XCircuit v2.5.3 ----------------------------------------------------------------------------- An X11 drawing program [especially for circuit schematics] Copyright (c) 2002 Tim Edwards August 1993 -- January 2002 ----------------------------------------------------------------------------- This README file contains additional notes about the program which may or may not be of interest to anyone. ----------------------------------------------------------------------------- Rationale: This program was written with a number of things in mind. The major point in writing it was that I found all of the drawing programs freely distributed at the usual X11 ftp sources (ftp.uu.net, export.lcs.mit.edu, etc.), which includes xpic and xfig, and even some other programs like idraw and commercial programs like framemaker, were lacking in some manner. Some of them, like xpic, are missing fundamental parts, while others, like xfig and framemaker, have a cumbersome user interface and require inordinately large amounts of time to create simple pictures. The really powerful programs like Adobe Illustrator are, naturally, expensive. There has been a long-standing tradition of making MacDraw lookalikes which I find particularly disturbing, since a number of features of that GUI are fundamentally screwed up, including the dependence on a black-and-white color scheme for things such as grid lines and edit points which can make the screen cluttered and difficult to work with. I have chosen to freely ignore all such standards in cases where they seem to hinder rather than help the user. Disclaimer: The above comments refer to versions of the abovementioned programs available as of 1993 and do not necessarily reflect the programs' current status. Particularly the latest (from 1995 or so) version of xfig is quite good, though it continues to have a "MacDraw" feel to it. The properties of xcircuit are as follows: A) Structural backbone 1) There are five drawing elements which are considered "primary". These are as follows: a) polygon (multiple lines which may or may not be closed and filled) b) arc (ellipse segment which may be closed and/or filled as above) c) label (any text) d) curve (based on the PostScript "curveto" algorithm) e) object instance (see below) 2) There are two drawing elements which are considered "secondary", which is to say, contain instances of primary elements. These are: a) path (a connected series of polygons, arcs, and/or curves) b) object (something containing polygons, arcs, labels, curves, paths, and instances of other objects) Each object is instanced by a primary element called the "object instance", a self-contained unit which allows an object to be scaled, rotated, and translated within another object. Since objects contain object instances and object instances point to objects, there is a two-step recursion which is central to the concept of xcircuit. 3) There is one primary object instance called the TopObject, which is the program window, and its associated object, which is whatever appears on the screen. TopObject is a pointer, so that any object in memory may be the top object, allowing a push/pop edit stack. All other objects are organized in an array of pointers called the Library. The Library is filled on startup with the contents of a Library file, and is expanded whenever a new object is created. Actually, there are many different TopObjects, called "pages", which can be switched between at will by typing the number of the page, 1 through 9 and 0 for page 10, or through the "Page" menu command, which allows access to as many pages as are defined. The "load" and "save" commands act only on the present page (unless multiple pages are loaded at a time), as do all the drawing commands. 4) All elements allocate memory as they are created and release the memory as they are destroyed, so the only limit on the number of elements in a drawing is the memory of the workstation. B) Input/Output 1) All input and output is in PostScript, albeit a version of PostScript with extremely restricted syntax: xcircuit is in no sense a PS interpreter! The primary element types are defined as procedures in the PostScript prologue; all secondary elements are defined as "def" structures in PostScript, the only restriction being that no definition can be called before it is defined. 2) Text is vector-drawn, in order to best match the flexibility of PostScript, which unlike X11 allows text to be scaled to any size and rotated to any orientation (modern font renderers can do this, but are not good at fast on-the-fly rendering needed for a drawing The quality of the vector-drawn text on the screen is relatively poor; however, the end product of xcircuit is the PostScript file, which does not suffer from those limitations. Text vectors are xcircuit elements read from an xcircuit library file, with encoding information read from a separate file. 3) X11 does not have any capability for generalized curves (splines). Therefore, splines are constructed by an N-segment approximation which internally looks like a polygon. The PostScript output is a smooth curve instead of the approximation. 4) X11 does not have any capability for generalized ellipses (ellipses under any rotation). Similarly to the splines, arcs are constructed by an N-segment approximation. 5) Implementing all arcs and curves as N-segment approximation allows the possibility of general paths, or sequences of polygons, arc sections, and curves which form a path that can be bordered, closed and/or filled like an individual arc, curve, or polygon. 6) Other than the qualitative appearance of the text, the screen output of xcircuit is meant to be the closest possible match to the rendering of the PostScript output. A PostScript hack allows stipple pattern fills to be effectively "transparent" (something that PostScript does not do naturally). However, the effect is *extremely* device-dependent because it overrides the printer's halftoning operators. One effect of this is that halftoning will look abnormally large when viewed at screen resolutions, e.g., with GhostScript. C) User Interface 1) The mouse button system and the object library are based on the Caltech circuit-simulation program "log" (either "analog" or "diglog"). As is usual for most applications, mouse button 1 is used to select things or cycle between selections, button 2 usually terminates a command, and button 3 will abort a command. In addition, button 1 has a function called "grab", which occurs after the button has been continually pressed for a short length of time (about 1/5 second). As the name implies, "grab" grabs hold of an element which can then be moved around the screen. Because this program is tailored to circuit drawing, the most common functions are drawing lines and moving object instances. Therefore, these two functions are made directly available from the mouse button 1 (ater a "tap" or a "grab", respectively). The next most common function is selection of elements singly or in groups. Button 2 can be used to select an item if tapped, and if pressed and held down, a box will be drawn and everything inside that box selected when the button is released. All other commands are available from the pulldown menus and/or from the keyboard as single-key macros. Keyboard macros are quicker, since they act on the present cursor position, whereas menu commands require an extra step. The libraries are intended to provide a convenient way to store and retrieve elements of a picture which will be used more than once. For the application of circuit drawing, a built-in library provides basic objects such as transistors, amplifiers, resistors, capacitors, arrows, circles, power and ground symbols, and the like. This file ("builtins.lps") is loaded on startup; the program first looks in the current directory, and then searches in a given global directory (something like ~cad/lib/xcircuit/) if it could not find it initially. Thus each user can add to or modify the file of builtins to reflect personal taste. Since the PostScript output contains all object definitions, these changes to the built-in functions are inherently transferrable. The program checks objects with the same name for equivalence of their contents, and changes names as necessary to avoid conflicts. An additional library, the user library, contains all of the objects which are created (using the "make object" command) during a session or objects which are loaded from a file but do not belong to the built-in library. The user library can be saved by itself and reloaded later either into the user library or into the built-in library. This is the way to create a personalized built-in library set. The special file "builtins.lps" can be edited to include lines such as the following: % filename loadlibrary The loadlibrary command will automatically include another library file. This method makes it convenient to divide up libraries into separate files according to (for instance) function (digital, analog, clip art, etc.), and use the loadlibrary commands to choose which ones will be loaded on startup. Caveat: If the order of loading is such that an object contains an instance of another object which has not yet been loaded, xcircuit will complain. By default, libraries have the extension ".lps". As they contain only macros, they cannot be displayed with any PostScript interpreter. The "loadlibrary" command is hidden behind a PostScript comment (%) character, and so is not recognized by general-purpose PS interpreters. 2) Xcircuit has a strict sense of zooming and snap-to grid. Objects scale absolutely; line widths and text sizes will increase/decrease proportionally with the zoom, as well as dot/dash spacing and all other features. Xcircuit does have a minimum integer grid in coordinate space, which translates to 0.005 inches at an output scale of 1. The maximum zoom scale gives a screen size translating to about 100 by 100 inches at an output scale of 1. The effective scale can be varied by changing the output scale (reached from the "File/Write" menu selection) in order to fit a drawing to a page or to get a grid matched to a specific dimension. A separate scale parameter changes the scale of the reported position relative to the output scale (as it will appear on a printed page). The snap-to grid is an all-important feature for circuit drawing, wherein it is critical that wires line up properly with one another. In xcircuit, there is no way to get off the snap-to grid except by turning the snap function off and physically pushing elements off the grid. In any case, objects can always be returned to the snap grid with the "snap" function (key 'S'). D) Schematic Capture XCircuit implements a sophisticated schematic capture. Unlike virtually all schematic capture software currently available, xcircuit allows the designer to draw the circuit in a "natural" way, making use both of schematic hierarchies and simple hierarchies created simply by grouping elements together. If the chosen netlist format is hierarchical (like SPICE), both hierarchical forms will be retained in the output. For element grouping, input/output ports connecting into to the group will be determined automatically, from context. Individual networks can be queried (key 'Alt-W') to highlight the entire visible part of the network, with the network name printed in the message window. ----------------------------------------------------------------------------- Xcircuit reference: Local: See the xcircuit manpage ("man xcircuit") Online: http://xcircuit.ece.jhu.edu/features.html ----------------------------------------------------------------------------- Online tutorials: See Standard: http://xcircuit.ece.jhu.edu/tutorial/tutorial.html Schematic capture: http://xcircuit.ece.jhu.edu/tutorial/tutorial2.html ----------------------------------------------------------------------------- Things to do: See the file "Manifest" -----------------------------------------------------------------------------