feat(audio): add underwater low-pass filter effect

include/Cubed/audio/audio_engine.hpp

@@ -35,6 +35,8 @@ public:
     void update();
     void reload_config();
 
+    void underwater_change(bool underwater);
+
     float& bgm_target_volume();
 
 private:
@@ -47,8 +49,10 @@ private:
     FadeMap m_fade_map;
     SoundManager m_sounds;
     std::shared_ptr<SourcePool> m_pool;
-
+    bool m_efx_supported = false;
+    bool m_underwater = false;
     float m_music_volume = 1.0f;
     float m_sfx_volume = 1.0f;
+    std::unique_ptr<AudioFilter> m_low_pass_filter;
 };
 } // namespace Cubed

include/Cubed/audio/audio_filter.hpp

@@ -0,0 +1,19 @@
+#pragma once
+#include <AL/al.h>
+namespace Cubed {
+class AudioFilter {
+public:
+    AudioFilter();
+    AudioFilter(const AudioFilter&) = delete;
+    AudioFilter(AudioFilter&&) = delete;
+    AudioFilter& operator=(const AudioFilter&) = delete;
+    AudioFilter& operator=(AudioFilter&&) = delete;
+    ~AudioFilter();
+
+    void set_lowpass(float gain, float gain_hf);
+    ALuint filter() const;
+
+private:
+    ALuint m_filter = 0;
+};
+} // namespace Cubed

include/Cubed/audio/audio_source.hpp

@@ -1,5 +1,6 @@
 #pragma once
 #include "Cubed/audio/audio_buffer.hpp"
+#include "Cubed/audio/audio_filter.hpp"
 
 #include <AL/al.h>
 #include <glm/glm.hpp>
@@ -34,6 +35,9 @@ public:
     bool in_use() const;
     void reset();
 
+    void set_filter(const AudioFilter& filter);
+    void clear_filter();
+
 private:
     ALuint m_source = 0;
     float m_target_volume = 1.0f;

include/Cubed/audio/source_pool.hpp

@@ -16,6 +16,8 @@ public:
 
     void update();
     AudioSource* acquire();
+
+    std::vector<AudioSource>& sources();
 };
 
 } // namespace Cubed