add display accessors to conky.cc

we want to be able to access either all outputs, or the currently
selected one (if any, else return the top one, which ought to be the GUI
one if we have one).

src/conky.cc

@@ -166,6 +166,35 @@ static conky::simple_config_setting<bool> disable_auto_reload(
 /* two strings for internal use */
 static char *tmpstring1, *tmpstring2;
 
+/*
+ * the list of the only current output, when inside draw_text,
+ * else we iterate over each active outputs.
+ */
+std::vector<conky::display_output_base *> current_display_outputs;
+
+static inline std::vector<conky::display_output_base *> &display_outputs() {
+  if (current_display_outputs.size())
+    return current_display_outputs;
+  return conky::active_display_outputs;
+}
+
+static inline conky::display_output_base *display_output() {
+  if (current_display_outputs.size())
+    return current_display_outputs[0];
+//XXX; not really what intended yet...
+  return conky::active_display_outputs[0];
+  //return nullptr;
+}
+
+static inline void unset_display_output() {
+  current_display_outputs.clear();
+}
+
+static inline void set_display_output(conky::display_output_base *output) {
+  current_display_outputs.clear();
+  current_display_outputs.push_back(output);
+}
+
 enum spacer_state { NO_SPACER = 0, LEFT_SPACER, RIGHT_SPACER };
 template <>
 conky::lua_traits<spacer_state>::Map conky::lua_traits<spacer_state>::map = {