[WIP] Libretro: Add audio support (#714)

* Libretro: Add audio support

* Adding audio interface part 1

* Audio device pt 2

* More audio device

* More audio device

* Morea uudi odevice

* More audio device

* More audio device

* More audio device

---------

Co-authored-by: wheremyfoodat <44909372+wheremyfoodat@users.noreply.github.com>

include/audio/audio_device.hpp

@@ -0,0 +1,9 @@
+#pragma once
+
+#ifdef __LIBRETRO__
+#include "audio/libretro_audio_device.hpp"
+using AudioDevice = LibretroAudioDevice;
+#else
+#include "audio/miniaudio_device.hpp"
+using AudioDevice = MiniAudioDevice;
+#endif

include/audio/audio_device_interface.hpp

@@ -0,0 +1,36 @@
+#pragma once
+#include <array>
+
+#include "config.hpp"
+#include "helpers.hpp"
+#include "ring_buffer.hpp"
+
+class AudioDeviceInterface {
+  protected:
+	static constexpr usize maxFrameCount = 0x2000;
+
+	using Samples = Common::RingBuffer<s16, maxFrameCount * 2>;
+	using RenderBatchCallback = usize (*)(const s16*, usize);
+
+	Samples* samples = nullptr;
+
+	const AudioDeviceConfig& audioSettings;
+	// Store the last stereo sample we output. We play this when underruning to avoid pops.
+	std::array<s16, 2> lastStereoSample{};
+
+  public:
+	AudioDeviceInterface(Samples* samples, const AudioDeviceConfig& audioSettings) : samples(samples), audioSettings(audioSettings) {}
+
+	bool running = false;
+	Samples* getSamples() { return samples; }
+
+	// If safe is on, we create a null audio device
+	virtual void init(Samples& samples, bool safe = false) = 0;
+	virtual void close() = 0;
+
+	virtual void start() = 0;
+	virtual void stop() = 0;
+
+	// Only used for audio devices that render multiple audio frames in one go, eg the libretro audio device.
+	virtual void renderBatch(RenderBatchCallback callback) {}
+};

include/audio/libretro_audio_device.hpp

@@ -0,0 +1,60 @@
+#pragma once
+#include <cstring>
+
+#include "audio/audio_device_interface.hpp"
+
+class LibretroAudioDevice : public AudioDeviceInterface {
+	bool initialized = false;
+
+  public:
+	LibretroAudioDevice(const AudioDeviceConfig& audioSettings) : AudioDeviceInterface(nullptr, audioSettings), initialized(false) {
+		running = false;
+	}
+
+	void init(Samples& samples, bool safe = false) override {
+		this->samples = &samples;
+
+		initialized = true;
+		running = false;
+	}
+
+	void close() override {
+		initialized = false;
+		running = false;
+	};
+
+	void start() override { running = true; }
+	void stop() override { running = false; };
+
+	void renderBatch(RenderBatchCallback callback) override {
+		if (running) {
+			static constexpr usize frameCount = 774;
+			static constexpr usize channelCount = 2;
+			static s16 audioBuffer[frameCount * channelCount];
+
+			usize samplesWritten = 0;
+			samplesWritten += samples->pop(audioBuffer, frameCount * channelCount);
+
+			// Get the last sample for underrun handling
+			if (samplesWritten != 0) {
+				std::memcpy(&lastStereoSample[0], &audioBuffer[(samplesWritten - 1) * 2], sizeof(lastStereoSample));
+			}
+
+			// If underruning, copy the last output sample
+			{
+				s16* pointer = &audioBuffer[samplesWritten * 2];
+				s16 l = lastStereoSample[0];
+				s16 r = lastStereoSample[1];
+
+				for (usize i = samplesWritten; i < frameCount; i++) {
+					*pointer++ = l;
+					*pointer++ = r;
+				}
+			}
+
+			callback(audioBuffer, sizeof(audioBuffer) / (channelCount * sizeof(s16)));
+		}
+	}
+
+	bool isInitialized() const { return initialized; }
+};

include/audio/miniaudio_device.hpp

@@ -3,39 +3,31 @@
 #include <string>
 #include <vector>
 
-#include "config.hpp"
-#include "helpers.hpp"
+#include "audio/audio_device_interface.hpp"
 #include "miniaudio.h"
-#include "ring_buffer.hpp"
 
-class MiniAudioDevice {
-	using Samples = Common::RingBuffer<ma_int16, 0x2000 * 2>;
+class MiniAudioDevice : public AudioDeviceInterface {
 	static constexpr ma_uint32 sampleRate = 32768;  // 3DS sample rate
 	static constexpr ma_uint32 channelCount = 2;    // Audio output is stereo
 
+	bool initialized = false;
+
 	ma_device device;
 	ma_context context;
 	ma_device_config deviceConfig;
-	Samples* samples = nullptr;
-
-	const AudioDeviceConfig& audioSettings;
-
-	bool initialized = false;
-	bool running = false;
 
 	// Store the last stereo sample we output. We play this when underruning to avoid pops.
-	std::array<s16, 2> lastStereoSample;
 	std::vector<std::string> audioDevices;
 
   public:
 	MiniAudioDevice(const AudioDeviceConfig& audioSettings);
 
 	// If safe is on, we create a null audio device
-	void init(Samples& samples, bool safe = false);
-	void close();
+	void init(Samples& samples, bool safe = false) override;
+	void close() override;
 
-	void start();
-	void stop();
+	void start() override;
+	void stop() override;
 
 	bool isInitialized() const { return initialized; }
 };