[Chromecast] Implement new volume control API

chromecast/media/cma/backend/alsa/stream_mixer_alsa.h

Index: chromecast/media/cma/backend/alsa/stream_mixer_alsa.h
diff --git a/chromecast/media/cma/backend/alsa/stream_mixer_alsa.h b/chromecast/media/cma/backend/alsa/stream_mixer_alsa.h
index b522f09024cb274daf1aea6adfe5a1775ded5788..4b7f35b48d15ea24fbc080d188c63f9db1718935 100644
--- a/chromecast/media/cma/backend/alsa/stream_mixer_alsa.h
+++ b/chromecast/media/cma/backend/alsa/stream_mixer_alsa.h
@@ -8,6 +8,7 @@
 #include <alsa/asoundlib.h>
 #include <stdint.h>
 
+#include <map>
 #include <memory>
 #include <string>
 #include <vector>
@@ -20,6 +21,7 @@
 #include "chromecast/media/cma/backend/alsa/media_pipeline_backend_alsa.h"
 #include "chromecast/media/cma/backend/alsa/stream_mixer_alsa_input.h"
 #include "chromecast/public/cast_media_shlib.h"
+#include "chromecast/public/volume_control.h"
 
 namespace media {
 class AudioBus;
@@ -73,6 +75,9 @@ class StreamMixerAlsa {
     // or media/audio/audio_device_description.h
     virtual std::string device_id() const = 0;
 
+    // Returns the content type for volume control.
+    virtual AudioContentType content_type() const = 0;
+
     // Returns true if PrepareToDelete() has been called.
     virtual bool IsDeleting() const = 0;
 
@@ -129,6 +134,14 @@ class StreamMixerAlsa {
     // Once the input is ready to be removed, it should call the supplied
     // |delete_cb|; this should only happen once per input.
     virtual void PrepareToDelete(const OnReadyToDeleteCb& delete_cb) = 0;
+
+    // Sets the multiplier based on this stream's content type. The resulting
+    // output volume should be the content type volume * the per-stream volume
+    // multiplier.
+    virtual void SetContentTypeVolume(float volume) = 0;
+
+    // Sets whether or not this stream should be muted.
+    virtual void SetMuted(bool muted) = 0;
   };
 
   enum State {
@@ -169,6 +182,15 @@ class StreamMixerAlsa {
   void RemoveLoopbackAudioObserver(
       CastMediaShlib::LoopbackAudioObserver* observer);
 
+  // Sets the volume multiplier for the given content |type|.
+  void SetVolume(AudioContentType type, float level);
+
+  // Sets the mute state for the given content |type|.
+  void SetMuted(AudioContentType type, bool muted);
+
+  // Sets the volume multiplier limit for the given content |type|.
+  void SetOutputLimit(AudioContentType type, float limit);
+
  protected:
   StreamMixerAlsa();
   virtual ~StreamMixerAlsa();
@@ -232,7 +254,6 @@ class StreamMixerAlsa {
   // only has to interact with the command line parameters once.
   std::string alsa_device_name_;
   snd_pcm_uframes_t alsa_buffer_size_;
-  bool alsa_period_explicitly_set;
   snd_pcm_uframes_t alsa_period_size_;
   snd_pcm_uframes_t alsa_start_threshold_;
   snd_pcm_uframes_t alsa_avail_min_;
@@ -251,6 +272,10 @@ class StreamMixerAlsa {
   std::vector<std::unique_ptr<FilterGroup>> filter_groups_;
   std::vector<CastMediaShlib::LoopbackAudioObserver*> loopback_observers_;
 
+  std::map<AudioContentType, float> volume_;

[slan, 2017/03/13 22:09:51]

Why not std::unordered_map?

I think that Chrome actually prefers a vector of pairs over small maps for
speed, but I like the syntax of maps way better.

[kmackay, 2017/03/14 00:21:00]

The comment in
https://cs.chromium.org/chromium/src/base/containers/small_map.h?dr=C&l=27
indicates that std::map should be the default. I don't think it matters for
performance reasons since there are only 3 entries, and the callsites are not
performance-critical. Also, to use unordered_map, I would need to define some
hash function for AudioContentType, which is a bit of a pain.

[slan, 2017/03/14 17:21:28]

Acknowledged.

+  std::map<AudioContentType, float> volume_limit_;
+  std::map<AudioContentType, bool> muted_;
+
   DISALLOW_COPY_AND_ASSIGN(StreamMixerAlsa);
 };