RTD to build doxygen xml before using Sphinx

docs/sphinx/conf.py

@@ -61,3 +61,14 @@ html_theme = 'alabaster'
 # relative to this directory. They are copied after the builtin static files,
 # so a file named "default.css" will overwrite the builtin "default.css".
 html_static_path = ['_static']
+
+
+
+# let RTD know it must run doxygen first, for breathe/Sphinx to pick it up
+import subprocess, os
+
+read_the_docs_build = os.environ.get('READTHEDOCS', None) == 'True'
+
+if read_the_docs_build:
+
+    subprocess.call('cd ../doxygen; doxygen', shell=True)