Issue/591 add assets file browsing (#3798)

* create download event topic wip

* Make topic connection thread safe & rate limit downloadeventtopic data to reduce traffic


* add LDEBUG and LERROR on donwload start/finish/failed

* Add new AssetLoadingEvent
event 
* fix pr comments

include/openspace/engine/globals.h

@@ -35,6 +35,7 @@ namespace openspace {
 struct Configuration;
 class Dashboard;
 class DeferredcasterManager;
+class DownloadEventEngine;
 class DownloadManager;
 class EventEngine;
 class LuaConsole;
@@ -72,6 +73,7 @@ namespace global {
 inline ghoul::fontrendering::FontManager* fontManager;
 inline Dashboard* dashboard;
 inline DeferredcasterManager* deferredcasterManager;
+inline DownloadEventEngine* downloadEventEngine;
 inline DownloadManager* downloadManager;
 inline EventEngine* eventEngine;
 inline LuaConsole* luaConsole;

include/openspace/events/event.h

@@ -60,7 +60,7 @@ struct Event {
     enum class Type : uint8_t {
         ParallelConnection,
         ProfileLoadingFinished,
-        AssetLoadingFinished,
+		AssetLoading,
         ApplicationShutdown,
         CameraFocusTransition,
         TimeOfInterestReached,
@@ -152,17 +152,32 @@ struct EventProfileLoadingFinished : public Event {
 };
 
 /**
-* This event is created when the loading of all assets are finished. This is emitted
-* regardless of whether it is the initial startup of a profile, or any subsequent asset
-* being loaded e.g., through add or drag-and-drop.
+* This event is created whenever the loading state of an assets changes. An asset can
+* enter one of four states: `Loading`, `Loaded`, `Unloaded`, or `Error`. This event is
+* emitted regardless of whether it is the initial startup of a profile, or any subsequent
+* asset being added or revmoed e.g., through add or drag-and-drop.
 */
-struct EventAssetLoadingFinished : public Event {
-    static constexpr Type Type = Event::Type::AssetLoadingFinished;
+struct EventAssetLoading : public Event {
+    static constexpr Type Type = Event::Type::AssetLoading;
+
+	enum class State {
+		Loaded,
+		Loading,
+		Unloaded,
+		Error
+	};
 
     /**
-     * Creates an instance of an AssetLoadingFinished event.
+     * Creates an instance of an AssetLoading event.
+	 *
+	 * \param assetPath_ The path to the asset
+	 * \param state_ The new state of the asset given by 'asstPath_'; is one of `Loading`,
+	 *               `Loaded`, `Unloaded`, or `Error`
      */
-    EventAssetLoadingFinished();
+    EventAssetLoading(const std::filesystem::path& assetPath_, State newState);
+
+	std::filesystem::path assetPath;
+	State state;
 };
 
 /**

include/openspace/scene/asset.h

@@ -207,6 +207,14 @@ public:
      */
     bool hasInitializedParent() const;
 
+    /**
+     * Returns a list of the parents of this Asset that is currently in an initialized
+     * state, meaning any parent that is still interested in this Asset at all.
+     *
+     * \return A list of parent filepaths that are interested in this asset
+     */
+    std::vector<std::filesystem::path> initializedParents() const;
+
     /**
      * Deinitializes this Asset and recursively deinitializes the required assets if this
      * Asset was their ownly initialized parent. If the Asset was already deinitialized,

include/openspace/util/downloadeventengine.h

@@ -0,0 +1,72 @@
+/*****************************************************************************************
+ *                                                                                       *
+ * OpenSpace                                                                             *
+ *                                                                                       *
+ * Copyright (c) 2014-2025                                                               *
+ *                                                                                       *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of this  *
+ * software and associated documentation files (the "Software"), to deal in the Software *
+ * without restriction, including without limitation the rights to use, copy, modify,    *
+ * merge, publish, distribute, sublicense, and/or sell copies of the Software, and to    *
+ * permit persons to whom the Software is furnished to do so, subject to the following   *
+ * conditions:                                                                           *
+ *                                                                                       *
+ * The above copyright notice and this permission notice shall be included in all copies *
+ * or substantial portions of the Software.                                              *
+ *                                                                                       *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,   *
+ * INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A         *
+ * PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT    *
+ * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF  *
+ * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE  *
+ * OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                                         *
+ ****************************************************************************************/
+
+#ifndef __OPENSPACE_MODULE_SYNC___DOWNLOAD_EVENT_ENGINE___H__
+#define __OPENSPACE_MODULE_SYNC___DOWNLOAD_EVENT_ENGINE___H__
+
+#include <functional>
+#include <map>
+#include <mutex>
+#include <optional>
+#include <string>
+
+namespace openspace {
+
+// @TODO (anden88 2025-10-10): This class was specifically written for the multi-threaded
+// url- and httpSynchronization events. In the future we should make this more general
+// purposed.
+class DownloadEventEngine {
+public:
+    struct DownloadEvent {
+        enum class Type {
+            Started,
+            Progress,
+            Finished,
+            Failed
+        };
+
+        Type type;
+        std::string id;
+        int64_t downloadedBytes;
+        std::optional<int64_t> totalBytes;
+    };
+
+    using Callback = std::function<void(const DownloadEvent&)>;
+
+    int subscribe(Callback cb);
+    void unsubscribe(int id);
+
+    void publish(const DownloadEvent& event);
+    void publish(const std::string& id, DownloadEvent::Type type,
+        int64_t downloadedBytes = 0, std::optional<int64_t> totalBytes = std::nullopt);
+
+private:
+    std::mutex _mutex;
+    int _id = 0;
+    std::unordered_map<int, Callback> _subscribers;
+};
+
+} // namespace openspace
+
+#endif // __OPENSPACE_MODULE_SYNC___DOWNLOAD_EVENT_ENGINE___H__