Book jacket generation: Add ability to customize the book jacket template and add custom columns into the jacket. Fixes #889912 ([Enhancement] Add metadata from custom columns to jacket)

resources/jacket/template.xhtml

@@ -36,6 +36,14 @@
             <div class="cbj_footer">{footer}</div>
         </div>
         <hr class="cbj_kindle_banner_hr" />
+        <!-- 
+        In addition you can add code to show the values of custom columns here.
+        The value is available as _column_name and the title as _column_name_label.
+        For example, if you have a custom column with label #genre, you can add it to
+        this template with:
+        <div>{_genre_label}: {_genre}</div>
+        -->
+
         <div class="cbj_comments">{comments}</div>
     </body>
 </html>

src/calibre/ebooks/oeb/transforms/jacket.py

@@ -171,6 +171,14 @@ def render_jacket(mi, output_profile,
                     comments=comments,
                     footer=''
                     )
+        for key in mi.custom_field_keys():
+            try:
+                display_name, val = mi.format_field_extended(key)[:2]
+                key = key.replace('#', '_')
+                args[key] = val
+                args[key+'_label'] = display_name
+            except:
+                pass
 
         generated_html = P('jacket/template.xhtml',
                 data=True).decode('utf-8').format(**args)