text: // Copyright (c) 2010 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.
  
  #ifndef CHROME_BROWSER_CHROMEOS_AUDIO_MIXER_H_
  #define CHROME_BROWSER_CHROMEOS_AUDIO_MIXER_H_
  #pragma once
  
  #include "base/basictypes.h"
  #include "base/callback.h"
  
  namespace chromeos {
  
  class AudioMixer {
   public:
    // Approximation of pure silence expressed in decibels.
    static const double kSilenceDb = -200.0;
  
    enum State {
      UNINITIALIZED = 0,
      INITIALIZING,
      READY,
      SHUTTING_DOWN,
      IN_ERROR,
    };
  
    AudioMixer() {}
    virtual ~AudioMixer() {}
  
    // Non-Blocking call.  Connect to Mixer, find a default device, then call the
    // callback when complete with success code.
    typedef Callback1<bool>::Type InitDoneCallback;
    virtual void Init(InitDoneCallback* callback) = 0;
  
    // Call may block.  Mixer will be connected before returning, unless error.
    virtual bool InitSync() = 0;
  
    // Call may block.  Returns a default of kSilenceDb on error.
    virtual double GetVolumeDb() const = 0;
  
    // Non-Blocking call.  Returns the actual volume limits possible according
    // to the mixer.  Limits are left unchanged on error
    virtual bool GetVolumeLimits(double* vol_min, double* vol_max) = 0;
  
    // Non-blocking call.
    virtual void SetVolumeDb(double vol_db) = 0;
  
    // Call may block.  Gets the mute state of the default device (true == mute).
    // Returns a default of false on error.
    virtual bool IsMute() const = 0;
  
    // Non-Blocking call.
    virtual void SetMute(bool mute) = 0;
  
    // Returns READY if we have a valid working connection to the Mixer.
    // This can return IN_ERROR if we lose the connection, even after an original
    // successful init.  Non-blocking call.
    virtual State GetState() const = 0;
  
   private:
    DISALLOW_COPY_AND_ASSIGN(AudioMixer);
  };
  
  }  // namespace chromeos
  
  #endif  // CHROME_BROWSER_CHROMEOS_AUDIO_MIXER_H_
  
  