72 lines
2.2 KiB
C++
72 lines
2.2 KiB
C++
#include "BuzzerSDL.hpp"
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#include <cmath>
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#include <limits>
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#include <stdexcept>
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#include <cstring>
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void SDLCALL BuzzerSDL::audioCallback(void *userdata, Uint8 *stream, int len) {
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static_cast<BuzzerSDL*>(userdata)->copySamples(stream, len);
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}
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BuzzerSDL::BuzzerSDL(unsigned buzzerFrequency) {
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SDL_AudioSpec desired;
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SDL_AudioSpec obtained;
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SDL_zero(desired);
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desired.channels = 1;
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desired.freq = 44000;
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desired.format = AUDIO_S16SYS;
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desired.samples = 4096;
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desired.callback = audioCallback;
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desired.userdata = this;
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mAudioDevice = SDL_OpenAudioDevice(NULL, SDL_FALSE, &desired, &obtained, SDL_AUDIO_ALLOW_FREQUENCY_CHANGE | SDL_AUDIO_ALLOW_SAMPLES_CHANGE);
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if(mAudioDevice == 0) {
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throw std::runtime_error(SDL_GetError());
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}
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// period of the sine wave, in samples, to obtained the desired
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// buffer buzzer frequency at a particular audio sample rate
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double waveLength = double(obtained.freq) / buzzerFrequency;
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// buffer size that fits a whole number of sine waves and is roughly the same size of obtained.samples
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size_t numSamples = waveLength * std::max(std::floor(obtained.samples / waveLength), 1.0);
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mSamples.resize(numSamples);
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// generate the sine wave
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auto amplitude = std::numeric_limits<sample_t>::max();
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auto angularFreq = 2.0 * M_PI / waveLength;
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for(size_t iSample = 0; iSample < numSamples; iSample++) {
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mSamples[iSample] = amplitude * std::sin(angularFreq * iSample);
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}
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miCurrentSample = 0;
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}
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BuzzerSDL::~BuzzerSDL() {
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SDL_CloseAudioDevice(mAudioDevice);
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}
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void BuzzerSDL::on() {
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SDL_PauseAudioDevice(mAudioDevice, SDL_FALSE);
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}
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void BuzzerSDL::off() {
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SDL_PauseAudioDevice(mAudioDevice, SDL_TRUE);
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}
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void BuzzerSDL::copySamples(Uint8 *stream, int len) {
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// Copy len samples from the current position of the buffer,
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// looping back to the start of the buffer when needed.
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while(len > 0) {
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size_t numBytes = std::min(sizeof(sample_t) * (mSamples.size() - miCurrentSample), size_t(len));
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size_t numSamples = numBytes / sizeof(sample_t);
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std::memcpy(stream, mSamples.data() + miCurrentSample, numBytes);
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stream += numBytes;
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len -= numBytes;
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miCurrentSample += numSamples;
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if(miCurrentSample >= mSamples.size()) {
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miCurrentSample = 0;
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}
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}
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}
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