alSelectEvents(3dm) alSelectEvents(3dm)
alSelectEvents - Setup event queue to receive audio events.
#include <dmedia/audio.h>
int alSelectEvents(ALeventQueue eventq, int resource
int *params, int nparams)
eventq expects an ALeventQueue structure properly initialized by
alOpenEventQueue(3dm).
resource expects a resource ID from which you desire events.
params expects an int pointer with a list of parameters for which you
desire events.
nparams expects an int with the total number of parameters in the list
params.
alSelectEvents(3dm) sets up eventq to receive audio events from resource
(see alResources(3dm)). An event will be generated whenever the value of
a parameter from params changes on the given resource. Please refer to
alParams(3dm) for a complete list of parameters that can generate events.
To retrieve events, use alNextEvent(3dm) and alCheckEvent(3dm).
You can call alSelectEvents(3dm) several times on an event queue. Thus a
single event queue can monitor events from multiple resources.
In some cases, the resource that generates an event will differ from the
resource specified in alSelectEvents. As noted in alParams(3dm),
parameters addressed to one resource can be passed on to other resources.
For example, an AL_RATE passed to a device is actually handled by the
device's clock-generator, a separate resource. In this case, if you
request AL_RATE events from the device, you will be notified when the
value of AL_RATE changes on the device's clock-generator; both resource
ID's will show up in the event. Refer to alGetEventSrcResource(3dm) and
alGetEventResource(3dm) for more information.
Event queues monitoring either AL_DEFAULT_INPUT or AL_DEFAULT_OUTPUT will
change to monitor the new device when the default is changed. Note that
events with certain parameters will cease to be generated due to the
characteristics of the new resource.
To deselect event notification on an event queue, use
alDeselectEvents(3dm).
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alSelectEvents(3dm) alSelectEvents(3dm)
The following example sets up an event queue to receive events with
either AL_RATE or AL_MUTE parameters from the default output device.
int params[2];
ALeventQueue eventq;
/*
* Open event queue and set it up to receive events.
*/
eventq = alOpenEventQueue("output");
if(eventq == NULL) {
fprintf(stderr,"Open event queue failed \n");
return -1;
}
params[0] = AL_RATE;
params[1] = AL_MUTE;
status = alSelectEvents(eventq,AL_DEFAULT_OUTPUT,params,2);
if(status == -1) {
fprintf(stderr,"Select event queue failed \n");
return -1;
}
Upon successful completion, alSelectEvents returns 0. Otherwise,
alSelectEvents returns -1 and sets an error number which can be retrieved
with oserror(3C).
alSelectEvents can fail for the following reason:
AL_BAD_INVALID_EVENTQ eventq is either invalid or null.
AL_BAD_RESOURCE resource is invalid.
AL_BAD_PARAM params is either invalid or null.
AL_BAD_BUFFERLENGTH_NEG nparams is either less than or equal to zero.
alOpenEventQueue(3dm), alDelectEvents(2), alParams(3dm),
alNextEvent(3dm), alCheckEvent(3dm), alGetEventResource(3dm),
alGetEventSrcResource(3dm), oserror(3C)
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