Merge branch 'v0.20.x' into master

contains OSX mixer

src/mixer/MixerList.hxx

@@ -32,6 +32,7 @@ extern const MixerPlugin software_mixer_plugin;
 extern const MixerPlugin alsa_mixer_plugin;
 extern const MixerPlugin haiku_mixer_plugin;
 extern const MixerPlugin oss_mixer_plugin;
+extern const MixerPlugin osx_mixer_plugin;
 extern const MixerPlugin roar_mixer_plugin;
 extern const MixerPlugin pulse_mixer_plugin;
 extern const MixerPlugin winmm_mixer_plugin;

src/mixer/plugins/OSXMixerPlugin.cxx

@@ -0,0 +1,69 @@
+/*
+ * Copyright 2003-2017 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 "config.h"
+#include "mixer/MixerInternal.hxx"
+#include "output/plugins/OSXOutputPlugin.hxx"
+
+class OSXMixer final : public Mixer {
+	OSXOutput &output;
+
+public:
+	OSXMixer(OSXOutput &_output, MixerListener &_listener)
+		:Mixer(osx_mixer_plugin, _listener),
+		 output(_output)
+	{
+	}
+
+	/* virtual methods from class Mixer */
+	void Open() noexcept override {
+	}
+
+	void Close() noexcept override {
+	}
+
+	int GetVolume() override;
+	void SetVolume(unsigned volume) override;
+};
+
+int
+OSXMixer::GetVolume()
+{
+	return osx_output_get_volume(output);
+}
+
+void
+OSXMixer::SetVolume(unsigned new_volume)
+{
+	osx_output_set_volume(output, new_volume);
+}
+
+static Mixer *
+osx_mixer_init(gcc_unused EventLoop &event_loop, AudioOutput &ao,
+		MixerListener &listener,
+		gcc_unused const ConfigBlock &block)
+{
+	OSXOutput &osxo = (OSXOutput &)ao;
+	return new OSXMixer(osxo, listener);
+}
+
+const MixerPlugin osx_mixer_plugin = {
+	osx_mixer_init,
+	true,
+};