1 files changed, 88 insertions, 0 deletions
diff --git a/src/audio.cpp b/src/audio.cpp
new file mode 100644
index 0000000..db915e1
--- /dev/null
+++ b/src/audio.cpp
@@ -0,0 +1,88 @@
+#include "audio.h"
+
+#define _USE_MATH_DEFINES
+#include <cmath>
+#include <iostream>
+#include <SDL.h>
+
+#include "sequence.h"
+
+static const float AMPLITUDE = 0.2f;
+
+// SDL periodically calls this function to fill a chunk of the audio output buffer
+static void AudioCallback(void* userData, Uint8* rawBuffer, int bytes)
+{
+	float* buffer = (float*)rawBuffer;
+	int length = bytes / sizeof(float);
+	CallbackInfo* info = (CallbackInfo*)userData;
+	StepData& step = info->seq->steps[info->currentStep];
+
+	for (int i = 0; i < length; i++, info->samplesDone++) {
+		float time = (float)info->samplesDone / (float)info->sampleRate;
+		float modWave = sinf(2.0f * M_PI * step.modFreq * time);
+		float freq = step.carrierFreq + modWave * step.modDepth;
+
+		// Check if enough samples have been generated for this step
+		if (info->samplesDone >= info->samplesPerStep) {
+			// If so, move on to the next step
+			info->samplesDone = 0;
+			step = info->seq->steps[info->currentStep];
+			info->currentStep = (info->currentStep + 1) % 8;
+		}
+
+		buffer[i] = (sinf(2.0f * M_PI * freq * time)) * AMPLITUDE;
+	}
+}
+
+AudioContext::AudioContext(Sequence& seq)
+{
+	SDL_AudioSpec desiredSpec;
+	desiredSpec.freq = 44100;
+	desiredSpec.format = AUDIO_F32SYS;
+	desiredSpec.channels = 1;
+	desiredSpec.samples = 2048;
+	desiredSpec.callback = AudioCallback;
+	desiredSpec.userdata = &m_info;
+
+	SDL_AudioSpec obtainedSpec;
+	if (SDL_OpenAudio(&desiredSpec, &obtainedSpec) < 0) {
+		std::cerr << "Failed to initalize audio! " << SDL_GetError() << std::endl;
+		std::exit(1);
+	}
+
+	// The audio callback expects float values, so if a different data type 
+	// is obtained we should throw an error.
+	if (desiredSpec.format != obtainedSpec.format) {
+		std::cerr << "Unexpected audio format: " << obtainedSpec.format << std::endl;
+		std::exit(1);
+	}
+
+	m_info.samplesDone = 0;
+	m_info.samplesPerStep = obtainedSpec.freq * 0.4f;
+	m_info.currentStep = 0;
+	m_info.sampleRate = obtainedSpec.freq;
+	m_info.seq = &seq;
+
+	this->Start();
+}
+
+AudioContext::~AudioContext()
+{
+	this->Stop();
+	SDL_CloseAudio();
+}
+
+void AudioContext::Start()
+{
+	SDL_PauseAudio(0);
+}
+
+void AudioContext::Stop()
+{
+	SDL_PauseAudio(1);
+}
+
+int AudioContext::CurrentStep()
+{
+	return m_info.currentStep;
+}
+\ No newline at end of file