view src/audio/dummy/SDL_dummyaudio.c @ 2042:3908e1f808e1

Fixed bug #292 I might be on crack here. It looks like SDL_ConvertMono() in src/audio/SDL_audiocvt.c adds the left and right channels of a stereo stream together, and clamps the new mono channel if it would overflow. Shouldn't it be dividing by 2 to average the two sample points instead of clamping? Otherwise the mono sample point's volume doubles in the conversion. This would also make the conversion faster, as it replaces two branches per sample frame with a bitwise shift. --ryan.
author Sam Lantinga <slouken@libsdl.org>
date Sun, 24 Sep 2006 15:56:36 +0000
parents c121d94672cb
children 5f6550e5184f 37c9c4590689
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/*
    SDL - Simple DirectMedia Layer
    Copyright (C) 1997-2006 Sam Lantinga

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Lesser General Public
    License as published by the Free Software Foundation; either
    version 2.1 of the License, or (at your option) any later version.

    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public
    License along with this library; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

    Sam Lantinga
    slouken@libsdl.org

    This file written by Ryan C. Gordon (icculus@icculus.org)
*/
#include "SDL_config.h"

/* Output audio to nowhere... */

#include "SDL_rwops.h"
#include "SDL_timer.h"
#include "SDL_audio.h"
#include "../SDL_audiomem.h"
#include "../SDL_audio_c.h"
#include "../SDL_audiodev_c.h"
#include "SDL_dummyaudio.h"

/* The tag name used by DUMMY audio */
#define DUMMYAUD_DRIVER_NAME         "dummy"

/* Audio driver functions */
static int DUMMYAUD_OpenAudio(_THIS, SDL_AudioSpec * spec);
static void DUMMYAUD_WaitAudio(_THIS);
static void DUMMYAUD_PlayAudio(_THIS);
static Uint8 *DUMMYAUD_GetAudioBuf(_THIS);
static void DUMMYAUD_CloseAudio(_THIS);

/* Audio driver bootstrap functions */
static int
DUMMYAUD_Available(void)
{
    const char *envr = SDL_getenv("SDL_AUDIODRIVER");
    if (envr && (SDL_strcmp(envr, DUMMYAUD_DRIVER_NAME) == 0)) {
        return (1);
    }
    return (0);
}

static void
DUMMYAUD_DeleteDevice(SDL_AudioDevice * device)
{
    SDL_free(device->hidden);
    SDL_free(device);
}

static SDL_AudioDevice *
DUMMYAUD_CreateDevice(int devindex)
{
    SDL_AudioDevice *this;

    /* Initialize all variables that we clean on shutdown */
    this = (SDL_AudioDevice *) SDL_malloc(sizeof(SDL_AudioDevice));
    if (this) {
        SDL_memset(this, 0, (sizeof *this));
        this->hidden = (struct SDL_PrivateAudioData *)
            SDL_malloc((sizeof *this->hidden));
    }
    if ((this == NULL) || (this->hidden == NULL)) {
        SDL_OutOfMemory();
        if (this) {
            SDL_free(this);
        }
        return (0);
    }
    SDL_memset(this->hidden, 0, (sizeof *this->hidden));

    /* Set the function pointers */
    this->OpenAudio = DUMMYAUD_OpenAudio;
    this->WaitAudio = DUMMYAUD_WaitAudio;
    this->PlayAudio = DUMMYAUD_PlayAudio;
    this->GetAudioBuf = DUMMYAUD_GetAudioBuf;
    this->CloseAudio = DUMMYAUD_CloseAudio;

    this->free = DUMMYAUD_DeleteDevice;

    return this;
}

AudioBootStrap DUMMYAUD_bootstrap = {
    DUMMYAUD_DRIVER_NAME, "SDL dummy audio driver",
    DUMMYAUD_Available, DUMMYAUD_CreateDevice
};

/* This function waits until it is possible to write a full sound buffer */
static void
DUMMYAUD_WaitAudio(_THIS)
{
    /* Don't block on first calls to simulate initial fragment filling. */
    if (this->hidden->initial_calls)
        this->hidden->initial_calls--;
    else
        SDL_Delay(this->hidden->write_delay);
}

static void
DUMMYAUD_PlayAudio(_THIS)
{
    /* no-op...this is a null driver. */
}

static Uint8 *
DUMMYAUD_GetAudioBuf(_THIS)
{
    return (this->hidden->mixbuf);
}

static void
DUMMYAUD_CloseAudio(_THIS)
{
    if (this->hidden->mixbuf != NULL) {
        SDL_FreeAudioMem(this->hidden->mixbuf);
        this->hidden->mixbuf = NULL;
    }
}

static int
DUMMYAUD_OpenAudio(_THIS, SDL_AudioSpec * spec)
{
    float bytes_per_sec = 0.0f;

    /* Allocate mixing buffer */
    this->hidden->mixlen = spec->size;
    this->hidden->mixbuf = (Uint8 *) SDL_AllocAudioMem(this->hidden->mixlen);
    if (this->hidden->mixbuf == NULL) {
        return (-1);
    }
    SDL_memset(this->hidden->mixbuf, spec->silence, spec->size);

    bytes_per_sec = (float) (((spec->format & 0xFF) / 8) *
                             spec->channels * spec->freq);

    /*
     * We try to make this request more audio at the correct rate for
     *  a given audio spec, so timing stays fairly faithful.
     * Also, we have it not block at all for the first two calls, so
     *  it seems like we're filling two audio fragments right out of the
     *  gate, like other SDL drivers tend to do.
     */
    this->hidden->initial_calls = 2;
    this->hidden->write_delay =
        (Uint32) ((((float) spec->size) / bytes_per_sec) * 1000.0f);

    /* We're ready to rock and roll. :-) */
    return (0);
}

/* vi: set ts=4 sw=4 expandtab: */