lxdream.org :: lxdream/src/drivers/audio

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     1 /**

     2  * $Id$

     3  *

     4  * The SDL sound driver

     5  *

     6  * Copyright (c) 2009 wahrhaft

     7  *

     8  * This program is free software; you can redistribute it and/or modify

     9  * it under the terms of the GNU General Public License as published by

    10  * the Free Software Foundation; either version 2 of the License, or

    11  * (at your option) any later version.

    12  *

    13  * This program is distributed in the hope that it will be useful,

    14  * but WITHOUT ANY WARRANTY; without even the implied warranty of

    15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

    16  * GNU General Public License for more details.

    17  */

    18 #include <stdio.h>

    19 #include <unistd.h>

    20 #include <SDL.h>

    21 #include <SDL_audio.h>

    22 #include "aica/audio.h"

    23 #include "lxdream.h"

    25 #define SDL_SAMPLES 512        //tweaking this value may help with audio dropouts

    26 #define BYTES_PER_SAMPLE 4     //should be changed if samples are not S16 stereo

    28 #define BUFFER_MIN_SIZE SDL_SAMPLES * BYTES_PER_SAMPLE * 4

    29 #define BUFFER_MAX_SIZE SDL_SAMPLES * BYTES_PER_SAMPLE * 16

    31 static char *audio_buffer;

    32 static int buffer_pos;

    34 static void mix_audio(void *userdata, Uint8 *stream, int len);

    36 static gboolean audio_sdl_init( )

    37 {

    38     int rate = DEFAULT_SAMPLE_RATE;

    39     int format = DEFAULT_SAMPLE_FORMAT;

    41     SDL_AudioSpec fmt;

    42     fmt.freq = rate;

    43     if (format & AUDIO_FMT_16BIT)

    44         fmt.format = AUDIO_S16;

    45     else

    46         fmt.format = AUDIO_U8;

    47     if (format & AUDIO_FMT_STEREO)

    48         fmt.channels = 2;

    49     else

    50         fmt.channels = 1;

    52     fmt.samples = SDL_SAMPLES;

    53     fmt.callback = mix_audio;

    54     fmt.userdata = NULL;

    56     if (SDL_OpenAudio(&fmt, NULL) < 0)

    57     {

    58         ERROR("Unable to open audio output (SDL)");

    59         return FALSE;

    60     }

    61     buffer_pos = 0;

    62     audio_buffer = (char*)malloc(BUFFER_MAX_SIZE * sizeof(char));

    63     if (audio_buffer == NULL)

    64     {

    65         ERROR("Could not allocate audio buffer (SDL)");

    66         return FALSE;

    67     }

    69     return TRUE;

    70 }

    72 gboolean audio_sdl_process_buffer( audio_buffer_t buffer )

    73 {

    74     SDL_LockAudio();

    75     if (buffer_pos + buffer->length >= BUFFER_MAX_SIZE)

    76     {

    77         DEBUG("Audio buffer full, dropping a chunk\n");

    78     }

    79     else

    80     {

    81         memcpy(audio_buffer, buffer->data, buffer->length);

    82         buffer_pos += buffer->length;

    83     }

    84     SDL_UnlockAudio();

    86     return TRUE;

    87 }

    89 static void mix_audio(void *userdata, Uint8 *stream, int len)

    90 {

    91     if (len < buffer_pos)

    92     {

    93         memcpy(stream, audio_buffer, len);

    94     }

    95     if (buffer_pos > BUFFER_MIN_SIZE)

    96     {

    97         memcpy(audio_buffer, &audio_buffer[len], buffer_pos - len);

    98         buffer_pos -= len;

    99     }

   100     else

   101     {

   102         DEBUG("Audio buffer low, repeating a chunk\n");

   103     }

   104 }

   106 static gboolean audio_sdl_shutdown()

   107 {

   108     SDL_CloseAudio();

   109     free(audio_buffer);

   110     return TRUE;

   111 }

   113 static void audio_sdl_start()

   114 {

   115     SDL_PauseAudio(0);

   116 }

   118 static void audio_sdl_stop()

   119 {

   120     SDL_PauseAudio(1);

   121 }

   123 static struct audio_driver audio_sdl_driver = {

   124     "sdl",

   125     N_("SDL sound driver"),

   126     20,

   127     DEFAULT_SAMPLE_RATE,

   128     DEFAULT_SAMPLE_FORMAT,

   129     audio_sdl_init,

   130     audio_sdl_start,

   131     audio_sdl_process_buffer,

   132     audio_sdl_stop,

   133     audio_sdl_shutdown

   134 };

   136 AUDIO_DRIVER( "sdl", audio_sdl_driver );