Tech Arsenal 1/Tech Arsenal (Arsenal Computer).ISO/tek-04/gs24src.zip/LANGUAGE.DOC

Text File | 1992-02-26 | 17KB | 419 lines

   Copyright (C) 1989, 1990, 1991 Aladdin Enterprises.  All rights reserved.
   Distributed by Free Software Foundation, Inc.

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.

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

    - A few other PostScript Level 2 operators, listed below.

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.

Character and font operators:
    cshow, rootfont, setcachedevice2

Graphics state operators:
    currentblackgeneration, currentcmykcolor, currentcolorscreen,
    currentcolortransfer, currenthalftonephase, currentundercolorremoval,
    setblackgeneration, setcmykcolor, setcolorscreen,
    setcolortransfer, sethalftonephase, setundercolorremoval,
    currenthalftone, sethalftone,
    currentstrokeadjust, setstrokeadjust,
    setbbox

Interpreter parameter operators:
    setucacheparams, ucachestatus

Path construction operators:
    ucache

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

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

The following PostScript Level 2 operators are available in Ghostscript:

       filter (not all filters are implemented, and most of the
      implemented ones are only available if the filter feature was
      selected when Ghostscript was built)

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.

copy works on devices, as well as on the standard PostScript types.

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

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

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

Dictionary operators
--------------------

    <dict> <integer> setmaxlength -
        Changes the capacity of a dictionary, preserving its
          contents.  Causes a dictfull error if the requested
          capacity is less than the current number of occupied
          entries.

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

    <string|name|other> <patternString> stringmatch <boolean>
        Determines whether the string or name matches the given
          pattern.  In the pattern, `*' matches any substring of
          the string, `?' matches any single character, and `\'
          quotes the next character.  If the first argument is not
          a string or name, stringmatch returns true if
          patternString is a single *, and false otherwise.

    <state> <fromString> <toString> type1encrypt <newState> <toSubstring>
        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.

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

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

    <number|string> <number|string> max <number|string>
        Returns the larger of two numbers or strings.

    <number|string> <number|string> min <number|string>
        Returns the smaller of two numbers or strings.

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

    <string> findlibfile <foundstring> <file> true or <string> 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.

    <file> <integer> unread -
         Pushes back the given character onto the front of the
          file.  If the file is only open for writing, or if the
          C library call (ungetc) fails, causes an ioerror error.
          If the integer is not in the range [0..255], causes
          a rangecheck error.

    <file> <device> 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
--------------

    <x> <y> <width> <height> rectappend -
    <numarray> rectappend -
    <numstring> 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 only the filters listed below.  Ghostscript does not
support the use of a procedure as a data source or sink, only a file or a
string.  The eexecDecode filter is specific to Ghostscript.

The LZW filters are not provided, even though they have been implemented,
because IBM and Unisys both claim a legal monopoly right (patent) to
prevent anyone else from distributing any implementation of the (freely
available) specification of these algorithms.  For more information about
the damaging effects of software patents, contact the League for
Programming Freedom, Cambridge, Massachusetts, U.S.A.

    <file|string> /ASCII85Encode filter <file>
        Creates a filter that converts each group of 4 bytes to 5
          printable characters.  Closing the filter writes a '~>'
          on the underlying file.

    <file|string> /ASCII85Decode filter <file>
        Creates a filter that reverses the action of
          ASCII85Encode.

    <file|string> /ASCIIHexEncode filter <file>
        Creates a filter that converts each byte to two hex
          digits.  Closing the filter writes a '>' on the
          underlying file.

    <file|string> /ASCIIHexDecode filter <file>
        Creates a filter that reverses the action of
          ASCIIHexEncode.

    <file|string> <seed_integer> /eexecDecode filter <file>
        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.

    <file|string> /NullEncode filter <file>
        Creates a filter that does no transformations.  Only
          useful for creating a "file" that writes to a string.

    <file|string> /PFBDecode filter <file>
        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.

    <file|string> 0 () /SubFileDecode filter <file>
        Creates a filter that does no transformations.  Only
          useful for creating a "file" that reads from a string.
          (This is the null subcase of the general SubFileDecode
          filter, which Ghostscript does not yet support.)

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

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

    <string> getenv   <string> 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.

    <name> <array> makeoperator <operator>
        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.

    <string> <boolean> 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.

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

    <index> getdevice <device>
        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.

    <matrix> <width> <height> <palette> makeimagedevice <device>
        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 <ff 00>; 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 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.  (4-entry or 16-entry palettes, corresponding
          to 2- or 4-bit pixels, may be supported eventually.)
        Alternatively, palette can be null.  This is interpreted
          as 32-bit-per-pixel color, where the four bytes of each
          pixel are respectively unused, 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 copy operator.

    <device> <index> <string> copyscanlines <substring>
        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.

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

    - currentdevice <device>
        Gets the current device from the graphics state.

    <device> devicename <string>
        Gets the name of a device.

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

    <device> getdeviceprops <mark> <name1> <value1> ... <namen> <valuen>
        Gets all the properties of a device.  Currently defined
          names and values for all devices are:
            Name <string>
                device name
            HWResolution [<float> <float>]
                X and Y resolution in pixels/inch
            HWSize [<integer> <integer>]
                X and Y size in pixels
            InitialMatrix [<6 floats>]
                initial transformation matrix
        For printers, the following are also defined:
            MaxBitmap <integer>
                maximum space for a full bitmap in RAM
            BufferSpace <integer>
                buffer space for band lists, if the bitmap
                  is too big to fit in RAM
            OutputFile <string>
                () means send to printer directly,
                  otherwise specifies the file name for
                  output; a * is replaced by the page #;
                  on Unix systems, (|command) writes to a pipe

    <mark> <name1> <value1> ... <namen> <valuen> <device>
        putdeviceprops <device>
        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
-------------------

    <string> type1addpath -
        Adds the description of a character to the current path,
          and then optionally renders the character.  The string
          argument is a scalable description encoded in Adobe Type
          1 format.  This operator is only valid in the context of
          a show operator, like setcharwidth and setcachedevice.
          It uses information from the current font, in addition
          to the argument.

    <image> <width> <height> <wx> <wy> <ox> <oy> <string>
      type1imagepath <substring>
        Converts an image (bitmap) description of a character into
          a scalable description in Adobe Type 1 format.  The
          current transformation matrix should be the same as the
          FontMatrix of the font in which this character will be
          used: this establishes the scaling relationship between
          image pixels (the image is assumed to be 1 unit high in
          user space) and the character coordinate system used in
          the scalable description.  wx and wy are the character
          width, and ox and oy are the character origin relative
          to the lower left corner of the bitmap, in *pixels*.
        All coordinates in the scalable description are rounded to
          integers, so the coefficients in the FontMatrix should
          be on the order of 1/N for some value of N that is
          either a multiple of the height/width or is large
          compared to the width and height.  (There is a
          convention, which some PostScript programs rely on, that
          N=1000.)
        Note that the encoded description has *not* been subjected
          to CharString encryption, which is necessary before the
          description can be given to type1addpath: to do this,
          follow the type1imagepath with
            4330 exch dup type1encrypt exch pop
        If the description is too complex to fit into the supplied
          string, a limitcheck error results.  A good rule of
          thumb is that the size of the string should be about 6
          times the number of 1-bits in the image that are not
          completely surrounded by other 1-bits.

    <font> <char> 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.