Add ability to specify a material assignment to a mesh asset.

This extends both the spec and the XML definition to allow specification of a material name on a mesh. This material acts as a fallback in the case that the referencing geom element does not specify a material of it's own.

PiperOrigin-RevId: 798232378
Change-Id: Iaf300c727732744ea1b613e64334ee505ac6e209

src/user/user_mesh.cc

@@ -278,6 +278,7 @@ void mjCMesh::PointToLocal() {
   spec.userface = &spec_face_;
   spec.usertexcoord = &spec_texcoord_;
   spec.userfacetexcoord = &spec_facetexcoord_;
+  spec.material = &spec_material_;
   spec.plugin.plugin_name = &plugin_name;
   spec.plugin.name = &plugin_instance_name;
   spec.info = &info;
@@ -317,6 +318,7 @@ void mjCMesh::CopyFromSpec() {
   content_type_ = spec_content_type_;
   normal_ = spec_normal_;
   face_ = spec_face_;
+  material_ = spec_material_;
   ProcessVertices(spec_vert_);
   texcoord_ = spec_texcoord_;
   facetexcoord_ = spec_facetexcoord_;
@@ -476,6 +478,7 @@ void mjCMesh::CacheMesh(mjCCache* cache, const mjResource* resource) {
   mesh->polygon_map_ = polygon_map_;
   mesh->surface_ = surface_;
   mesh->volume_ = volume_;
+  mesh->material_ = material_;
   std::copy(boxsz_, boxsz_ + 3, mesh->boxsz_);
   std::copy(aamm_, aamm_ + 6, mesh->aamm_);
   std::copy(pos_, pos_ + 3, mesh->pos_);

src/user/user_model.cc

@@ -1879,7 +1879,23 @@ void mjCModel::IndexAssets(bool discard) {
   for (int i=0; i < geoms_.size(); i++) {
     mjCGeom* geom = geoms_[i];
 
-    // find material by name
+
+    // find mesh by name
+    if (!geom->get_meshname().empty()) {
+      mjCMesh* mesh = static_cast<mjCMesh*>(FindObject(mjOBJ_MESH, geom->get_meshname()));
+      if (mesh) {
+        if (!geom->visual_) {
+          mesh->SetNotVisual();  // reset to true by mesh->Compile()
+        }
+        geom->mesh = (discard && geom->visual_) ? nullptr : mesh;
+        mesh->spec.needsdf |= geom->spec.type == mjGEOM_SDF;
+      } else {
+        throw mjCError(geom, "mesh '%s' not found in geom %d", geom->get_meshname().c_str(), i);
+      }
+    }
+
+    // find material by name, this has to happen after mesh assignment so that if
+    // the geom does not specify a material but the mesh does it can fall back.
     if (!geom->get_material().empty()) {
       mjCBase* material = FindObject(mjOBJ_MATERIAL, geom->get_material());
       if (material) {
@@ -1889,20 +1905,6 @@ void mjCModel::IndexAssets(bool discard) {
       }
     }
 
-    // find mesh by name
-    if (!geom->get_meshname().empty()) {
-      mjCBase* mesh = FindObject(mjOBJ_MESH, geom->get_meshname());
-      if (mesh) {
-        if (!geom->visual_) {
-          ((mjCMesh*)mesh)->SetNotVisual();  // reset to true by mesh->Compile()
-        }
-        geom->mesh = (discard && geom->visual_) ? nullptr : (mjCMesh*)mesh;
-        static_cast<mjCMesh*>(mesh)->spec.needsdf |= geom->spec.type == mjGEOM_SDF;
-      } else {
-        throw mjCError(geom, "mesh '%s' not found in geom %d", geom->get_meshname().c_str(), i);
-      }
-    }
-
     // find hfield by name
     if (!geom->get_hfieldname().empty()) {
       mjCBase* hfield = FindObject(mjOBJ_HFIELD, geom->get_hfieldname());

src/user/user_objects.cc

@@ -3365,7 +3365,12 @@ void mjCGeom::ComputeAABB(void) {
   mjuu_copyvec(aabb+3, size, 3);
 }
 
-
+const std::string& mjCGeom::get_material() const {
+  if (mesh && spec_material_.empty()) {
+    return mesh->Material();
+  }
+  return spec_material_;
+}
 
 // compiler
 void mjCGeom::Compile(void) {

src/user/user_objects.h

@@ -49,9 +49,9 @@ class mjCSite;
 class mjCCamera;
 class mjCLight;
 class mjCHField;
-class mjCFlex;         // defined in user_mesh.h
-class mjCMesh;         // defined in user_mesh.h
-class mjCSkin;         // defined in user_mesh.h
+class mjCFlex;
+class mjCMesh;
+class mjCSkin;
 class mjCTexture;
 class mjCMaterial;
 class mjCPair;
@@ -753,7 +753,7 @@ class mjCGeom : public mjCGeom_, private mjsGeom {
   const std::vector<double>& get_userdata() const { return userdata_; }
   const std::string& get_hfieldname() const { return spec_hfieldname_; }
   const std::string& get_meshname() const { return spec_meshname_; }
-  const std::string& get_material() const { return spec_material_; }
+  const std::string& get_material() const;
   void del_material() { spec_material_.clear(); }
 
  private:
@@ -1029,6 +1029,7 @@ class mjCMesh_ : public mjCBase {
   std::vector<int> face_;                        // vertex indices
   std::vector<int> facenormal_;                  // normal indices
   std::vector<int> facetexcoord_;                // texcoord indices
+  std::string material_;                         // mesh fallback material
 
   std::string spec_content_type_;
   std::string spec_file_;
@@ -1038,6 +1039,7 @@ class mjCMesh_ : public mjCBase {
   std::vector<int> spec_face_;
   std::vector<int> spec_facenormal_;
   std::vector<int> spec_facetexcoord_;
+  std::string spec_material_;
 
   // used by the compiler
   bool needreorient_;                            // needs reorientation
@@ -1117,6 +1119,8 @@ class mjCMesh: public mjCMesh_, private mjsMesh {
   const std::vector<int>& Face() const { return face_; }
   const std::vector<int>& UserFace() const { return spec_face_; }
   mjtMeshInertia Inertia() const { return spec.inertia; }
+  const std::string& Material() const { return material_; }
+
   // setters
   void SetNeedHull(bool needhull) { needhull_ = needhull; }
 

src/xml/xml_native_reader.cc

@@ -230,9 +230,9 @@ const char* MJCF[nMJCF][mjXATTRNUM] = {
 
     {"asset", "*", "0"},
     {"<"},
-        {"mesh", "*", "16", "name", "class", "content_type", "file", "vertex", "normal",
+        {"mesh", "*", "17", "name", "class", "content_type", "file", "vertex", "normal",
             "texcoord", "face", "refpos", "refquat", "scale", "smoothnormal",
-            "maxhullvert", "inertia", "builtin", "params"},
+            "maxhullvert", "inertia", "builtin", "params", "material"},
         {"<"},
           {"plugin", "*", "2", "plugin", "instance"},
           {"<"},
@@ -1569,6 +1569,11 @@ void mjXReader::OneMesh(XMLElement* elem, mjsMesh* mesh, const mjVFS* vfs) {
     }
   }
 
+  std::string material;
+  if (ReadAttrTxt(elem, "material", material)) {
+    mjs_setString(mesh->material, material.c_str());
+  }
+
   // write error info
   mjs_setString(mesh->info, ("line " + std::to_string(elem->GetLineNum())).c_str());
 }