Event System (#1741)

* Add implementation of the EventEngine to handle global event chains
* Add properties to SceneGraphNodes to determine two distance radii for camera-based events

include/openspace/engine/configuration.h

@@ -89,6 +89,7 @@ struct Configuration {
 
     bool isCheckingOpenGLState = false;
     bool isLoggingOpenGLCalls = false;
+    bool isPrintingEvents = false;
 
     float shutdownCountdown = 0.f;
 

include/openspace/engine/globals.h

@@ -36,6 +36,7 @@ namespace openspace {
 class Dashboard;
 class DeferredcasterManager;
 class DownloadManager;
+class EventEngine;
 class LuaConsole;
 class MemoryManager;
 class MissionManager;
@@ -74,6 +75,7 @@ inline ghoul::fontrendering::FontManager* fontManager;
 inline Dashboard* dashboard;
 inline DeferredcasterManager* deferredcasterManager;
 inline DownloadManager* downloadManager;
+inline EventEngine* eventEngine;
 inline LuaConsole* luaConsole;
 inline MemoryManager* memoryManager;
 inline MissionManager* missionManager;

include/openspace/engine/openspaceengine.h

@@ -26,6 +26,7 @@
 #define __OPENSPACE_CORE___OPENSPACEENGINE___H__
 
 #include <openspace/properties/stringproperty.h>
+#include <openspace/properties/scalar/boolproperty.h>
 #include <openspace/scene/profile.h>
 #include <openspace/util/keys.h>
 #include <openspace/util/mouse.h>
@@ -117,6 +118,8 @@ private:
     std::string generateFilePath(std::string openspaceRelativePath);
     void resetPropertyChangeFlagsOfSubowners(openspace::properties::PropertyOwner* po);
 
+    properties::BoolProperty _printEvents;
+
     std::unique_ptr<Scene> _scene;
     std::unique_ptr<AssetManager> _assetManager;
     bool _shouldAbortLoading = false;