Displaying MetaPost output in ghostscript

MetaPost ordinarily expects its output to be included in some context where the “standard” MetaFont fonts (that you’ve specified) are already defined — for example, as a figure in TeX document. If you’re debugging your MetaPost code, you may want to view it in a ghostscript-based (or some other PostScript) previewer, but note that viewers (even ghostscript) don’t ordinarily have the fonts loaded, and you’ll experience an error such as

Error: /undefined in cmmi10

There is provision in MetaPost for avoiding this problem: issue the command prologues := 2; at the start of the mp file.

Unfortunately, the PostScript that MetaPost inserts in its output, following this command, is incompatible with ordinary use of the PostScript in inclusions into (La)TeX documents, so it’s best to make the prologues command optional. Furthermore, MetaPost takes a very simple-minded approach to font encoding: since TeX font encodings are anything but simple, encoding of text in diagrams are another source of problems. If you’re suffering such problems (the symptom is that characters disappear, or are wrongly presented) the solution is to view the “original” MetaPost output after processing through LaTeX and dvips.

Conditional compilation may be done either by inputting MyFigure.mp indirectly from a simple wrapper MyFigureDisplay.mp:

prologues := 2;
input MyFigure

or by issuing a shell command such as

mp "\prologues:=2; input MyFigure"

(which will work without the quote marks if you’re not using a Unix shell).

A suitable LaTeX route would involve processing MyFigure.tex, which contains:

\documentclass{article}
\usepackage{graphicx}
\begin{document}
\thispagestyle{empty}
\includegraphics{MyFigure.1}
\end{document}

Processing the resulting DVI file with the dvips command

dvips -E -o MyFigure.eps MyFigure

would then give a satisfactory Encapsulated PostScript file. This procedure may be automated using the Perl script mps2eps, thus saving a certain amount of tedium.

The Plain TeX user may use an adaptation, by Dan Luecking, of a jiffy of Knuth’s. Dan’s version mpsproof.tex will work under TeX to produce a DVI file for use with dvips, or under pdfTeX to produce a PDF file, direct. The output is set up to look like a proof sheet.

A script application, mptopdf, is available in recent (La)TeX distributions: it seems fairly reliably to produce PDF from MetaPost, so may reasonably be considered an answer to the question…

FAQ ID: Q-mpprologues