Question

I’m looking for a library (or a cleverer solution) in C or C++ that would make an image file (PNG|jpeg) from LaTeX code. The use of packages is a prerequisite.

For now I’m thinking of compiling a .tex file into a .dvi and using dvipng to get a .PNG.

There’s also the possibility of compiling a .tex file into a .ps file and then converting it into a .PNG by the mean of extern utilities like pstopng or pstoedit.

But these solutions are cumbersome and not always portable. I would like to integrate this conversion in my program transparently.

Answer 1

I’ve used the dvipng route several times before, but in python. It’s a common path, that lots of people have taken. Here’s the code, to give you something to get started, and in case anyone wants Python code. I do realise you asked for C/C++; this is for a starter, or for others. This is for generating equations, but it would be trivial to adapt it for more general structures. It does support packages.

In terms of integrating it transparently, I feel your pain. Not everyone has tex / latex of course, and if they don’t, it’s often a pain to get. The best way to do it, I think, is to provide that functionality as a web service – but of course that’s not always an option.

Finally, note all the options for dvipng. They control the appearance, via various anti-alisaing options etc. I tuned them extensively to get what I thought looked good.

def geneq(f, eq, dpi, wl, outname, packages):
    # First check if there is an existing file.
    eqname = os.path.join(f.eqdir, outname + '.png')

    # Open tex file.
    tempdir = tempfile.gettempdir()
    fd, texfile = tempfile.mkstemp('.tex', '', tempdir, True)
    basefile = texfile[:-4]
    g = os.fdopen(fd, 'w')

    preamble = '\documentclass{article}\n'
    for p in packages:
        preamble += '\usepackage{%s}\n' % p

    preamble += '\pagestyle{empty}\n\\begin{document}\n'
    g.write(preamble)

    # Write the equation itself.
    if wl:
        g.write('\\[%s\\]' % eq)
    else:
        g.write('$%s$' % eq)

    # Finish off the tex file.
    g.write('\n\\newpage\n\end{document}')
    g.close()

    exts = ['.tex', '.aux', '.dvi', '.log']
    try:
        # Generate the DVI file
        latexcmd = 'latex -file-line-error-style -interaction=nonstopmode ' + \
               '-output-directory %s %s' % (tempdir, texfile)
        p = Popen(latexcmd, shell=True, stdout=PIPE)
        rc = p.wait()
        if rc != 0:
            for l in p.stdout.readlines():
                print '  ' + l.rstrip()
            exts.remove('.tex')
            raise Exception('latex error')

        dvifile = basefile + '.dvi'
        dvicmd = 'dvipng --freetype0 -Q 9 -z 3 --depth -q -T tight -D %i -bg Transparent -o %s %s' % (dpi, eqname, dvifile)
        # discard warnings, as well.
        p = Popen(dvicmd, shell=True, stdout=PIPE, stderr=PIPE)
        rc = p.wait()
        if rc != 0:
            print p.stderr.readlines()
            raise Exception('dvipng error')
        depth = int(p.stdout.readlines()[-1].split('=')[-1])
    finally:
        # Clean up.
        for ext in exts:
            g = basefile + ext
            if os.path.exists(g):
                os.remove(g)