source: roaraudio/doc/man7/roartut.7 @ 4609:60f562b4b516

.\" RoarAudio
.TH "roartut" "7" "July 2008" "RoarAudio" "System Manager's Manual: RoarAuido"

.SH NAME
roartut \- RoarAudio sound library developer tutorial

.\".SH SYNOPSIS

.\" #include <roaraudio.h>

.SH "DESCRIPTION"
This tutorial descipes some basics with working with libroar. We will create a simple application
that can play some sines. A lot of other examples can be found in RoarAudio's sources in the roarclients
directory.

.SH "PLAYING A SINE"
First of all we need the correct header files to be included:
 #include <math.h>       /* sin() */
 #include <stdio.h>      /* *printf*() */
 #include <roaraudio.h>  /* libroar */

After that we need some basic varibales with data about the audio we want to play back:
 int rate     = ROAR_RATE_DEFAULT;
 int bits     = 8;
 int channels = 1; /* mono */

Next we need to set the 'codec'. The codec is how the data is encoded.
We want PCM as signed ints in the native byte order of our machine.
 int codec    = ROAR_CODEC_DEFAULT;

Now we need to store the frequency of our sine:
 float freq = 523.2;            /* middle C */
 float step = M_PI*2*freq/rate; /* how much time per sample we have to encode ... */

In addition we need some variables to store the current time and the length of time sine:
 float t      = 0; /* current time */
 float length = 5; /* 5 sec */

The final thing we need is a socket to send data to the demon, a buffer to store the audio data and
a varibale to go thru the array:
 int fh;
 int i;
 char out[1024];

To open the connection we use the call \fBroar_simple_play\fR(3):
 if ( (fh = roar_simple_play(rate, channels, bits, codec, NULL, "sine gen")) == \-1 ) {
  fprintf(stderr, "Error: can not open playback!\\n");
  exit(1);
 }

Now we want to loop for \fBlength\fR seconds:
 while (t < 2*M_PI*freq*length) {
 }

In this loop we need to calculate our samples:
  for (i = 0; i < 1024; i++) {
   out[i] = 127*sin(t);
   t += step;
  }

The sine is multiplyed by 127 as our amplitude range for 8 bit signed int is from \-128 to +127.

After we have our current data in \fBout\fR we want to write them to the server:
  write(fh, out, 1024);

\fBNOTE:\fR In a real application you may want to check the return value but in our simple application
we should get \fBSIGPIPE\fR on error and simply die.

After we are finished with our main loop we have to close the socket to the server.
This is done by \fBroar_simple_close\fR(3):
 roar_simple_close(fh);

After adding some standard main() construct we should have something like this:
 #include <math.h>       /* sin() */
 #include <stdio.h>      /* *printf*() */
 #include <roaraudio.h>  /* libroar */

 int main (void) {
  int rate     = ROAR_RATE_DEFAULT;
  int bits     = 8;
  int channels = 1; /* mono */
  int codec    = ROAR_CODEC_DEFAULT;
  float freq   = 523.2;            /* middle C */
  float step   = M_PI*2*freq/rate; /* how much time per sample we have to encode ... */
  float t      = 0; /* current time */
  float length = 5; /* 5 sec */
  int fh;
  int i;
  char out[1024];

  if ( (fh = roar_simple_play(rate, channels, bits, codec, NULL, "sine gen")) == \-1 ) {
   fprintf(stderr, "Error: can not open playback!\\n");
   exit(1);
  }

  while (t < 2*M_PI*freq*length) {
   for (i = 0; i < 1024; i++) {
    out[i] = 127*sin(t);
    t += step;
   }
   write(fh, out, 1024);
  }

  roar_simple_close(fh);

  return 0;
 }

To compile and link we can use a command like this one:
 cc \-o roarsin roarsin.c \-lm `roar\-config \-\-libs \-\-cflags`

We need to use \fB-lm\fR to link the math library for \fBsin()\fR.
The tool \fBroar-config\fR(1) will keep care for us about all flags needed for libraor.

Now we should have a working binary \fBroarsin\fR playing a sin() for 5 sec.

Happy hacking!

.SH "SEE ALSO"
\fBroar-config\fR(1),
\fBroarcat\fR(1),
\fBlibroar\fR(7).
\fBRoarAudio\fR(7).

.\"ll