examples: Add audio/01-simple-playback.

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)

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 <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 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. */
+}
+