mfpic-doc.pdf.

4.12 FOR ADVANCED USERS. 71
\globalsetmfvariable{picture}{Dan}{Jan}
would make Dan globally defined to be equal to the current value of the picture Jan. Note that picture
variables can consume a lot of METAFONT’s memory. Copying one variable to another doubles the
amount of memory, at least until the end of the mfpic environment.
You can use \putmfpimage inside a mfpimage environment, provided the picture being placed
has been previously defined. Nesting a mfpimage inside another has not been tested at all and
so is not recommended. But if it works, the inner image would be local to the environment created
by the outer one, and so would be of limited use. One can use the LATEX environment construct
\begin{mfpimage} ... \end{mfpimage} in a LaTeX document instead of \mfpimage ...
\endmfpimage.
4.12.7 METAFONT LOOPS
All the MFPIC loop commands create a loop (in the METAFONT language) in the output file. The
METAFONT commands in that loop are executed repeatedly by METAFONT or METAPOST. From the
point of view of TEX, however each command occurs only once. Starting with version 0.9, these
loops can be created inside or outside the mfpic drawing environment. If outside, they must not
contain any drawing commands, but can contain commands that set variables, perform computations,
etc.
\mfpfor{〈for-loop header〉}
〈MFPIC commands〉
\endmfpfor
This creates a for-loop in the METAFONT output file. The \mfpfor writes the start of the loop and
\endmfpfor writes the end. Any code written in the output file between them is executed repeatedly
by METAFONT, according to the information in 〈for-loop header〉. There are two types of headers
possible, illustrated by the following examples.
\mfpfor{center = (0,0), (1,0), (0,1)}
\gfill\circle{center,1}
\endmfpfor
This example will fill three circles of radius 1 with centers at the three given points. This type of
header has the format
〈variable〉 = 〈list〉
where 〈variable〉 should be a simple variable name and 〈list〉 is a comma separated list of items of
the appropriate data type. In the above, center is equated to pairs, but in the following
\mfpfor{radius = 1,3,4}
\dotted\circle{(0,0),radius}
\endmfpfor
radius gets numeric values.
The other type of header uses a stepped variable:
\mfpfor{level = 3 step 2 until 9}
\circle{(0,0),sqrt(level)}
\endmfpfor
This will cause the METAFONT variable level to step through the values 3, 5, 7 and 9 and the circles
with radius √ 3, √ 5, etc. will be drawn. This type of header has the format
〈variable〉 = 〈start〉 step 〈delta〉 until 〈stop〉