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XCircuit v2.0a3 (alpha)
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An X11 drawing program [especially for circuit schematics]
Copyright (c) 1998 Tim Edwards
August 1993 -- July 1997
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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. The limitation is that different
font types (other than some characters from the "Symbol" font)
cannot be differentiated on the drawing window. The quality of
the text on the screen is relatively poor; however, the end
product of xcircuit is the PostScript file, which does not suffer
from those limitations. Spacing of the text is accurate under
all scalings except for user-defined fonts, for which spacing
information is not available.
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 an absolute 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').
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Using Xcircuit: See the manpage, "xcircuit.man"
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Online tutorial: See
"http://olympus.ece.jhu.edu/~tim/programs/xcircuit/tutorial.html"
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Things to do: See the file "Manifest"
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