include/SDL_audio.h
author Ryan C. Gordon <icculus@icculus.org>
Sun, 12 Apr 2015 21:02:21 -0400
changeset 9556 db92b9d74129
parent 9012 aa058c87737b
child 9619 b94b6d0bff0f
permissions -rw-r--r--
Patched to compile on C89 compilers.
     1 /*
     2   Simple DirectMedia Layer
     3   Copyright (C) 1997-2014 Sam Lantinga <slouken@libsdl.org>
     4 
     5   This software is provided 'as-is', without any express or implied
     6   warranty.  In no event will the authors be held liable for any damages
     7   arising from the use of this software.
     8 
     9   Permission is granted to anyone to use this software for any purpose,
    10   including commercial applications, and to alter it and redistribute it
    11   freely, subject to the following restrictions:
    12 
    13   1. The origin of this software must not be misrepresented; you must not
    14      claim that you wrote the original software. If you use this software
    15      in a product, an acknowledgment in the product documentation would be
    16      appreciated but is not required.
    17   2. Altered source versions must be plainly marked as such, and must not be
    18      misrepresented as being the original software.
    19   3. This notice may not be removed or altered from any source distribution.
    20 */
    21 
    22 /**
    23  *  \file SDL_audio.h
    24  *
    25  *  Access to the raw audio mixing buffer for the SDL library.
    26  */
    27 
    28 #ifndef _SDL_audio_h
    29 #define _SDL_audio_h
    30 
    31 #include "SDL_stdinc.h"
    32 #include "SDL_error.h"
    33 #include "SDL_endian.h"
    34 #include "SDL_mutex.h"
    35 #include "SDL_thread.h"
    36 #include "SDL_rwops.h"
    37 
    38 #include "begin_code.h"
    39 /* Set up for C function definitions, even when using C++ */
    40 #ifdef __cplusplus
    41 extern "C" {
    42 #endif
    43 
    44 /**
    45  *  \brief Audio format flags.
    46  *
    47  *  These are what the 16 bits in SDL_AudioFormat currently mean...
    48  *  (Unspecified bits are always zero).
    49  *
    50  *  \verbatim
    51     ++-----------------------sample is signed if set
    52     ||
    53     ||       ++-----------sample is bigendian if set
    54     ||       ||
    55     ||       ||          ++---sample is float if set
    56     ||       ||          ||
    57     ||       ||          || +---sample bit size---+
    58     ||       ||          || |                     |
    59     15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00
    60     \endverbatim
    61  *
    62  *  There are macros in SDL 2.0 and later to query these bits.
    63  */
    64 typedef Uint16 SDL_AudioFormat;
    65 
    66 /**
    67  *  \name Audio flags
    68  */
    69 /* @{ */
    70 
    71 #define SDL_AUDIO_MASK_BITSIZE       (0xFF)
    72 #define SDL_AUDIO_MASK_DATATYPE      (1<<8)
    73 #define SDL_AUDIO_MASK_ENDIAN        (1<<12)
    74 #define SDL_AUDIO_MASK_SIGNED        (1<<15)
    75 #define SDL_AUDIO_BITSIZE(x)         (x & SDL_AUDIO_MASK_BITSIZE)
    76 #define SDL_AUDIO_ISFLOAT(x)         (x & SDL_AUDIO_MASK_DATATYPE)
    77 #define SDL_AUDIO_ISBIGENDIAN(x)     (x & SDL_AUDIO_MASK_ENDIAN)
    78 #define SDL_AUDIO_ISSIGNED(x)        (x & SDL_AUDIO_MASK_SIGNED)
    79 #define SDL_AUDIO_ISINT(x)           (!SDL_AUDIO_ISFLOAT(x))
    80 #define SDL_AUDIO_ISLITTLEENDIAN(x)  (!SDL_AUDIO_ISBIGENDIAN(x))
    81 #define SDL_AUDIO_ISUNSIGNED(x)      (!SDL_AUDIO_ISSIGNED(x))
    82 
    83 /**
    84  *  \name Audio format flags
    85  *
    86  *  Defaults to LSB byte order.
    87  */
    88 /* @{ */
    89 #define AUDIO_U8        0x0008  /**< Unsigned 8-bit samples */
    90 #define AUDIO_S8        0x8008  /**< Signed 8-bit samples */
    91 #define AUDIO_U16LSB    0x0010  /**< Unsigned 16-bit samples */
    92 #define AUDIO_S16LSB    0x8010  /**< Signed 16-bit samples */
    93 #define AUDIO_U16MSB    0x1010  /**< As above, but big-endian byte order */
    94 #define AUDIO_S16MSB    0x9010  /**< As above, but big-endian byte order */
    95 #define AUDIO_U16       AUDIO_U16LSB
    96 #define AUDIO_S16       AUDIO_S16LSB
    97 /* @} */
    98 
    99 /**
   100  *  \name int32 support
   101  */
   102 /* @{ */
   103 #define AUDIO_S32LSB    0x8020  /**< 32-bit integer samples */
   104 #define AUDIO_S32MSB    0x9020  /**< As above, but big-endian byte order */
   105 #define AUDIO_S32       AUDIO_S32LSB
   106 /* @} */
   107 
   108 /**
   109  *  \name float32 support
   110  */
   111 /* @{ */
   112 #define AUDIO_F32LSB    0x8120  /**< 32-bit floating point samples */
   113 #define AUDIO_F32MSB    0x9120  /**< As above, but big-endian byte order */
   114 #define AUDIO_F32       AUDIO_F32LSB
   115 /* @} */
   116 
   117 /**
   118  *  \name Native audio byte ordering
   119  */
   120 /* @{ */
   121 #if SDL_BYTEORDER == SDL_LIL_ENDIAN
   122 #define AUDIO_U16SYS    AUDIO_U16LSB
   123 #define AUDIO_S16SYS    AUDIO_S16LSB
   124 #define AUDIO_S32SYS    AUDIO_S32LSB
   125 #define AUDIO_F32SYS    AUDIO_F32LSB
   126 #else
   127 #define AUDIO_U16SYS    AUDIO_U16MSB
   128 #define AUDIO_S16SYS    AUDIO_S16MSB
   129 #define AUDIO_S32SYS    AUDIO_S32MSB
   130 #define AUDIO_F32SYS    AUDIO_F32MSB
   131 #endif
   132 /* @} */
   133 
   134 /**
   135  *  \name Allow change flags
   136  *
   137  *  Which audio format changes are allowed when opening a device.
   138  */
   139 /* @{ */
   140 #define SDL_AUDIO_ALLOW_FREQUENCY_CHANGE    0x00000001
   141 #define SDL_AUDIO_ALLOW_FORMAT_CHANGE       0x00000002
   142 #define SDL_AUDIO_ALLOW_CHANNELS_CHANGE     0x00000004
   143 #define SDL_AUDIO_ALLOW_ANY_CHANGE          (SDL_AUDIO_ALLOW_FREQUENCY_CHANGE|SDL_AUDIO_ALLOW_FORMAT_CHANGE|SDL_AUDIO_ALLOW_CHANNELS_CHANGE)
   144 /* @} */
   145 
   146 /* @} *//* Audio flags */
   147 
   148 /**
   149  *  This function is called when the audio device needs more data.
   150  *
   151  *  \param userdata An application-specific parameter saved in
   152  *                  the SDL_AudioSpec structure
   153  *  \param stream A pointer to the audio data buffer.
   154  *  \param len    The length of that buffer in bytes.
   155  *
   156  *  Once the callback returns, the buffer will no longer be valid.
   157  *  Stereo samples are stored in a LRLRLR ordering.
   158  *
   159  *  You can choose to avoid callbacks and use SDL_QueueAudio() instead, if
   160  *  you like. Just open your audio device with a NULL callback.
   161  */
   162 typedef void (SDLCALL * SDL_AudioCallback) (void *userdata, Uint8 * stream,
   163                                             int len);
   164 
   165 /**
   166  *  The calculated values in this structure are calculated by SDL_OpenAudio().
   167  */
   168 typedef struct SDL_AudioSpec
   169 {
   170     int freq;                   /**< DSP frequency -- samples per second */
   171     SDL_AudioFormat format;     /**< Audio data format */
   172     Uint8 channels;             /**< Number of channels: 1 mono, 2 stereo */
   173     Uint8 silence;              /**< Audio buffer silence value (calculated) */
   174     Uint16 samples;             /**< Audio buffer size in samples (power of 2) */
   175     Uint16 padding;             /**< Necessary for some compile environments */
   176     Uint32 size;                /**< Audio buffer size in bytes (calculated) */
   177     SDL_AudioCallback callback; /**< Callback that feeds the audio device (NULL to use SDL_QueueAudio()). */
   178     void *userdata;             /**< Userdata passed to callback (ignored for NULL callbacks). */
   179 } SDL_AudioSpec;
   180 
   181 
   182 struct SDL_AudioCVT;
   183 typedef void (SDLCALL * SDL_AudioFilter) (struct SDL_AudioCVT * cvt,
   184                                           SDL_AudioFormat format);
   185 
   186 /**
   187  *  A structure to hold a set of audio conversion filters and buffers.
   188  */
   189 #ifdef __GNUC__
   190 /* This structure is 84 bytes on 32-bit architectures, make sure GCC doesn't
   191    pad it out to 88 bytes to guarantee ABI compatibility between compilers.
   192    vvv
   193    The next time we rev the ABI, make sure to size the ints and add padding.
   194 */
   195 #define SDL_AUDIOCVT_PACKED __attribute__((packed))
   196 #else
   197 #define SDL_AUDIOCVT_PACKED
   198 #endif
   199 /* */
   200 typedef struct SDL_AudioCVT
   201 {
   202     int needed;                 /**< Set to 1 if conversion possible */
   203     SDL_AudioFormat src_format; /**< Source audio format */
   204     SDL_AudioFormat dst_format; /**< Target audio format */
   205     double rate_incr;           /**< Rate conversion increment */
   206     Uint8 *buf;                 /**< Buffer to hold entire audio data */
   207     int len;                    /**< Length of original audio buffer */
   208     int len_cvt;                /**< Length of converted audio buffer */
   209     int len_mult;               /**< buffer must be len*len_mult big */
   210     double len_ratio;           /**< Given len, final size is len*len_ratio */
   211     SDL_AudioFilter filters[10];        /**< Filter list */
   212     int filter_index;           /**< Current audio conversion function */
   213 } SDL_AUDIOCVT_PACKED SDL_AudioCVT;
   214 
   215 
   216 /* Function prototypes */
   217 
   218 /**
   219  *  \name Driver discovery functions
   220  *
   221  *  These functions return the list of built in audio drivers, in the
   222  *  order that they are normally initialized by default.
   223  */
   224 /* @{ */
   225 extern DECLSPEC int SDLCALL SDL_GetNumAudioDrivers(void);
   226 extern DECLSPEC const char *SDLCALL SDL_GetAudioDriver(int index);
   227 /* @} */
   228 
   229 /**
   230  *  \name Initialization and cleanup
   231  *
   232  *  \internal These functions are used internally, and should not be used unless
   233  *            you have a specific need to specify the audio driver you want to
   234  *            use.  You should normally use SDL_Init() or SDL_InitSubSystem().
   235  */
   236 /* @{ */
   237 extern DECLSPEC int SDLCALL SDL_AudioInit(const char *driver_name);
   238 extern DECLSPEC void SDLCALL SDL_AudioQuit(void);
   239 /* @} */
   240 
   241 /**
   242  *  This function returns the name of the current audio driver, or NULL
   243  *  if no driver has been initialized.
   244  */
   245 extern DECLSPEC const char *SDLCALL SDL_GetCurrentAudioDriver(void);
   246 
   247 /**
   248  *  This function opens the audio device with the desired parameters, and
   249  *  returns 0 if successful, placing the actual hardware parameters in the
   250  *  structure pointed to by \c obtained.  If \c obtained is NULL, the audio
   251  *  data passed to the callback function will be guaranteed to be in the
   252  *  requested format, and will be automatically converted to the hardware
   253  *  audio format if necessary.  This function returns -1 if it failed
   254  *  to open the audio device, or couldn't set up the audio thread.
   255  *
   256  *  When filling in the desired audio spec structure,
   257  *    - \c desired->freq should be the desired audio frequency in samples-per-
   258  *      second.
   259  *    - \c desired->format should be the desired audio format.
   260  *    - \c desired->samples is the desired size of the audio buffer, in
   261  *      samples.  This number should be a power of two, and may be adjusted by
   262  *      the audio driver to a value more suitable for the hardware.  Good values
   263  *      seem to range between 512 and 8096 inclusive, depending on the
   264  *      application and CPU speed.  Smaller values yield faster response time,
   265  *      but can lead to underflow if the application is doing heavy processing
   266  *      and cannot fill the audio buffer in time.  A stereo sample consists of
   267  *      both right and left channels in LR ordering.
   268  *      Note that the number of samples is directly related to time by the
   269  *      following formula:  \code ms = (samples*1000)/freq \endcode
   270  *    - \c desired->size is the size in bytes of the audio buffer, and is
   271  *      calculated by SDL_OpenAudio().
   272  *    - \c desired->silence is the value used to set the buffer to silence,
   273  *      and is calculated by SDL_OpenAudio().
   274  *    - \c desired->callback should be set to a function that will be called
   275  *      when the audio device is ready for more data.  It is passed a pointer
   276  *      to the audio buffer, and the length in bytes of the audio buffer.
   277  *      This function usually runs in a separate thread, and so you should
   278  *      protect data structures that it accesses by calling SDL_LockAudio()
   279  *      and SDL_UnlockAudio() in your code. Alternately, you may pass a NULL
   280  *      pointer here, and call SDL_QueueAudio() with some frequency, to queue
   281  *      more audio samples to be played.
   282  *    - \c desired->userdata is passed as the first parameter to your callback
   283  *      function. If you passed a NULL callback, this value is ignored.
   284  *
   285  *  The audio device starts out playing silence when it's opened, and should
   286  *  be enabled for playing by calling \c SDL_PauseAudio(0) when you are ready
   287  *  for your audio callback function to be called.  Since the audio driver
   288  *  may modify the requested size of the audio buffer, you should allocate
   289  *  any local mixing buffers after you open the audio device.
   290  */
   291 extern DECLSPEC int SDLCALL SDL_OpenAudio(SDL_AudioSpec * desired,
   292                                           SDL_AudioSpec * obtained);
   293 
   294 /**
   295  *  SDL Audio Device IDs.
   296  *
   297  *  A successful call to SDL_OpenAudio() is always device id 1, and legacy
   298  *  SDL audio APIs assume you want this device ID. SDL_OpenAudioDevice() calls
   299  *  always returns devices >= 2 on success. The legacy calls are good both
   300  *  for backwards compatibility and when you don't care about multiple,
   301  *  specific, or capture devices.
   302  */
   303 typedef Uint32 SDL_AudioDeviceID;
   304 
   305 /**
   306  *  Get the number of available devices exposed by the current driver.
   307  *  Only valid after a successfully initializing the audio subsystem.
   308  *  Returns -1 if an explicit list of devices can't be determined; this is
   309  *  not an error. For example, if SDL is set up to talk to a remote audio
   310  *  server, it can't list every one available on the Internet, but it will
   311  *  still allow a specific host to be specified to SDL_OpenAudioDevice().
   312  *
   313  *  In many common cases, when this function returns a value <= 0, it can still
   314  *  successfully open the default device (NULL for first argument of
   315  *  SDL_OpenAudioDevice()).
   316  */
   317 extern DECLSPEC int SDLCALL SDL_GetNumAudioDevices(int iscapture);
   318 
   319 /**
   320  *  Get the human-readable name of a specific audio device.
   321  *  Must be a value between 0 and (number of audio devices-1).
   322  *  Only valid after a successfully initializing the audio subsystem.
   323  *  The values returned by this function reflect the latest call to
   324  *  SDL_GetNumAudioDevices(); recall that function to redetect available
   325  *  hardware.
   326  *
   327  *  The string returned by this function is UTF-8 encoded, read-only, and
   328  *  managed internally. You are not to free it. If you need to keep the
   329  *  string for any length of time, you should make your own copy of it, as it
   330  *  will be invalid next time any of several other SDL functions is called.
   331  */
   332 extern DECLSPEC const char *SDLCALL SDL_GetAudioDeviceName(int index,
   333                                                            int iscapture);
   334 
   335 
   336 /**
   337  *  Open a specific audio device. Passing in a device name of NULL requests
   338  *  the most reasonable default (and is equivalent to calling SDL_OpenAudio()).
   339  *
   340  *  The device name is a UTF-8 string reported by SDL_GetAudioDeviceName(), but
   341  *  some drivers allow arbitrary and driver-specific strings, such as a
   342  *  hostname/IP address for a remote audio server, or a filename in the
   343  *  diskaudio driver.
   344  *
   345  *  \return 0 on error, a valid device ID that is >= 2 on success.
   346  *
   347  *  SDL_OpenAudio(), unlike this function, always acts on device ID 1.
   348  */
   349 extern DECLSPEC SDL_AudioDeviceID SDLCALL SDL_OpenAudioDevice(const char
   350                                                               *device,
   351                                                               int iscapture,
   352                                                               const
   353                                                               SDL_AudioSpec *
   354                                                               desired,
   355                                                               SDL_AudioSpec *
   356                                                               obtained,
   357                                                               int
   358                                                               allowed_changes);
   359 
   360 
   361 
   362 /**
   363  *  \name Audio state
   364  *
   365  *  Get the current audio state.
   366  */
   367 /* @{ */
   368 typedef enum
   369 {
   370     SDL_AUDIO_STOPPED = 0,
   371     SDL_AUDIO_PLAYING,
   372     SDL_AUDIO_PAUSED
   373 } SDL_AudioStatus;
   374 extern DECLSPEC SDL_AudioStatus SDLCALL SDL_GetAudioStatus(void);
   375 
   376 extern DECLSPEC SDL_AudioStatus SDLCALL
   377 SDL_GetAudioDeviceStatus(SDL_AudioDeviceID dev);
   378 /* @} *//* Audio State */
   379 
   380 /**
   381  *  \name Pause audio functions
   382  *
   383  *  These functions pause and unpause the audio callback processing.
   384  *  They should be called with a parameter of 0 after opening the audio
   385  *  device to start playing sound.  This is so you can safely initialize
   386  *  data for your callback function after opening the audio device.
   387  *  Silence will be written to the audio device during the pause.
   388  */
   389 /* @{ */
   390 extern DECLSPEC void SDLCALL SDL_PauseAudio(int pause_on);
   391 extern DECLSPEC void SDLCALL SDL_PauseAudioDevice(SDL_AudioDeviceID dev,
   392                                                   int pause_on);
   393 /* @} *//* Pause audio functions */
   394 
   395 /**
   396  *  This function loads a WAVE from the data source, automatically freeing
   397  *  that source if \c freesrc is non-zero.  For example, to load a WAVE file,
   398  *  you could do:
   399  *  \code
   400  *      SDL_LoadWAV_RW(SDL_RWFromFile("sample.wav", "rb"), 1, ...);
   401  *  \endcode
   402  *
   403  *  If this function succeeds, it returns the given SDL_AudioSpec,
   404  *  filled with the audio data format of the wave data, and sets
   405  *  \c *audio_buf to a malloc()'d buffer containing the audio data,
   406  *  and sets \c *audio_len to the length of that audio buffer, in bytes.
   407  *  You need to free the audio buffer with SDL_FreeWAV() when you are
   408  *  done with it.
   409  *
   410  *  This function returns NULL and sets the SDL error message if the
   411  *  wave file cannot be opened, uses an unknown data format, or is
   412  *  corrupt.  Currently raw and MS-ADPCM WAVE files are supported.
   413  */
   414 extern DECLSPEC SDL_AudioSpec *SDLCALL SDL_LoadWAV_RW(SDL_RWops * src,
   415                                                       int freesrc,
   416                                                       SDL_AudioSpec * spec,
   417                                                       Uint8 ** audio_buf,
   418                                                       Uint32 * audio_len);
   419 
   420 /**
   421  *  Loads a WAV from a file.
   422  *  Compatibility convenience function.
   423  */
   424 #define SDL_LoadWAV(file, spec, audio_buf, audio_len) \
   425     SDL_LoadWAV_RW(SDL_RWFromFile(file, "rb"),1, spec,audio_buf,audio_len)
   426 
   427 /**
   428  *  This function frees data previously allocated with SDL_LoadWAV_RW()
   429  */
   430 extern DECLSPEC void SDLCALL SDL_FreeWAV(Uint8 * audio_buf);
   431 
   432 /**
   433  *  This function takes a source format and rate and a destination format
   434  *  and rate, and initializes the \c cvt structure with information needed
   435  *  by SDL_ConvertAudio() to convert a buffer of audio data from one format
   436  *  to the other.
   437  *
   438  *  \return -1 if the format conversion is not supported, 0 if there's
   439  *  no conversion needed, or 1 if the audio filter is set up.
   440  */
   441 extern DECLSPEC int SDLCALL SDL_BuildAudioCVT(SDL_AudioCVT * cvt,
   442                                               SDL_AudioFormat src_format,
   443                                               Uint8 src_channels,
   444                                               int src_rate,
   445                                               SDL_AudioFormat dst_format,
   446                                               Uint8 dst_channels,
   447                                               int dst_rate);
   448 
   449 /**
   450  *  Once you have initialized the \c cvt structure using SDL_BuildAudioCVT(),
   451  *  created an audio buffer \c cvt->buf, and filled it with \c cvt->len bytes of
   452  *  audio data in the source format, this function will convert it in-place
   453  *  to the desired format.
   454  *
   455  *  The data conversion may expand the size of the audio data, so the buffer
   456  *  \c cvt->buf should be allocated after the \c cvt structure is initialized by
   457  *  SDL_BuildAudioCVT(), and should be \c cvt->len*cvt->len_mult bytes long.
   458  */
   459 extern DECLSPEC int SDLCALL SDL_ConvertAudio(SDL_AudioCVT * cvt);
   460 
   461 #define SDL_MIX_MAXVOLUME 128
   462 /**
   463  *  This takes two audio buffers of the playing audio format and mixes
   464  *  them, performing addition, volume adjustment, and overflow clipping.
   465  *  The volume ranges from 0 - 128, and should be set to ::SDL_MIX_MAXVOLUME
   466  *  for full audio volume.  Note this does not change hardware volume.
   467  *  This is provided for convenience -- you can mix your own audio data.
   468  */
   469 extern DECLSPEC void SDLCALL SDL_MixAudio(Uint8 * dst, const Uint8 * src,
   470                                           Uint32 len, int volume);
   471 
   472 /**
   473  *  This works like SDL_MixAudio(), but you specify the audio format instead of
   474  *  using the format of audio device 1. Thus it can be used when no audio
   475  *  device is open at all.
   476  */
   477 extern DECLSPEC void SDLCALL SDL_MixAudioFormat(Uint8 * dst,
   478                                                 const Uint8 * src,
   479                                                 SDL_AudioFormat format,
   480                                                 Uint32 len, int volume);
   481 
   482 /**
   483  *  Queue more audio on non-callback devices.
   484  *
   485  *  SDL offers two ways to feed audio to the device: you can either supply a
   486  *  callback that SDL triggers with some frequency to obtain more audio
   487  *  (pull method), or you can supply no callback, and then SDL will expect
   488  *  you to supply data at regular intervals (push method) with this function.
   489  *
   490  *  There are no limits on the amount of data you can queue, short of
   491  *  exhaustion of address space. Queued data will drain to the device as
   492  *  necessary without further intervention from you. If the device needs
   493  *  audio but there is not enough queued, it will play silence to make up
   494  *  the difference. This means you will have skips in your audio playback
   495  *  if you aren't routinely queueing sufficient data.
   496  *
   497  *  This function copies the supplied data, so you are safe to free it when
   498  *  the function returns. This function is thread-safe, but queueing to the
   499  *  same device from two threads at once does not promise which buffer will
   500  *  be queued first.
   501  *
   502  *  You may not queue audio on a device that is using an application-supplied
   503  *  callback; doing so returns an error. You have to use the audio callback
   504  *  or queue audio with this function, but not both.
   505  *
   506  *  You should not call SDL_LockAudio() on the device before queueing; SDL
   507  *  handles locking internally for this function.
   508  *
   509  *  \param dev The device ID to which we will queue audio.
   510  *  \param data The data to queue to the device for later playback.
   511  *  \param len The number of bytes (not samples!) to which (data) points.
   512  *  \return zero on success, -1 on error.
   513  *
   514  *  \sa SDL_GetQueuedAudioSize
   515  *  \sa SDL_ClearQueuedAudio
   516  */
   517 extern DECLSPEC int SDLCALL SDL_QueueAudio(SDL_AudioDeviceID dev, const void *data, Uint32 len);
   518 
   519 /**
   520  *  Get the number of bytes of still-queued audio.
   521  *
   522  *  This is the number of bytes that have been queued for playback with
   523  *  SDL_QueueAudio(), but have not yet been sent to the hardware.
   524  *
   525  *  Once we've sent it to the hardware, this function can not decide the exact
   526  *  byte boundary of what has been played. It's possible that we just gave the
   527  *  hardware several kilobytes right before you called this function, but it
   528  *  hasn't played any of it yet, or maybe half of it, etc.
   529  *
   530  *  You may not queue audio on a device that is using an application-supplied
   531  *  callback; calling this function on such a device always returns 0.
   532  *  You have to use the audio callback or queue audio with SDL_QueueAudio(),
   533  *  but not both.
   534  *
   535  *  You should not call SDL_LockAudio() on the device before querying; SDL
   536  *  handles locking internally for this function.
   537  *
   538  *  \param dev The device ID of which we will query queued audio size.
   539  *  \return Number of bytes (not samples!) of queued audio.
   540  *
   541  *  \sa SDL_QueueAudio
   542  *  \sa SDL_ClearQueuedAudio
   543  */
   544 extern DECLSPEC Uint32 SDLCALL SDL_GetQueuedAudioSize(SDL_AudioDeviceID dev);
   545 
   546 /**
   547  *  Drop any queued audio data waiting to be sent to the hardware.
   548  *
   549  *  Immediately after this call, SDL_GetQueuedAudioSize() will return 0 and
   550  *  the hardware will start playing silence if more audio isn't queued.
   551  *
   552  *  This will not prevent playback of queued audio that's already been sent
   553  *  to the hardware, as we can not undo that, so expect there to be some
   554  *  fraction of a second of audio that might still be heard. This can be
   555  *  useful if you want to, say, drop any pending music during a level change
   556  *  in your game.
   557  *
   558  *  You may not queue audio on a device that is using an application-supplied
   559  *  callback; calling this function on such a device is always a no-op.
   560  *  You have to use the audio callback or queue audio with SDL_QueueAudio(),
   561  *  but not both.
   562  *
   563  *  You should not call SDL_LockAudio() on the device before clearing the
   564  *  queue; SDL handles locking internally for this function.
   565  *
   566  *  This function always succeeds and thus returns void.
   567  *
   568  *  \param dev The device ID of which to clear the audio queue.
   569  *
   570  *  \sa SDL_QueueAudio
   571  *  \sa SDL_GetQueuedAudioSize
   572  */
   573 extern DECLSPEC void SDLCALL SDL_ClearQueuedAudio(SDL_AudioDeviceID dev);
   574 
   575 
   576 /**
   577  *  \name Audio lock functions
   578  *
   579  *  The lock manipulated by these functions protects the callback function.
   580  *  During a SDL_LockAudio()/SDL_UnlockAudio() pair, you can be guaranteed that
   581  *  the callback function is not running.  Do not call these from the callback
   582  *  function or you will cause deadlock.
   583  */
   584 /* @{ */
   585 extern DECLSPEC void SDLCALL SDL_LockAudio(void);
   586 extern DECLSPEC void SDLCALL SDL_LockAudioDevice(SDL_AudioDeviceID dev);
   587 extern DECLSPEC void SDLCALL SDL_UnlockAudio(void);
   588 extern DECLSPEC void SDLCALL SDL_UnlockAudioDevice(SDL_AudioDeviceID dev);
   589 /* @} *//* Audio lock functions */
   590 
   591 /**
   592  *  This function shuts down audio processing and closes the audio device.
   593  */
   594 extern DECLSPEC void SDLCALL SDL_CloseAudio(void);
   595 extern DECLSPEC void SDLCALL SDL_CloseAudioDevice(SDL_AudioDeviceID dev);
   596 
   597 /* Ends C function definitions when using C++ */
   598 #ifdef __cplusplus
   599 }
   600 #endif
   601 #include "close_code.h"
   602 
   603 #endif /* _SDL_audio_h */
   604 
   605 /* vi: set ts=4 sw=4 expandtab: */