`snd_mixer_callbacks_t`

List of mixer callback functions

Synopsis:

typedef struct snd_mixer_callbacks {
    void *private_data; /* should be used with an application */
    void (*rebuild) (void *private_data);
    void (*element) (void *private_data, int cmd,
                     snd_mixer_eid_t *eid);
    void (*group) (void *private_data, int cmd,
                   snd_mixer_gid_t *gid);
    void *reserved[28]; /* reserved for the future use - must be NULL!!! */
} snd_mixer_callbacks_t;

Description:

The snd_mixer_callbacks_t structure defines a list of callbacks that you can provide to handle events read by snd_mixer_read(). The members include:

private_data, a pointer to arbitrary data that you want to pass to the callbacks
pointers to the callbacks, which are described below.

Make sure that you zero-fill any members that you aren't interested in. You can zero-fill the entire snd_mixer_callbacks_t structure if you aren't interested in tracking any of these events. The wave.c example does this.

rebuild callback

The rebuild callback is called whenever the mixer is rebuilt. Its only argument is the private_data that you specified in this structure.

element callback

The element callback is called whenever an element event occurs. The arguments to this function are:

private_data

A pointer to the arbitrary data that you specified in this structure.

cmd

A SND_MIXER_READ_ELEMENT_* event code:

SND_MIXER_READ_ELEMENT_VALUE -- the element's value changed.
SND_MIXER_READ_ELEMENT_CHANGE -- the element changed (something other than its value).
SND_MIXER_READ_ELEMENT_ADD -- the element was added (i.e. created).
SND_MIXER_READ_ELEMENT_REMOVE -- the element was removed (i.e. destroyed).
SND_MIXER_READ_ELEMENT_ROUTE -- the element's routing information changed.

eid

A pointer to a snd_mixer_eid_t structure that holds the ID of the element affected by the event.

group callback

The group callback is called whenever a group event occurs. The arguments are:

private_data

A pointer to the arbitrary data that you specified in this structure.

cmd

A SND_MIXER_READ_GROUP_* event code:

SND_MIXER_READ_GROUP_VALUE -- the group's value changed.
SND_MIXER_READ_GROUP_CHANGE -- the group changed (something other than the value).
SND_MIXER_READ_GROUP_ADD -- the group was added (i.e. created).
SND_MIXER_READ_GROUP_REMOVE -- the group was removed (i.e. destroyed).

gid

A pointer to a snd_mixer_gid_t structure that holds the ID of the group affected by the event.

Examples:

static void
mixer_callback_group (void *private_data, int cmd, snd_mixer_gid_t * gid)
{
    Control_t *control, *prev;
    PtWidget_t *above_wgt;
    int     i;

    switch (cmd)
    {
    case SND_MIXER_READ_GROUP_VALUE:
        for (control = control_head; control; control = control->next)
        {
            if (strcmp (control->group.gid.name, gid->name) == 0 &&
                control->group.gid.index == gid->index)
            {
                if (snd_mixer_group_read (mixer_handle, &control->group) == 0)
                    base_update_control (control, NULL);
            }
        }
        break;

    case SND_MIXER_READ_GROUP_ADD:
        if ((control = mixer_create_control (gid, control_tail)))
        {
            if (control->group.caps & SND_MIXER_GRPCAP_PLAY_GRP)
                above_wgt = PtWidgetBrotherBehind (ABW_base_capture_pane);
            else
                above_wgt = PtWidgetBrotherBehind (ABW_base_status);
            PtContainerHold (ABW_base_controls);
            base_create_control (ABW_base_controls, &above_wgt, control);
            PtContainerRelease (ABW_base_controls);
        }
        break;

    case SND_MIXER_READ_GROUP_REMOVE:
        for (prev = NULL, control = control_head; control; 
                            prev = control, control = control->next)
        {
            if (strcmp (control->group.gid.name, gid->name) == 0 &&
                control->group.gid.index == gid->index)
                mixer_delete_control (control, prev);
        }
        break;
    }

}


int
mixer_update (int fd, void *data, unsigned mode)
{
    snd_mixer_callbacks_t callbacks = { 0, 0, 0, 0 };

    callbacks.group = mixer_callback_group;
    snd_mixer_read (mixer_handle, &callbacks);
    return (Pt_CONTINUE);
}

Classification:

QNX Neutrino