statusicon-qt: Set basic tooltip

Even though we override the QSystemTrayIcon::event() method,
it is never called by Qt (at least on Linux). And therefore our
custom info popop is not shown. Set a proper tooltip as workaround.

src/statusicon-qt/statusicon.cc

@@ -32,7 +32,8 @@
 #include <QSystemTrayIcon>
 #include <QWheelEvent>
 
-class StatusIcon : public GeneralPlugin {
+class StatusIcon : public GeneralPlugin
+{
 public:
     static const char about[];
     static const char * const defaults[];
@@ -53,6 +54,8 @@ class StatusIcon : public GeneralPlugin {
     bool init ();
     void cleanup ();
 
+private:
+    static void title_changed (void * data, void * user_data);
     static void window_closed (void * data, void * user_data);
     static void activate (QSystemTrayIcon::ActivationReason);
     static void open_files ();
@@ -188,13 +191,15 @@ bool StatusIcon::init ()
     tray->setContextMenu (menu);
     tray->show ();
 
+    hook_associate ("title change", title_changed, nullptr);
     hook_associate ("window close", window_closed, nullptr);
 
     return true;
 }
 
 void StatusIcon::cleanup ()
 {
+    hook_dissociate ("title change", title_changed);
     hook_dissociate ("window close", window_closed);
 
     /* Prevent accidentally hiding the interface by disabling
@@ -211,6 +216,12 @@ void StatusIcon::cleanup ()
     audqt::cleanup ();
 }
 
+void StatusIcon::title_changed (void * data, void * user_data)
+{
+    const char * title = aud_drct_get_title ();
+    tray->setToolTip (title);
+}
+
 void StatusIcon::window_closed (void * data, void * user_data)
 {
     bool * handled = (bool *) data;