[Unity-plugin] Context menu for creating Unity terrain components

unity/Editor/Components/MjGeomEditor.cs

@@ -77,5 +77,26 @@ private static void AddMatchingGeom(MenuCommand menuCommand) {
       GameObject.DestroyImmediate(geom);
     }
   }
+
+  void OnEnable() {
+    // Ensure we only subscribe handler once
+    EditorApplication.contextualPropertyMenu -= OnHeightFieldContextMenu;
+    EditorApplication.contextualPropertyMenu += OnHeightFieldContextMenu;
+  }
+
+  void OnDestroy() {
+    EditorApplication.contextualPropertyMenu -= OnHeightFieldContextMenu;
+  }
+
+  void OnHeightFieldContextMenu(GenericMenu menu, SerializedProperty property) {
+    if (property.type != nameof(MjHeightFieldShape))
+      return;
+
+    menu.AddItem(new GUIContent("Add Unity Terrain"), false, () =>
+    {
+      var geom = target as MjGeom;
+      geom.HField.AddTerrain();
+    });
+  }
 }
 }

unity/Runtime/Components/Shapes/MjHeightFieldShape.cs

@@ -17,19 +17,24 @@
 using System.Linq;
 using System.Xml;
 using UnityEngine;
+
 // internal imports
 namespace Mujoco {
 
 [Serializable]
 public class MjHeightFieldShape : IMjShape {
-  [Tooltip("Terrain's heightmap should have a minimum value of zero (fully black).")]
+  [Tooltip("Terrain's heightmap should have a minimum value of zero (fully black). Right click HField to add Unity Terrain."),
+  ContextMenuItem("Add Unity Terrain", "AddTerrain")]
   public Terrain Terrain;
 
   [Tooltip("The path, relative to Application.dataPath, where the heightmap " +
            "data will be saved/exported in PNG format. Leave blank if hfield data should " +
            "be set instead programmatically (faster).")]
   public string HeightMapExportPath;
 
+  [Tooltip("This thickness will be added below the 0 height in the hfield, to prevent penetration. ")]
+  public float BaseHeight = 0.1f;
+
   public bool ExportImage => !string.IsNullOrEmpty(HeightMapExportPath);
 
   public string FullHeightMapPath => Path.GetFullPath(Path.Combine(Application.dataPath,
@@ -75,7 +80,7 @@ public unsafe void ToMjcf(XmlElement mjcf, Transform transform) {
     var assetName = scene.GenerationContext.AddHeightFieldAsset(this);
 
     if (Application.isPlaying) {
-      scene.postInitEvent += (unused_first, unused_second) =>
+      scene.postInitEvent += (_, _) =>
           HeightFieldId =
               MujocoLib.mj_name2id(scene.Model, (int)MujocoLib.mjtObj.mjOBJ_HFIELD, assetName);
     }
@@ -160,5 +165,23 @@ public Tuple<Vector3[], int[]> BuildMesh() {
   }
 
   public void DebugDraw(Transform transform) {}
+
+  public void AddTerrain() {
+    GameObject terrainObject = new GameObject("Terrain");
+    Terrain newTerrain = terrainObject.AddComponent<Terrain>();
+    newTerrain.terrainData = new TerrainData();
+    newTerrain.terrainData.size = new Vector3(100, 1, 100);
+
+    var transform = GameObject
+      .FindObjectsByType<MjGeom>(FindObjectsInactive.Include, FindObjectsSortMode.None)
+      .First(g => g.HField == this).transform;
+
+    terrainObject.transform.parent = transform;
+    newTerrain.materialTemplate = new Material(Shader.Find("Nature/Terrain/Diffuse"));
+    var coll = newTerrain.gameObject.AddComponent<TerrainCollider>();
+    coll.terrainData = newTerrain.terrainData;
+    Terrain = newTerrain;
+    terrainObject.transform.localPosition = new Vector3(-50, 0, -50);
+  }
 }
 }

unity/Runtime/Tools/MjcfGenerationContext.cs

@@ -128,8 +128,7 @@ private static void GenerateHeightFieldMjcf(MjHeightFieldShape hFieldComponent,
       mjcf.SetAttribute("ncol", hFieldComponent.HeightMapWidth.ToString());
     }
 
-    var baseHeight = hFieldComponent.Terrain.transform.localPosition.y +
-                     hFieldComponent.MinimumHeight;
+    var baseHeight = hFieldComponent.BaseHeight;
     var heightRange = Mathf.Clamp(
         hFieldComponent.MaximumHeight - hFieldComponent.MinimumHeight,
         0.00001f,