diff --git a/examples/CMakeLists.txt b/examples/CMakeLists.txt index ba6b577eb9..8ac66d911f 100644 --- a/examples/CMakeLists.txt +++ b/examples/CMakeLists.txt @@ -179,6 +179,7 @@ endmacro() add_sdl_example_executable(renderer-clear SOURCES renderer/01-clear/renderer-clear.c) add_sdl_example_executable(renderer-primitives SOURCES renderer/02-primitives/renderer-primitives.c) add_sdl_example_executable(audio-simple-playback SOURCES audio/01-simple-playback/simple-playback.c) +add_sdl_example_executable(audio-simple-playback-callback SOURCES audio/02-simple-playback-callback/simple-playback-callback.c) if(PSP) diff --git a/examples/audio/02-simple-playback-callback/simple-playback-callback.c b/examples/audio/02-simple-playback-callback/simple-playback-callback.c new file mode 100644 index 0000000000..4d21296ecf --- /dev/null +++ b/examples/audio/02-simple-playback-callback/simple-playback-callback.c @@ -0,0 +1,114 @@ +/* + * 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 +#include + +/* 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. */ +int SDL_AppInit(void **appstate, int argc, char *argv[]) +{ + SDL_AudioSpec spec; + + if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO) == -1) { + 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) == -1) { + 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); + + /* (this is a web browser requirement, not an SDL thing.) */ + SDL_Log("If you're running this in a web browser, you need to click the window before you'll hear anything."); + + return SDL_APP_CONTINUE; /* carry on with the program! */ +} + +/* This function runs when a new event (mouse input, keypresses, etc) occurs. */ +int 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. */ +int 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. */ +} +