XCodeiPhoneOS/Demos/src/mixer.c

/*
 *	mixer.c
 *	written by Holmes Futrell
 *	use however you want
 */

#import "SDL.h"
#import "common.h"

#define NUM_CHANNELS 8				/* max number of sounds we can play at once */
#define NUM_DRUMS 4					/* number of drums in our set */
#define MILLESECONDS_PER_FRAME 16	/* about 60 frames per second */

static struct {
	SDL_Rect rect;			/* where the button is drawn */
	SDL_Color upColor;		/* color when button is not active */
	SDL_Color downColor;	/* color when button is active */
	int isPressed;			/* is the button being pressed ? */
	int touchIndex;			/* what mouse (touch) index pressed the button ? */
} buttons[NUM_DRUMS];

struct sound {
	Uint8 *buffer;			/* audio buffer for sound file */
	Uint32 length;			/* length of the buffer (in bytes) */
};

/* this array holds the audio for the drum noises */
static struct sound drums[NUM_DRUMS];

/* function declarations */
void handleMouseButtonDown(SDL_Event *event);
void handleMouseButtonUp(SDL_Event *event);
int playSound(struct sound *);
void render(void);
void initializeButtons();
void audioCallback(void *userdata, Uint8 *stream, int len);
void loadSound(const char *file, struct sound *s);

struct {
	/* channel array holds information about currently playing sounds */
	struct {
		Uint8 *position;		/* what is the current position in the buffer of this sound ? */
		Uint32 remaining;		/* how many bytes remaining before we're done playing the sound ? */
		Uint32 timestamp;		/* when did this sound start playing ? */
	} channels[NUM_CHANNELS];
	SDL_AudioSpec outputSpec;	/* what audio format are we using for output? */
	int numSoundsPlaying;		/* how many sounds are currently playing */
} mixer;

/* sets up the buttons (color, position, state) */
void initializeButtons() {
	
	int i;
	int spacing = 10;														/* gap between drum buttons */
	SDL_Rect buttonRect;													/* keeps track of where to position drum */
	SDL_Color upColor = { 86, 86, 140, 255 };								/* color of drum when not pressed */
	SDL_Color downColor = { 191, 191, 221, 255 };							/* color of drum when pressed */
	
	buttonRect.x = spacing;
	buttonRect.y = spacing;
	buttonRect.w = SCREEN_WIDTH - 2 * spacing;
	buttonRect.h = ( SCREEN_HEIGHT - (NUM_DRUMS + 1) * spacing ) / NUM_DRUMS;
	
	/* setup each button */
	for (i=0; i<NUM_DRUMS; i++) {
		
		buttons[i].rect = buttonRect;
		buttons[i].isPressed = 0;
		buttons[i].upColor = upColor;
		buttons[i].downColor = downColor;
		
		buttonRect.y += spacing + buttonRect.h;								/* setup y coordinate for next drum */
		
	}	
}
/*
 loads a wav file (stored in 'file'), converts it to the mixer's output format,
 and stores the resulting buffer and length in the sound structure
 */
void loadSound(const char *file, struct sound *s) {
	SDL_AudioSpec spec;		/* the audio format of the .wav file */
	SDL_AudioCVT cvt;		/* used to convert .wav to output format when formats differ */
	int result;
	if (SDL_LoadWAV(file, &spec, &s->buffer, &s->length) == NULL) {
		fatalError("could not load .wav");
	}
	/* build the audio converter */
	result = SDL_BuildAudioCVT(&cvt, spec.format, spec.channels, spec.freq,
							   mixer.outputSpec.format, mixer.outputSpec.channels, mixer.outputSpec.freq);
	if (result == -1) {
		fatalError("could not build audio CVT");
	}
	else if (result != 0) {
		/* 
		 this happens when the .wav format differs from the output format.
		 we convert the .wav buffer here
		 */
		cvt.buf = (Uint8 *)SDL_malloc(s->length * cvt.len_mult); /* allocate conversion buffer */
		cvt.len = s->length;									  /* set conversion buffer length */
		SDL_memcpy(cvt.buf, s->buffer, s->length);				  /* copy sound to conversion buffer */
		if (SDL_ConvertAudio(&cvt) == -1) {					  /* convert the sound */
			fatalError("could not convert .wav");
		}
		SDL_free(s->buffer);									  /* free the original (unconverted) buffer */
		s->buffer = cvt.buf;									  /* point sound buffer to converted buffer */
		s->length = cvt.len_cvt;								  /* set sound buffer's new length */
	}
}

/* called from main event loop */
void handleMouseButtonDown(SDL_Event *event) {

	int x, y, mouseIndex, i, drumIndex;
	
	mouseIndex = event->button.which;
	drumIndex = -1;
	
	SDL_SelectMouse(mouseIndex);
	SDL_GetMouseState(&x, &y);
	/* check if we hit any of the drum buttons */
	for (i=0; i<NUM_DRUMS; i++) {
		if (x >= buttons[i].rect.x && x < buttons[i].rect.x + buttons[i].rect.w \
			&& y >= buttons[i].rect.y && y < buttons[i].rect.y + buttons[i].rect.h) {
			drumIndex = i;
			break; 
		}
	}
	if (drumIndex != -1) {
		/* if we hit a button */
		buttons[drumIndex].touchIndex = mouseIndex;
		buttons[drumIndex].isPressed = 1;
		playSound(&drums[drumIndex]);
	}
	
}

/* called from main event loop */
void handleMouseButtonUp(SDL_Event *event) {
	int i;
	int mouseIndex = event->button.which;
	/* check if this should cause any of the buttons to become unpressed */
	for (i=0; i<NUM_DRUMS; i++) {
		if (buttons[i].touchIndex == mouseIndex) {
			buttons[i].isPressed = 0;
		}
	}
}

/* draws buttons to screen */
void render(void) {
	int i;
	SDL_RenderFill(50, 50, 50, 255, NULL);	/* draw background (gray) */
	/* draw the drum buttons */
	for (i=0; i<NUM_DRUMS; i++) {
		SDL_Color color = buttons[i].isPressed ? buttons[i].downColor : buttons[i].upColor;
		SDL_RenderFill(color.r, color.g, color.b, color.unused, &buttons[i].rect);
	}
	/* update the screen */
	SDL_RenderPresent();
}

/*
	finds a sound channel in the mixer for a sound
	and sets it up to start playing
*/
int playSound(struct sound *s) {
	/*
		find an empty channel to play on.
		if no channel is available, use oldest channel
	*/
	int i;
	int selected_channel = -1;
	int oldest_channel = 0;
	
	if (mixer.numSoundsPlaying == 0) {
		/* we're playing a sound now, so start audio callback back up */
		SDL_PauseAudio(0);
	}	
	
	/* find a sound channel to play the sound on */
	for (i=0; i<NUM_CHANNELS; i++) {
		if (mixer.channels[i].position == NULL) {
			/* if no sound on this channel, select it */
			selected_channel = i;
			break;
		}
		/* if this channel's sound is older than the oldest so far, set it to oldest */
		if (mixer.channels[i].timestamp < mixer.channels[oldest_channel].timestamp)
			oldest_channel = i;
	}
	
	/* no empty channels, take the oldest one */
	if (selected_channel == -1) 
		selected_channel = oldest_channel;
	else 
		mixer.numSoundsPlaying++;
	
	/* point channel data to wav data */
	mixer.channels[selected_channel].position	= s->buffer;
	mixer.channels[selected_channel].remaining	= s->length;
	mixer.channels[selected_channel].timestamp  = SDL_GetTicks();
	
	return selected_channel;
}

/* 
	Called from SDL's audio system.  Supplies sound input with data by mixing together all
	currently playing sound effects.
*/
void audioCallback(void *userdata, Uint8 *stream, int len) {
	int i;
	int copy_amt;
	SDL_memset(stream, mixer.outputSpec.silence, len); /* initialize buffer to silence */
	/* for each channel, mix in whatever is playing on that channel */
	for (i=0; i<NUM_CHANNELS; i++) {		
		if (mixer.channels[i].position == NULL) {
			/* if no sound is playing on this channel */ 
			continue; /* nothing to do for this channel */
		}
		
		/* copy len bytes to the buffer, unless we have fewer than len bytes remaining */
		copy_amt = mixer.channels[i].remaining < len ? mixer.channels[i].remaining : len;
		
		/* mix this sound effect with the output */
		SDL_MixAudioFormat(stream, mixer.channels[i].position, mixer.outputSpec.format, copy_amt, 150);
		
		/* update buffer position in sound effect and the number of bytes left */
		mixer.channels[i].position    += copy_amt;
		mixer.channels[i].remaining   -= copy_amt;
		
		/* did we finish playing the sound effect ? */
		if (mixer.channels[i].remaining == 0) {
			mixer.channels[i].position = NULL; /* indicates no sound playing on channel anymore */
			mixer.numSoundsPlaying--;
			if (mixer.numSoundsPlaying == 0) {
				/* if no sounds left playing, pause audio callback */
				SDL_PauseAudio(1);
			}
		}
	}
}

int main(int argc, char *argv[]) {
	
	int done;				/* has user tried to quit ? */
	SDL_WindowID windowID;	/* our main window */
	SDL_Event event;	
	Uint32 startFrame;		/* holds when frame started processing */
	Uint32 endFrame;		/* holds when frame ended processing */
	Uint32 delay;			/* calculated delay, how long should we wait before next frame? */
	
	if (SDL_Init(SDL_INIT_VIDEO|SDL_INIT_AUDIO) < 0) {
		fatalError("could not initialize SDL");
	}
	windowID = SDL_CreateWindow(NULL, 0, 0, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_OPENGL | SDL_WINDOW_BORDERLESS);
	SDL_CreateRenderer(windowID, 0, 0);		
	
	/* initialize the mixer */
	SDL_memset(&mixer, 0, sizeof(mixer));
	/* setup output format */
	mixer.outputSpec.freq = 44100;
	mixer.outputSpec.format = AUDIO_S16LSB;
	mixer.outputSpec.channels = 2;
	mixer.outputSpec.samples = 256;
	mixer.outputSpec.callback = audioCallback;
	mixer.outputSpec.userdata = NULL;	
	
	/* open audio for output */
	if (SDL_OpenAudio(&mixer.outputSpec, NULL) != 0) {
		fatalError("Opening audio failed");
	}	
	
	/* load our drum noises */
	loadSound("ds_kick_big_amb.wav", &drums[3]);
	loadSound("ds_brush_snare.wav", &drums[2]);
	loadSound("ds_loose_skin_mute.wav", &drums[1]);
	loadSound("ds_china.wav", &drums[0]);

	/* setup positions, colors, and state of buttons */
	initializeButtons();
	
	/* enter main loop */
	done = 0;
	while(!done) {
		startFrame = SDL_GetTicks();
        while (SDL_PollEvent(&event)) {
			switch(event.type) {
				case SDL_MOUSEBUTTONDOWN:
					handleMouseButtonDown(&event);
					break;
				case SDL_MOUSEBUTTONUP:
					handleMouseButtonUp(&event);
					break;
				case SDL_QUIT:
					done = 1;
					break;
			}
        }
		render(); /* draw buttons */
		endFrame = SDL_GetTicks();
		
		/* figure out how much time we have left, and then sleep */
		delay = MILLESECONDS_PER_FRAME - (endFrame - startFrame);
		if (delay < 0) {
			delay = 0;
		} else if (delay > MILLESECONDS_PER_FRAME) {
			delay = MILLESECONDS_PER_FRAME;
		}
		SDL_Delay(delay);
	}
	
	/* cleanup code, let's free up those sound buffers */
	int i;
	for (i=0; i<NUM_DRUMS; i++) {
		SDL_free(drums[i].buffer);
	}
	/* let SDL do its exit code */
	SDL_Quit();
	
	return 0;
}