Stuff

static void
bacon_volume_button_update_icon (BaconVolumeButton *button)
{
  GtkRange *range = GTK_RANGE (button->scale);
  float val = gtk_range_get_value (range);
  GtkAdjustment *adj;
  GdkPixbuf *pixbuf;
  float step;

  adj = gtk_range_get_adjustment (range);
  step = (adj->upper - adj->lower) / 4;

  if (val == adj->lower)
    pixbuf = button->icon[0];
  else if (val > adj->lower && val <= adj->lower + step)
    pixbuf = button->icon[1];
  else if (val > adj->lower + step && val <= adj->lower + step * 2)
    pixbuf = button->icon[2];
  else
    pixbuf = button->icon[3];

  gtk_image_set_from_pixbuf (GTK_IMAGE (button->image), pixbuf);
}