Add NULL macOs implementation for 'MAINT-6950 Shared media a great distance...

Add NULL macOs implementation for 'MAINT-6950 Shared media a great distance away (different region even) sometimes plays at maximum volume when entering a region or moving camera slightly.' - until we can understand how to make real mac_volume_catcher work

indra/media_plugins/cef/CMakeLists.txt

@@ -57,9 +57,21 @@ set (media_plugin_cef_LINK_LIBRARIES
   ${LLCOMMON_LIBRARIES}
   ${PLUGIN_API_WINDOWS_LIBRARIES})
 
-if (WINDOWS)
+# Select which VolumeCatcher implementation to use
+if (LINUX)
+  message(FATAL_ERROR "CEF plugin has been enabled for a Linux compile.\n"
+    "  Please create a volume_catcher implementation for this platform.")
+elseif (DARWIN)
+  list(APPEND media_plugin_cef_SOURCE_FILES mac_volume_catcher_null.cpp)
+  find_library(CORESERVICES_LIBRARY CoreServices)
+  find_library(AUDIOUNIT_LIBRARY AudioUnit)
+  list(APPEND media_plugin_cef_LINK_LIBRARIES
+       ${CORESERVICES_LIBRARY}     # for Component Manager calls
+       ${AUDIOUNIT_LIBRARY}        # for AudioUnit calls
+       )
+elseif (WINDOWS)
   list(APPEND media_plugin_cef_SOURCE_FILES windows_volume_catcher.cpp)
-endif (WINDOWS)
+endif (LINUX)
 
 set_source_files_properties(${media_plugin_cef_HEADER_FILES}
                             PROPERTIES HEADER_FILE_ONLY TRUE)

indra/media_plugins/cef/mac_volume_catcher_null.cpp

+/** 
+ * @file windows_volume_catcher.cpp
+ * @brief A null implementation of volume level control of all audio channels opened by a process.
+ *        We are using this for the macOS version for now until we can understand how to make the 
+ *        exitising mac_volume_catcher.cpp work without the (now, non-existant) QuickTime dependency
+ *
+ * @cond
+ * $LicenseInfo:firstyear=2010&license=viewerlgpl$
+ * Second Life Viewer Source Code
+ * Copyright (C) 2010, Linden Research, Inc.
+ * 
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation;
+ * version 2.1 of the License only.
+ * 
+ * This library 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
+ * Lesser General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ * 
+ * Linden Research, Inc., 945 Battery Street, San Francisco, CA  94111  USA
+ * $/LicenseInfo$
+ * @endcond
+ */
+
+#include "volume_catcher.h"
+#include "llsingleton.h"
+class VolumeCatcherImpl : public LLSingleton<VolumeCatcherImpl>
+{
+	LLSINGLETON(VolumeCatcherImpl);
+	// This is a singleton class -- both callers and the component implementation should use getInstance() to find the instance.
+	~VolumeCatcherImpl();
+
+public:
+
+	void setVolume(F32 volume);
+	void setPan(F32 pan);
+	
+private:
+	F32 	mVolume;
+	F32 	mPan;
+	bool mSystemIsVistaOrHigher;
+};
+
+VolumeCatcherImpl::VolumeCatcherImpl()
+:	mVolume(1.0f),			// default volume is max
+	mPan(0.f)				// default pan is centered
+{
+}
+
+VolumeCatcherImpl::~VolumeCatcherImpl()
+{
+}
+
+void VolumeCatcherImpl::setVolume(F32 volume)
+{
+	mVolume = volume;
+}
+
+void VolumeCatcherImpl::setPan(F32 pan)
+{	// remember pan for calculating individual channel levels later
+	mPan = pan;
+}
+
+/////////////////////////////////////////////////////
+
+VolumeCatcher::VolumeCatcher()
+{
+	pimpl = VolumeCatcherImpl::getInstance();
+}
+
+VolumeCatcher::~VolumeCatcher()
+{
+	// Let the instance persist until exit.
+}
+
+void VolumeCatcher::setVolume(F32 volume)
+{
+	pimpl->setVolume(volume);
+}
+
+void VolumeCatcher::setPan(F32 pan)
+{
+	pimpl->setPan(pan);
+}
+
+void VolumeCatcher::pump()
+{
+	// No periodic tasks are necessary for this implementation.
+}