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      1 /*
      2     SDL - Simple DirectMedia Layer
      3     Copyright (C) 1997-2012 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 (at) libsdl.org
     21 
     22     This file written by Ryan C. Gordon (icculus (at) 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 
    157