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#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;
}
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