Turn GetSizeFromImages into a "post transform"

Closes #230.

src/nbsphinx.py

@@ -760,7 +760,6 @@ def get_transforms(self):
             CreateNotebookSectionAnchors,
             ReplaceAlertDivs,
             CopyLinkedFiles,
-            GetSizeFromImages,
         ]
 
     def parse(self, inputstring, document):
@@ -1482,21 +1481,27 @@ def apply(self):
             env.nbsphinx_files.setdefault(env.docname, []).append(file)
 
 
-class GetSizeFromImages(docutils.transforms.Transform):
-    """Get size from images and store it as node attributes."""
+class GetSizeFromImages(
+        sphinx.transforms.post_transforms.images.BaseImageConverter):
+    """Get size from images and store it as node attributes.
 
-    default_priority = 500  # Doesn't really matter?
+    This is only done for LaTeX output.
 
-    def apply(self):
-        env = self.document.settings.env
-        for node in self.document.traverse(docutils.nodes.image):
-            if 'width' not in node and 'height' not in node:
-                uri = node['uri']
-                srcdir = os.path.dirname(env.doc2path(env.docname))
-                size = sphinx.util.images.get_image_size(
-                        os.path.join(srcdir, uri))
-                if size is not None:
-                    node['width'], node['height'] = map(str, size)
+    """
+
+    # After ImageDownloader (100) and DataURIExtractor (150):
+    default_priority = 200
+
+    def match(self, node):
+        return self.app.builder.format == 'latex'
+
+    def handle(self, node):
+        if 'width' not in node and 'height' not in node:
+            srcdir = os.path.dirname(self.env.doc2path(self.env.docname))
+            image_path = os.path.normpath(os.path.join(srcdir, node['uri']))
+            size = sphinx.util.images.get_image_size(image_path)
+            if size is not None:
+                node['width'], node['height'] = map(str, size)
 
 
 def builder_inited(app):
@@ -1747,6 +1752,7 @@ def setup(app):
     app.add_transform(CreateSectionLabels)
     app.add_transform(CreateDomainObjectLabels)
     app.add_transform(RewriteLocalLinks)
+    app.add_post_transform(GetSizeFromImages)
 
     # Make docutils' "code" directive (generated by markdown2rst/pandoc)
     # behave like Sphinx's "code-block",