/*
Simple DirectMedia Layer
- Copyright (C) 1997-2014 Sam Lantinga <slouken@libsdl.org>
+ Copyright (C) 1997-2016 Sam Lantinga <slouken@libsdl.org>
This software is provided 'as-is', without any express or implied
warranty. In no event will the authors be held liable for any damages
*
* Once the callback returns, the buffer will no longer be valid.
* Stereo samples are stored in a LRLRLR ordering.
+ *
+ * You can choose to avoid callbacks and use SDL_QueueAudio() instead, if
+ * you like. Just open your audio device with a NULL callback.
*/
typedef void (SDLCALL * SDL_AudioCallback) (void *userdata, Uint8 * stream,
int len);
Uint16 samples; /**< Audio buffer size in samples (power of 2) */
Uint16 padding; /**< Necessary for some compile environments */
Uint32 size; /**< Audio buffer size in bytes (calculated) */
- SDL_AudioCallback callback;
- void *userdata;
+ SDL_AudioCallback callback; /**< Callback that feeds the audio device (NULL to use SDL_QueueAudio()). */
+ void *userdata; /**< Userdata passed to callback (ignored for NULL callbacks). */
} SDL_AudioSpec;
* to the audio buffer, and the length in bytes of the audio buffer.
* This function usually runs in a separate thread, and so you should
* protect data structures that it accesses by calling SDL_LockAudio()
- * and SDL_UnlockAudio() in your code.
+ * and SDL_UnlockAudio() in your code. Alternately, you may pass a NULL
+ * pointer here, and call SDL_QueueAudio() with some frequency, to queue
+ * more audio samples to be played.
* - \c desired->userdata is passed as the first parameter to your callback
- * function.
+ * function. If you passed a NULL callback, this value is ignored.
*
* The audio device starts out playing silence when it's opened, and should
* be enabled for playing by calling \c SDL_PauseAudio(0) when you are ready
SDL_AudioFormat format,
Uint32 len, int volume);
+/**
+ * Queue more audio on non-callback devices.
+ *
+ * SDL offers two ways to feed audio to the device: you can either supply a
+ * callback that SDL triggers with some frequency to obtain more audio
+ * (pull method), or you can supply no callback, and then SDL will expect
+ * you to supply data at regular intervals (push method) with this function.
+ *
+ * There are no limits on the amount of data you can queue, short of
+ * exhaustion of address space. Queued data will drain to the device as
+ * necessary without further intervention from you. If the device needs
+ * audio but there is not enough queued, it will play silence to make up
+ * the difference. This means you will have skips in your audio playback
+ * if you aren't routinely queueing sufficient data.
+ *
+ * This function copies the supplied data, so you are safe to free it when
+ * the function returns. This function is thread-safe, but queueing to the
+ * same device from two threads at once does not promise which buffer will
+ * be queued first.
+ *
+ * You may not queue audio on a device that is using an application-supplied
+ * callback; doing so returns an error. You have to use the audio callback
+ * or queue audio with this function, but not both.
+ *
+ * You should not call SDL_LockAudio() on the device before queueing; SDL
+ * handles locking internally for this function.
+ *
+ * \param dev The device ID to which we will queue audio.
+ * \param data The data to queue to the device for later playback.
+ * \param len The number of bytes (not samples!) to which (data) points.
+ * \return zero on success, -1 on error.
+ *
+ * \sa SDL_GetQueuedAudioSize
+ * \sa SDL_ClearQueuedAudio
+ */
+extern DECLSPEC int SDLCALL SDL_QueueAudio(SDL_AudioDeviceID dev, const void *data, Uint32 len);
+
+/**
+ * Get the number of bytes of still-queued audio.
+ *
+ * This is the number of bytes that have been queued for playback with
+ * SDL_QueueAudio(), but have not yet been sent to the hardware.
+ *
+ * Once we've sent it to the hardware, this function can not decide the exact
+ * byte boundary of what has been played. It's possible that we just gave the
+ * hardware several kilobytes right before you called this function, but it
+ * hasn't played any of it yet, or maybe half of it, etc.
+ *
+ * You may not queue audio on a device that is using an application-supplied
+ * callback; calling this function on such a device always returns 0.
+ * You have to use the audio callback or queue audio with SDL_QueueAudio(),
+ * but not both.
+ *
+ * You should not call SDL_LockAudio() on the device before querying; SDL
+ * handles locking internally for this function.
+ *
+ * \param dev The device ID of which we will query queued audio size.
+ * \return Number of bytes (not samples!) of queued audio.
+ *
+ * \sa SDL_QueueAudio
+ * \sa SDL_ClearQueuedAudio
+ */
+extern DECLSPEC Uint32 SDLCALL SDL_GetQueuedAudioSize(SDL_AudioDeviceID dev);
+
+/**
+ * Drop any queued audio data waiting to be sent to the hardware.
+ *
+ * Immediately after this call, SDL_GetQueuedAudioSize() will return 0 and
+ * the hardware will start playing silence if more audio isn't queued.
+ *
+ * This will not prevent playback of queued audio that's already been sent
+ * to the hardware, as we can not undo that, so expect there to be some
+ * fraction of a second of audio that might still be heard. This can be
+ * useful if you want to, say, drop any pending music during a level change
+ * in your game.
+ *
+ * You may not queue audio on a device that is using an application-supplied
+ * callback; calling this function on such a device is always a no-op.
+ * You have to use the audio callback or queue audio with SDL_QueueAudio(),
+ * but not both.
+ *
+ * You should not call SDL_LockAudio() on the device before clearing the
+ * queue; SDL handles locking internally for this function.
+ *
+ * This function always succeeds and thus returns void.
+ *
+ * \param dev The device ID of which to clear the audio queue.
+ *
+ * \sa SDL_QueueAudio
+ * \sa SDL_GetQueuedAudioSize
+ */
+extern DECLSPEC void SDLCALL SDL_ClearQueuedAudio(SDL_AudioDeviceID dev);
+
+
/**
* \name Audio lock functions
*
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