Update audio engine

Provides a more backend-independent audio system
Also fixes some sounds being played at half speed (chapter introductions)

src/audio/AudioEngine.h

@@ -1,66 +1,175 @@
 #pragma once
 
-#include <string>
+#include <cstddef>
+#include <cstdint>
+#include <functional>
+#include <memory>
 #include <vector>
 
-#include <glm/glm.hpp>
-
-typedef struct ALCdevice_struct ALCdevice;
+#include <math/mathlib.h>
 
 namespace Audio
 {
-    class AudioWorld;
+    enum class State {
+        Stopped,
+        Paused,
+        Playing
+    };
 
-    /** The AudioEngine represents the target OS sound system.
-     *
-     * The engine class matches the OpenAL device level.
+    enum class Format {
+        Mono,
+        Stereo
+    };
+
+    /**
+     * @brief Sounds represent audio sources.
+     * 
+     * All of the information about a sound should be re-set before it is played
+     * after it had been stopped.
+     * 
+     */
+    class Sound {
+    public:
+        /**
+         * @brief Set sound pitch, must be positive
+         * 
+         * 1 means original pitch, values < 1 mean lower, > 1 mean higher.
+         * 
+         * @return float 
+         */
+        virtual void pitch(float) = 0;
+
+        /**
+         * @brief Set sound gain
+         * 
+         * 1 means original volume, <1 means lower gain, >1 means higher.
+         * 
+         * @return float 
+         */
+        virtual void gain(float) = 0;
+
+        /**
+         * @brief Set the maximum distance from which this sound can be heard.
+         *        Must be positive.
+         * 
+         */
+        virtual void maxDistance(float) = 0;
+
+        /**
+         * @brief Set the coordinates of the sound's position.
+         * 
+         */
+        virtual void position(const Math::float3&) = 0;
+
+        /**
+         * @brief Set the components of the sound's velocity.
+         * 
+         */
+        virtual void velocity(const Math::float3&) = 0;
+
+        /**
+         * @brief Set the componenets of the sound's direction.
+         * 
+         */
+        virtual void direction(const Math::float3&) = 0;
+
+        /**
+         * @brief Set whether the sound's position is relative to the listener.
+         * 
+         */
+        virtual void relative(bool) = 0;
+
+        /**
+         * @brief Set wheter the sound should loop back to the beginning once it
+         *        finishes playing.
+         * 
+         * This is ignored in the case of streming sounds
+         */
+        virtual void looping(bool) = 0;
+
+        /**
+         * @brief Get the playback state of this sound.
+         * 
+         * @return State 
+         */
+        virtual State state() = 0;
+
+        /**
+         * @brief Starts sound playback.
+         * 
+         * This method is idempotent: if the sound was already playing,
+         * nothing happens.
+         */
+        virtual void play() = 0;
+        /**
+         * @brief Pauses sound playback.
+         * 
+         * This method is idempotent: if the sound was already paused,
+         * nothing happens.
+         */
+        virtual void pause() = 0;
+        /**
+         * @brief Stops sound playback.
+         * 
+         * Playback will resume from the beginning.
+         * This method is idempotent: if the sound was already stopped,
+         * nothing happens.
+         */
+        virtual void stop() = 0;
+    };
+
+    using SoundRef = std::shared_ptr<Sound>;
+    using SoundStream = std::function<int(std::int16_t* buf, std::size_t size)>;
+
+    struct Orientation {
+        Math::float3 at;
+        Math::float3 up;
+    };
+
+    /** An AudioEngine is the interface to the system's audio driver
      *
      */
-    class AudioEngine final
+    class AudioEngine
     {
     public:
-        /** Initializes the AudioEngine.
-         *
-         * The @p device param specifies the device to use and can be determined
-         * using enumerateDevices().
-         *
-         * @param device_name The name of the device to use.
-         *
-         * @see AudioEngine::enumerateDevices()
-         *
-         */
-        AudioEngine(const std::string& device_name = std::string());
-
-        /** Deinitializes the AudioEngine.
-         */
-        ~AudioEngine();
-
-        /** Returns the OpenAL device used by this engine.
-         *
-         * @return The OpenAL device or nullptr when initialization has failed.
-         */
-        ALCdevice* getDevice() const { return m_Device; }
-        /** Enumerates the audio devices available on the current machine.
-         *
-         * Note that not all OpenAL implementations support enumeration. In this case you'll
-         * retrieve a single element list with an empty device name, indicating that it is
-         * the default device.
-         *
-         * @param[out] devices A list of available devices.
-         *
-         */
-        static void enumerateDevices(std::vector<std::string>& devices);
-
-        /** Returns a text representation of an error code.
-         *
-         * @param The error code returned by alGetError() or alcGetError().
-         *
-         * @return The error text.
-         *
-         */
-        static const char* getErrorString(size_t errorCode);
-
-    private:
-        ALCdevice* m_Device = nullptr;
+        /**
+         * @brief Set master listener gain, must be positive
+         * 
+         * 1 means original volume, <1 means lower gain, >1 means higher.
+         * 
+         */
+        virtual void gain(float) = 0;
+
+        /**
+         * @brief Set coordinates of listener's position
+         * 
+         */
+        virtual void position(const Math::float3&) = 0;
+
+        /**
+         * @brief Set components of listener's velocity
+         * 
+         */
+        virtual void velocity(const Math::float3&) = 0;
+
+        /**
+         * @brief Set listener's orientation
+         * 
+         */
+        virtual void orientation(const Orientation&) = 0;
+
+        /**
+         * @brief Creates a sound object from an audio buffer
+         * 
+         * @return SoundRef 
+         */
+        virtual SoundRef createSound(const std::int16_t* buf, std::size_t len, Format, std::size_t samplingFreq) = 0;
+
+        /**
+         * @brief Creates a sound object from an audio stream
+         * 
+         * @return SoundRef 
+         */
+        virtual SoundRef createSound(SoundStream, Format, std::size_t samplingFreq) = 0;
     };
 }