Pause the music when the game loses focus

src/game_launcher.cpp

@@ -112,6 +112,7 @@ game_launcher::game_launcher(const commandline_options& cmdline_opts, const char
 	main_event_context_(),
 	hotkey_manager_(),
 	music_thinker_(),
+	music_muter_(),
 	test_scenario_("test"),
 	screenshot_map_(),
 	screenshot_filename_(),

src/game_launcher.hpp

@@ -114,6 +114,7 @@ private:
 	const events::event_context main_event_context_;
 	const hotkey::manager hotkey_manager_;
 	sound::music_thinker music_thinker_;
+	sound::music_muter music_muter_;
 
 	std::string test_scenario_;
 

src/sound.cpp

@@ -618,6 +618,30 @@ void music_thinker::process(events::pump_info &info) {
 	}
 }
 
+music_muter::music_muter() :
+	events::sdl_handler(false)
+{
+	join_global();
+}
+
+void music_muter::handle_window_event(const SDL_Event& event)
+{
+	if (preferences::music_on())
+	{
+		if (event.window.event == SDL_WINDOWEVENT_FOCUS_GAINED)
+		{
+			Mix_ResumeMusic();
+		}
+		else if (event.window.event == SDL_WINDOWEVENT_FOCUS_LOST)
+		{
+			if (Mix_PlayingMusic())
+			{
+				Mix_PauseMusic();
+			}
+		}
+	}
+}
+
 void commit_music_changes()
 {
 	played_before.clear();

src/sound.hpp

@@ -85,6 +85,14 @@ class music_thinker : public events::pump_monitor {
 	void process(events::pump_info &info);
 };
 
+// A class to mute music when the game is in background
+class music_muter : public events::sdl_handler {
+public:
+	music_muter();
+	void handle_event(const SDL_Event&) override {}
+	void handle_window_event(const SDL_Event& event) override;
+};
+
 // Save music playlist for snapshot
 void write_music_play_list(config& snapshot);