Alsa mixer and GtkVolumeButton - gtk

Question

I make code to get and set alsa mixer volume:
snd_mixer_elem_t *elem = NULL;
long alsa_min, alsa_max, alsa_vol;
int alsa_get_volume( void )
{
long val;
assert (elem);
if (snd_mixer_selem_is_playback_mono(elem)) {
snd_mixer_selem_get_playback_volume(elem, SND_MIXER_SCHN_MONO, &val);
return val;
} else {
int c, n = 0;
long sum = 0;
for (c = 0; c <= SND_MIXER_SCHN_LAST; c++) {
if (snd_mixer_selem_has_playback_channel(elem, c)) {
snd_mixer_selem_get_playback_volume(elem, SND_MIXER_SCHN_FRONT_LEFT, &val);
sum += val;
n++;
}
}
if (! n) {
return 0;
}
val = sum / n;
sum = (long)((double)(alsa_vol * (alsa_max - alsa_min)) / 100. + 0.5);
if (sum != val) {
alsa_vol = (long)(((val * 100.) / (alsa_max - alsa_min)) + 0.5);
}
return alsa_vol;
}
}
int alsa_set_volume( int percentdiff )
{
long volume;
alsa_get_volume();
alsa_vol += percentdiff;
if( alsa_vol > 100 ) alsa_vol = 100;
if( alsa_vol < 0 ) alsa_vol = 0;
volume = (long)((alsa_vol * (alsa_max - alsa_min) / 100.) + 0.5);
snd_mixer_selem_set_playback_volume_all(elem, volume + alsa_min);
snd_mixer_selem_set_playback_switch_all(elem, 1);
muted = 0;
mutecount = 0;
return alsa_vol;
}
I wont to make alsa mixer volume to changed by GtkVolumeButton. Tried this but when value from gtk button is changed up or down, alsa mixer always jumps to 100 %:
int gtk_volume_button_get_value (GtkWidget *button)
{
return (int) (gtk_scale_button_get_value(GTK_SCALE_BUTTON(button)) * 100);
}
void gtk_volume_button_set_value (GtkWidget *button, int value)
{
gtk_scale_button_set_value(GTK_SCALE_BUTTON(button), (gdouble) value / 100);
}
void volume_value_changed_cb(GtkVolumeButton *button, gpointer user_data)
{
int vol = (int)(gtk_volume_button_get_value(volume_button) + 0.5);
alsa_set_volume(vol);
}
Please help me to write a corect code for GtkVolumeButton.

Answer 1

Your problem has nothing to do with GtkVolume. In fact, it comes from you using two different approaches to handle volume. alsa_get_volume gives you an absolute sound level, which is an integer. One would expect alsa_set_volume to accept the same kind of value range. And that's how you use it in volume_value_changed_cb: « get the volume level of the volume control, between 0 and 100, and set it as current volume. ».
However, the implementation is completely different. It's implemented as if you wanted to tell it « add or substract x% of the current sound volume ». You get the current volume level and add that percentage, thus you're computing a relative sound level, not an absolute one. So, if your initial sound level is 50%, and you want to lower it to 45%, one would expect you'd call alsa_set_volume (45) to do it. But currently, calling alsa_set_volume (45) will set alsa_vol to 50 + 45 = 95%.
So you need to use absolute volume, not relative.
/* newvol: Desired volume level in the [0;100] range */
int alsa_set_volume (int newvol)
{
long volume;
alsa_vol = CLAMP(absvol, 0, 100);
volume = (long)((alsa_vol * (alsa_max - alsa_min) / 100.) + alsa_min);
snd_mixer_selem_set_playback_volume_all(elem, volume);
snd_mixer_selem_set_playback_switch_all(elem, 1);
muted = 0;
mutecount = 0;
return alsa_vol;
}