feat(render): support pseudo-transparency

This adds pseudo-transparency for the background of the bar and the
background of the systray.

include/components/renderer.hpp

@@ -17,6 +17,7 @@ POLYBAR_NS
 class connection;
 class config;
 class logger;
+class background_manager;
 // }}}
 
 using std::map;
@@ -39,7 +40,7 @@ class renderer
   static make_type make(const bar_settings& bar);
 
   explicit renderer(
-      connection& conn, signal_emitter& sig, const config&, const logger& logger, const bar_settings& bar);
+      connection& conn, signal_emitter& sig, const config&, const logger& logger, const bar_settings& bar, background_manager& background_manager);
   ~renderer();
 
   xcb_window_t window() const;
@@ -95,6 +96,7 @@ class renderer
   const config& m_conf;
   const logger& m_log;
   const bar_settings& m_bar;
+  background_manager& m_background;
 
   int m_depth{32};
   xcb_window_t m_window;