mixer: add AndroidMixerPlugin

src/mixer/MixerList.hxx

@@ -29,6 +29,7 @@ struct MixerPlugin;
 
 extern const MixerPlugin null_mixer_plugin;
 extern const MixerPlugin software_mixer_plugin;
+extern const MixerPlugin android_mixer_plugin;
 extern const MixerPlugin alsa_mixer_plugin;
 extern const MixerPlugin haiku_mixer_plugin;
 extern const MixerPlugin oss_mixer_plugin;

src/mixer/plugins/AndroidMixerPlugin.cxx

@@ -0,0 +1,116 @@
+/*
+ * Copyright 2003-2020 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "mixer/MixerInternal.hxx"
+#include "filter/plugins/VolumeFilterPlugin.hxx"
+#include "pcm/Volume.hxx"
+#include "android/Context.hxx"
+#include "android/AudioManager.hxx"
+
+#include "Main.hxx"
+
+#include <cassert>
+#include <cmath>
+
+class AndroidMixer final : public Mixer {
+	AudioManager *audioManager;
+	int currentVolume;
+	int maxAndroidVolume;
+	int lastAndroidVolume;
+public:
+	explicit AndroidMixer(MixerListener &_listener);
+
+	~AndroidMixer() override;
+
+	/* virtual methods from class Mixer */
+	void Open() override {
+	}
+
+	void Close() noexcept override {
+	}
+
+	int GetVolume() override;
+
+	void SetVolume(unsigned volume) override;
+};
+
+static Mixer *
+android_mixer_init([[maybe_unused]] EventLoop &event_loop,
+		    [[maybe_unused]] AudioOutput &ao,
+		    MixerListener &listener,
+		    [[maybe_unused]] const ConfigBlock &block)
+{
+	return new AndroidMixer(listener);
+}
+
+AndroidMixer::AndroidMixer(MixerListener &_listener)
+	:Mixer(android_mixer_plugin, _listener)
+{
+	JNIEnv *env = Java::GetEnv();
+	audioManager = context->GetAudioManager(env);
+
+	maxAndroidVolume = audioManager->GetMaxVolume();
+	if (maxAndroidVolume != 0)
+	{
+		lastAndroidVolume = audioManager->GetVolume(env);
+		currentVolume = 100 * lastAndroidVolume / maxAndroidVolume;
+	}
+}
+
+AndroidMixer::~AndroidMixer()
+{
+	delete audioManager;
+}
+
+int
+AndroidMixer::GetVolume()
+{
+	JNIEnv *env = Java::GetEnv();
+	if (maxAndroidVolume == 0)
+		return -1;
+
+	// The android volume index (or scale) is very likely inferior to the
+	// MPD one (100). The last volume set by MPD is saved into
+	// currentVolume, this volume is returned instead of the Android one
+	// when the Android mixer was not touched by an other application. This
+	// allows to fake a 0..100 scale from MPD.
+
+	int volume = audioManager->GetVolume(env);
+	if (volume == lastAndroidVolume)
+		return currentVolume;
+
+	return 100 * volume / maxAndroidVolume;
+}
+
+void
+AndroidMixer::SetVolume(unsigned newVolume)
+{
+	JNIEnv *env = Java::GetEnv();
+	if (maxAndroidVolume == 0)
+		return;
+	currentVolume = newVolume;
+	lastAndroidVolume = currentVolume * maxAndroidVolume / 100;
+	audioManager->SetVolume(env, lastAndroidVolume);
+
+}
+
+const MixerPlugin android_mixer_plugin = {
+	android_mixer_init,
+	true,
+};

src/mixer/plugins/meson.build

@@ -34,6 +34,10 @@ if is_windows
   mixer_plugins_sources += 'WinmmMixerPlugin.cxx'
 endif
 
+if is_android
+  mixer_plugins_sources += 'AndroidMixerPlugin.cxx'
+endif
+
 mixer_plugins = static_library(
   'mixer_plugins',
   mixer_plugins_sources,