Add ALSA support to volume keys

chrome/browser/chromeos/audio_mixer.h

+// 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:
+  enum State {
+    UNINITIALIZED = 0,
+    INITIALIZING,
+    READY,
+    SHUTTING_DOWN,
+    IN_ERROR,
+  };
+
+  AudioMixer();
+  virtual ~AudioMixer();
+

[davejcool, 2011/01/05 21:11:05]

I'm inlining the constructor and destructor again since the style guide says
it's fine for a pure abstract base class.

+  // 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 bool 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 CheckState() const = 0;
+
+  // Approximation of pure silence expressed in decibels.
+  static const double kSilenceDb = -200.0;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(AudioMixer);
+};
+
+}  // namespace chromeos
+
+#endif  // CHROME_BROWSER_CHROMEOS_AUDIO_MIXER_H_
+