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-<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
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- <meta name="GENERATOR" content="Mozilla/4.77 [en]C-gatewaynet (Win98; U) [Netscape]">
- <meta name="Author" content="Phil Burk">
- <meta name="Description" content="Tutorial for PortAudio, a cross platform, open-source, audio I/O library.It provides a very simple API for recording and/or playing sound using a simple callback function.">
- <meta name="KeyWords" content="audio, tutorial, library, portable, open-source, DirectSound,sound, music, JSyn, synthesis,">
- <title>PortAudio Tutorial</title>
-</head>
-<body>
-&nbsp;
-<center><table COLS=1 WIDTH="100%" BGCOLOR="#FADA7A" >
-<tr>
-<td>
-<center>
-<h1>
-PortAudio Tutorial</h1></center>
-</td>
-</tr>
-</table></center>
-
-<h2>
-Writing a Callback Function</h2>
-
-<blockquote>To write a program using PortAudio, you must include the "portaudio.h"
-include file. You may wish to read "<a href="portaudio_h.txt">portaudio.h</a>"
-because it contains a complete description of the PortAudio functions and
-constants.
-<blockquote>
-<pre>#include "portaudio.h"</pre>
-</blockquote>
-The next task is to write your custom callback function. It is a function
-that is called by the PortAudio engine whenever it has captured audio data,
-or when it needs more audio data for output.
-<p>Your callback function is often called by an interrupt, or low level
-process so you should not do any complex system activities like allocating
-memory, or reading or writing files, or printf(). Just crunch numbers and
-generate audio signals. What is safe or not safe will vary from platform
-to platform. On the Macintosh, for example, you can only call "interrupt
-safe" routines. Also do not call any PortAudio functions in the callback
-except for Pa_StreamTime() and Pa_GetCPULoad().
-<p>Your callback function must return an int and accept the exact parameters
-specified in this typedef:
-<blockquote>
-<pre>typedef int (PortAudioCallback)(
-&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; void *inputBuffer, void *outputBuffer,
-&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; unsigned long framesPerBuffer,
-&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; PaTimestamp outTime, void *userData );</pre>
-</blockquote>
-Here is an example callback function from the test file "patests/patest_saw.c".
-It calculates a simple left and right sawtooth signal and writes it to
-the output buffer. Notice that in this example, the signals are of <tt>float</tt>
-data type. The signals must be between -1.0 and +1.0. You can also use
-16 bit integers or other formats which are specified during setup. You
-can pass a pointer to your data structure through PortAudio which will
-appear as <tt>userData</tt>.
-<blockquote>
-<pre>int patestCallback(&nbsp; void *inputBuffer, void *outputBuffer,
-&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; unsigned long framesPerBuffer,
-&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; PaTimestamp outTime, void *userData )
-{
-&nbsp;&nbsp;&nbsp; unsigned int i;
-/* Cast data passed through stream to our structure type. */
-&nbsp;&nbsp;&nbsp; paTestData *data = (paTestData*)userData;
-&nbsp;&nbsp;&nbsp; float *out = (float*)outputBuffer;
-&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
-&nbsp;&nbsp;&nbsp; for( i=0; i&lt;framesPerBuffer; i++ )
-&nbsp;&nbsp;&nbsp; {
-&nbsp;&nbsp;&nbsp; /* Stereo channels are interleaved. */
-&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; *out++ = data->left_phase;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; /* left */
-&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; *out++ = data->right_phase;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; /* right */
-
-&nbsp;&nbsp;&nbsp; /* Generate simple sawtooth phaser that ranges between -1.0 and 1.0. */
-&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; data->left_phase += 0.01f;
-&nbsp;&nbsp;&nbsp; /* When signal reaches top, drop back down. */
-&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if( data->left_phase >= 1.0f ) data->left_phase -= 2.0f;
-
-&nbsp;&nbsp;&nbsp; /* higher pitch so we can distinguish left and right. */
-&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; data->right_phase += 0.03f;&nbsp;
-&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if( data->right_phase >= 1.0f ) data->right_phase -= 2.0f;
-&nbsp;&nbsp;&nbsp; }
-&nbsp;&nbsp;&nbsp; return 0;
-}</pre>
-</blockquote>
-</blockquote>
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