----In the code below, I’m wondering why the function fillerup can be called
like this ONLY:
wave.spec.callback = fillerup;
----When the function itself takes the form:
void SDLCALL fillerup(void *unused, Uint8 *stream, int len)
Doesn’t it need parameters or arguments???-----------------------------------------------------------------------------
/* Program to load a wave file and loop playing it using SDL sound */
/* loopwaves.c is much more robust in handling WAVE files –
This is only for simple WAVEs
*/
#include “SDL_config.h”
#include <stdio.h>
#include <stdlib.h>
#if HAVE_SIGNAL_H
#include <signal.h>
#endif
#include “SDL.h”
#include “SDL_audio.h”
static double volume = 1.0f;
struct {
SDL_AudioSpec spec;
Uint8 sound; / Pointer to wave data /
Uint32 soundlen; / Length of wave data /
int soundpos; / Current play position */
} wave;
static int done = 0;
void poked(int sig)
{
done = 1;
}
/* Call this instead of exit(), so we can clean up SDL: atexit() is evil. */
static void quit(int rc)
{
SDL_Quit();
exit(rc);
}
/* Process the audio buffer, here only adjust the volume. */
void process_audio(Uint8 *audio_buf, int buf_size) {
int i;
switch (wave.spec.format) {
case AUDIO_U8: {
// unsigned 8-bit sample
Uint8 *ptr = (Uint8 *)audio_buf;
if (wave.spec.channels == 1) {
// process mono audio
for (i=0; i<buf_size; i += sizeof(Uint8)) {
double tmp = (*ptr) * volume;
tmp = tmp > 255.0 ? 255.0 : tmp;
*ptr = (Uint8)tmp;
ptr++;
}
} else if (wave.spec.channels == 2) {
// process stero audio
for (i=0; i<buf_size; i += sizeof(Uint8)*2) {
// process left channel
double tmp = (*ptr) * volume;
tmp = tmp > 255.0 ? 255.0 : tmp;
*ptr = (Uint8)tmp;
ptr++;
// process right channel
tmp = (*ptr) * volume;
tmp = tmp > 255.0 ? 255.0 : tmp;
*ptr = (Uint8)tmp;
ptr++;
}
} else {
fprintf(stderr, "Doesn't support more than 2 channels!\n");
exit(1);
}
break; }
case AUDIO_S8: {
// signed 8-bit sample
Sint8 *ptr = (Sint8 *)audio_buf;
if (wave.spec.channels == 1) {
// process mono audio
for (i=0; i<buf_size; i += sizeof(Sint8)) {
double tmp = (*ptr) * volume;
tmp = tmp > 127.0 ? 127.0 : tmp;
tmp = tmp < -128.0 ? -128.0 : tmp;
*ptr = (Sint8)tmp;
ptr++; // note here ptr will move to 8 bits higher
}
} else if (wave.spec.channels == 2) {
// process stero audio
for (i=0; i<buf_size; i += sizeof(Uint8)*2) {
// process left channel
double tmp = (*ptr) * volume;
tmp = tmp > 127.0 ? 127.0 : tmp;
tmp = tmp < -128.0 ? -128.0 : tmp;
*ptr = (Sint8)tmp;
ptr++;
// process right channel
tmp = (*ptr) * volume;
tmp = tmp > 127.0 ? 127.0 : tmp;
tmp = tmp < -128.0 ? -128.0 : tmp;
*ptr = (Sint8)tmp;
ptr++;
}
} else {
fprintf(stderr, "Doesn't support more than 2 channels!\n");
exit(1);
}
break; }
case AUDIO_U16LSB: {
// unsigned 16-bit sample, little-endian
Uint16 *ptr = (Uint16 *)audio_buf;
if (wave.spec.channels == 1) {
// process mono audio
for (i=0; i<buf_size; i += sizeof(Uint16)) {
#if (SDL_BYTE_ORDER == SDL_BIG_ENDIAN)
Uint16 swap = SDL_Swap16(*ptr);
double tmp = swap * volume;
tmp = tmp > 65535.0 ? 65535.0 : tmp;
swap = (Uint16)tmp;
*ptr = SDL_Swap16(swap);
ptr++; // note here ptr will move to 16 bits higher
#else
double tmp = (*ptr) * volume;
tmp = tmp > 65535.0 ? 65535.0 : tmp;
*ptr = (Uint16)tmp;
ptr++;
#endif
}
} else if (wave.spec.channels == 2) {
// process stero audio
for (i=0; i<buf_size; i += sizeof(Uint16)*2) {
#if (SDL_BYTE_ORDER == SDL_BIG_ENDIAN)
// process left channel
Uint16 swap = SDL_Swap16(*ptr);
double tmp = swap * volume;
tmp = tmp > 65535.0 ? 65535.0 : tmp;
swap = (Uint16)tmp;
*ptr = SDL_Swap16(swap);
ptr++;
// process right channel
swap = SDL_Swap16(*ptr);
tmp = swap * volume;
tmp = tmp > 65535.0 ? 65535.0 : tmp;
swap = (Uint16)tmp;
*ptr = SDL_Swap16(swap);
ptr++;
#else
// process left channel
double tmp = (*ptr) * volume;
tmp = tmp > 65535.0 ? 65535.0 : tmp;
*ptr = (Uint16)tmp;
ptr++;
// process right channel
tmp = (*ptr) * volume;
tmp = tmp > 65535.0 ? 65535.0 : tmp;
*ptr = (Uint16)tmp;
ptr++;
#endif
}
} else {
fprintf(stderr, “Doesn’t support more than 2 channels!\n”);
exit(1);
}
break; }
case AUDIO_S16LSB: {
// signed 16-bit sample, little-endian
Sint16 *ptr = (Sint16 *)audio_buf;
if (wave.spec.channels == 1) {
// process mono audio
for (i=0; i<buf_size; i += sizeof(Sint16)) {
#if (SDL_BYTE_ORDER == SDL_BIG_ENDIAN)
Sint16 swap = SDL_Swap16(*ptr);
double tmp = swap * volume;
tmp = tmp > 32767.0 ? 32767.0 : tmp;
tmp = tmp < -32768.0 ? -32768.0 : tmp;
swap = (Sint16)tmp;
*ptr = SDL_Swap16(swap);
ptr++;
#else
double tmp = (*ptr) * volume;
tmp = tmp > 32767.0 ? 32767.0 : tmp;
tmp = tmp < -32768.0 ? -32768.0 : tmp;
*ptr = (Sint16)tmp;
ptr++;
#endif
}
} else if (wave.spec.channels == 2) {
// process stero audio
for (i=0; i<buf_size; i += sizeof(Sint16)*2) {
#if (SDL_BYTE_ORDER == SDL_BIG_ENDIAN)
// process left channel
Sint16 swap = SDL_Swap(*ptr);
double tmp = swap * volume;
tmp = tmp > 32767.0 ? 32767.0 : tmp;
tmp = tmp < -32768.0 ? -32768.0 : tmp;
swap = (Sint16)tmp;
*ptr = SDL_Swap16(swap);
ptr++;
// process right channel
swap = SDL_Swap(*ptr);
tmp = swap * volume;
tmp = tmp > 32767.0 ? 32767.0 : tmp;
tmp = tmp < -32768.0 ? -32768.0 : tmp;
swap = (Sint16)tmp;
*ptr = SDL_Swap16(swap);
ptr++;
#else
// process left channel
double tmp = (*ptr) * volume;
tmp = tmp > 32767.0 ? 32767.0 : tmp;
tmp = tmp < -32768.0 ? -32768.0 : tmp;
*ptr = (Sint16)tmp;
ptr++;
// process right channel
tmp = (*ptr) * volume;
tmp = tmp > 32767.0 ? 32767.0 : tmp;
tmp = tmp < -32768.0 ? -32768.0 : tmp;
*ptr = (Sint16)tmp;
ptr++;
#endif
}
} else {
fprintf(stderr, “Doesn’t support more than 2 channels!\n”);
exit(1);
}
break; }
case AUDIO_U16MSB: {
// unsigned 16-bit sample, big-endian
Uint16 *ptr = (Uint16 *)audio_buf;
if (wave.spec.channels == 1) {
// process mono audio
for (i=0; i<buf_size; i += sizeof(Uint16)) {
#if (SDL_BYTE_ORDER == SDL_LIL_ENDIAN)
Uint16 swap = SDL_Swap16(*ptr);
double tmp = swap * volume;
tmp = tmp > 65535.0 ? 65535.0 : tmp;
swap = (Uint16)tmp;
*ptr = SDL_Swap16(swap);
ptr++; // note here ptr will move to 16 bits higher
#else
double tmp = (*ptr) * volume;
tmp = tmp > 65535.0 ? 65535.0 : tmp;
*ptr = (Uint16)tmp;
ptr++;
#endif
}
} else if (wave.spec.channels == 2) {
// process stero audio
for (i=0; i<buf_size; i += sizeof(Uint16)*2) {
#if (SDL_BYTE_ORDER == SDL_LIL_ENDIAN)
// process left channel
Uint16 swap = SDL_Swap16(*ptr);
double tmp = swap * volume;
tmp = tmp > 65535.0 ? 65535.0 : tmp;
swap = (Uint16)tmp;
*ptr = SDL_Swap16(swap);
ptr++;
// process right channel
swap = SDL_Swap16(*ptr);
tmp = swap * volume;
tmp = tmp > 65535.0 ? 65535.0 : tmp;
swap = (Uint16)tmp;
*ptr = SDL_Swap16(swap);
ptr++;
#else
// process left channel
double tmp = (*ptr) * volume;
tmp = tmp > 65535.0 ? 65535.0 : tmp;
*ptr = (Uint16)tmp;
ptr++;
// process right channel
tmp = (*ptr) * volume;
tmp = tmp > 65535.0 ? 65535.0 : tmp;
*ptr = (Uint16)tmp;
ptr++;
#endif
}
} else {
fprintf(stderr, “Doesn’t support more than 2 channels!\n”);
exit(1);
}
break; }
case AUDIO_S16MSB: {
// signed 16-bit sample, big-endian
Sint16 *ptr = (Sint16 *)audio_buf;
if (wave.spec.channels == 1) {
// process mono audio
for (i=0; i<buf_size; i += sizeof(Sint16)) {
#if (SDL_BYTE_ORDER == SDL_LIL_ENDIAN)
Sint16 swap = SDL_Swap16(*ptr);
double tmp = swap * volume;
tmp = tmp > 32767.0 ? 32767.0 : tmp;
tmp = tmp < -32768.0 ? -32768.0 : tmp;
swap = (Sint16)tmp;
*ptr = SDL_Swap16(swap);
ptr++;
#else
double tmp = (*ptr) * volume;
tmp = tmp > 32767.0 ? 32767.0 : tmp;
tmp = tmp < -32768.0 ? -32768.0 : tmp;
*ptr = (Sint16)tmp;
ptr++;
#endif
}
} else if (wave.spec.channels == 2) {
// process stero audio
for (i=0; i<buf_size; i += sizeof(Sint16)*2) {
#if (SDL_BYTE_ORDER == SDL_LIL_ENDIAN)
// process left channel
Sint16 swap = SDL_Swap(*ptr);
double tmp = swap * volume;
tmp = tmp > 32767.0 ? 32767.0 : tmp;
tmp = tmp < -32768.0 ? -32768.0 : tmp;
swap = (Sint16)tmp;
*ptr = SDL_Swap16(swap);
ptr++;
// process right channel
swap = SDL_Swap(*ptr);
tmp = swap * volume;
tmp = tmp > 32767.0 ? 32767.0 : tmp;
tmp = tmp < -32768.0 ? -32768.0 : tmp;
swap = (Sint16)tmp;
*ptr = SDL_Swap16(swap);
ptr++;
#else
// process left channel
double tmp = (*ptr) * volume;
tmp = tmp > 32767.0 ? 32767.0 : tmp;
tmp = tmp < -32768.0 ? -32768.0 : tmp;
*ptr = (Sint16)tmp;
ptr++;
// process right channel
tmp = (*ptr) * volume;
tmp = tmp > 32767.0 ? 32767.0 : tmp;
tmp = tmp < -32768.0 ? -32768.0 : tmp;
*ptr = (Sint16)tmp;
ptr++;
#endif
}
} else {
fprintf(stderr, “Doesn’t support more than 2 channels!\n”);
exit(1);
}
break; }
}
}
void SDLCALL fillerup(void *unused, Uint8 *stream, int len)
{
Uint8 *waveptr;
int waveleft;
/* Set up the pointers */
waveptr = wave.sound + wave.soundpos;
waveleft = wave.soundlen - wave.soundpos;
/* Go! */
while ( waveleft <= len ) {
/* Process samples */
Uint8 process_buf[waveleft];
SDL_memcpy(process_buf, waveptr, waveleft);
process_audio(process_buf, waveleft);
// play the end of the audio
SDL_memcpy(stream, process_buf, waveleft);
stream += waveleft;
len -= waveleft;
// ready to repeat play the audio
waveptr = wave.sound;
waveleft = wave.soundlen;
wave.soundpos = 0;
}
/* Process samples */
Uint8 process_buf[len];
SDL_memcpy(process_buf, waveptr, len);
process_audio(process_buf, len);
// play the processed samples
SDL_memcpy(stream, process_buf, len);
wave.soundpos += len;
}
static const int SCR_WIDTH = 240;
static const int SCR_HEIGHT = 180;
int main(int argc, char *argv[])
{
char name[32];
SDL_Event event;
Uint8 *keys;
SDL_Surface *screen;
/* Load the SDL library */
if ( SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO) < 0 ) {
fprintf(stderr, "Couldn't initialize SDL: %s\n",SDL_GetError());
return(1);
}
if ( argv[1] == NULL ) {
argv[1] = "sample.wav";
}
// Make a screen to put our video
#ifndef DARWIN
screen = SDL_SetVideoMode(SCR_WIDTH, SCR_HEIGHT, 0, 0);
#else
screen = SDL_SetVideoMode(SCR_WIDTH, SCR_HEIGHT, 24, 0);
#endif
if (!screen) {
fprintf(stderr, "SDL: could not set video mode - exiting\n");
quit(1);
}
/* Load the wave file into memory */
if ( SDL_LoadWAV(argv[1],
&wave.spec, &wave.sound, &wave.soundlen) == NULL ) {
fprintf(stderr, "Couldn't load %s: %s\n",
argv[1], SDL_GetError());
quit(1);
}
wave.spec.callback = fillerup;
#if HAVE_SIGNAL_H
/* Set the signals /
#ifdef SIGHUP
signal(SIGHUP, poked);
#endif
signal(SIGINT, poked);
#ifdef SIGQUIT
signal(SIGQUIT, poked);
#endif
signal(SIGTERM, poked);
#endif / HAVE_SIGNAL_H */
/* Initialize fillerup() variables */
if ( SDL_OpenAudio(&wave.spec, NULL) < 0 ) {
fprintf(stderr, "Couldn't open audio: %s\n", SDL_GetError());
SDL_FreeWAV(wave.sound);
quit(2);
}
// start playing
SDL_PauseAudio(0);
/* Let the audio run */
printf("Using audio driver: %s\n", SDL_AudioDriverName(name, 32));
while ( ! done && (SDL_GetAudioStatus() == SDL_AUDIO_PLAYING) ) {
// Poll input queue, run keyboard loop
while ( SDL_PollEvent(&event) ) {
if ( event.type == SDL_QUIT )
done = 1;
}
keys = SDL_GetKeyState(NULL);
if (keys[SDLK_q]) {
done = 1;
} else if (keys[SDLK_MINUS]) {
volume /= 2.0f;
} else if (keys[SDLK_EQUALS]) {
volume *= 2.0f;
}
SDL_Delay(100);
}
/* Clean up on signal */
SDL_CloseAudio();
SDL_FreeWAV(wave.sound);
SDL_Quit();
return(0);
}