simple mixer element from a control event

[flatmax]

I would like to get a snd_mixer_elem_t from a control event :

snd_ctl_event_t *event;
snd_ctl_event_alloca(&event);
int err = snd_ctl_read(ctl, event);
if (err < 0)
  return ALSADebug().evaluateError(err, "snd_ctl_read error when handling poll events\n");

My problem is sometimes there are mixer elements with the same names. I can get the mixer element's name like so :

std::string elemName(snd_ctl_event_elem_get_name(event));

But when I search for the simple mixer element based on the element name, the search will stop at the first found matching element. A few issues arise with this approach, for example when the same simple mixer element is in both the playback and capture alsamixer sections. None the less I can iterate through the name for comparson :

 for (snd_mixer_elem_t *elem = snd_mixer_first_elem(handle); elem; elem = snd_mixer_elem_next(elem)){
  // Do a search using elemName here breaking on the first match, which may not be the correct match.

It would be better if there was a way to find the exact simple mixer element which triggered the event in the first place. Is that possible ? I am aware of the snd_ctl_event_elem_get_numid function, but I can't see how to find a simple mixer element which matches that numid.

[perexg]

The name is only one from multiple fields identifying the control element. Use snd_ctl_event_elem_get_id to get the id structure which contains all fields.

[perexg]

Also, it seems that you mix two APIs. Do not use raw snd_ctl_* functions with the snd_mixer_* functions. It won't work. The control mapping between those two APIs is not straight (control elements and mixer elements are two different things).

[perexg]

What you're trying to implement?

[flatmax]

I'm trying to catch mixer element changes as events. Then I want to fetch the changed mixer element and propagate that element state through other user applications (over the network for example),

On 6/1/23 21:06, Jaroslav Kysela wrote:

What you're trying to implement?

— Reply to this email directly, view it on GitHub https://github.com/alsa-project/alsa-lib/issues/291#issuecomment-1373425572, or unsubscribe https://github.com/notifications/unsubscribe-auth/AAFLUB3T3VMPTPBGZTPIL33WQ7VCPANCNFSM6AAAAAATS45PGI. You are receiving this because you authored the thread.Message ID: @.***>

[flatmax]

I added a MixerEvents class code to handle mixer events in the same way amixer handles it. Unfortunately I can't seem to get my threaded snd_mixer_wait function to release with an event.

https://github.com/flatmax/gtkiostream/commit/6f4ed685c95db2321e267d0b65025742fccf3931#diff-ccebe112c934530cd53d80c769c599ab3abd878d40278bf66909aa0c66fb3a47R35-R38

Matt

On 9/1/23 10:14, Matt Flax wrote:

I'm trying to catch mixer element changes as events. Then I want to fetch the changed mixer element and propagate that element state through other user applications (over the network for example),

On 6/1/23 21:06, Jaroslav Kysela wrote:

What you're trying to implement?

— Reply to this email directly, view it on GitHub https://github.com/alsa-project/alsa-lib/issues/291#issuecomment-1373425572, or unsubscribe https://github.com/notifications/unsubscribe-auth/AAFLUB3T3VMPTPBGZTPIL33WQ7VCPANCNFSM6AAAAAATS45PGI. You are receiving this because you authored the thread.Message ID: @.***>

[flatmax]

OK, got it to work now.

The thing I missed was that snd_mixer_wait should only be called once the mixer has been loaded. If it is called before, then it will wait forever missing events.

Here is the code :

https://github.com/flatmax/gtkiostream/blob/master/include/ALSA/MixerEvents.H

On 9/1/23 14:47, Matt Flax wrote:

I added a MixerEvents class code to handle mixer events in the same way amixer handles it. Unfortunately I can't seem to get my threaded snd_mixer_wait function to release with an event.

https://github.com/flatmax/gtkiostream/commit/6f4ed685c95db2321e267d0b65025742fccf3931#diff-ccebe112c934530cd53d80c769c599ab3abd878d40278bf66909aa0c66fb3a47R35-R38

Matt

On 9/1/23 10:14, Matt Flax wrote:

I'm trying to catch mixer element changes as events. Then I want to fetch the changed mixer element and propagate that element state through other user applications (over the network for example),

On 6/1/23 21:06, Jaroslav Kysela wrote:

What you're trying to implement?

— Reply to this email directly, view it on GitHub https://github.com/alsa-project/alsa-lib/issues/291#issuecomment-1373425572, or unsubscribe https://github.com/notifications/unsubscribe-auth/AAFLUB3T3VMPTPBGZTPIL33WQ7VCPANCNFSM6AAAAAATS45PGI. You are receiving this because you authored the thread.Message ID: @.***>