From f5f44de155732e3045b3f069aaed97c761ded80b Mon Sep 17 00:00:00 2001 From: "Ryan C. Gordon" Date: Tue, 23 Jul 2024 14:52:16 -0400 Subject: [PATCH] examples: Add audio/01-simple-playback. --- examples/CMakeLists.txt | 1 + .../01-simple-playback/simple-playback.c | 100 ++++++++++++++++++ 2 files changed, 101 insertions(+) create mode 100644 examples/audio/01-simple-playback/simple-playback.c diff --git a/examples/CMakeLists.txt b/examples/CMakeLists.txt index a2a2441bb8..ba6b577eb9 100644 --- a/examples/CMakeLists.txt +++ b/examples/CMakeLists.txt @@ -178,6 +178,7 @@ 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) if(PSP) diff --git a/examples/audio/01-simple-playback/simple-playback.c b/examples/audio/01-simple-playback/simple-playback.c new file mode 100644 index 0000000000..08b5b70c53 --- /dev/null +++ b/examples/audio/01-simple-playback/simple-playback.c @@ -0,0 +1,100 @@ +/* + * This example code $WHAT_IT_DOES. + * + * 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 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/renderer/clear", 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, NULL, 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) +{ + /* see if we need to feed the audio stream more data yet. + We're being lazy here, but if there's less than half a second queued, generate more. + A sine wave is unchanging audio--easy to stream--but for video games, you'll want + to generate significantly _less_ audio ahead of time! */ + const int minimum_audio = (8000 * sizeof (float)) / 2; /* 8000 float samples per second. Half of that. */ + if (SDL_GetAudioStreamAvailable(stream) < minimum_audio) { + static float samples[512]; /* this will feed 512 samples each frame until we get to our maximum. */ + int i; + + for (i = 0; i < SDL_arraysize(samples); 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(stream, samples, sizeof (samples)); + } + + /* we're not doing anything with the renderer, so just blank it out. */ + SDL_RenderClear(renderer); + SDL_RenderPresent(renderer); + + 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. */ +} +