media::WebAudioSourceProviderImpl, add support for getting a copy of passing AudioBuses

media/blink/webaudiosourceprovider_impl.h

 // Copyright 2013 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 MEDIA_BLINK_WEBAUDIOSOURCEPROVIDER_IMPL_H_
 #define MEDIA_BLINK_WEBAUDIOSOURCEPROVIDER_IMPL_H_
 
 #include <stddef.h>
 
 #include <string>
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/synchronization/lock.h"
 #include "media/base/audio_renderer_sink.h"
 #include "media/blink/media_blink_export.h"
 #include "third_party/WebKit/public/platform/WebAudioSourceProvider.h"
 #include "third_party/WebKit/public/platform/WebVector.h"
 
 namespace blink {
 class WebAudioSourceProviderClient;
 }
 
 namespace media {
 
-// WebAudioSourceProviderImpl provides a bridge between classes:
-//     blink::WebAudioSourceProvider <---> AudioRendererSink
-//
-// WebAudioSourceProviderImpl wraps an existing audio sink that is used unless
-// WebKit has set a client via setClient(). While a client is set WebKit will
-// periodically call provideInput() to render a certain number of audio
-// sample-frames using the sink's RenderCallback to get the data.
+// WebAudioSourceProviderImpl is either one of two things:
+// - a connection between a RestartableAudioRendererSink passed in constructor
+//   and an AudioRendererSink::RenderCallback passed on Initialize(), by being
+//   itself a forwarding AudioRendererSink::RenderCallback - which also
+//   eavesdrops if listeners are configured.
+// - a connection between the said AudioRendererSink::RenderCallback and a
+//   blink::WebAudioSourceProviderClient passed via setClient(), by being itself
+//   a blink::WebAudioSourceProvider. Blink calls provideInput() periodically
+//   to fetch the appropriate data.
+// Finally, WASPImpl is also a RestartableAudioRendererSink to be controlled by
+// an AudioRenderer (which happens to be our AudioRendererSink::RenderCallback).
 //
 // All calls are protected by a lock.
 class MEDIA_BLINK_EXPORT WebAudioSourceProviderImpl
     : NON_EXPORTED_BASE(public blink::WebAudioSourceProvider),
-      NON_EXPORTED_BASE(public RestartableAudioRendererSink) {
+      NON_EXPORTED_BASE(public RestartableAudioRendererSink),
+      NON_EXPORTED_BASE(public AudioRendererSink::RenderCallback) {

[DaleCurtis, 2016/03/11 01:41:42]

Instead of inheriting from this can you create a new RenderCallbackCopier
(naming up to you) which WASPI can own that implements the RenderCallback
interface? This allows to prevent further inheritance bloat by this class.

[mcasas, 2016/03/11 04:06:23]

I think is messier but done.

Called the inner thing TeeFilter which is quite
understandable, otherwise please suggest.

  public:
+  using OnAudioBusCB =

[DaleCurtis, 2016/03/11 01:41:42]

OnAudioBusCB is a bit specific. How about something like CopyAudioCB? This also
needs the sample rate of the audio at least. Probably you'll want the channel
layout too, but could add that later.

[mcasas, 2016/03/11 04:06:23]

Done
Why wait? Now that I've got some review 
time I'd rather add that too ;)

+      base::Callback<void(scoped_ptr<AudioBus>, uint32_t delay_milliseconds)>;
+
   explicit WebAudioSourceProviderImpl(
       const scoped_refptr<RestartableAudioRendererSink>& sink);
 
   // blink::WebAudioSourceProvider implementation.
   void setClient(blink::WebAudioSourceProviderClient* client) override;
   void provideInput(const blink::WebVector<float*>& audio_data,
                     size_t number_of_frames) override;
 
   // RestartableAudioRendererSink implementation.
   void Start() override;
   void Stop() override;
   void Play() override;
   void Pause() override;
   bool SetVolume(double volume) override;
   OutputDevice* GetOutputDevice() override;
   void Initialize(const AudioParameters& params,
-                  RenderCallback* renderer) override;
+                  AudioRendererSink::RenderCallback* renderer) override;
+
+  // AudioRendererSink::RenderCallback implementation.
+  // These are forwarders to |renderer_| and are here to allow for a client to
+  // get a copy of the rendered audio by RegisterOnAudioBusCallback().
+  int Render(AudioBus* audio_bus,
+             uint32_t delay_milliseconds,
+             uint32_t frames_skipped) override;
+  void OnRenderError() override;
+
+  void RegisterOnAudioBusCallback(const OnAudioBusCB& callback);
+  void ResetOnAudioBusCallback();
 
  protected:
   ~WebAudioSourceProviderImpl() override;
 
  private:
   // Calls setFormat() on |client_| from the Blink renderer thread.
   void OnSetFormat();
 
   // Closure that posts a task to call OnSetFormat() on the renderer thread.
   base::Closure set_format_cb_;
@@ skipping 11 matching lines @@
   AudioRendererSink::RenderCallback* renderer_;
 
   // When set via setClient() it overrides |sink_| for consuming audio.
   blink::WebAudioSourceProviderClient* client_;
 
   // Where audio ends up unless overridden by |client_|.
   base::Lock sink_lock_;
   scoped_refptr<RestartableAudioRendererSink> sink_;
   scoped_ptr<AudioBus> bus_wrapper_;
 
+  OnAudioBusCB onaudiobus_callback_;
+
   // NOTE: Weak pointers must be invalidated before all other member variables.
+  // TODO(mcasas): This class is ref-counted via (Restartable)AudioRendererSink.
+  // and that does not seem to go well with this.
   base::WeakPtrFactory<WebAudioSourceProviderImpl> weak_factory_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(WebAudioSourceProviderImpl);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BLINK_WEBAUDIOSOURCEPROVIDER_IMPL_H_