Implement adjusting music volume via .music files

data/music/forest/forest-cave.music

@@ -1,7 +1,8 @@
-(supertux-music
-  (file "forest-cave.ogg")
-  (authors "Jason Lavallée")
-  (license "CC-BY-SA / GPL 2+")
-  (loop-begin 0)
-  (loop-at    149)
-)
+(supertux-music
+  (file "forest-cave.ogg")
+  (authors "Jason Lavallée")
+  (license "CC-BY-SA / GPL 2+")
+  (volume 0.4)
+  (loop-begin 0)
+  (loop-at    149)
+)

src/audio/sound_file.cpp

@@ -93,6 +93,7 @@ std::unique_ptr<SoundFile> load_music_file(const std::string& filename_original)
       sound_file = std::make_unique<OggSoundFile>(file, loop_begin, loop_at);
     }
 
+    music.get("volume", sound_file->m_volume, 1.0f);
     music.get("authors", sound_file->m_authors);
     music.get("license", sound_file->m_license);
     music.get("title", sound_file->m_title);

src/audio/sound_file.hpp

@@ -39,6 +39,7 @@ class SoundFile
     m_rate(),
     m_bits_per_sample(),
     m_size(),
+    m_volume(1.0f),
     m_authors(),
     m_license(),
     m_title()
@@ -55,6 +56,8 @@ class SoundFile
   int m_bits_per_sample;
   /// size in bytes
   size_t m_size;
+  /// innate volume adjustment, 0.0 to 1.0
+  float m_volume;
   std::vector<std::string> m_authors;
   std::string m_license;
   std::string m_title;

src/audio/stream_sound_source.cpp

@@ -63,6 +63,8 @@ StreamSoundSource::set_sound_file(std::unique_ptr<SoundFile> newfile)
 {
   m_file = std::move(newfile);
 
+  alSourcef(m_source, AL_GAIN, m_gain * m_volume * m_file->m_volume);
+
   ALint queued;
   alGetSourcei(m_source, AL_BUFFERS_QUEUED, &queued);
   for (size_t i = 0; i < STREAMFRAGMENTS - queued; ++i) {
@@ -131,6 +133,24 @@ StreamSoundSource::update()
   }
 }
 
+void
+StreamSoundSource::set_gain(float gain)
+{
+  m_gain = gain;
+  if (m_file) {
+    alSourcef(m_source, AL_GAIN, m_gain * m_volume * m_file->m_volume);
+  }
+}
+
+void
+StreamSoundSource::set_volume(float volume)
+{
+  m_volume = volume;
+  if (m_file) {
+    alSourcef(m_source, AL_GAIN, m_gain * m_volume * m_file->m_volume);
+  }
+}
+
 void
 StreamSoundSource::set_fading(FadeState state, float fade_time_)
 {

src/audio/stream_sound_source.hpp

@@ -16,6 +16,8 @@
 
 #pragma once
 
+#include <memory>
+
 #include "audio/openal_sound_source.hpp"
 
 class SoundFile;
@@ -37,6 +39,8 @@ class StreamSoundSource final : public OpenALSoundSource
   virtual void resume() override;
   virtual void update() override;
   virtual void set_looping(bool looping_) override { m_looping = looping_; }
+  virtual void set_gain(float gain) override;
+  virtual void set_volume(float gain) override;
 
   void set_sound_file(std::unique_ptr<SoundFile> newfile);