mixer/software: move Filter management to the AudioOutput

src/mixer/plugins/SoftwareMixerPlugin.cxx

@@ -31,23 +31,8 @@
 #include <assert.h>
 #include <math.h>
 
-static Filter *
-CreateVolumeFilter()
-{
-	return filter_new(&volume_filter_plugin, ConfigBlock(),
-			  IgnoreError());
-}
-
 class SoftwareMixer final : public Mixer {
-	Filter *filter;
-
-	/**
-	 * If this is true, then this object "owns" the #Filter
-	 * instance (see above).  It will be set to false by
-	 * software_mixer_get_filter(); after that, the caller will be
-	 * responsible for the #Filter.
-	 */
-	bool owns_filter = true;
+	Filter *filter = nullptr;
 
 	/**
 	 * The current volume in percent (0..100).
@@ -56,18 +41,11 @@ class SoftwareMixer final : public Mixer {
 
 public:
 	SoftwareMixer(MixerListener &_listener)
-		:Mixer(software_mixer_plugin, _listener),
-		 filter(CreateVolumeFilter())
+		:Mixer(software_mixer_plugin, _listener)
 	{
-		assert(filter != nullptr);
 	}
 
-	virtual ~SoftwareMixer() {
-		if (owns_filter)
-			delete filter;
-	}
-
-	Filter *GetFilter();
+	void SetFilter(Filter *_filter);
 
 	/* virtual methods from class Mixer */
 	virtual bool Open(gcc_unused Error &error) override {
@@ -115,7 +93,9 @@ SoftwareMixer::SetVolume(unsigned new_volume, gcc_unused Error &error)
 	assert(new_volume <= 100);
 
 	volume = new_volume;
-	volume_filter_set(filter, PercentVolumeToSoftwareVolume(new_volume));
+
+	if (filter != nullptr)
+		volume_filter_set(filter, PercentVolumeToSoftwareVolume(new_volume));
 	return true;
 }
 
@@ -124,19 +104,19 @@ const MixerPlugin software_mixer_plugin = {
 	true,
 };
 
-inline Filter *
-SoftwareMixer::GetFilter()
+inline void
+SoftwareMixer::SetFilter(Filter *_filter)
 {
-	assert(owns_filter);
+	filter = _filter;
 
-	owns_filter = false;
-	return filter;
+	if (filter != nullptr)
+		volume_filter_set(filter,
+				  PercentVolumeToSoftwareVolume(volume));
 }
 
-Filter *
-software_mixer_get_filter(Mixer *mixer)
+void
+software_mixer_set_filter(Mixer &mixer, Filter *filter)
 {
-	SoftwareMixer *sm = (SoftwareMixer *)mixer;
-	assert(sm->IsPlugin(software_mixer_plugin));
-	return sm->GetFilter();
+	SoftwareMixer &sm = (SoftwareMixer &)mixer;
+	sm.SetFilter(filter);
 }

src/mixer/plugins/SoftwareMixerPlugin.hxx

@@ -24,10 +24,12 @@ class Mixer;
 class Filter;
 
 /**
- * Returns the (volume) filter associated with this mixer.  All users
- * of this mixer plugin should install this filter.
+ * Attach a #VolumeFilter to this mixer.  The #VolumeFilter is the
+ * entity which actually applies the volume; it is created and managed
+ * by the output.  Mixer::SetVolume() calls will be forwarded to
+ * volume_filter_set().
  */
-Filter *
-software_mixer_get_filter(Mixer *mixer);
+void
+software_mixer_set_filter(Mixer &mixer, Filter *filter);
 
 #endif

src/output/Init.cxx

@@ -102,6 +102,13 @@ audio_output_mixer_type(const ConfigBlock &block)
 						  "hardware"));
 }
 
+static Filter *
+CreateVolumeFilter()
+{
+	return filter_new(&volume_filter_plugin, ConfigBlock(),
+			  IgnoreError());
+}
+
 static Mixer *
 audio_output_load_mixer(EventLoop &event_loop, AudioOutput &ao,
 			const ConfigBlock &block,
@@ -110,6 +117,8 @@ audio_output_load_mixer(EventLoop &event_loop, AudioOutput &ao,
 			MixerListener &listener,
 			Error &error)
 {
+	assert(ao.volume_filter == nullptr);
+
 	Mixer *mixer;
 
 	switch (audio_output_mixer_type(block)) {
@@ -135,8 +144,13 @@ audio_output_load_mixer(EventLoop &event_loop, AudioOutput &ao,
 				  IgnoreError());
 		assert(mixer != nullptr);
 
+		ao.volume_filter = CreateVolumeFilter();
+		assert(ao.volume_filter != nullptr);
+
 		filter_chain_append(filter_chain, "software_mixer",
-				    software_mixer_get_filter(mixer));
+				    ao.volume_filter);
+
+		software_mixer_set_filter(*mixer, ao.volume_filter);
 		return mixer;
 	}
 

src/output/Internal.hxx

@@ -189,6 +189,12 @@ struct AudioOutput {
 	 */
 	Filter *filter = nullptr;
 
+	/**
+	 * The #VolumeFilter instance of this audio output.  It is
+	 * used by the #SoftwareMixer.
+	 */
+	Filter *volume_filter = nullptr;
+
 	/**
 	 * The replay_gain_filter_plugin instance of this audio
 	 * output.