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Diffstat (limited to 'distrib/sdl-1.2.15/docs/man3/SDL_OpenAudio.3')
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diff --git a/distrib/sdl-1.2.15/docs/man3/SDL_OpenAudio.3 b/distrib/sdl-1.2.15/docs/man3/SDL_OpenAudio.3 new file mode 100644 index 0000000..38a232c --- /dev/null +++ b/distrib/sdl-1.2.15/docs/man3/SDL_OpenAudio.3 @@ -0,0 +1,97 @@ +.TH "SDL_OpenAudio" "3" "Tue 11 Sep 2001, 22:58" "SDL" "SDL API Reference" +.SH "NAME" +SDL_OpenAudio \- Opens the audio device with the desired parameters\&. +.SH "SYNOPSIS" +.PP +\fB#include "SDL\&.h" +.sp +\fBint \fBSDL_OpenAudio\fP\fR(\fBSDL_AudioSpec *desired, SDL_AudioSpec *obtained\fR); +.SH "DESCRIPTION" +.PP +This function opens the audio device with the \fBdesired\fR parameters, and returns 0 if successful, placing the actual hardware parameters in the structure pointed to by \fBobtained\fR\&. If \fBobtained\fR is NULL, the audio data passed to the callback function will be guaranteed to be in the requested format, and will be automatically converted to the hardware audio format if necessary\&. This function returns -1 if it failed to open the audio device, or couldn\&'t set up the audio thread\&. +.PP +To open the audio device a \fBdesired\fR \fI\fBSDL_AudioSpec\fR\fR must be created\&. +.PP +.nf +\f(CWSDL_AudioSpec *desired; +\&. +\&. +desired=(SDL_AudioSpec *)malloc(sizeof(SDL_AudioSpec));\fR +.fi +.PP + You must then fill this structure with your desired audio specifications\&. +.IP "\fBdesired\fR->\fBfreq\fR" 10The desired audio frequency in samples-per-second\&. +.IP "\fBdesired\fR->\fBformat\fR" 10The desired audio format (see \fI\fBSDL_AudioSpec\fR\fR) +.IP "\fBdesired\fR->\fBsamples\fR" 10The desired size of the audio buffer in samples\&. This number should be a power of two, and may be adjusted by the audio driver to a value more suitable for the hardware\&. Good values seem to range between 512 and 8192 inclusive, depending on the application and CPU speed\&. Smaller values yield faster response time, but can lead to underflow if the application is doing heavy processing and cannot fill the audio buffer in time\&. A stereo sample consists of both right and left channels in LR ordering\&. Note that the number of samples is directly related to time by the following formula: ms = (samples*1000)/freq +.IP "\fBdesired\fR->\fBcallback\fR" 10This should be set to a function that will be called when the audio device is ready for more data\&. It is passed a pointer to the audio buffer, and the length in bytes of the audio buffer\&. This function usually runs in a separate thread, and so you should protect data structures that it accesses by calling \fI\fBSDL_LockAudio\fP\fR and \fI\fBSDL_UnlockAudio\fP\fR in your code\&. The callback prototype is: +.PP +.nf +\f(CWvoid callback(void *userdata, Uint8 *stream, int len);\fR +.fi +.PP + \fBuserdata\fR is the pointer stored in \fBuserdata\fR field of the \fBSDL_AudioSpec\fR\&. \fBstream\fR is a pointer to the audio buffer you want to fill with information and \fBlen\fR is the length of the audio buffer in bytes\&. +.IP "\fBdesired\fR->\fBuserdata\fR" 10This pointer is passed as the first parameter to the \fBcallback\fP function\&. +.PP +\fBSDL_OpenAudio\fP reads these fields from the \fBdesired\fR \fBSDL_AudioSpec\fR structure pass to the function and attempts to find an audio configuration matching your \fBdesired\fR\&. As mentioned above, if the \fBobtained\fR parameter is \fBNULL\fP then SDL with convert from your \fBdesired\fR audio settings to the hardware settings as it plays\&. +.PP +If \fBobtained\fR is \fBNULL\fP then the \fBdesired\fR \fBSDL_AudioSpec\fR is your working specification, otherwise the \fBobtained\fR \fBSDL_AudioSpec\fR becomes the working specification and the \fBdesirec\fR specification can be deleted\&. The data in the working specification is used when building \fBSDL_AudioCVT\fR\&'s for converting loaded data to the hardware format\&. +.PP +\fBSDL_OpenAudio\fP calculates the \fBsize\fR and \fBsilence\fR fields for both the \fBdesired\fR and \fBobtained\fR specifications\&. The \fBsize\fR field stores the total size of the audio buffer in bytes, while the \fBsilence\fR stores the value used to represent silence in the audio buffer +.PP +The audio device starts out playing \fBsilence\fR when it\&'s opened, and should be enabled for playing by calling \fI\fBSDL_PauseAudio\fP(\fB0\fR)\fR when you are ready for your audio \fBcallback\fR function to be called\&. Since the audio driver may modify the requested \fBsize\fR of the audio buffer, you should allocate any local mixing buffers after you open the audio device\&. +.SH "EXAMPLES" +.PP +.nf +\f(CW/* Prototype of our callback function */ +void my_audio_callback(void *userdata, Uint8 *stream, int len); + +/* Open the audio device */ +SDL_AudioSpec *desired, *obtained; +SDL_AudioSpec *hardware_spec; + +/* Allocate a desired SDL_AudioSpec */ +desired=(SDL_AudioSpec *)malloc(sizeof(SDL_AudioSpec)); + +/* Allocate space for the obtained SDL_AudioSpec */ +obtained=(SDL_AudioSpec *)malloc(sizeof(SDL_AudioSpec)); + +/* 22050Hz - FM Radio quality */ +desired->freq=22050; + +/* 16-bit signed audio */ +desired->format=AUDIO_S16LSB; + +/* Mono */ +desired->channels=0; + +/* Large audio buffer reduces risk of dropouts but increases response time */ +desired->samples=8192; + +/* Our callback function */ +desired->callback=my_audio_callback; + +desired->userdata=NULL; + +/* Open the audio device */ +if ( SDL_OpenAudio(desired, obtained) < 0 ){ + fprintf(stderr, "Couldn\&'t open audio: %s +", SDL_GetError()); + exit(-1); +} +/* desired spec is no longer needed */ +free(desired); +hardware_spec=obtained; +\&. +\&. +/* Prepare callback for playing */ +\&. +\&. +\&. +/* Start playing */ +SDL_PauseAudio(0);\fR +.fi +.PP +.SH "SEE ALSO" +.PP +\fI\fBSDL_AudioSpec\fP\fR, \fI\fBSDL_LockAudio\fP\fR, \fI\fBSDL_UnlockAudio\fP\fR, \fI\fBSDL_PauseAudio\fP\fR +.\" created by instant / docbook-to-man, Tue 11 Sep 2001, 22:58 |