Volume setting

src/resource/audio.cpp

@@ -12,6 +12,12 @@ namespace game::resource
     return mixer;
   }
 
+  void Audio::set_gain(float gain)
+  {
+    auto mixer = mixer_get();
+    MIX_SetMasterGain(mixer, gain);
+  }
+
   void Audio::retain()
   {
     if (refCount) ++(*refCount);

src/resource/audio.h

@@ -10,7 +10,7 @@ namespace game::resource
     MIX_Audio* internal{nullptr};
     MIX_Track* track{nullptr};
     int* refCount{nullptr};
-    MIX_Mixer* mixer_get();
+    static MIX_Mixer* mixer_get();
     void unload();
     void retain();
     void release();
@@ -27,5 +27,6 @@ namespace game::resource
     void play(bool isLoop = false);
     void stop();
     bool is_playing() const;
+    static void set_gain(float vol);
   };
 }