Add function allowing insight into currently loaded assets. Don't print info message when loading asset that was already loaded

scripts/drag_drop_handler.lua

@@ -40,7 +40,10 @@ if is_image_file(extension) then
     TexturePath = "]] .. filename .. [["
   });]] .. ReloadUIScript
 elseif extension == ".asset" then
-  return [[openspace.printInfo("Adding asset: ']] .. filename .. [[' (drag-and-drop)");
+  return [[
+    if openspace.asset.isLoaded("]] .. filename .. [[") ~= true then
+      openspace.printInfo("Adding asset: ']] .. filename .. [[' (drag-and-drop)");
+    end
     openspace.asset.add("]] .. filename .. [[");]] .. ReloadUIScript
 elseif extension == ".osrec" or extension == ".osrectxt" then
   return [[openspace.sessionRecording.startPlayback("]] .. filename .. [[")]]

src/scene/assetmanager.cpp

@@ -885,6 +885,21 @@ scripting::LuaLibrary AssetManager::luaLibrary() {
                 "Removes the asset with the specfied name from the scene. The parameter "
                 "to this function is the same that was originally used to load this "
                 "asset, i.e. the path to the asset file"
+            },
+            {
+                "isLoaded",
+                &luascriptfunctions::asset::isLoaded,
+                "string",
+                "Returns true if the referenced asset already has been loaded. Otherwise "
+                "false is returned. The parameter to this function is the path of the "
+                "asset that should be tested"
+            },
+            {
+                "allAssets",
+                &luascriptfunctions::asset::allAssets,
+                "",
+                "Returns the paths to all loaded assets, loaded directly or indirectly, "
+                "as a table containing the paths to all loaded assets."
             }
         }
     };

src/scene/assetmanager_lua.inl

@@ -42,4 +42,33 @@ int remove(lua_State* L) {
     return 0;
 }
 
+int isLoaded(lua_State* L) {
+    ghoul::lua::checkArgumentsAndThrow(L, 1, "lua::isLoaded");
+    const std::string assetName = ghoul::lua::value<std::string>(L);
+
+    std::vector<const Asset*> as = global::openSpaceEngine->assetManager().allAssets();
+    for (const Asset* a : as) {
+        if (a->path() == assetName) {
+            ghoul::lua::push(L, true);
+            return 1;
+        }
+    }
+
+    ghoul::lua::push(L, false);
+    return 1;
+}
+
+int allAssets(lua_State* L) {
+    ghoul::lua::checkArgumentsAndThrow(L, 0, "lua::allAssets");
+
+    std::vector<const Asset*> as = global::openSpaceEngine->assetManager().allAssets();
+    std::vector<std::string> res;
+    res.reserve(as.size());
+    for (const Asset* a : as) {
+        res.push_back(a->path().string());
+    }
+    ghoul::lua::push(L, res);
+    return 1;
+}
+
 } // namespace openspace::luascriptfunctions