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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. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - This file, language.doc, describes the Ghostscript language. For an overview of Ghostscript and a list of the documentation files, see README. The Ghostscript language bears a very strong resemblance to the PostScript (TM) language. In fact, the current release of Ghostscript, unless otherwise noted, is intended to execute properly any source program that conforms to the definition of the Level 1 PostScript Language as presented in the December 1990 printing of the PostScript Language Reference Manual (Second Edition) published by Addison-Wesley, plus a subset of the Display PostScript and Level 2 PostScript operators (indicated below). Some of the operators of the Ghostscript language are actually implemented as procedures. For this reason, `bind' will not necessarily bind every `operator' of the language. Extended PostScript Facilities ------------------------------ Aladdin Enterprises intends to extend Ghostscript over time to implement many of the facilities of Display PostScript and of Level 2 PostScript. The following operators provided in the current release are not part of the original Level 1 PostScript specification, and are intended to have the same meanings in Ghostscript as in Display PostScript or Level 2 PostScript, unless otherwise noted. Operators or categories marked with * have only a partial or dummy implementation. Language features: // syntax for immediately evaluated names CR, LF, or CRLF as end-of-line Character and font operators: ISOLatin1Encoding, selectfont Dictionary operators: undef File operators: deletefile, eexec, filenameforall (MS-DOS and VMS only), fileposition, renamefile, setfileposition * Graphics state operators: currentblackgeneration, currentcmykcolor, currentcolorscreen, currentcolortransfer, currenthalftonephase, currentundercolorremoval, setblackgeneration, setcmykcolor, setcolorscreen, setcolortransfer, sethalftonephase, setundercolorremoval Interpreter parameter operators: currentcacheparams, setcacheparams Packed array operators: currentpacking, packedarray, setpacking Painting operators: colorimage Path construction operators: arct Ghostscript-specific additions ============================== Miscellaneous ------------- ^Z is counted as whitespace. readhexstring can take either a file or a string as the source of characters. In the latter case, it leaves the remainder of the string on the stack, just as for the token operator. 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 ---------------------- <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 -------------- <state> <file> type1decryptfile <newFile> Creates a pseudo-file for decrypting a file that contains hex characters (as for readhexstring) that represent an encrypted string. The pseudo-file is only available for reading. <string> findlibfile <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. 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. Graphics state operators ------------------------ - currentgscolor <color> Returns a color object (a new kind of object) representing the current color/gray from the graphics state. <color> setgscolor - Sets the current color in the graphics state according to a color object. 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. <device> devicename <string> Gets the name of a device. The devices currently supported are listed in gdevs.mak. <matrix> <width> <height> <palette> makeimagedevice <device> Makes a new device that accumulates an image in memory. palette is an array of color objects that specify how the pixel values will be interpreted, e.g., if you want a monochrome image for which 0=white and 1=black, the palette should be the result of executing [ 1 setgray currentgscolor 0 setgray currentgscolor ] The palette must contain exactly 2, 4, 16, or 256 entries, and must contain an entry for black and an entry for white; aside from this, its contents are arbitrary. Each pixel occupies log2(colormap size) bits. 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 colormap as an existing image device) using makedevice. ****** NOTE: the current implementation of makeimagedevice only supports 1-, 8-, and 32-bit-per-pixel devices. ****** <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> <matrix> <width> <height> makedevice <device> Makes a new device just like an existing one, but with a specified width, height, and initial transformation. Note that the width is in pixels, not in bytes as in framedevice. <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> <matrix> deviceparams <<mark>> <matrix> <width> <height> Gets the parameters of a device. Some devices may have additional parameters betwen the mark and the matrix: one should use cleartomark to remove the output of deviceparams from the stack. - 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 P*stScr*pt 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. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - PostScript is a trademark of Adobe Systems, Incorporated.