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- /*
- * This example code creates an simple audio stream for playing sound, and
- * generates a sine wave sound effect for it to play as time goes on. Unlike
- * the previous example, this uses a callback to generate sound.
- *
- * This might be the path of least resistance if you're moving an SDL2
- * program's audio code to SDL3.
- *
- * This code is public domain. Feel free to use it for any purpose!
- */
- #define SDL_MAIN_USE_CALLBACKS 1 /* use the callbacks instead of main() */
- #include <SDL3/SDL.h>
- #include <SDL3/SDL_main.h>
- /* We will use this renderer to draw into this window every frame. */
- static SDL_Window *window = NULL;
- static SDL_Renderer *renderer = NULL;
- static SDL_AudioStream *stream = NULL;
- static int total_samples_generated = 0;
- /* this function will be called (usually in a background thread) when the audio stream is consuming data. */
- static void SDLCALL FeedTheAudioStreamMore(void *userdata, SDL_AudioStream *astream, int additional_amount, int total_amount)
- {
- /* total_amount is how much data the audio stream is eating right now, additional_amount is how much more it needs
- than what it currently has queued (which might be zero!). You can supply any amount of data here; it will take what
- it needs and use the extra later. If you don't give it enough, it will take everything and then feed silence to the
- hardware for the rest. Ideally, though, we always give it what it needs and no extra, so we aren't buffering more
- than necessary. */
- additional_amount /= sizeof (float); /* convert from bytes to samples */
- while (additional_amount > 0) {
- float samples[128]; /* this will feed 128 samples each iteration until we have enough. */
- const int total = SDL_min(additional_amount, SDL_arraysize(samples));
- int i;
- for (i = 0; i < total; i++) {
- /* You don't have to care about this math; we're just generating a simple sine wave as we go.
- https://en.wikipedia.org/wiki/Sine_wave */
- const float time = total_samples_generated / 8000.0f;
- const int sine_freq = 500; /* run the wave at 500Hz */
- samples[i] = SDL_sinf(6.283185f * sine_freq * time);
- total_samples_generated++;
- }
- /* feed the new data to the stream. It will queue at the end, and trickle out as the hardware needs more data. */
- SDL_PutAudioStreamData(astream, samples, total * sizeof (float));
- additional_amount -= total; /* subtract what we've just fed the stream. */
- }
- }
- /* This function runs once at startup. */
- SDL_AppResult SDL_AppInit(void **appstate, int argc, char *argv[])
- {
- SDL_AudioSpec spec;
- if (!SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO)) {
- SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR, "Couldn't initialize SDL!", SDL_GetError(), NULL);
- return SDL_APP_FAILURE;
- }
- /* we don't _need_ a window for audio-only things but it's good policy to have one. */
- if (!SDL_CreateWindowAndRenderer("examples/audio/simple-playback-callback", 640, 480, 0, &window, &renderer)) {
- SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR, "Couldn't create window/renderer!", SDL_GetError(), NULL);
- return SDL_APP_FAILURE;
- }
- /* We're just playing a single thing here, so we'll use the simplified option.
- We are always going to feed audio in as mono, float32 data at 8000Hz.
- The stream will convert it to whatever the hardware wants on the other side. */
- spec.channels = 1;
- spec.format = SDL_AUDIO_F32;
- spec.freq = 8000;
- stream = SDL_OpenAudioDeviceStream(SDL_AUDIO_DEVICE_DEFAULT_PLAYBACK, &spec, FeedTheAudioStreamMore, NULL);
- if (!stream) {
- SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR, "Couldn't create audio stream!", SDL_GetError(), window);
- return SDL_APP_FAILURE;
- }
- /* SDL_OpenAudioDeviceStream starts the device paused. You have to tell it to start! */
- SDL_ResumeAudioStreamDevice(stream);
- return SDL_APP_CONTINUE; /* carry on with the program! */
- }
- /* This function runs when a new event (mouse input, keypresses, etc) occurs. */
- SDL_AppResult SDL_AppEvent(void *appstate, const SDL_Event *event)
- {
- if (event->type == SDL_EVENT_QUIT) {
- return SDL_APP_SUCCESS; /* end the program, reporting success to the OS. */
- }
- return SDL_APP_CONTINUE; /* carry on with the program! */
- }
- /* This function runs once per frame, and is the heart of the program. */
- SDL_AppResult SDL_AppIterate(void *appstate)
- {
- /* we're not doing anything with the renderer, so just blank it out. */
- SDL_RenderClear(renderer);
- SDL_RenderPresent(renderer);
- /* all the work of feeding the audio stream is happening in a callback in a background thread. */
- return SDL_APP_CONTINUE; /* carry on with the program! */
- }
- /* This function runs once at shutdown. */
- void SDL_AppQuit(void *appstate)
- {
- /* SDL will clean up the window/renderer for us. */
- }
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