidth and setcachedevice, is
only valid in the context of a show operator. It
uses information from the current font, in addition
to the argument(s).
The optional lsbx and lsby arguments are left side
bearing values that override the ones in the
character outline.

Type1BuildChar -
This is not a new operator: rather, it is a name known
specially to the interpreter. Whenever the interpreter
needs to render a character (during a ...show,
stringwidth, or charpath), it looks up the name
BuildChar in the font dictionary to find a procedure to
run. If it does not find this name, and if the FontType
is 1, the interpreter instead uses the value (looked up
on the dictionary stack in the usual way) of the name
Type1BuildChar.
The standard definition of Type1BuildChar is in gs_fonts.ps.
Users should not need to redefine Type1BuildChar, except
perhaps for tracing or debugging.

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PostScript is a trademark of Adobe Systems, Incorporated.