mixer.c

SDL_mixer 是一个基于 SDL 的混音器

	int frame_width = 1;

	if ((mixer.format & 0xFF) == 16) frame_width = 2;
	frame_width *= mixer.channels;
	while (chunk->alen % frame_width) chunk->alen--;
	return chunk->alen;
}

/* Play an audio chunk on a specific channel.
   If the specified channel is -1, play on the first free channel.
   'ticks' is the number of milliseconds at most to play the sample, or -1
   if there is no limit.
   Returns which channel was used to play the sound.
*/
int Mix_PlayChannelTimed(int which, Mix_Chunk *chunk, int loops, int ticks)
{
	int i;

	/* Don't play null pointers :-) */
	if ( chunk == NULL ) {
		Mix_SetError("Tried to play a NULL chunk");
		return(-1);
	}
	if ( !checkchunkintegral(chunk)) {
		Mix_SetError("Tried to play a chunk with a bad frame");
		return(-1);
	}

	/* Lock the mixer while modifying the playing channels */
	SDL_LockAudio();
	{
		/* If which is -1, play on the first free channel */
		if ( which == -1 ) {
			for ( i=reserved_channels; i<num_channels; ++i ) {
				if ( mix_channel[i].playing <= 0 )
					break;
			}
			if ( i == num_channels ) {
				Mix_SetError("No free channels available");
				which = -1;
			} else {
				which = i;
			}
		}

		/* Queue up the audio data for this channel */
		if ( which >= 0 ) {
			Uint32 sdl_ticks = SDL_GetTicks();
			if (Mix_Playing(which))
				_Mix_channel_done_playing(which);
			mix_channel[which].samples = chunk->abuf;
			mix_channel[which].playing = chunk->alen;
			mix_channel[which].looping = loops;
			mix_channel[which].chunk = chunk;
			mix_channel[which].paused = 0;
			mix_channel[which].fading = MIX_NO_FADING;
			mix_channel[which].start_time = sdl_ticks;
			mix_channel[which].expire = (ticks>0) ? (sdl_ticks + ticks) : 0;
		}
	}
	SDL_UnlockAudio();

	/* Return the channel on which the sound is being played */
	return(which);
}

/* Change the expiration delay for a channel */
int Mix_ExpireChannel(int which, int ticks)
{
	int status = 0;

	if ( which == -1 ) {
		int i;
		for ( i=0; i < num_channels; ++ i ) {
			status += Mix_ExpireChannel(i, ticks);
		}
	} else if ( which < num_channels ) {
		SDL_LockAudio();
		mix_channel[which].expire = (ticks>0) ? (SDL_GetTicks() + ticks) : 0;
		SDL_UnlockAudio();
		++ status;
	}
	return(status);
}

/* Fade in a sound on a channel, over ms milliseconds */
int Mix_FadeInChannelTimed(int which, Mix_Chunk *chunk, int loops, int ms, int ticks)
{
	int i;

	/* Don't play null pointers :-) */
	if ( chunk == NULL ) {
		return(-1);
	}
	if ( !checkchunkintegral(chunk)) {
		Mix_SetError("Tried to play a chunk with a bad frame");
		return(-1);
	}

	/* Lock the mixer while modifying the playing channels */
	SDL_LockAudio();
	{
		/* If which is -1, play on the first free channel */
		if ( which == -1 ) {
			for ( i=reserved_channels; i<num_channels; ++i ) {
				if ( mix_channel[i].playing <= 0 )
					break;
			}
			if ( i == num_channels ) {
				which = -1;
			} else {
				which = i;
			}
		}

		/* Queue up the audio data for this channel */
		if ( which >= 0 ) {
			Uint32 sdl_ticks = SDL_GetTicks();
			if (Mix_Playing(which))
				_Mix_channel_done_playing(which);
			mix_channel[which].samples = chunk->abuf;
			mix_channel[which].playing = chunk->alen;
			mix_channel[which].looping = loops;
			mix_channel[which].chunk = chunk;
			mix_channel[which].paused = 0;
			mix_channel[which].fading = MIX_FADING_IN;
			mix_channel[which].fade_volume = mix_channel[which].volume;
			mix_channel[which].volume = 0;
			mix_channel[which].fade_length = (Uint32)ms;
			mix_channel[which].start_time = mix_channel[which].ticks_fade = sdl_ticks;
			mix_channel[which].expire = (ticks > 0) ? (sdl_ticks+ticks) : 0;
		}
	}
	SDL_UnlockAudio();

	/* Return the channel on which the sound is being played */
	return(which);
}

/* Set volume of a particular channel */
int Mix_Volume(int which, int volume)
{
	int i;
	int prev_volume;

	if ( which == -1 ) {
		prev_volume = 0;
		for ( i=0; i<num_channels; ++i ) {
			prev_volume += Mix_Volume(i, volume);
		}
		prev_volume /= num_channels;
	} else {
		prev_volume = mix_channel[which].volume;
		if ( volume >= 0 ) {
			if ( volume > SDL_MIX_MAXVOLUME ) {
				volume = SDL_MIX_MAXVOLUME;
			}
			mix_channel[which].volume = volume;
		}
	}
	return(prev_volume);
}
/* Set volume of a particular chunk */
int Mix_VolumeChunk(Mix_Chunk *chunk, int volume)
{
	int prev_volume;

	prev_volume = chunk->volume;
	if ( volume >= 0 ) {
		if ( volume > MIX_MAX_VOLUME ) {
			volume = MIX_MAX_VOLUME;
		}
		chunk->volume = volume;
	}
	return(prev_volume);
}

/* Halt playing of a particular channel */
int Mix_HaltChannel(int which)
{
	int i;

	if ( which == -1 ) {
		for ( i=0; i<num_channels; ++i ) {
			Mix_HaltChannel(i);
		}
	} else {
		SDL_LockAudio();
		if (mix_channel[which].playing) {
			_Mix_channel_done_playing(which);
		mix_channel[which].playing = 0;
		}
		mix_channel[which].expire = 0;
		if(mix_channel[which].fading != MIX_NO_FADING) /* Restore volume */
			mix_channel[which].volume = mix_channel[which].fade_volume;
		mix_channel[which].fading = MIX_NO_FADING;
		SDL_UnlockAudio();
	}
	return(0);
}

/* Halt playing of a particular group of channels */
int Mix_HaltGroup(int tag)
{
	int i;

	for ( i=0; i<num_channels; ++i ) {
		if( mix_channel[i].tag == tag ) {
			Mix_HaltChannel(i);
		}
	}
	return(0);
}

/* Fade out a channel and then stop it automatically */
int Mix_FadeOutChannel(int which, int ms)
{
	int status;

	status = 0;
	if ( audio_opened ) {
		if ( which == -1 ) {
			int i;

			for ( i=0; i<num_channels; ++i ) {
				status += Mix_FadeOutChannel(i, ms);
			}
		} else {
			SDL_LockAudio();
			if ( mix_channel[which].playing && 
			    (mix_channel[which].volume > 0) &&
			    (mix_channel[which].fading != MIX_FADING_OUT) ) {

				mix_channel[which].fading = MIX_FADING_OUT;
				mix_channel[which].fade_volume = mix_channel[which].volume;
				mix_channel[which].fade_length = ms;
				mix_channel[which].ticks_fade = SDL_GetTicks();
				++status;
			}
			SDL_UnlockAudio();
		}
	}
	return(status);
}

/* Halt playing of a particular group of channels */
int Mix_FadeOutGroup(int tag, int ms)
{
	int i;
	int status = 0;
	for ( i=0; i<num_channels; ++i ) {
		if( mix_channel[i].tag == tag ) {
			status += Mix_FadeOutChannel(i,ms);
		}
	}
	return(status);
}

Mix_Fading Mix_FadingChannel(int which)
{
	return mix_channel[which].fading;
}

/* Check the status of a specific channel.
   If the specified mix_channel is -1, check all mix channels.
*/
int Mix_Playing(int which)
{
	int status;

	status = 0;
	if ( which == -1 ) {
		int i;

		for ( i=0; i<num_channels; ++i ) {
			if ((mix_channel[i].playing > 0) ||
				(mix_channel[i].looping > 0))
			{
				++status;
			}
		}
	} else {
		if ((mix_channel[which].playing > 0) ||
			(mix_channel[which].looping > 0))
		{
			++status;
		}
	}
	return(status);
}

/* rcg06072001 Get the chunk associated with a channel. */
Mix_Chunk *Mix_GetChunk(int channel)
{
	Mix_Chunk *retval = NULL;

	if ((channel >= 0) && (channel < num_channels)) {
		retval = mix_channel[channel].chunk;
	}

	return(retval);
}

/* Close the mixer, halting all playing audio */
void Mix_CloseAudio(void)
{
	int i;

	if ( audio_opened ) {
		if ( audio_opened == 1 ) {
			for (i = 0; i < num_channels; i++) {
				Mix_UnregisterAllEffects(i);
			}
			Mix_UnregisterAllEffects(MIX_CHANNEL_POST);
			close_music();
			Mix_HaltChannel(-1);
			SDL_CloseAudio();
			free(mix_channel);
			mix_channel = NULL;
		}
		--audio_opened;
	}
}

/* Pause a particular channel (or all) */
void Mix_Pause(int which)
{
	Uint32 sdl_ticks = SDL_GetTicks();
	if ( which == -1 ) {
		int i;

		for ( i=0; i<num_channels; ++i ) {
			if ( mix_channel[i].playing > 0 ) {
				mix_channel[i].paused = sdl_ticks;
			}
		}
	} else {
		if ( mix_channel[which].playing > 0 ) {
			mix_channel[which].paused = sdl_ticks;
		}
	}
}

/* Resume a paused channel */
void Mix_Resume(int which)
{
	Uint32 sdl_ticks = SDL_GetTicks();

	SDL_LockAudio();
	if ( which == -1 ) {
		int i;

		for ( i=0; i<num_channels; ++i ) {
			if ( mix_channel[i].playing > 0 ) {
				if(mix_channel[i].expire > 0)
					mix_channel[i].expire += sdl_ticks - mix_channel[i].paused;
				mix_channel[i].paused = 0;
			}
		}
	} else {
		if ( mix_channel[which].playing > 0 ) {
			if(mix_channel[which].expire > 0)
				mix_channel[which].expire += sdl_ticks - mix_channel[which].paused;
			mix_channel[which].paused = 0;
		}
	}
	SDL_UnlockAudio();
}

int Mix_Paused(int which)
{
	if ( which > num_channels )
		return(0);
	if ( which < 0 ) {
		int status = 0;
		int i;
		for( i=0; i < num_channels; ++i ) {
			if ( mix_channel[i].paused ) {
				++ status;
			}
		}
		return(status);
	} else {
		return(mix_channel[which].paused != 0);
	}
}

/* Change the group of a channel */
int Mix_GroupChannel(int which, int tag)
{
	if ( which < 0 || which > num_channels )
		return(0);

	SDL_LockAudio();
	mix_channel[which].tag = tag;
	SDL_UnlockAudio();
	return(1);
}

/* Assign several consecutive channels to a group */
int Mix_GroupChannels(int from, int to, int tag)
{
	int status = 0;
	for( ; from <= to; ++ from ) {
		status += Mix_GroupChannel(from, tag);
	}
	return(status);
}

/* Finds the first available channel in a group of channels */
int Mix_GroupAvailable(int tag)
{
	int i;
	for( i=0; i < num_channels; i ++ ) {
		if ( ((tag == -1) || (tag == mix_channel[i].tag)) &&
		                    (mix_channel[i].playing <= 0) )
			return i;
	}
	return(-1);
}

int Mix_GroupCount(int tag)
{
	int count = 0;
	int i;
	for( i=0; i < num_channels; i ++ ) {
		if ( mix_channel[i].tag==tag || tag==-1 )
			++ count;
	}
	return(count);
}

/* Finds the "oldest" sample playing in a group of channels */
int Mix_GroupOldest(int tag)
{
	int chan = -1;
	Uint32 mintime = SDL_GetTicks();
	int i;
	for( i=0; i < num_channels; i ++ ) {
		if ( (mix_channel[i].tag==tag || tag==-1) && mix_channel[i].playing > 0
			 && mix_channel[i].start_time <= mintime ) {
			mintime = mix_channel[i].start_time;
			chan = i;
		}
	}
	return(chan);
}

/* Finds the "most recent" (i.e. last) sample playing in a group of channels */
int Mix_GroupNewer(int tag)
{
	int chan = -1;
	Uint32 maxtime = 0;
	int i;
	for( i=0; i < num_channels; i ++ ) {
		if ( (mix_channel[i].tag==tag || tag==-1) && mix_channel[i].playing > 0
			 && mix_channel[i].start_time >= maxtime ) {
			maxtime = mix_channel[i].start_time;
			chan = i;
		}
	}
	return(chan);
}



/*
 * rcg06122001 The special effects exportable API.
 *  Please see effect_*.c for internally-implemented effects, such
 *  as Mix_SetPanning().
 */

/* MAKE SURE you hold the audio lock (SDL_LockAudio()) before calling this! */
static int _Mix_register_effect(effect_info **e, Mix_EffectFunc_t f,
				Mix_EffectDone_t d, void *arg)
{
	effect_info *new_e = malloc(sizeof (effect_info));

	if (!e) {
		Mix_SetError("Internal error");
		return(0);
	}

	if (f == NULL) {
		Mix_SetError("NULL effect callback");
		return(0);
	}

	if (new_e == NULL) {
		Mix_SetError("Out of memory");
		return(0);
	}

	new_e->callback = f;
	new_e->done_callback = d;
	new_e->udata = arg;
	new_e->next = NULL;

	/* add new effect to end of linked list... */
	if (*e == NULL) {
		*e = new_e;
	} else {
		effect_info *cur = *e;
		while (1) {
			if (cur->next == NULL) {
				cur->next = new_e;
				break;
			}
			cur = cur->next;
		}
	}

	return(1);
}


/* MAKE SURE you hold the audio lock (SDL_LockAudio()) before calling this! */
static int _Mix_remove_effect(int channel, effect_info **e, Mix_EffectFunc_t f)
{
	effect_info *cur;
	effect_info *prev = NULL;
	effect_info *next = NULL;

	if (!e) {
		Mix_SetError("Internal error");
		return(0);
	}

	for (cur = *e; cur != NULL; cur = cur->next) {
		if (cur->callback == f) {
			next = cur->next;
			if (cur->done_callback != NULL) {
				cur->done_callback(channel, cur->udata);
			}
			free(cur);

			if (prev == NULL) {   /* removing first item of list? */
				*e = next;
			} else {
				prev->next = next;
			}
			return(1);
		}
		prev = cur;
	}

	Mix_SetError("No such effect registered");
	return(0);
}


/* MAKE SURE you hold the audio lock (SDL_LockAudio()) before calling this! */
static int _Mix_remove_all_effects(int channel, effect_info **e)
{
	effect_info *cur;
	effect_info *next;

	if (!e) {
		Mix_SetError("Internal error");
		return(0);
	}

	for (cur = *e; cur != NULL; cur = next) {
		next = cur->next;
		if (cur->done_callback != NULL) {
			cur->done_callback(channel, cur->udata);
		}
		free(cur);
	}
	*e = NULL;

	return(1);
}


int Mix_RegisterEffect(int channel, Mix_EffectFunc_t f,
			Mix_EffectDone_t d, void *arg)
{
	effect_info **e = NULL;
	int retval;

	if (channel == MIX_CHANNEL_POST) {
		e = &posteffects;
	} else {
		if ((channel < 0) || (channel >= num_channels)) {
			Mix_SetError("Invalid channel number");
			return(0);
		}
		e = &mix_channel[channel].effects;
	}

	SDL_LockAudio();
	retval = _Mix_register_effect(e, f, d, arg);
	SDL_UnlockAudio();
	return(retval);
}


int Mix_UnregisterEffect(int channel, Mix_EffectFunc_t f)
{
	effect_info **e = NULL;
	int retval;

	if (channel == MIX_CHANNEL_POST) {
		e = &posteffects;
	} else {
		if ((channel < 0) || (channel >= num_channels)) {
			Mix_SetError("Invalid channel number");
			return(0);
		}
		e = &mix_channel[channel].effects;
	}

	SDL_LockAudio();
	retval = _Mix_remove_effect(channel, e, f);
	SDL_UnlockAudio();
	return(retval);
}


int Mix_UnregisterAllEffects(int channel)
{
	effect_info **e = NULL;
	int retval;

	if (channel == MIX_CHANNEL_POST) {
		e = &posteffects;
	} else {
		if ((channel < 0) || (channel >= num_channels)) {
			Mix_SetError("Invalid channel number");
			return(0);
		}
		e = &mix_channel[channel].effects;
	}

	SDL_LockAudio();
	retval = _Mix_remove_all_effects(channel, e);
	SDL_UnlockAudio();
	return(retval);
}

/* end of mixer.c ... */