Use breqn.sty in dvipng backend if possible

IPython/extensions/sympyprinting.py

@@ -65,7 +65,7 b' def print_display_png(o):'
     s = s.strip('$')
     # As matplotlib does not support display style, dvipng backend is
     # used here.
-    png = latex_to_png('$$%s$$' % s, backend='dvipng')
+    png = latex_to_png(s, backend='dvipng', wrap=True)
     return png
 
 

IPython/lib/latextools.py

@@ -31,7 +31,7 b' from IPython.utils.process import find_cmd, FindCmdError'
 #-----------------------------------------------------------------------------
 
 
-def latex_to_png(s, encode=False, backend='mpl'):
+def latex_to_png(s, encode=False, backend='mpl', wrap=False):
     """Render a LaTeX string to PNG.
 
     Parameters
@@ -42,6 +42,8 b" def latex_to_png(s, encode=False, backend='mpl'):"
         Should the PNG data bebase64 encoded to make it JSON'able.
     backend : {mpl, dvipng}
         Backend for producing PNG data.
+    wrap : bool
+        If true, Automatically wrap `s` as a LaTeX equation.
 
     None is returned when the backend cannot be used.
 
@@ -52,25 +54,27 b" def latex_to_png(s, encode=False, backend='mpl'):"
         f = latex_to_png_dvipng
     else:
         raise ValueError('No such backend {0}'.format(backend))
-    bin_data = f(s)
+    bin_data = f(s, wrap)
     if encode and bin_data:
         bin_data = encodestring(bin_data)
     return bin_data
 
 
-def latex_to_png_mpl(s):
+def latex_to_png_mpl(s, wrap):
     try:
         from matplotlib import mathtext
     except ImportError:
         return None
-    
+
+    if wrap:
+        s = '${0}$'.format(s)
     mt = mathtext.MathTextParser('bitmap')
     f = StringIO()
     mt.to_png(f, s, fontsize=12)
     return f.getvalue()
 
 
-def latex_to_png_dvipng(s):
+def latex_to_png_dvipng(s, wrap):
     try:
         find_cmd('latex')
         find_cmd('dvipng')
@@ -83,9 +87,7 b' def latex_to_png_dvipng(s):'
         outfile = os.path.join(workdir, "tmp.png")
 
         with open(tmpfile, "w") as f:
-            f.write(_latex_header)
-            f.write(s)
-            f.write(_latex_footer)
+            f.writelines(genelatex(s, wrap))
 
         subprocess.check_call(
             ["latex", "-halt-on-errror", tmpfile], cwd=workdir,
@@ -103,17 +105,39 b' def latex_to_png_dvipng(s):'
     return bin_data
 
 
-_latex_header = r'''
-\documentclass{article}
-\usepackage{amsmath}
-\usepackage{amsthm}
-\usepackage{amssymb}
-\usepackage{bm}
-\pagestyle{empty}
-\begin{document}
-'''
-
-_latex_footer = r'\end{document}'
+def kpsewhich(filename):
+    """Invoke kpsewhich command with an argument `filename`."""
+    try:
+        find_cmd("kpsewhich")
+        proc = subprocess.Popen(
+            ["kpsewhich", filename],
+            stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+        (stdout, stderr) = proc.communicate()
+        return stdout.strip()
+    except FindCmdError:
+        pass
+
+
+def genelatex(body, wrap):
+    """Generate LaTeX document for dvipng backend."""
+    breqn = wrap and kpsewhich("breqn.sty")
+    yield r'\documentclass{article}'
+    packages = ['amsmath', 'amsthm', 'amssymb', 'bm']
+    if breqn:
+        packages.append('breqn')
+    for pack in packages:
+        yield r'\usepackage{{{0}}}'.format(pack)
+    yield r'\pagestyle{empty}'
+    yield r'\begin{document}'
+    if breqn:
+        yield r'\begin{dmath*}'
+        yield body
+        yield r'\end{dmath*}'
+    elif wrap:
+        yield '$${0}$$'.format(body)
+    else:
+        yield body
+    yield r'\end{document}'
 
 
 _data_uri_template_png = """<img src="data:image/png;base64,%s" alt=%s />"""