1 files changed, 65 insertions, 0 deletions
diff --git a/equations/signals.py b/equations/signals.py
new file mode 100644
index 0000000..0fecc34
--- /dev/null
+++ b/equations/signals.py
@@ -0,0 +1,65 @@
+from django.conf import settings
+
+def update_render(sender, instance, signal, *args, **kwargs):
+    """Renders an object's .png representation using LaTeX and puts it 
+       in the right directory. Requires latex, dvipng, etc"""
+    import os, shutil, tempfile, subprocess
+    def call_command_in_dir(app, args, targetdir):
+        cwd = os.getcwd()
+        try:
+            os.chdir(targetdir)
+            p = subprocess.Popen(app + ' ' + ' '.join(args), shell=True)
+            sts = os.waitpid(p.pid, 0)
+            # FIXME -- should we raise an exception of status is non-zero?
+        finally:
+            # Restore working directory
+            os.chdir(cwd)
+
+    rawlatex = instance.latex    
+    dstdir = settings.MEDIA_ROOT + instance.renderdir
+    dstfile = "%s.png" % instance.id
+    dst = "%s" % instance.id
+
+    prologue = ""
+    latex_template = r'''
+    \documentclass[12pt]{article}
+    \pagestyle{empty}
+    %(prologue)s
+    \begin{document}
+    $$%(raw)s$$
+    \end{document}
+    '''
+    max_pages = 1
+    MAX_RUN_TIME = 5 # seconds
+    latex = "latex"
+    dvipng = "dvipng"
+    latex_args = ("--interaction=nonstopmode", "%s.tex")
+    dvipng_args = ("-q", "-bgTransparent", "-Ttight", "--noghostscript", 
+        "-l%s" % max_pages, "%s.dvi")
+    tex = latex_template % { 'raw': rawlatex, 'prologue': prologue }
+
+    tmpdir = tempfile.mkdtemp()
+    try:
+        data = open("%s/%s.tex" % (tmpdir, dst), "w")
+        data.write(tex)
+        data.close()
+        args = list(latex_args)
+        args[-1] = args[-1] % dst
+        res = call_command_in_dir(latex, args, tmpdir)
+        if not res is None:
+            # FIXME need to return some sort of error
+            return []
+        args = list(dvipng_args)
+        args[-1] = args[-1] % dst
+        res = call_command_in_dir(dvipng, args, tmpdir)
+        if not res is None:
+            # FIXME need to return some sort of error
+            return []
+
+        if os.access("%s/%s1.png" % (tmpdir, dst), os.R_OK):
+            shutil.copyfile("%s/%s1.png" % (tmpdir, dst),
+                dstdir + dstfile)
+    finally:
+        # FIXME do some tidy up here
+        instance.render = instance.renderdir + dstfile
+    shutil.rmtree(tmpdir)