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 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

See also:

snd_mixer_eid_t, snd_mixer_gid_t, snd_mixer_read()