citra_qt: Add a volume slider

src/citra/config.cpp

@@ -143,6 +143,7 @@ void Config::ReadValues() {
     Settings::values.enable_audio_stretching =
         sdl2_config->GetBoolean("Audio", "enable_audio_stretching", true);
     Settings::values.audio_device_id = sdl2_config->Get("Audio", "output_device", "auto");
+    Settings::values.volume = sdl2_config->GetReal("Audio", "volume", 1);
 
     // Data Storage
     Settings::values.use_virtual_sd =

src/citra/default_ini.h

@@ -164,6 +164,10 @@ enable_audio_stretching =
 # auto (default): Auto-select
 output_device =
 
+# Output volume.
+# 1.0 (default): 100%, 0.0; mute
+volume =
+
 [Data Storage]
 # Whether to create a virtual SD card.
 # 1 (default): Yes, 0: No