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diff --git a/pd/portaudio/docs/pa_tut_callback.html b/pd/portaudio/docs/pa_tut_callback.html new file mode 100644 index 00000000..f5ccaf0f --- /dev/null +++ b/pd/portaudio/docs/pa_tut_callback.html @@ -0,0 +1,91 @@ +<!doctype html public "-//w3c//dtd html 4.0 transitional//en"> +<html> +<head> + <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> + <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> + +<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)( + void *inputBuffer, void *outputBuffer, + unsigned long framesPerBuffer, + 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( void *inputBuffer, void *outputBuffer, + unsigned long framesPerBuffer, + PaTimestamp outTime, void *userData ) +{ + unsigned int i; +/* Cast data passed through stream to our structure type. */ + paTestData *data = (paTestData*)userData; + float *out = (float*)outputBuffer; + + for( i=0; i<framesPerBuffer; i++ ) + { + /* Stereo channels are interleaved. */ + *out++ = data->left_phase; /* left */ + *out++ = data->right_phase; /* right */ + + /* Generate simple sawtooth phaser that ranges between -1.0 and 1.0. */ + data->left_phase += 0.01f; + /* When signal reaches top, drop back down. */ + if( data->left_phase >= 1.0f ) data->left_phase -= 2.0f; + + /* higher pitch so we can distinguish left and right. */ + data->right_phase += 0.03f; + if( data->right_phase >= 1.0f ) data->right_phase -= 2.0f; + } + return 0; +}</pre> +</blockquote> +</blockquote> +<font size=+2><a href="http://www.portaudio.com/">home</a> | +<a href="pa_tutorial.html">contents</a> +| <a href="pa_tut_over.html">previous</a> | <a href="pa_tut_init.html">next</a></font> +</body> +</html> |