Add ALSA support to volume keys

chrome/browser/chromeos/audio_mixer_alsa.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_ALSA_H_
+#define CHROME_BROWSER_CHROMEOS_AUDIO_MIXER_ALSA_H_
+#pragma once
+
+#include "base/basictypes.h"
+#include "base/callback.h"
+#include "base/lock.h"
+#include "base/scoped_ptr.h"
+#include "base/threading/thread.h"
+#include "chrome/browser/chromeos/audio_mixer.h"
+
+struct _snd_mixer_elem;
+struct _snd_mixer;
+
+namespace chromeos {
+
+class AudioMixerAlsa : public AudioMixer {
+ public:
+  AudioMixerAlsa();
+  virtual ~AudioMixerAlsa();
+
+  // Implementation of AudioMixer, see AudioMixerBase for explanations.

[scherkus (not reviewing), 2011/01/11 00:24:12]

nit: remove ", see AudioMixerBase for explanations."

I also don't think AudioMixerBase exists anymore!

+  virtual bool Init(InitDoneCallback* callback);
+  virtual bool InitSync();
+  virtual double GetVolumeDb() const;
+  virtual bool GetVolumeLimits(double* vol_min, double* vol_max);
+  virtual void SetVolumeDb(double vol_db);
+  virtual bool IsMute() const;
+  virtual void SetMute(bool mute);
+  virtual State CheckState() const;
+
+ private:
+  // Called to do initialization in background from worker thread.
+  void DoInit(InitDoneCallback* callback);
+
+  // Helper function to just get our message loop thread going.
+  bool InitThread();
+
+  // Try to connect to the ALSA mixer through their simple controls interface,
+  // and cache mixer handle and mixer elements we'll be using.
+  bool InitializeAlsaMixer();
+  void FreeAlsaMixer();
+
+  // All these internal volume commands must be called with the lock held.
+  double DoGetVolumeDb() const;

[scherkus (not reviewing), 2011/01/11 00:24:12]

nit: a style we've used in media code is to append _Locked() as the method name
to offer a hint that it assumes lock is held

+  void DoSetVolumeDb(double vol_db);
+
+  struct _snd_mixer_elem* FindElementWithName(struct _snd_mixer* handle,

[scherkus (not reviewing), 2011/01/11 00:24:12]

question: do we actually have to use "struct _snd_mixer_elem" or can't we just
use "_snd_mixer_elem" ?

I thought C++ let you do that but I'm not 100% sure

[davejcool, 2011/01/11 02:52:54]

Eventually it'll stick that 'struct' is mostly superfluous now days :-) 

+                                        const char* element_name) const;

[scherkus (not reviewing), 2011/01/11 00:24:12]

since params don't find drop both params to next line + indent by 4

+
+  bool GetElementVolume(struct _snd_mixer_elem* elem,
+                        double* current_vol) const;
+
+  // Since volume is done in steps, we may not get the exact volume asked for,
+  // so actual_vol will contain the true volume that was set.  This information
+  // can be used to further refine the volume by adjust a different mixer
+  // element.  The rounding_bias is added in before rounding to the nearest
+  // volume step (use 0.5 to round to nearest).
+  bool SetElementVolume(struct _snd_mixer_elem* elem,
+                        double new_vol,
+                        double* actual_vol,
+                        double rounding_bias);
+
+  // In ALSA, the mixer element's 'switch' is turned off to mute.
+  bool GetElementMuted(struct _snd_mixer_elem* elem) const;
+  void SetElementMuted(struct _snd_mixer_elem* elem, bool mute);
+
+  // Volume range limits are computed once during InitializeAlsaMixer.
+  double min_volume_;
+  double max_volume_;
+
+  // Muting is done by setting volume to minimum, so we must save the original.
+  // This is the only state information kept in this object.  In some cases,
+  // ALSA can report it has a volume switch and we can turn it off, but it has
+  // no effect.
+  double save_volume_;
+
+  mutable Lock mixer_state_lock_;
+  mutable State mixer_state_;
+
+  // Cached contexts for use in ALSA calls.
+  struct _snd_mixer* alsa_mixer_;
+  struct _snd_mixer_elem* elem_master_;
+  struct _snd_mixer_elem* elem_pcm_;
+
+  scoped_ptr<base::Thread> thread_;
+
+  DISALLOW_COPY_AND_ASSIGN(AudioMixerAlsa);
+};
+
+}  // namespace chromeos
+
+DISABLE_RUNNABLE_METHOD_REFCOUNT(chromeos::AudioMixerAlsa);
+
+#endif  // CHROME_BROWSER_CHROMEOS_AUDIO_MIXER_ALSA_H_
+