Implemented Buzzer

Buzzer.cpp

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

Buzzer.hpp

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+#pragma once
+
+#include <vector>
+#include <SDL2/SDL_audio.h>
+
+class Buzzer {
+public:
+  using sample_t = Sint16;
+
+  Buzzer(unsigned frequency);
+  ~Buzzer();
+
+  void on();
+  void off();
+
+private:
+  static void SDLCALL audioCallback(void *userdata, Uint8 *stream, int len);
+  void copySamples(Uint8 *stream, int len);
+
+private:
+  std::vector<sample_t> mSamples;
+  SDL_AudioDeviceID mAudioDevice;
+  size_t miCurrentSample;
+};

CMakeLists.txt

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+cmake_minimum_required(VERSION 3.16)
+project(chocochip8)
+SET(CMAKE_BUILD_TYPE Debug)
+
+add_subdirectory(submodules/sdl2)
+
+SET(CMAKE_EXPORT_COMPILE_COMMANDS ON)
+add_executable(chocochip8 main.cpp Buzzer.cpp)
+target_link_libraries(chocochip8 SDL2::SDL2-static)

main.cpp

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+#include <iostream>
+#include <SDL2/SDL.h>
+
+#include "Buzzer.hpp"
+
+int main(int argc, char* args[]) {
+  if (SDL_Init(SDL_INIT_EVERYTHING) < 0) {
+    std::cerr << "Couldn't initialize SDL: " << SDL_GetError() << '\n';
+    return 1;
+  }
+
+  Buzzer buzzer(440);
+  buzzer.on();
+
+  SDL_Event event;
+  while(SDL_WaitEvent(&event) && event.type != SDL_QUIT) {
+  }
+  
+  buzzer.off();
+  SDL_Quit();
+  return 0;
+}
+