Support for showing/hiding status area volume controls in desktop devices

chrome/browser/chromeos/audio/audio_handler.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/chromeos/audio/audio_handler.h"
 
 #include <algorithm>
 #include <cmath>
 
 #include "base/logging.h"
@@ skipping 31 matching lines @@
   }
 }
 
 // static
 AudioHandler* AudioHandler::GetInstance() {
   VLOG_IF(1, !g_audio_handler)
       << "AudioHandler::GetInstance() called with NULL global instance.";
   return g_audio_handler;
 }
 
-bool AudioHandler::IsInitialized() {
-  return mixer_->IsInitialized();
+// static
+AudioHandler* AudioHandler::GetInstanceIfInitialized() {
+  return g_audio_handler && g_audio_handler->IsMixerInitialized() ?
+         g_audio_handler : NULL;
 }
 
 double AudioHandler::GetVolumePercent() {
   return VolumeDbToPercent(mixer_->GetVolumeDb());
 }
 
 void AudioHandler::SetVolumePercent(double volume_percent) {
   volume_percent = min(max(volume_percent, 0.0), 100.0);
   mixer_->SetVolumeDb(PercentToVolumeDb(volume_percent));
+  FOR_EACH_OBSERVER(VolumeObserver, volume_observers_, OnVolumeChanged());
 }
 
 void AudioHandler::AdjustVolumeByPercent(double adjust_by_percent) {
   const double old_volume_db = mixer_->GetVolumeDb();
   const double old_percent = VolumeDbToPercent(old_volume_db);
   SetVolumePercent(old_percent + adjust_by_percent);
 }
 
 bool AudioHandler::IsMuted() {
   return mixer_->IsMuted();
 }
 
 void AudioHandler::SetMuted(bool mute) {
   mixer_->SetMuted(mute);
+  FOR_EACH_OBSERVER(VolumeObserver, volume_observers_, OnVolumeChanged());
+}
+
+void AudioHandler::AddVolumeObserver(VolumeObserver* observer) {
+  volume_observers_.AddObserver(observer);
+}
+
+void AudioHandler::RemoveVolumeObserver(VolumeObserver* observer) {
+  volume_observers_.RemoveObserver(observer);
 }
 
 AudioHandler::AudioHandler()
     : mixer_(new AudioMixerAlsa()) {
   mixer_->Init();
 }
 
 AudioHandler::~AudioHandler() {
   mixer_.reset();
 };
 
+bool AudioHandler::IsMixerInitialized() {
+  return mixer_->IsInitialized();
+}
+
 // VolumeDbToPercent() and PercentToVolumeDb() conversion functions allow us
 // complete control over how the 0 to 100% range is mapped to actual loudness.
 //
 // The mapping is confined to these two functions to make it easy to adjust and
 // have everything else just work.  The range is biased to give finer resolution
 // in the higher volumes if kVolumeBias is less than 1.0.
 
 double AudioHandler::VolumeDbToPercent(double volume_db) const {
   double min_volume_db, max_volume_db;
   mixer_->GetVolumeLimits(&min_volume_db, &max_volume_db);
 
   if (volume_db < min_volume_db)
     return 0.0;
   // TODO(derat): Choose a better mapping between percent and decibels.  The
   // bottom twenty-five percent or so is useless on a CR-48's internal speakers;
   // it's all inaudible.
   return 100.0 * pow((volume_db - min_volume_db) /
       (max_volume_db - min_volume_db), 1/kVolumeBias);
 }
 
 double AudioHandler::PercentToVolumeDb(double volume_percent) const {
   double min_volume_db, max_volume_db;
   mixer_->GetVolumeLimits(&min_volume_db, &max_volume_db);
 
   return pow(volume_percent / 100.0, kVolumeBias) *
       (max_volume_db - min_volume_db) + min_volume_db;
 }
 
 }  // namespace chromeos