mfpic-doc.pdf.

4 The Macros.
Many of the commands of MFPIC have optional arguments. These are denoted just as in LATEX, with
square brackets. Thus, the command for drawing a circle can be given
\circle{(0,0),1}
having only the mandatory argument, or
\circle[p]{(0,0),1}
Whenever an optional argument is omitted, the behavior is equivalent to some choice of the optional
argument. In this example, the two forms have exactly the same behavior, drawing a circle
centered at (0,0) with radius 1. In this case we will say “[p] is the default”. Another example is
\point{(1,0)} versus \point[3pt]{(1,0)}. They both place a dot at the point (1,0). The second
one explicitly requests that it have diameter 3pt; the first will examine the length command
\pointsize, which the user can change, but it is initialized to 2pt. In this case we will say “the
default is the value of \pointsize, initially 2pt”.
If an MFPIC command that takes an optional argument finds only empty brackets (completely
empty, no spaces), then it will use the default value. This is useful for commands that have two
optional arguments and one wants the default value in the first one and some nondefault value in
the second. An optional argument should normally not contain any spaces. Even when the argument
contains more than one piece of data, spaces should not separate the parts. In some cases this will
cause no harm, but it would be better to avoid doing it altogether, because there are cases where it
will cause wrong results or error messages.
4.1 Files and Environments.
\opengraphsfile{〈file〉}
...
\closegraphsfile
These macros open and close the METAFONT or METAPOST file which will contain the pictures
to be included in this document. The name of the file will be 〈file〉.mf (or 〈file〉.mp). Do not specify
the extension, which is added automatically.
Note: This command may cause 〈file〉.mf or 〈file〉.mp to be overwritten if it already exists, so
be sure to consider that when selecting the name. Repeating the running of TEX will overwrite the
file created on previous runs, but that should be harmless. For if no changes are made to mfpic
environments, the identical file will be recreated, and if changes have been made, then you want the
file to be replaced with the new version.
It is possible (but has not been seriously tested) to close one file and open another, and even to
change between metapost and metafont in between. If anything goes wrong with this, contact the
maintainer and it might be fixed in some later version.
There may be limitations on what can be used as a filename. As of MFPIC version 1.00, we have
tried to permit \jobname as part of 〈file〉. Thus we permit TEX macros, but they should expand
to non-special characters. Permitting macros makes it essentially impossible for the filename to
contain the backslash and brace characters. Also spaces are problematic. However other special TEX
characters (for example: tilde, underscore and percent) can be used, though that is not recommended.
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