Add heightfield geom type with Unity terrain, import not yet supported

unity/Runtime/Components/Shapes/MjHeightFieldShape.cs

@@ -0,0 +1,75 @@
+// Copyright 2019 DeepMind Technologies Limited
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+using System;
+using System.IO;
+using System.Linq;
+using System.Xml;
+using UnityEngine;
+
+namespace Mujoco
+{
+
+[Serializable]
+public class MjHeightFieldShape : IMjShape
+{
+
+  public Terrain terrain;
+
+  [Tooltip("The path, relative to Application.dataPath, where the heightmap data will be save in PNG format.")]
+  public string heightMapExportPath;
+
+  public string FullHeightMapPath => Path.GetFullPath(Path.Combine(Application.dataPath, heightMapExportPath));
+  public int HeightMapWidth => terrain.terrainData.heightmapTexture.width; 
+  public int HeightMapHeight => terrain.terrainData.heightmapTexture.height;
+  public Vector3 HeightMapScale => terrain.terrainData.heightmapScale;
+
+  public void ToMjcf(XmlElement mjcf, Transform transform)
+  {
+    ExportHeightMap();
+    var scene = MjScene.Instance;
+    var assetName = scene.GenerationContext.AddHeightFieldAsset(this);
+    mjcf.SetAttribute("hfield", assetName);
+  }
+
+  public void FromMjcf(XmlElement mjcf)
+  {
+
+  }
+
+  public void ExportHeightMap()
+  {
+    RenderTexture.active = terrain.terrainData.heightmapTexture;
+    Texture2D texture = new Texture2D(RenderTexture.active.width, RenderTexture.active.height);
+    texture.ReadPixels(new Rect(0, 0, RenderTexture.active.width, RenderTexture.active.height), 0, 0);
+    RenderTexture.active = null;
+    File.WriteAllBytes(FullHeightMapPath, texture.EncodeToPNG());
+  }
+
+
+  public Vector4 GetChangeStamp()
+  {
+    return Vector4.one;
+  }
+
+  public Tuple<Vector3[], int[]> BuildMesh()
+  {
+    return Tuple.Create(new Vector3[]{}, new int[]{});
+  }
+
+  public void DebugDraw(Transform transform)
+  {
+  }
+}
+}