Postscript interpreter - user documentation =========================================== Post V0.2 Copyright Adrian Aylward 1989, 1990 Free use and non-commercial reproduction of the binaries of this prerelease is permitted, providing that the copyright notices are not removed. Distribution by disk libraries is permitted provided only a nominal copying fee is charged. All other rights are reserved. For queries and bug reports write to the author: Adrian Aylward, 20 Maidstone Road, SWINDON, Wiltsire. UK. No responsibilities accepted for bugs, but please let me know so I can fix them. Introduction ============ "Post" is a software based PostScript interpreter, presently running on the Amiga. The source code is written in C, and should be fairly portable to other machines. It supports the full Adobe language, with only minor variations. Being a prerelease there will likely be bugs. Command line interface ====================== usage: post [files...] [IFF file] [SCREEN] [SIZE xydxy..lhi?] [MEM fhlv..?] The input files --------------- The interpreter reads the input files in turn. If none are present, the standard input is read instead. (The standard input may also be explicity read as "%stdin".) If the input appears to be interactive, prompts will be displayed. When the end of the last file is reached, the program exits. Printer output -------------- This is the default if neither the IFF nor SCREEN options are used. The oputput is sent to the printer device as a graphic dump. The interpreter will obtain default values for the page size, density, and number of colors from the current preferences. If you use the default sizes make sure you have set the page size: run preferences and on the graphic 2 screen set the width and height limits - either bounded or absolute or in pixels. The output defaults to black and white or 3 colour, according to the preferences. IFF file output --------------- This option will send the output to an IFF file. Each IFF file comtains a single FORM ILBM. So that multiple pages may be created in a single run of the interpreter, sequence nubers are automatically generated: IFF path/fred*.pic will generate path/fred1.pic, path/fred2.pic ... and IFF path/fred??.pic will generate path/fred01.pic, path/fred02.pic ... The default page size etc. is the same as for screen output. SCREEN output ------------- This option will send the output to a screen. (Use Amiga/N, Amiga/M to view it.) You can generate both screen and IFF output at the same time. The default screen size is the same as the workbench screen, but in interlace mode. The default density is 75 pixels per inch. The default number of colours is 3. The SIZE option --------------- The SIZE option sets the page size and density etc.. SIZE "x..y..s..[x]d...[y]d..lhibc.?" The page sizes ("x..y..s..") are in pixels, as decimal numbers; "s" sets the size of the bands, for band rendering to the printer. Densities ([x]d..[y]d..) are in pixels per inch; "xd" or "yd" set the x or y density, and "d" sets both. The screen resolution is: "l" for low resolution no interlace, "h" for high resolution no interlace, and "i" for high resolution interlaced. The number of colours is: "b" for black and white (1 bit plane), "c" or "c3" for 3 colour rgb (3 bit planes), and "c4" for 4 colour cmyk (4 bit planes). To verify the sizes, type SIZE "?". The MEM option -------------- The MEM option controls the amount of memory allocated for workspace. The memory defaults are chosen to suit a large machine processing relatively complex pages. For simple screen output much lower minimums are possible - if you don't have enough memory on your machine try the small values instead. Default Small ------- ----- v280000 (40000) Virtual machine memory f60000 (1000) Font cache l60000 (8000) Line drawing and image workspace h20000 (1000) Halftone buffer (x + 32) * y / 8 Page buffer At the one extreme it should be possible to generate simple screen output using the small values on 512K machine, whereas the default values for a complex A4 page at 300 dpi. should fit on a machine with 2 megabytes. If you include "?" the interpreter will tell you the sizes it is using. Compatability ============= The interpreter is based upon the language (version "23.0") as described by the book: "PostScript Language Reference Manual" Adobe Systems Incorporated, Addison-Wesley 1985, ISBN 0-201-10174-2 File handling ------------- The files %stdin, %stdout, %stderr are permanently open as far as the operating system is concerned. Attempts to close them will invalidate the file object but not close them to the operating system. If they are connected to a terminal they will be unbuffered, so output will be transmitted immediately, without waiting for a "flush". The special files %statementedit and %lineedit are not supported. Error handling -------------- A new error "invalidstop" has been added. The execution stack ------------------- The exact contents of the execution stack are not defined by the language reference manual, and cannot therefore be guaranteed to be the same as other implementations. Dumping the stack is likely to yield useful debugging information but is not recommended for normal programming. Colour mapping -------------- The interpreter can run with one bit plane (for black and white printers), 3 bit planes (red, green, blue) or 4 bit planes (cyan, magenta, yellow, black). For screen output 3 bit planes are appropiate. For a colour printer the 3 or 4 colour model can be used. The output is always in binary; gray scale is supported only via the halftone mechanism. For low resolution colour printers the 3 colour model is probably best. The 4 color model is for high resolution colour printers that can generate high frequency halftone screens, where a fourth screen is used to improve the quality of the blacks and grays. (N.B. the preferences printer drivers only handle 3 colour model, so if you want to use the 4 colour model you will probably need to generate an IFF file and write your own print dump program. They will however automatically use black the ribbon/ink if the printer has one) The transformations between the RGB and the HSB models are based on those in the book: "Procedural Elements for Computer Graphics" David F. Rogers, McGraw-Hill 1985, ISBN 0-E07-053534-5. Band Rendwring -------------- For a high resolution printer the page buffer can be quite large (a megabyte or so). If you don't have enough memory to hold the entire page at once you can render each one in several bands. Set the "SIZE s..." option to the largest band size you have space for. (For matrix printers it will probably be best to make it a multiple of the number of printer pins times the number of vertically displaced passes). Then run the postscript program generating each page once for each band, using the "setband" operator, which is described below, to set the base for each band. Start at a base of zero and increment the base by the band size until you reach the page height. Each band is sent to the printer as a separate graphic dump; the last band generates a form feed to eject the page. You can use the "currentband" operator to calculate the number of bands needed: currentband 1 sub { setband pageproc } for 0 setband will execute "pageproc" once for each band (remaining) on the page. The procedure should execute copypage (or showpage) exactly once per iteration. N.B. this technique is only suitable for printer output. Fonts ----- There are no fonts built in to the interpreter; they must all be downloaded. The findfont operator will execute the error invalidfont if the font you request is not present in the font dictionary. You can redefine it, perhaps to search the Unix/Amiga filing system to automatically download fonts or to substitute a default font. The font caching will work significantly better if all your fonts have UniqueID's. Then repeated makes of the same font with the same matrix will be cached, and cached character bitmaps can be retained even if the font is removed by a restore operation. N.B. if fonts are downloaded after a save they will be removed by the corresponding restore; in the interests of efficiency it may therefore be better to preload them. Operators omitted or changed ---------------------------- banddevice Not appropiate for the Unix/Amiga environment. bytesavailable Since we can't tell how many bytes are available we always return -1. copypage For printer output this works like the standard. For screen output it does not need to do anything, as the screen is not buffered. Use Amiga/n and Amiga/m to view the screen and to return to the workbench screen. If you want to add a pause to view the results, redefine the operator to add one. For IFF file output it writes the page to the next file. echo Not appropiate for the Unix/Amiga environment. executive There is no executive, as the interpreter supports interactive usage directly. findfont Looks in the FontDirectory. If it can't find the supplied key, it exeuctes the error invalidfont. flushfile We don't check for errors when flushing an input file, to prevent recursion in the error handler. framedevice Not appropiate for the Unix/Amiga environment. prompt Not called by the interpreter. See "prompts" instead. renderbands Not appropiate for the Unix/Amiga environment. resetfile Does nothing. showpage See the notes for copypage above. start Not used. Write your own startup file if you want one. usertime Returns the time elapsed since the interpreter started, with a resolution of one second. Operators added --------------- currentband "currentband" base size height Returns the base of the current band, size of each band, and total height of the page. setband base "setband" Sets the base height of the band being rendered. The value must be greater than or equal to zero and less than the total height of the page. invalidstop (error) A "stop" has been executed for which there is no dynamically enclosing "stopped" context. prompts string string "prompts" The first string is used as the prompt when the interpreter is scanning terminal input and executing it immediately; the second string is used when execution is defered while scanning the contents of a procedure "{ ... }". No prompt is given when a newline is encountered within a string. vmhwm "vmhwm" hwmused maximum Returns two integers: the high water mark of the amount virtual memory used since the program was first started or the last "vmhwm", and the maximum available amount of memory. Colour operators not in the red book ------------------------------------ The Adobe 4 colour operators are supported: colorimage currentblackgeneration currentcmykcolor currentcolorscreen currentcolortransfer currentundercolorremoval setblackgeneration setcmykcolor setcolorscreen setcolortransfer setundercolorremoval Miscellaneous ------------- The system dictionary is left writeable so that standard preludes can add things to it - possibly removing write permission when they have finished. Device space ------------ The largest device that the interpreter can handle is 31767 (sic.) by 32767 pixels. In practice you will probably run out of memory long before reaching this limit. Versions ======== V0.0 14-Nov-89 (prerelease) The original. V0.1 06-Dec-89 (prerelease) Image routines added. Range checks eased on gray levels and colours etc.. Area filling speeded up, matrix manipulation and colour mapping rewritten, numeric conditioning improved for path fill. Bugs fixed: syntax error, == string escapes, error handling and quit when recursing, vm error handling, integer overflow in path fill, matrix save, interrupt after printing page, dictionary second save, name table restore, boolean type checking, multiple halftone screens memory allocation. V0.2 07-Jan-90 (prerelease) Font and character routines added. Null device added. Band rendering of printer output added. Matrix manipulation rewritten again. Interpreter recursion rewritten. Allocate stacks dynamically. Bugs fixed: missing access checks on strings, scan token negative chars, depth check in path flattening, pathbbox, strings or null objects as dictionary keys, shade after grestore(all), fill/image with clip region, clip unclosed subpath, dictstack/execstack.