PltDef.doc version 2.0 Tim Mooney 3/22/88 A PltDef file describes the physical specifications and command language of a plotter so that IntroCAD can render drawings on it. IntroCAD uses only the most primitive capabilities of a command language so that a wide variety of plotters can be supported. PltDef files, for the most part, are ASCII files which contain only printable characters and which can be edited with an ordinary text editor. This is because the most common plotter command languages use only printable ASCII characters. But the file format contains no strategy for encoding non-printable characters in terms of printable codes (as the format of a PrtDef file does) and so a PltDef file MAY contain non-printable ASCII codes. IntroCAD makes a few assumptions about plotter command languages that you must be clear on before attempting to write a PltDef file. 1) Coordinates: Points on the plotter page are referred to by pairs of integers; the X and Y coordinates. The X coordinate is the first number of the pair, the Y coordinate the second. The X and Y coordinates are separated by some character or string of characters--normally a space or a comma; you must tell IntroCAD what the SEPARATOR is. Pairs of coordinates are separated by the same character or string. Example: "100 200 150 300" Here: "100" and "150" are X coordinates; "200" and "300" are Y coordinates; coordinates are separated by space characters. 2) Pen Motion Commands: The command language contains at least a MOVE command and a DRAW command. The MOVE command instructs the plotter to move, with the pen up off the page, to some location. MOVE is followed by one pair of coordinates. The DRAW command instructs the plotter to put the pen down on the page and drag it, from wherever it now lies, to each of several locations. DRAW may be followed by any number of coordinate pairs. A complete command of any kind is followed by a TERMINATOR character or string. You must tell IntroCAD what the TERMINATOR is. Example: "PU 100 200; " Here: "PU" is a MOVE command; " " is the coordinate SEPARATOR; "100 200" is a coordinate pair; and ";" is a command TERMINATOR. Example: "PU 10 200; PD 10 300 20 400 10 200; " Here: "PU" is a MOVE command; "PD" is a DRAW command; "10 200", "10 300", and "20 400" are coordinate pairs. The coordinate SEPARATOR is a space and the command TERMINATOR is a semicolon. 3) Other Commands: IntroCAD also assumes the command language contains commands which direct the plotter to select a numbered pen, store the current pen, and select a numbered line type. (IntroCAD 2.0 tolerates command languages which don't have a "line type" command, plotting solid lines regardless of the line type shown on the screen.) A PltDef file consists of eleven lines of text. All lines must contain fewer than 80 characters. The first line is a comment line which is read but otherwise ignored by IntroCAD. The second line contains numbers used for scaling a drawing to the plotter page. The remaining lines contain portions of plotter commands--strings of ASCII characters which are to be sent to a plotter to accomplish some simple task. Line by line: 1) TITLE Normally this line contains the name of the plotter or command language for which the PltDef file was written. This line may contain anything or nothing. 2) SCALE This line must contain the following three numbers in order: a) "UNITS_PER_INCH" -- This is the number of plotter units per inch for both the X and Y directions. The number must be an integer. This number is not normally the same as the plotter "resolution" or "repeatability" specification. It is, rather, the scale factor which relates the numbers sent to the plotter with the distance the plotter pen moves. b) "X_INCHES" -- This number describes the page size in the X direction in inches and may be a real number. c) "Y_INCHES" -- This number describes the page size in the Y direction in inches and may be a real number. ----------------------------------------------------------------- | | | The remaining lines contain strings of characters which are | | typically plotter commands. Since the strings may contain a | | variable number of characters, a delimiting character is | | used to mark the end of the string. The delimiting | | character need not be the same for all lines. The first | | character on a line is the delimiter for that line. | | | | Example: | |@ACB@ | | Here, "@" is the delimiting character and "ABC" is | | the string to be sent to the plotter. | | | | Example: | |!! | | Here, "!" is the delimiting character and there is no | | string to be sent to the plotter. Note: if this is specified | | for a command which is to be followed by a number, the | | number will still be sent. (Exception: IntroCAD 2.0 doesn't | | send the line type number if the line type command is | | specified as !!.) | ----------------------------------------------------------------- 3) INITIALIZE The string enclosed in delimiters is sent to the plotter once before any command strings or data. (max length: 79 characters.) 4) SEPARATOR The string enclosed in delimiters may be sent to the plotter at any time except in the middle of a number or another command string. (max length: four characters.) 5) TERMINATOR The TERMINATOR string is sent to the plotter immediately following a complete command. See "Pen Motion Commands" above for examples of IntroCAD's use of the TERMINATOR. (max length: four characters.) 6) SELECT_PEN The SELECT_PEN string is always followed by an integer which tells the plotter which pen to select. Pen numbers begin at one. (max length: four characters.) 7) STORE_PEN The STORE_PEN string directs the plotter to put the current pen away in its holder. (This string will not be followed by a number.) (max length: four characters.) 8) MOVE The MOVE string instructs the plotter to move, with the pen up off the page, to a location given by a pair of coordinates which follow. MOVE will always be followed by one pair of numbers. (max length: four characters.) 9) DRAW The DRAW command instructs the plotter to put the pen down on the page and drag it, from wherever it now lies, to each of several locations. DRAW may be followed by any number of coordinate pairs. (max length: four characters.) 10) LINE_TYPE The LINE_TYPE string is always followed by a number which tells the plotter which line type to use. IntroCAD assumes the new line type will be used until another LINE_TYPE command is sent. (max length: four characters.) 11) CLOSE The string enclosed in delimiters is sent to the plotter once after all commands and data have been sent. (max length: 79 characters.) ---------------------------------------------------------------------------- BUGS: IntroCAD sends a space character after sending a one-digit number which selects a pen. This happens regardless of the SEPARATOR specification. After a complete DRAW command, IntroCAD sends a SEPARATOR followed by a TERMINATOR. (HPGL tolerates this behavior with no comment.) ---------------------------------------------------------------------------- Sample PltDef file. In the following file, the exclamation point is used as a delimiting character. The capitalized text in line two will be ignored by IntroCAD. In lines three through eleven, text which follows the second exclamation point will also be ignored. ---------------------------------------------------------------------------- HPGL 1.0 TITLE, VERSION 1016 10. 8. UNITS_PER_INCH, X_INCHES, Y_INCHES !DF;.N;19:.I81;;17: ! INITIALIZE ! ! SEPARATOR (use space character if possible) !;! TERMINATOR (for most languages, use nothing) !SP! SELECT_PEN !SP! STORE_PEN !PU! MOVE !PD! DRAW !LT! LINE_TYPE !! CLOSE (nothing needed for my HPGL plotter) ----------------------------------------------------------------------------