include/SDL_audio.h
author Ryan C. Gordon <icculus@icculus.org>
Tue, 24 Jan 2017 00:55:41 -0500
changeset 10845 c2b0d3d180f4
parent 10737 3406a0f8b041
child 10920 ffdf6433884c
permissions -rw-r--r--
Added a note about aligning SDL_AudioCVT data.
     1 /*
     2   Simple DirectMedia Layer
     3   Copyright (C) 1997-2017 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  *  Note that various parts of the conversion pipeline can take advantage
   190  *  of SIMD operations (like SSE2, for example). SDL_AudioCVT doesn't require
   191  *  you to pass it aligned data, but can possibly run much faster if you
   192  *  set both its (buf) field to a pointer that is aligned to 16 bytes, and its
   193  *  (len) field to something that's a multiple of 16, if possible.
   194  */
   195 #ifdef __GNUC__
   196 /* This structure is 84 bytes on 32-bit architectures, make sure GCC doesn't
   197    pad it out to 88 bytes to guarantee ABI compatibility between compilers.
   198    vvv
   199    The next time we rev the ABI, make sure to size the ints and add padding.
   200 */
   201 #define SDL_AUDIOCVT_PACKED __attribute__((packed))
   202 #else
   203 #define SDL_AUDIOCVT_PACKED
   204 #endif
   205 /* */
   206 typedef struct SDL_AudioCVT
   207 {
   208     int needed;                 /**< Set to 1 if conversion possible */
   209     SDL_AudioFormat src_format; /**< Source audio format */
   210     SDL_AudioFormat dst_format; /**< Target audio format */
   211     double rate_incr;           /**< Rate conversion increment */
   212     Uint8 *buf;                 /**< Buffer to hold entire audio data */
   213     int len;                    /**< Length of original audio buffer */
   214     int len_cvt;                /**< Length of converted audio buffer */
   215     int len_mult;               /**< buffer must be len*len_mult big */
   216     double len_ratio;           /**< Given len, final size is len*len_ratio */
   217     SDL_AudioFilter filters[10];        /**< Filter list */
   218     int filter_index;           /**< Current audio conversion function */
   219 } SDL_AUDIOCVT_PACKED SDL_AudioCVT;
   220 
   221 
   222 /* Function prototypes */
   223 
   224 /**
   225  *  \name Driver discovery functions
   226  *
   227  *  These functions return the list of built in audio drivers, in the
   228  *  order that they are normally initialized by default.
   229  */
   230 /* @{ */
   231 extern DECLSPEC int SDLCALL SDL_GetNumAudioDrivers(void);
   232 extern DECLSPEC const char *SDLCALL SDL_GetAudioDriver(int index);
   233 /* @} */
   234 
   235 /**
   236  *  \name Initialization and cleanup
   237  *
   238  *  \internal These functions are used internally, and should not be used unless
   239  *            you have a specific need to specify the audio driver you want to
   240  *            use.  You should normally use SDL_Init() or SDL_InitSubSystem().
   241  */
   242 /* @{ */
   243 extern DECLSPEC int SDLCALL SDL_AudioInit(const char *driver_name);
   244 extern DECLSPEC void SDLCALL SDL_AudioQuit(void);
   245 /* @} */
   246 
   247 /**
   248  *  This function returns the name of the current audio driver, or NULL
   249  *  if no driver has been initialized.
   250  */
   251 extern DECLSPEC const char *SDLCALL SDL_GetCurrentAudioDriver(void);
   252 
   253 /**
   254  *  This function opens the audio device with the desired parameters, and
   255  *  returns 0 if successful, placing the actual hardware parameters in the
   256  *  structure pointed to by \c obtained.  If \c obtained is NULL, the audio
   257  *  data passed to the callback function will be guaranteed to be in the
   258  *  requested format, and will be automatically converted to the hardware
   259  *  audio format if necessary.  This function returns -1 if it failed
   260  *  to open the audio device, or couldn't set up the audio thread.
   261  *
   262  *  When filling in the desired audio spec structure,
   263  *    - \c desired->freq should be the desired audio frequency in samples-per-
   264  *      second.
   265  *    - \c desired->format should be the desired audio format.
   266  *    - \c desired->samples is the desired size of the audio buffer, in
   267  *      samples.  This number should be a power of two, and may be adjusted by
   268  *      the audio driver to a value more suitable for the hardware.  Good values
   269  *      seem to range between 512 and 8096 inclusive, depending on the
   270  *      application and CPU speed.  Smaller values yield faster response time,
   271  *      but can lead to underflow if the application is doing heavy processing
   272  *      and cannot fill the audio buffer in time.  A stereo sample consists of
   273  *      both right and left channels in LR ordering.
   274  *      Note that the number of samples is directly related to time by the
   275  *      following formula:  \code ms = (samples*1000)/freq \endcode
   276  *    - \c desired->size is the size in bytes of the audio buffer, and is
   277  *      calculated by SDL_OpenAudio().
   278  *    - \c desired->silence is the value used to set the buffer to silence,
   279  *      and is calculated by SDL_OpenAudio().
   280  *    - \c desired->callback should be set to a function that will be called
   281  *      when the audio device is ready for more data.  It is passed a pointer
   282  *      to the audio buffer, and the length in bytes of the audio buffer.
   283  *      This function usually runs in a separate thread, and so you should
   284  *      protect data structures that it accesses by calling SDL_LockAudio()
   285  *      and SDL_UnlockAudio() in your code. Alternately, you may pass a NULL
   286  *      pointer here, and call SDL_QueueAudio() with some frequency, to queue
   287  *      more audio samples to be played (or for capture devices, call
   288  *      SDL_DequeueAudio() with some frequency, to obtain audio samples).
   289  *    - \c desired->userdata is passed as the first parameter to your callback
   290  *      function. If you passed a NULL callback, this value is ignored.
   291  *
   292  *  The audio device starts out playing silence when it's opened, and should
   293  *  be enabled for playing by calling \c SDL_PauseAudio(0) when you are ready
   294  *  for your audio callback function to be called.  Since the audio driver
   295  *  may modify the requested size of the audio buffer, you should allocate
   296  *  any local mixing buffers after you open the audio device.
   297  */
   298 extern DECLSPEC int SDLCALL SDL_OpenAudio(SDL_AudioSpec * desired,
   299                                           SDL_AudioSpec * obtained);
   300 
   301 /**
   302  *  SDL Audio Device IDs.
   303  *
   304  *  A successful call to SDL_OpenAudio() is always device id 1, and legacy
   305  *  SDL audio APIs assume you want this device ID. SDL_OpenAudioDevice() calls
   306  *  always returns devices >= 2 on success. The legacy calls are good both
   307  *  for backwards compatibility and when you don't care about multiple,
   308  *  specific, or capture devices.
   309  */
   310 typedef Uint32 SDL_AudioDeviceID;
   311 
   312 /**
   313  *  Get the number of available devices exposed by the current driver.
   314  *  Only valid after a successfully initializing the audio subsystem.
   315  *  Returns -1 if an explicit list of devices can't be determined; this is
   316  *  not an error. For example, if SDL is set up to talk to a remote audio
   317  *  server, it can't list every one available on the Internet, but it will
   318  *  still allow a specific host to be specified to SDL_OpenAudioDevice().
   319  *
   320  *  In many common cases, when this function returns a value <= 0, it can still
   321  *  successfully open the default device (NULL for first argument of
   322  *  SDL_OpenAudioDevice()).
   323  */
   324 extern DECLSPEC int SDLCALL SDL_GetNumAudioDevices(int iscapture);
   325 
   326 /**
   327  *  Get the human-readable name of a specific audio device.
   328  *  Must be a value between 0 and (number of audio devices-1).
   329  *  Only valid after a successfully initializing the audio subsystem.
   330  *  The values returned by this function reflect the latest call to
   331  *  SDL_GetNumAudioDevices(); recall that function to redetect available
   332  *  hardware.
   333  *
   334  *  The string returned by this function is UTF-8 encoded, read-only, and
   335  *  managed internally. You are not to free it. If you need to keep the
   336  *  string for any length of time, you should make your own copy of it, as it
   337  *  will be invalid next time any of several other SDL functions is called.
   338  */
   339 extern DECLSPEC const char *SDLCALL SDL_GetAudioDeviceName(int index,
   340                                                            int iscapture);
   341 
   342 
   343 /**
   344  *  Open a specific audio device. Passing in a device name of NULL requests
   345  *  the most reasonable default (and is equivalent to calling SDL_OpenAudio()).
   346  *
   347  *  The device name is a UTF-8 string reported by SDL_GetAudioDeviceName(), but
   348  *  some drivers allow arbitrary and driver-specific strings, such as a
   349  *  hostname/IP address for a remote audio server, or a filename in the
   350  *  diskaudio driver.
   351  *
   352  *  \return 0 on error, a valid device ID that is >= 2 on success.
   353  *
   354  *  SDL_OpenAudio(), unlike this function, always acts on device ID 1.
   355  */
   356 extern DECLSPEC SDL_AudioDeviceID SDLCALL SDL_OpenAudioDevice(const char
   357                                                               *device,
   358                                                               int iscapture,
   359                                                               const
   360                                                               SDL_AudioSpec *
   361                                                               desired,
   362                                                               SDL_AudioSpec *
   363                                                               obtained,
   364                                                               int
   365                                                               allowed_changes);
   366 
   367 
   368 
   369 /**
   370  *  \name Audio state
   371  *
   372  *  Get the current audio state.
   373  */
   374 /* @{ */
   375 typedef enum
   376 {
   377     SDL_AUDIO_STOPPED = 0,
   378     SDL_AUDIO_PLAYING,
   379     SDL_AUDIO_PAUSED
   380 } SDL_AudioStatus;
   381 extern DECLSPEC SDL_AudioStatus SDLCALL SDL_GetAudioStatus(void);
   382 
   383 extern DECLSPEC SDL_AudioStatus SDLCALL
   384 SDL_GetAudioDeviceStatus(SDL_AudioDeviceID dev);
   385 /* @} *//* Audio State */
   386 
   387 /**
   388  *  \name Pause audio functions
   389  *
   390  *  These functions pause and unpause the audio callback processing.
   391  *  They should be called with a parameter of 0 after opening the audio
   392  *  device to start playing sound.  This is so you can safely initialize
   393  *  data for your callback function after opening the audio device.
   394  *  Silence will be written to the audio device during the pause.
   395  */
   396 /* @{ */
   397 extern DECLSPEC void SDLCALL SDL_PauseAudio(int pause_on);
   398 extern DECLSPEC void SDLCALL SDL_PauseAudioDevice(SDL_AudioDeviceID dev,
   399                                                   int pause_on);
   400 /* @} *//* Pause audio functions */
   401 
   402 /**
   403  *  This function loads a WAVE from the data source, automatically freeing
   404  *  that source if \c freesrc is non-zero.  For example, to load a WAVE file,
   405  *  you could do:
   406  *  \code
   407  *      SDL_LoadWAV_RW(SDL_RWFromFile("sample.wav", "rb"), 1, ...);
   408  *  \endcode
   409  *
   410  *  If this function succeeds, it returns the given SDL_AudioSpec,
   411  *  filled with the audio data format of the wave data, and sets
   412  *  \c *audio_buf to a malloc()'d buffer containing the audio data,
   413  *  and sets \c *audio_len to the length of that audio buffer, in bytes.
   414  *  You need to free the audio buffer with SDL_FreeWAV() when you are
   415  *  done with it.
   416  *
   417  *  This function returns NULL and sets the SDL error message if the
   418  *  wave file cannot be opened, uses an unknown data format, or is
   419  *  corrupt.  Currently raw and MS-ADPCM WAVE files are supported.
   420  */
   421 extern DECLSPEC SDL_AudioSpec *SDLCALL SDL_LoadWAV_RW(SDL_RWops * src,
   422                                                       int freesrc,
   423                                                       SDL_AudioSpec * spec,
   424                                                       Uint8 ** audio_buf,
   425                                                       Uint32 * audio_len);
   426 
   427 /**
   428  *  Loads a WAV from a file.
   429  *  Compatibility convenience function.
   430  */
   431 #define SDL_LoadWAV(file, spec, audio_buf, audio_len) \
   432     SDL_LoadWAV_RW(SDL_RWFromFile(file, "rb"),1, spec,audio_buf,audio_len)
   433 
   434 /**
   435  *  This function frees data previously allocated with SDL_LoadWAV_RW()
   436  */
   437 extern DECLSPEC void SDLCALL SDL_FreeWAV(Uint8 * audio_buf);
   438 
   439 /**
   440  *  This function takes a source format and rate and a destination format
   441  *  and rate, and initializes the \c cvt structure with information needed
   442  *  by SDL_ConvertAudio() to convert a buffer of audio data from one format
   443  *  to the other.
   444  *
   445  *  \return -1 if the format conversion is not supported, 0 if there's
   446  *  no conversion needed, or 1 if the audio filter is set up.
   447  */
   448 extern DECLSPEC int SDLCALL SDL_BuildAudioCVT(SDL_AudioCVT * cvt,
   449                                               SDL_AudioFormat src_format,
   450                                               Uint8 src_channels,
   451                                               int src_rate,
   452                                               SDL_AudioFormat dst_format,
   453                                               Uint8 dst_channels,
   454                                               int dst_rate);
   455 
   456 /**
   457  *  Once you have initialized the \c cvt structure using SDL_BuildAudioCVT(),
   458  *  created an audio buffer \c cvt->buf, and filled it with \c cvt->len bytes of
   459  *  audio data in the source format, this function will convert it in-place
   460  *  to the desired format.
   461  *
   462  *  The data conversion may expand the size of the audio data, so the buffer
   463  *  \c cvt->buf should be allocated after the \c cvt structure is initialized by
   464  *  SDL_BuildAudioCVT(), and should be \c cvt->len*cvt->len_mult bytes long.
   465  */
   466 extern DECLSPEC int SDLCALL SDL_ConvertAudio(SDL_AudioCVT * cvt);
   467 
   468 #define SDL_MIX_MAXVOLUME 128
   469 /**
   470  *  This takes two audio buffers of the playing audio format and mixes
   471  *  them, performing addition, volume adjustment, and overflow clipping.
   472  *  The volume ranges from 0 - 128, and should be set to ::SDL_MIX_MAXVOLUME
   473  *  for full audio volume.  Note this does not change hardware volume.
   474  *  This is provided for convenience -- you can mix your own audio data.
   475  */
   476 extern DECLSPEC void SDLCALL SDL_MixAudio(Uint8 * dst, const Uint8 * src,
   477                                           Uint32 len, int volume);
   478 
   479 /**
   480  *  This works like SDL_MixAudio(), but you specify the audio format instead of
   481  *  using the format of audio device 1. Thus it can be used when no audio
   482  *  device is open at all.
   483  */
   484 extern DECLSPEC void SDLCALL SDL_MixAudioFormat(Uint8 * dst,
   485                                                 const Uint8 * src,
   486                                                 SDL_AudioFormat format,
   487                                                 Uint32 len, int volume);
   488 
   489 /**
   490  *  Queue more audio on non-callback devices.
   491  *
   492  *  (If you are looking to retrieve queued audio from a non-callback capture
   493  *  device, you want SDL_DequeueAudio() instead. This will return -1 to
   494  *  signify an error if you use it with capture devices.)
   495  *
   496  *  SDL offers two ways to feed audio to the device: you can either supply a
   497  *  callback that SDL triggers with some frequency to obtain more audio
   498  *  (pull method), or you can supply no callback, and then SDL will expect
   499  *  you to supply data at regular intervals (push method) with this function.
   500  *
   501  *  There are no limits on the amount of data you can queue, short of
   502  *  exhaustion of address space. Queued data will drain to the device as
   503  *  necessary without further intervention from you. If the device needs
   504  *  audio but there is not enough queued, it will play silence to make up
   505  *  the difference. This means you will have skips in your audio playback
   506  *  if you aren't routinely queueing sufficient data.
   507  *
   508  *  This function copies the supplied data, so you are safe to free it when
   509  *  the function returns. This function is thread-safe, but queueing to the
   510  *  same device from two threads at once does not promise which buffer will
   511  *  be queued first.
   512  *
   513  *  You may not queue audio on a device that is using an application-supplied
   514  *  callback; doing so returns an error. You have to use the audio callback
   515  *  or queue audio with this function, but not both.
   516  *
   517  *  You should not call SDL_LockAudio() on the device before queueing; SDL
   518  *  handles locking internally for this function.
   519  *
   520  *  \param dev The device ID to which we will queue audio.
   521  *  \param data The data to queue to the device for later playback.
   522  *  \param len The number of bytes (not samples!) to which (data) points.
   523  *  \return zero on success, -1 on error.
   524  *
   525  *  \sa SDL_GetQueuedAudioSize
   526  *  \sa SDL_ClearQueuedAudio
   527  */
   528 extern DECLSPEC int SDLCALL SDL_QueueAudio(SDL_AudioDeviceID dev, const void *data, Uint32 len);
   529 
   530 /**
   531  *  Dequeue more audio on non-callback devices.
   532  *
   533  *  (If you are looking to queue audio for output on a non-callback playback
   534  *  device, you want SDL_QueueAudio() instead. This will always return 0
   535  *  if you use it with playback devices.)
   536  *
   537  *  SDL offers two ways to retrieve audio from a capture device: you can
   538  *  either supply a callback that SDL triggers with some frequency as the
   539  *  device records more audio data, (push method), or you can supply no
   540  *  callback, and then SDL will expect you to retrieve data at regular
   541  *  intervals (pull method) with this function.
   542  *
   543  *  There are no limits on the amount of data you can queue, short of
   544  *  exhaustion of address space. Data from the device will keep queuing as
   545  *  necessary without further intervention from you. This means you will
   546  *  eventually run out of memory if you aren't routinely dequeueing data.
   547  *
   548  *  Capture devices will not queue data when paused; if you are expecting
   549  *  to not need captured audio for some length of time, use
   550  *  SDL_PauseAudioDevice() to stop the capture device from queueing more
   551  *  data. This can be useful during, say, level loading times. When
   552  *  unpaused, capture devices will start queueing data from that point,
   553  *  having flushed any capturable data available while paused.
   554  *
   555  *  This function is thread-safe, but dequeueing from the same device from
   556  *  two threads at once does not promise which thread will dequeued data
   557  *  first.
   558  *
   559  *  You may not dequeue audio from a device that is using an
   560  *  application-supplied callback; doing so returns an error. You have to use
   561  *  the audio callback, or dequeue audio with this function, but not both.
   562  *
   563  *  You should not call SDL_LockAudio() on the device before queueing; SDL
   564  *  handles locking internally for this function.
   565  *
   566  *  \param dev The device ID from which we will dequeue audio.
   567  *  \param data A pointer into where audio data should be copied.
   568  *  \param len The number of bytes (not samples!) to which (data) points.
   569  *  \return number of bytes dequeued, which could be less than requested.
   570  *
   571  *  \sa SDL_GetQueuedAudioSize
   572  *  \sa SDL_ClearQueuedAudio
   573  */
   574 extern DECLSPEC Uint32 SDLCALL SDL_DequeueAudio(SDL_AudioDeviceID dev, void *data, Uint32 len);
   575 
   576 /**
   577  *  Get the number of bytes of still-queued audio.
   578  *
   579  *  For playback device:
   580  *
   581  *    This is the number of bytes that have been queued for playback with
   582  *    SDL_QueueAudio(), but have not yet been sent to the hardware. This
   583  *    number may shrink at any time, so this only informs of pending data.
   584  *
   585  *    Once we've sent it to the hardware, this function can not decide the
   586  *    exact byte boundary of what has been played. It's possible that we just
   587  *    gave the hardware several kilobytes right before you called this
   588  *    function, but it hasn't played any of it yet, or maybe half of it, etc.
   589  *
   590  *  For capture devices:
   591  *
   592  *    This is the number of bytes that have been captured by the device and
   593  *    are waiting for you to dequeue. This number may grow at any time, so
   594  *    this only informs of the lower-bound of available data.
   595  *
   596  *  You may not queue audio on a device that is using an application-supplied
   597  *  callback; calling this function on such a device always returns 0.
   598  *  You have to queue audio with SDL_QueueAudio()/SDL_DequeueAudio(), or use
   599  *  the audio callback, but not both.
   600  *
   601  *  You should not call SDL_LockAudio() on the device before querying; SDL
   602  *  handles locking internally for this function.
   603  *
   604  *  \param dev The device ID of which we will query queued audio size.
   605  *  \return Number of bytes (not samples!) of queued audio.
   606  *
   607  *  \sa SDL_QueueAudio
   608  *  \sa SDL_ClearQueuedAudio
   609  */
   610 extern DECLSPEC Uint32 SDLCALL SDL_GetQueuedAudioSize(SDL_AudioDeviceID dev);
   611 
   612 /**
   613  *  Drop any queued audio data. For playback devices, this is any queued data
   614  *  still waiting to be submitted to the hardware. For capture devices, this
   615  *  is any data that was queued by the device that hasn't yet been dequeued by
   616  *  the application.
   617  *
   618  *  Immediately after this call, SDL_GetQueuedAudioSize() will return 0. For
   619  *  playback devices, the hardware will start playing silence if more audio
   620  *  isn't queued. Unpaused capture devices will start filling the queue again
   621  *  as soon as they have more data available (which, depending on the state
   622  *  of the hardware and the thread, could be before this function call
   623  *  returns!).
   624  *
   625  *  This will not prevent playback of queued audio that's already been sent
   626  *  to the hardware, as we can not undo that, so expect there to be some
   627  *  fraction of a second of audio that might still be heard. This can be
   628  *  useful if you want to, say, drop any pending music during a level change
   629  *  in your game.
   630  *
   631  *  You may not queue audio on a device that is using an application-supplied
   632  *  callback; calling this function on such a device is always a no-op.
   633  *  You have to queue audio with SDL_QueueAudio()/SDL_DequeueAudio(), or use
   634  *  the audio callback, but not both.
   635  *
   636  *  You should not call SDL_LockAudio() on the device before clearing the
   637  *  queue; SDL handles locking internally for this function.
   638  *
   639  *  This function always succeeds and thus returns void.
   640  *
   641  *  \param dev The device ID of which to clear the audio queue.
   642  *
   643  *  \sa SDL_QueueAudio
   644  *  \sa SDL_GetQueuedAudioSize
   645  */
   646 extern DECLSPEC void SDLCALL SDL_ClearQueuedAudio(SDL_AudioDeviceID dev);
   647 
   648 
   649 /**
   650  *  \name Audio lock functions
   651  *
   652  *  The lock manipulated by these functions protects the callback function.
   653  *  During a SDL_LockAudio()/SDL_UnlockAudio() pair, you can be guaranteed that
   654  *  the callback function is not running.  Do not call these from the callback
   655  *  function or you will cause deadlock.
   656  */
   657 /* @{ */
   658 extern DECLSPEC void SDLCALL SDL_LockAudio(void);
   659 extern DECLSPEC void SDLCALL SDL_LockAudioDevice(SDL_AudioDeviceID dev);
   660 extern DECLSPEC void SDLCALL SDL_UnlockAudio(void);
   661 extern DECLSPEC void SDLCALL SDL_UnlockAudioDevice(SDL_AudioDeviceID dev);
   662 /* @} *//* Audio lock functions */
   663 
   664 /**
   665  *  This function shuts down audio processing and closes the audio device.
   666  */
   667 extern DECLSPEC void SDLCALL SDL_CloseAudio(void);
   668 extern DECLSPEC void SDLCALL SDL_CloseAudioDevice(SDL_AudioDeviceID dev);
   669 
   670 /* Ends C function definitions when using C++ */
   671 #ifdef __cplusplus
   672 }
   673 #endif
   674 #include "close_code.h"
   675 
   676 #endif /* SDL_audio_h_ */
   677 
   678 /* vi: set ts=4 sw=4 expandtab: */