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Text File | 1998-05-21 | 17.0 KB | 461 lines

Copyright (C) 1989, 1995 Aladdin Enterprises. All rights reserved. This file is part of GNU Ghostscript. GNU 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 GNU Ghostscript General Public License for full details. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - This file, language.doc, describes the relationship between the Ghostscript interpreter and the PostScript language. This file describes version 3.33 of Ghostscript. 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 the (Level 2) PostScript language as defined in the December 1990 printing of the PostScript Language Reference Manual (Second Edition) published by Addison-Wesley (ISBN 0-201-18127-4). However, the interpreter is configurable in ways that can restrict it to various subsets of this language. Specifically, the base interpreter accepts the Level 1 subset of the PostScript language, as defined in the first edition of the PostScript Language Reference Manual, ISBN 0-201-10174-2, Addison-Wesley, 1985, plus the file system, version 25.0 language, and miscellaneous additions listed in sections 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 base interpreter may be configured by adding any combination of the following: - The ability to process PostScript Type 1 fonts. This facility is normally included in the interpreter. - The CMYK color extensions listed in section A.1.4 of the Second Edition (including colorimage). These facilities are only available if the color, dps, or level2 feature was selected at the time that Ghostscript was compiled and linked. - 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, and 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. - The PostScript Level 2 "filter" facilities aside from DCTEncode and DCTDecode filters. These facilities are only available if the filter, dps, or level2 feature was selected at the time that Ghostscript was compiled and linked. - The PostScript Level 2 DCTEncode and DCTDecode filters. These facilities are only available if the dct or level2 feature was selected at the time that Ghostscript was compiled and linked. - All the other PostScript Level 2 operators and facilities listed in section A.1.1 of the Second Edition and not listed in any of the other A.1.n sections. These facilities are only available if the level2 feature was selected at the time that Ghostscript was compiled and linked. Adding all of these produces a full Level 2 PostScript language interpreter. Ghostscript also includes a number of operators defined below that are not in the PostScript language. Implementation limits ===================== The following implementation limits correspond to those in Table B.1 and B.2 of the Second Edition. Those marked with * are different from the ones in the Second Edition. Architectural limits -------------------- integer 32-bit two's complement integer real single-precision IEEE float *array On 16-bit systems: 8191 elements On 32-bit systems: 65535 elements *dictionary On 16-bit systems: 8190 elements On 32-bit systems: 65534 elements *string 65535 characters *name 16383 characters filename 100 characters *save level none (capacity of memory) *gsave level none (capacity of memory) Typical memory limits in Level 1 -------------------------------- userdict 200 FontDirectory 100 *operand stack 800 dictionary stack 20 execution stack 250 *interpreter level none (capacity of memory) *path none (capacity of memory) dash 11 *VM capacity of memory *file determined by operating system *image 65535 values (samples x components) for 1, 2, 4, or 8-bit samples; 32767 values for 12-bit samples Other differences in VM consumption ----------------------------------- Packed array elements occupy either 2 bytes or 8 bytes. The average element size is probably about 5 bytes. Names occupy 12 bytes plus the space for the string. Ghostscript-specific additions ============================== Miscellaneous ------------- ^D and ^Z are self-delimiting tokens, like [ and ]. They are initially defined as empty procedures so that they will be ignored in the input stream. run can take either a string or a file as its argument. 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 ---------------------- <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. String operators ---------------- <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 <string> findlibfile <string> false Opens the file of the given name for reading, searching 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 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. <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 all the standard PostScript Level 2 filters. In addition, Ghostscript supports the following non-standard filters: <target> <seed_integer> /eexecEncode filter <file> Creates a filter for encrypting data into the eexec encrypted format described in the Adobe Type 1 Font Format documentation. The seed_integer must be 55665 for proper operation. This filter produces binary output and does not include the initial 4 garbage bytes. <source> <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. <source> <hex_boolean> /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. If hex_boolean is true, binary packets are converted to hex; if false, binary packets are not converted. Various versions of Ghostscript may also support other non-standard filters for experimental purposes. The current version includes the following non-standard filters, which are not documented further. No guarantee is made that these filters will exist in compatible form, or at all, in future versions. <target/source> <string> ByteTranslateEncode/Decode <target> <int> BigStringEncode <target/source> BCPEncode/Decode <target/source> TBCPEncode/Decode <target/source> <dict> BoundedHuffmanEncode/Decode FirstBitLowOrder <bool> false MaxCodeLength <int> 16 EndOfData <bool> true EncodeZeroRuns <int> 256 Tables <int_array> <target/source> <dict> BWBlockSortEncode/Decode BlockSize <int> 16384 <target/source> MoveToFrontEncode/Decode Ghostscript also supports a non-standard optional dictionary operand for the LZWDecode filter, with the following keys (all optional): InitialCodeLength <integer> An integer between 2 and 11 specifying the initial number of data bits per code. Note that the actual initial code length is 1 greater than this, to allow for the reset and end-of-data code values. Default value: 8. FirstBitLowOrder <boolean> If true, codes appear with their low-order bit first. Default value: false. BlockData <boolean> If true, the data is broken into blocks in the manner specified for the GIF file format. Default value: false. EarlyChange <integer> If 0, codes become one bit longer one code earlier than they need to; if 1, codes become one bit longer as specified in the PostScript Language Reference Manual. Default value: 1. Virtual memory operators ------------------------ <save> .forgetsave - Cancels the effect of a save -- makes it as though the save never happened. 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 <string> getenv 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. - .oserrno <errno> Returns the error code for the most recent OS error. - .oserror <string> Returns the error string for the most recent OS error. Device operators ---------------- <device> copydevice <device> Copies a device. <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, 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. <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> getdeviceprops <mark> <name1> <value1> ... <namen> <valuen> Gets all the properties of a device. Currently defined names and values for all devices are: BitsPerPixel <integer> Usually read-only. Number of bits per pixel. .HWMargins [<4 floats>] Size of non-imageable regions around edges of page, in 1/72" units. HWSize [<integer> <integer>] X and Y size in pixels. Name <string> Read-only. The device name. Currently, same as OutputDevice. Colors, GrayValues, RedValues, GreenValues, BlueValues, ColorValues As for the 'deviceinfo' operator of Display PostScript. In addition, the following are defined per Adobe's documentation for the setpagedevice operator: Duplex (if supported) HWResolution ImagingBBox Margins NumCopies (for printers only) Orientation (if supported) OutputDevice PageSize ProcessColorModel Some devices may only allow certain values for HWResolution and PageSize. The null device ignores attempts to set PageSize; its size is always [0 0]. Red/Green/Blue/ColorValues are only defined if Colors > 1. For printers, the following are also defined: BufferSpace <integer> Buffer space for band lists, if the bitmap is too big to fit in RAM. MaxBitmap <integer> Maximum space for a full bitmap in RAM. OutputFile <string> () 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 OpenOutputFile <boolean> If true, open the device's output file when the device is opened, rather than waiting until the first page is ready to print. .PageCount <integer> Read-only. Counts the number of pages printed on the device. <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 - <string> <lsbx> <lsby> .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. <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. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - PostScript is a trademark of Adobe Systems, Incorporated.