src/audio/dummy/SDL_dummyaudio.c
author Sam Lantinga
Wed, 15 Mar 2006 03:50:34 +0000
changeset 1538 b1f8c14f0df5
parent 1537 60620d71e324
child 1662 782fd950bd46
child 1895 c121d94672cb
child 4159 a1b03ba2fcd0
permissions -rw-r--r--
*** empty log message ***
     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 DUMMYAUD_Available(void)
    48 {
    49 	const char *envr = SDL_getenv("SDL_AUDIODRIVER");
    50 	if (envr && (SDL_strcmp(envr, DUMMYAUD_DRIVER_NAME) == 0)) {
    51 		return(1);
    52 	}
    53 	return(0);
    54 }
    55 
    56 static void DUMMYAUD_DeleteDevice(SDL_AudioDevice *device)
    57 {
    58 	SDL_free(device->hidden);
    59 	SDL_free(device);
    60 }
    61 
    62 static SDL_AudioDevice *DUMMYAUD_CreateDevice(int devindex)
    63 {
    64 	SDL_AudioDevice *this;
    65 
    66 	/* Initialize all variables that we clean on shutdown */
    67 	this = (SDL_AudioDevice *)SDL_malloc(sizeof(SDL_AudioDevice));
    68 	if ( this ) {
    69 		SDL_memset(this, 0, (sizeof *this));
    70 		this->hidden = (struct SDL_PrivateAudioData *)
    71 				SDL_malloc((sizeof *this->hidden));
    72 	}
    73 	if ( (this == NULL) || (this->hidden == NULL) ) {
    74 		SDL_OutOfMemory();
    75 		if ( this ) {
    76 			SDL_free(this);
    77 		}
    78 		return(0);
    79 	}
    80 	SDL_memset(this->hidden, 0, (sizeof *this->hidden));
    81 
    82 	/* Set the function pointers */
    83 	this->OpenAudio = DUMMYAUD_OpenAudio;
    84 	this->WaitAudio = DUMMYAUD_WaitAudio;
    85 	this->PlayAudio = DUMMYAUD_PlayAudio;
    86 	this->GetAudioBuf = DUMMYAUD_GetAudioBuf;
    87 	this->CloseAudio = DUMMYAUD_CloseAudio;
    88 
    89 	this->free = DUMMYAUD_DeleteDevice;
    90 
    91 	return this;
    92 }
    93 
    94 AudioBootStrap DUMMYAUD_bootstrap = {
    95 	DUMMYAUD_DRIVER_NAME, "SDL dummy audio driver",
    96 	DUMMYAUD_Available, DUMMYAUD_CreateDevice
    97 };
    98 
    99 /* This function waits until it is possible to write a full sound buffer */
   100 static void DUMMYAUD_WaitAudio(_THIS)
   101 {
   102 	/* Don't block on first calls to simulate initial fragment filling. */
   103 	if (this->hidden->initial_calls)
   104 		this->hidden->initial_calls--;
   105 	else
   106 		SDL_Delay(this->hidden->write_delay);
   107 }
   108 
   109 static void DUMMYAUD_PlayAudio(_THIS)
   110 {
   111 	/* no-op...this is a null driver. */
   112 }
   113 
   114 static Uint8 *DUMMYAUD_GetAudioBuf(_THIS)
   115 {
   116 	return(this->hidden->mixbuf);
   117 }
   118 
   119 static void DUMMYAUD_CloseAudio(_THIS)
   120 {
   121 	if ( this->hidden->mixbuf != NULL ) {
   122 		SDL_FreeAudioMem(this->hidden->mixbuf);
   123 		this->hidden->mixbuf = NULL;
   124 	}
   125 }
   126 
   127 static int DUMMYAUD_OpenAudio(_THIS, SDL_AudioSpec *spec)
   128 {
   129 	float bytes_per_sec = 0.0f;
   130 
   131 	/* Allocate mixing buffer */
   132 	this->hidden->mixlen = spec->size;
   133 	this->hidden->mixbuf = (Uint8 *) SDL_AllocAudioMem(this->hidden->mixlen);
   134 	if ( this->hidden->mixbuf == NULL ) {
   135 		return(-1);
   136 	}
   137 	SDL_memset(this->hidden->mixbuf, spec->silence, spec->size);
   138 
   139 	bytes_per_sec = (float) (((spec->format & 0xFF) / 8) *
   140 	                   spec->channels * spec->freq);
   141 
   142 	/*
   143 	 * We try to make this request more audio at the correct rate for
   144 	 *  a given audio spec, so timing stays fairly faithful.
   145 	 * Also, we have it not block at all for the first two calls, so
   146 	 *  it seems like we're filling two audio fragments right out of the
   147 	 *  gate, like other SDL drivers tend to do.
   148 	 */
   149 	this->hidden->initial_calls = 2;
   150 	this->hidden->write_delay =
   151 	               (Uint32) ((((float) spec->size) / bytes_per_sec) * 1000.0f);
   152 
   153 	/* We're ready to rock and roll. :-) */
   154 	return(0);
   155 }
   156