audio_system.h

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#pragma once
 
#include <span>
#include <string>
 
#include <rex/apu/audio_driver.h>
#include <rex/platform.h>
#include <rex/module.h>
#include <rex/result.h>
#include <rex/setting.h>
#include <rex/settings_registry.h>
#include <rex/types.h>
#include <rex/utility.h>
 
namespace rex::apu {
 
enum class AudioStreamID : u32 {};

using AudioFrame = std::span<const f32, kAudioFrameSamples>;
 
struct AudioStats {
  u32 open_streams = 0;
  u32 queued_frames = 0;
  u64 underruns = 0;  
  u32 latency_us = 0; 
};
 
class REX_APU_API AudioSettings final : public SettingOwner {
 public:
  AudioSettings();
 
  REX_SETTING(std::string, driver, "sdl3",
              "Audio driver, none for silence in an app that does not require audio", kStartupOnly);
  REX_SETTING(bool, mute, false, "Mute the audio output");
  REX_SETTING(bool, mute_unfocused, false, "Mute while the window does not have focus");
  REX_SETTING(f64, gain, 1.0, "Output gain, 1 is unity", Range{0.0, 4.0});
  REX_SETTING(f64, center, 1.0, "Center level on a surround device", Range{0.0, 2.0});
  REX_SETTING(f64, surround, 1.0, "Surround level on a surround device", Range{0.0, 2.0});
  REX_SETTING(f64, lfe, 1.0, "LFE level on a surround device", Range{0.0, 2.0});
  REX_SETTING(f64, peak_limit, 0.0, "Silence a stream that stays above this peak, 0 is off",
              Range{0.0, 8.0});
  REX_SETTING(u32, max_queued_frames, 8, "Frames a stream may queue", Range{4, 64}, kUntilLaunch);
};

REX_DECLARE_INTERFACE(IAudioSystem, 1)
  static constexpr u32 kMaxStreams = 8;
 
  virtual AudioSettings& GetSettings() = 0;

  [[nodiscard]] virtual Result<AudioStreamID> OpenStream(
      MoveOnlyFunction<void()> on_frame_played) = 0;

  virtual void CloseStream(AudioStreamID stream) = 0;

  [[nodiscard]] virtual Result<void> Submit(AudioStreamID stream, AudioFrame frame) = 0;

  virtual u32 GetOutputChannels() const = 0;

  virtual AudioStats GetStats() const = 0;

  virtual void SetFocused(bool focused) = 0;
};
 
}  // namespace rex::apu