Added support for post_render_hooks to Renderer

holoviews/plotting/bokeh/renderer.py

@@ -56,15 +56,15 @@ def __call__(self, obj, fmt=None):
         elif fmt == 'html':
             html = self.figure_data(plot)
             html = '<center>%s</center>' % html
-            return html, info
+            return self._apply_post_render_hooks(html, obj, fmt), info
         elif fmt == 'json':
             plotobjects = [h for handles in plot.traverse(lambda x: x.current_handles)
                            for h in handles]
             data = dict(data=[])
             if not bokeh_lt_011:
                 data['root'] = plot.state._id
             data['data'] = models_to_json(plotobjects)
-            return serialize_json(data), info
+            return self._apply_post_render_hooks(serialize_json(data), obj, fmt), info
 
 
     def figure_data(self, plot, fmt='html', **kwargs):

holoviews/plotting/mpl/renderer.py

@@ -97,6 +97,7 @@ def __call__(self, obj, fmt='auto'):
             anim = plot.anim(fps=self.fps)
             data = self._anim_data(anim, fmt)
 
+        data = self._apply_post_render_hooks(data, obj, fmt)
         return data, {'file-ext':fmt,
                       'mime_type':MIME_TYPES[fmt]}
 

holoviews/plotting/renderer.py

@@ -116,6 +116,14 @@ class Renderer(Exporter):
     key_fn = param.Callable(None, allow_None=True, constant=True,  doc="""
         Renderers do not support the saving of object key metadata""")
 
+    post_render_hooks = param.Dict(default={'svg':[], 'png':[]}, doc="""
+       Optional dictionary of hooks that are applied to the rendered
+       data (according to the output format) before it is returned.
+
+       Each hook is passed the rendered data and the object that is
+       being rendered. These hooks allow post-processing of renderered
+       data before output is saved to file or displayed.""")
+
     # Defines the valid output formats for each mode.
     mode_formats = {'fig': {'default': [None, 'auto']},
                     'holomap': {'default': [None, 'auto']}}
@@ -204,10 +212,27 @@ def __call__(self, obj, fmt=None):
         """
         plot, fmt =  self._validate(obj, fmt)
         if plot is None: return
-        # [Backend specific code goes here]
+        # [Backend specific code goes here to generate data]
+        data = None
 
+        # Example of how post_render_hooks are applied
+        data = self._apply_post_render_hooks(data, obj, fmt)
         # Example of the return format where the first value is the rendered data.
-        return None, {'file-ext':fmt, 'mime_type':MIME_TYPES[fmt]}
+        return data, {'file-ext':fmt, 'mime_type':MIME_TYPES[fmt]}
+
+
+    def _apply_post_render_hooks(self, data, obj, fmt):
+        """
+        Apply the post-render hooks to the data.
+        """
+        hooks = self.post_render_hooks.get(fmt)
+        for hook in hooks:
+            try:
+                data = hook(data, obj, fmt, self.backend)
+            except Exception as e:
+                self.warning("The post_render_hook %r could not be applied:\n\n %s"
+                             % (hook, e))
+        return data
 
 
     def html(self, obj, fmt=None, css=None):