src/audio/dummy/SDL_dummyaudio.c
author Ryan C. Gordon
Wed, 04 Oct 2006 19:54:23 +0000
branchSDL-ryan-multiple-audio-device
changeset 3796 b19680c84cdf
parent 3792 866c310e2cb5
child 3798 c8b3d3d13ed1
permissions -rw-r--r--
Bunch of 1.3 audio cleanups to remove FIXMEs, get driver specific crap out of
the core and into the drivers where it belongs, and push generic
responsibilities out of the drivers and into the core where they belong.
     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_OpenDevice(_THIS, const char *devname, int iscapture);
    41 static void DUMMYAUD_WaitDevice(_THIS);
    42 static void DUMMYAUD_PlayDevice(_THIS);
    43 static Uint8 *DUMMYAUD_GetDeviceBuf(_THIS);
    44 static void DUMMYAUD_CloseDevice(_THIS);
    45 
    46 /* Audio driver bootstrap functions */
    47 static int
    48 DUMMYAUD_Available(void)
    49 {
    50     /* !!! FIXME: check this at a higher level... */
    51     /* only ever use this driver if explicitly requested. */
    52     const char *envr = SDL_getenv("SDL_AUDIODRIVER");
    53     if (envr && (SDL_strcmp(envr, DUMMYAUD_DRIVER_NAME) == 0)) {
    54         return (1);
    55     }
    56     return (0);
    57 }
    58 
    59 static int
    60 DUMMYAUD_Init(SDL_AudioDriverImpl *impl)
    61 {
    62     /* Set the function pointers */
    63     impl->OpenDevice = DUMMYAUD_OpenDevice;
    64     impl->WaitDevice = DUMMYAUD_WaitDevice;
    65     impl->PlayDevice = DUMMYAUD_PlayDevice;
    66     impl->GetDeviceBuf = DUMMYAUD_GetDeviceBuf;
    67     impl->CloseDevice = DUMMYAUD_CloseDevice;
    68     impl->OnlyHasDefaultOutputDevice = 1;
    69 
    70     return 1;
    71 }
    72 
    73 AudioBootStrap DUMMYAUD_bootstrap = {
    74     DUMMYAUD_DRIVER_NAME, "SDL dummy audio driver",
    75     DUMMYAUD_Available, DUMMYAUD_Init
    76 };
    77 
    78 /* This function waits until it is possible to write a full sound buffer */
    79 static void
    80 DUMMYAUD_WaitDevice(_THIS)
    81 {
    82     /* Don't block on first calls to simulate initial fragment filling. */
    83     if (this->hidden->initial_calls)
    84         this->hidden->initial_calls--;
    85     else
    86         SDL_Delay(this->hidden->write_delay);
    87 }
    88 
    89 static void
    90 DUMMYAUD_PlayDevice(_THIS)
    91 {
    92     /* no-op...this is a null driver. */
    93 }
    94 
    95 static Uint8 *
    96 DUMMYAUD_GetDeviceBuf(_THIS)
    97 {
    98     return (this->hidden->mixbuf);
    99 }
   100 
   101 static void
   102 DUMMYAUD_CloseDevice(_THIS)
   103 {
   104     if (this->hidden->mixbuf != NULL) {
   105         SDL_FreeAudioMem(this->hidden->mixbuf);
   106         this->hidden->mixbuf = NULL;
   107     }
   108     SDL_free(this->hidden);
   109     this->hidden = NULL;
   110 }
   111 
   112 static int
   113 DUMMYAUD_OpenDevice(_THIS, const char *devname, int iscapture)
   114 {
   115     float bytes_per_sec = 0.0f;
   116 
   117     /* Initialize all variables that we clean on shutdown */
   118     this->hidden = (struct SDL_PrivateAudioData *)
   119                     SDL_malloc((sizeof *this->hidden));
   120     if (this->hidden == NULL) {
   121         SDL_OutOfMemory();
   122         return 0;
   123     }
   124     SDL_memset(this->hidden, 0, (sizeof *this->hidden));
   125 
   126     /* Allocate mixing buffer */
   127     this->hidden->mixlen = this->spec.size;
   128     this->hidden->mixbuf = (Uint8 *) SDL_AllocAudioMem(this->hidden->mixlen);
   129     if (this->hidden->mixbuf == NULL) {
   130         DUMMYAUD_CloseDevice(this);
   131         return 0;
   132     }
   133     SDL_memset(this->hidden->mixbuf, this->spec.silence, this->spec.size);
   134 
   135     bytes_per_sec = (float) (SDL_AUDIO_BITSIZE(this->spec.format) / 8) *
   136                              this->spec.channels * this->spec.freq;
   137 
   138     /*
   139      * We try to make this request more audio at the correct rate for
   140      *  a given audio spec, so timing stays fairly faithful.
   141      * Also, we have it not block at all for the first two calls, so
   142      *  it seems like we're filling two audio fragments right out of the
   143      *  gate, like other SDL drivers tend to do.
   144      */
   145     this->hidden->initial_calls = 2;
   146     this->hidden->write_delay =
   147         (Uint32) ((((float) this->spec.size) / bytes_per_sec) * 1000.0f);
   148 
   149     /* We're ready to rock and roll. :-) */
   150     return 1;
   151 }
   152 
   153 /* vi: set ts=4 sw=4 expandtab: */