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 <alsa/asoundlib.h>

[scherkus (not reviewing), 2010/12/22 22:31:58]

avoid system includes in header files at all costs and instead forward declare
all necessary ALSA types

[davejcool, 2010/12/23 03:09:02]

OK, I considered that too until I saw several header files elsewhere including
the same asoundlib.h.

+
+#include "base/basictypes.h"
+#include "base/callback.h"
+#include "base/lock.h"
+#include "base/scoped_ptr.h"
+#include "base/thread.h"
+

[scherkus (not reviewing), 2010/12/22 22:31:58]

nit: no blank line

+#include "chrome/browser/chromeos/audio_mixer_base.h"
+
+namespace chromeos {
+
+class AudioMixerAlsa : public AudioMixerBase {
+ public:
+

[scherkus (not reviewing), 2010/12/22 22:31:58]

nit: no blank line

+  AudioMixerAlsa();
+  ~AudioMixerAlsa();

[scherkus (not reviewing), 2010/12/22 22:31:58]

add virtual

+
+  // Implementation of AudioMixer, see AudioMixerBase for explanations.
+  virtual bool Init(InitDoneCallback* callback);
+  virtual bool InitSync();
+  virtual double GetVolumeDb() const;
+  virtual void 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();
+
+  snd_mixer_elem_t* FindElementWithName(snd_mixer_t* handle,
+                                        const char* element_name) const;
+
+  bool GetElementVolume(snd_mixer_elem_t* elem,
+                        float* 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(snd_mixer_elem_t* elem,
+                        float new_vol,
+                        float* actual_vol,
+                        float rounding_bias);
+
+  // In ALSA, the mixer element's 'switch' is turned off for mute.
+  bool GetElementSwitched(snd_mixer_elem_t* elem,

[scherkus (not reviewing), 2010/12/22 22:31:58]

maybe these should be renamed IsElementMuted / SetElementMuted ?

Switched seems like a strange choice of wording (even though it's what ALSA
uses)

+                         int* switched) const;
+
+  bool SetElementSwitched(snd_mixer_elem_t* elem,
+                          int switched);
+
+  bool MixerReady() const;
+
+  // Volume range limits are computed once during InitializeAlsaMixer.
+  float min_volume_;
+  float 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.
+  float save_volume_;
+
+  mutable Lock mixer_state_lock_;
+  mutable State mixer_state_;
+
+  // Cached contexts for use in ALSA calls.
+  snd_mixer_t* alsa_mixer_;
+  snd_mixer_elem_t* elem_master_;
+  snd_mixer_elem_t* 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_
+