src/audio/dummy/SDL_dummyaudio.c
author Sam Lantinga <slouken@libsdl.org>
Mon, 29 May 2006 04:04:35 +0000
branchSDL-1.3
changeset 1668 4da1ee79c9af
parent 1662 782fd950bd46
permissions -rw-r--r--
more tweaking indent options
     1 /*
     2     SDL - Simple DirectMedia Layer
     3     Copyright (C) 1997-2006 Sam Lantinga
     4 
     5     This library is free software; you can redistribute it and/or
     6     modify it under the terms of the GNU Lesser General Public
     7     License as published by the Free Software Foundation; either
     8     version 2.1 of the License, or (at your option) any later version.
     9 
    10     This library is distributed in the hope that it will be useful,
    11     but WITHOUT ANY WARRANTY; without even the implied warranty of
    12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    13     Lesser General Public License for more details.
    14 
    15     You should have received a copy of the GNU Lesser General Public
    16     License along with this library; if not, write to the Free Software
    17     Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
    18 
    19     Sam Lantinga
    20     slouken@libsdl.org
    21 
    22     This file written by Ryan C. Gordon (icculus@icculus.org)
    23 */
    24 #include "SDL_config.h"
    25 
    26 /* Output audio to nowhere... */
    27 
    28 #include "SDL_rwops.h"
    29 #include "SDL_timer.h"
    30 #include "SDL_audio.h"
    31 #include "../SDL_audiomem.h"
    32 #include "../SDL_audio_c.h"
    33 #include "../SDL_audiodev_c.h"
    34 #include "SDL_dummyaudio.h"
    35 
    36 /* The tag name used by DUMMY audio */
    37 #define DUMMYAUD_DRIVER_NAME         "dummy"
    38 
    39 /* Audio driver functions */
    40 static int DUMMYAUD_OpenAudio(_THIS, SDL_AudioSpec * spec);
    41 static void DUMMYAUD_WaitAudio(_THIS);
    42 static void DUMMYAUD_PlayAudio(_THIS);
    43 static Uint8 *DUMMYAUD_GetAudioBuf(_THIS);
    44 static void DUMMYAUD_CloseAudio(_THIS);
    45 
    46 /* Audio driver bootstrap functions */
    47 static int
    48 DUMMYAUD_Available(void)
    49 {
    50     const char *envr = SDL_getenv("SDL_AUDIODRIVER");
    51     if (envr && (SDL_strcmp(envr, DUMMYAUD_DRIVER_NAME) == 0)) {
    52         return (1);
    53     }
    54     return (0);
    55 }
    56 
    57 static void
    58 DUMMYAUD_DeleteDevice(SDL_AudioDevice * device)
    59 {
    60     SDL_free(device->hidden);
    61     SDL_free(device);
    62 }
    63 
    64 static SDL_AudioDevice *
    65 DUMMYAUD_CreateDevice(int devindex)
    66 {
    67     SDL_AudioDevice *this;
    68 
    69     /* Initialize all variables that we clean on shutdown */
    70     this = (SDL_AudioDevice *) SDL_malloc(sizeof(SDL_AudioDevice));
    71     if (this) {
    72         SDL_memset(this, 0, (sizeof *this));
    73         this->hidden = (struct SDL_PrivateAudioData *)
    74             SDL_malloc((sizeof *this->hidden));
    75     }
    76     if ((this == NULL) || (this->hidden == NULL)) {
    77         SDL_OutOfMemory();
    78         if (this) {
    79             SDL_free(this);
    80         }
    81         return (0);
    82     }
    83     SDL_memset(this->hidden, 0, (sizeof *this->hidden));
    84 
    85     /* Set the function pointers */
    86     this->OpenAudio = DUMMYAUD_OpenAudio;
    87     this->WaitAudio = DUMMYAUD_WaitAudio;
    88     this->PlayAudio = DUMMYAUD_PlayAudio;
    89     this->GetAudioBuf = DUMMYAUD_GetAudioBuf;
    90     this->CloseAudio = DUMMYAUD_CloseAudio;
    91 
    92     this->free = DUMMYAUD_DeleteDevice;
    93 
    94     return this;
    95 }
    96 
    97 AudioBootStrap DUMMYAUD_bootstrap = {
    98     DUMMYAUD_DRIVER_NAME, "SDL dummy audio driver",
    99     DUMMYAUD_Available, DUMMYAUD_CreateDevice
   100 };
   101 
   102 /* This function waits until it is possible to write a full sound buffer */
   103 static void
   104 DUMMYAUD_WaitAudio(_THIS)
   105 {
   106     /* Don't block on first calls to simulate initial fragment filling. */
   107     if (this->hidden->initial_calls)
   108         this->hidden->initial_calls--;
   109     else
   110         SDL_Delay(this->hidden->write_delay);
   111 }
   112 
   113 static void
   114 DUMMYAUD_PlayAudio(_THIS)
   115 {
   116     /* no-op...this is a null driver. */
   117 }
   118 
   119 static Uint8 *
   120 DUMMYAUD_GetAudioBuf(_THIS)
   121 {
   122     return (this->hidden->mixbuf);
   123 }
   124 
   125 static void
   126 DUMMYAUD_CloseAudio(_THIS)
   127 {
   128     if (this->hidden->mixbuf != NULL) {
   129         SDL_FreeAudioMem(this->hidden->mixbuf);
   130         this->hidden->mixbuf = NULL;
   131     }
   132 }
   133 
   134 static int
   135 DUMMYAUD_OpenAudio(_THIS, SDL_AudioSpec * spec)
   136 {
   137     float bytes_per_sec = 0.0f;
   138 
   139     /* Allocate mixing buffer */
   140     this->hidden->mixlen = spec->size;
   141     this->hidden->mixbuf = (Uint8 *) SDL_AllocAudioMem(this->hidden->mixlen);
   142     if (this->hidden->mixbuf == NULL) {
   143         return (-1);
   144     }
   145     SDL_memset(this->hidden->mixbuf, spec->silence, spec->size);
   146 
   147     bytes_per_sec = (float) (((spec->format & 0xFF) / 8) *
   148                              spec->channels * spec->freq);
   149 
   150     /*
   151      * We try to make this request more audio at the correct rate for
   152      *  a given audio spec, so timing stays fairly faithful.
   153      * Also, we have it not block at all for the first two calls, so
   154      *  it seems like we're filling two audio fragments right out of the
   155      *  gate, like other SDL drivers tend to do.
   156      */
   157     this->hidden->initial_calls = 2;
   158     this->hidden->write_delay =
   159         (Uint32) ((((float) spec->size) / bytes_per_sec) * 1000.0f);
   160 
   161     /* We're ready to rock and roll. :-) */
   162     return (0);
   163 }
   164 
   165 /* vi: set ts=4 sw=4 expandtab: */