Implement audio mixing

src/AudioManager.cpp

@@ -0,0 +1,137 @@
+#include "AudioManager.h"
+#include <cmath>
+
+namespace NGame {
+
+TAudioManager::TAudioManager(TFileManager& fileManager) 
+    : FileManager_(fileManager) {
+
+    SDL_AudioSpec desired;
+    desired.freq = 44100;
+    desired.format = AUDIO_F32;
+    desired.channels = 2;
+    desired.samples = 4096;
+    desired.callback = NULL;
+
+    Device_ = SDL_OpenAudioDevice(NULL, 0, &desired, NULL, 0);
+    if (!Device_) {
+        throw std::runtime_error("no audio device");
+    }
+
+    Stream_ = SDL_NewAudioStream(AUDIO_U8, 1, 22050, AUDIO_F32, 2, 44100);
+    if (!Stream_) {
+        throw std::runtime_error("can't create audio stream");
+    }
+
+    for (std::size_t i = 0; i < 16; ++i) {
+        Channels_[i].InUse = false;
+    }
+    SDL_PauseAudioDevice(Device_, SDL_FALSE);
+
+    LastTick_ = SDL_GetTicks();
+}
+
+void TAudioManager::Run() {
+    std::uint32_t currentTick = SDL_GetTicks();
+
+    Paint(Stream_, currentTick - LastTick_);
+    if (SDL_GetQueuedAudioSize(Device_) < 8192) {
+        const int bytesRemaining = SDL_AudioStreamAvailable(Stream_);
+        if (bytesRemaining > 0) {
+            const int samplesRemaining = SDL_min(bytesRemaining, 32 * 1024);
+            static Uint8 convertedBuffer[32 * 1024];
+            auto bytesRead = SDL_AudioStreamGet(Stream_, convertedBuffer, samplesRemaining);
+            SDL_QueueAudio(Device_, convertedBuffer, bytesRead);
+        }
+    }
+
+    LastTick_ = currentTick;
+}
+
+void TAudioManager::Play(const std::string& path) {
+    TSound* sound = Load(path);
+
+    for (std::size_t i = 0; i < 16; i++) {
+        if (Channels_[i].InUse) {
+            continue;
+        }
+
+        Channels_[i].InUse = true;
+        Channels_[i].Position = 0;
+        Channels_[i].Sound = sound;
+        break;
+    }
+}
+
+void TAudioManager::Paint(SDL_AudioStream* stream, std::uint32_t ticks) {
+    std::uint8_t temporary[512];
+    std::size_t samples = std::min((ticks * 22050 + 999) / 1000, 512u);
+
+    // Mix
+    for (size_t i = 0; i < samples; ++i) {
+        int16_t accumulator = 0;
+
+        for (size_t j = 0; j < 16; j++) {
+            auto& channel = Channels_[j];
+            if (!channel.InUse) {
+                continue;
+            }
+            
+            accumulator += channel.Sound->Data[channel.Position];
+            accumulator -= 128;
+            channel.Position++;
+
+            if (channel.Position > channel.Sound->Size) {
+                channel.InUse = false;
+            }
+        }
+
+        accumulator += 128;
+        if (accumulator < 0) {
+            accumulator = 0;
+        } 
+        if (accumulator > 255) {
+            accumulator = 255;
+        }
+
+        temporary[i] = accumulator;
+    }
+
+    // Output
+    if (samples > 0) {
+        SDL_AudioStreamPut(stream, temporary, samples * sizeof (std::uint8_t));
+    }
+}
+
+
+
+TAudioManager::TSound* TAudioManager::Load(const std::string& path) {
+    auto it = Sounds_.find(path);
+    if (it != Sounds_.end()) {
+        return it->second;
+    }
+
+    TSound* newSound = new TSound;
+    auto data = FileManager_.Get(path);
+    SDL_RWops* rw = SDL_RWFromConstMem(data.data(), data.size());
+    if (!SDL_LoadWAV_RW(rw, 1, &newSound->Spec, &newSound->Data, &newSound->Size)) {
+        throw std::runtime_error("can't read WAV file " + path);
+    }
+
+    if (newSound->Spec.channels != 1) {
+        throw std::runtime_error("not mono WAV file " + path);
+    }
+
+    if (newSound->Spec.format != AUDIO_U8) {
+        throw std::runtime_error("not 8bit pcm WAV file " + path);
+    }
+
+    if (newSound->Spec.freq != 22050) {
+        throw std::runtime_error("not 22050hz WAV file " + path);
+    }
+
+    Sounds_[path] = newSound;
+    return newSound;
+}
+
+} // namespace NGame