Preliminary support for plugins. Load all plugins in plugin folder.

unity/Editor/Importer/MjImporterWithAssets.cs

@@ -50,6 +50,7 @@ public class MjImporterWithAssets : MjcfImporter {
     // mjcfString.
     var name = Path.GetFileNameWithoutExtension(filePath) + $"{UnityEngine.Random.Range(0,999)}";
     string newPath = Path.Combine(Application.temporaryCachePath, $"{name}.xml");
+    MjEngineTool.LoadPlugins();
     _mjModel = MjEngineTool.LoadModelFromFile(filePath);
     MjEngineTool.SaveModelToFile(newPath, _mjModel);
     Debug.Log($"Imported MJCF loaded, saved to {newPath}");

unity/Runtime/Importer/MjcfImporter.cs

@@ -284,6 +284,11 @@ public class MjcfImporter {
         CreateGameObjectWithCamera(parentObject, child);
         break;
       }
+      case "plugin": {
+        Debug.Log($"Plugin elements are only partially supported.");
+        break;
+      }
+
       default: {
         Debug.Log($"The importer does not yet support tags <{child.Name}>.");
         break;

unity/Runtime/Plugins.meta

@@ -0,0 +1,8 @@
+fileFormatVersion: 2
+guid: 1135ed488170c0444b32c18cc61fb9ef
+folderAsset: yes
+DefaultImporter:
+  externalObjects: {}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

unity/Runtime/Tools/MjEngineTool.cs

@@ -368,6 +368,16 @@ public static class MjEngineTool {
       }
     }
   }
+
+  public static void LoadPlugins() {
+    if(!Directory.Exists("Packages/org.mujoco/Runtime/Plugins/")) return;
+
+    foreach (string pluginPath in Directory.GetFiles("Packages/org.mujoco/Runtime/Plugins/")) {
+      MujocoLib.mj_loadPluginLibrary(pluginPath);
+    }
+    
+  }
+
 }
 
 public static class MjSceneImportSettings {