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

unity/Runtime/Tools/MjcfGenerationContext.cs

@@ -34,6 +34,7 @@ public class MjcfGenerationContext {
   private int _nuserSensor;
   private int _numGeneratedNames = 0;
   private Dictionary<Mesh, string> _meshAssets = new Dictionary<Mesh, string>();
+  private Dictionary<MjHeightFieldShape, string> _hFieldAssets = new Dictionary<MjHeightFieldShape, string>();
 
   public void GenerateMjcf(XmlElement mjcf) {
     GenerateConfigurationMjcf(mjcf);
@@ -50,6 +51,17 @@ public class MjcfGenerationContext {
     }
     return _meshAssets[mesh];
   }
+  
+  // Adds a mesh to the list of assets that will be added to the generated MJCF.
+  // Returns the unique name that identifies this new asset.
+  public string AddHeightFieldAsset(MjHeightFieldShape hField) {
+    if (!_hFieldAssets.ContainsKey(hField)) {
+      var uniqueName = $"hfield_{_numGeneratedNames}";
+      _numGeneratedNames++;
+      _hFieldAssets.Add(hField, uniqueName);
+    }
+    return _hFieldAssets[hField];
+  }
 
   public string GenerateName(Component comp) {
     var settings = MjGlobalSettings.Instance;
@@ -81,10 +93,15 @@ public class MjcfGenerationContext {
   private void GenerateAssetsMjcf(XmlElement mjcf) {
     var doc = mjcf.OwnerDocument;
     var assetMjcf = (XmlElement)mjcf.AppendChild(doc.CreateElement("asset"));
-    foreach (var asset in _meshAssets) {
+    foreach (var meshAsset in _meshAssets) {
       var meshMjcf = (XmlElement)assetMjcf.AppendChild(doc.CreateElement("mesh"));
-      meshMjcf.SetAttribute("name", asset.Value);
-      GenerateMeshMjcf(asset.Key, meshMjcf);
+      meshMjcf.SetAttribute("name", meshAsset.Value);
+      GenerateMeshMjcf(meshAsset.Key, meshMjcf);
+    }
+   foreach (var hFieldAsset in _hFieldAssets) {
+      var hFieldMjcf = (XmlElement)assetMjcf.AppendChild(doc.CreateElement("hfield"));
+      hFieldMjcf.SetAttribute("name", hFieldAsset.Value);
+      GenerateHeightFieldMjcf(hFieldAsset.Key, hFieldMjcf);
     }
   }
 
@@ -97,5 +114,15 @@ public class MjcfGenerationContext {
     }
     mjcf.SetAttribute("vertex", vertexPositionsStr.ToString());
   }
+  
+  private static void GenerateHeightFieldMjcf(MjHeightFieldShape hFieldComponent, XmlElement mjcf) {
+    mjcf.SetAttribute("nrow", "0");
+    mjcf.SetAttribute("ncol", "0");
+    mjcf.SetAttribute("content_type", "image/png");
+    mjcf.SetAttribute("file", hFieldComponent.FullHeightMapPath);
+            
+    mjcf.SetAttribute("size", MjEngineTool.MakeLocaleInvariant($"{hFieldComponent.HeightMapScale.x*hFieldComponent.HeightMapHeight/2} {hFieldComponent.HeightMapScale.z * hFieldComponent.HeightMapWidth/2} {hFieldComponent.HeightMapScale.y*2} {hFieldComponent.terrain.transform.position.y}"));
+
+  }
 }
 }