Closes #923: Take the entire LaTeX document into account when caching

pngmath-generated images.  This rebuilds them correctly when
``pngmath_latex_preamble`` changes.

1 files changed, 3 insertions, 4 deletions

diff --git a/sphinx/ext/pngmath.py b/sphinx/ext/pngmath.py
index a9a2203ac..e23bbd06f 100644
--- a/sphinx/ext/pngmath.py
+++ b/sphinx/ext/pngmath.py
@@ -82,8 +82,10 @@ def render_math(self, math):
     may not fail since that indicates a problem in the math source.
     """
     use_preview = self.builder.config.pngmath_use_preview
+    latex = DOC_HEAD + self.builder.config.pngmath_latex_preamble
+    latex += (use_preview and DOC_BODY_PREVIEW or DOC_BODY) % math
 
-    shasum = "%s.png" % sha(math.encode('utf-8')).hexdigest()
+    shasum = "%s.png" % sha(latex.encode('utf-8')).hexdigest()
     relfn = posixpath.join(self.builder.imgpath, 'math', shasum)
     outfn = path.join(self.builder.outdir, '_images', 'math', shasum)
     if path.isfile(outfn):
@@ -95,9 +97,6 @@ def render_math(self, math):
        hasattr(self.builder, '_mathpng_warned_dvipng'):
         return None, None
 
-    latex = DOC_HEAD + self.builder.config.pngmath_latex_preamble
-    latex += (use_preview and DOC_BODY_PREVIEW or DOC_BODY) % math
-
     # use only one tempdir per build -- the use of a directory is cleaner
     # than using temporary files, since we can clean up everything at once
     # just removing the whole directory (see cleanup_tempdir)