Add mjs_makeMesh to create a builtin mesh.

PiperOrigin-RevId: 788538127
Change-Id: I999733399a1a0da07b0f915f34d31364ab8b3b52

src/xml/xml_native_reader.cc

@@ -230,9 +230,9 @@ const char* MJCF[nMJCF][mjXATTRNUM] = {
 
     {"asset", "*", "0"},
     {"<"},
-        {"mesh", "*", "14", "name", "class", "content_type", "file", "vertex", "normal",
+        {"mesh", "*", "16", "name", "class", "content_type", "file", "vertex", "normal",
             "texcoord", "face", "refpos", "refquat", "scale", "smoothnormal",
-            "maxhullvert", "inertia"},
+            "maxhullvert", "inertia", "builtin", "params"},
         {"<"},
           {"plugin", "*", "2", "plugin", "instance"},
           {"<"},
@@ -825,6 +825,20 @@ const mjMap meshinertia_map[4] = {
 };
 
 
+// mesh builtin type
+const int meshbuiltin_sz = 8;
+const mjMap meshbuiltin_map[meshbuiltin_sz] = {
+  {"none", mjMESH_BUILTIN_NONE},
+  {"sphere", mjMESH_BUILTIN_SPHERE},
+  {"hemisphere", mjMESH_BUILTIN_HEMISPHERE},
+  {"prism", mjMESH_BUILTIN_PRISM},
+  {"cone", mjMESH_BUILTIN_CONE},
+  {"torus", mjMESH_BUILTIN_TORUS},
+  {"wedge", mjMESH_BUILTIN_WEDGE},
+  {"plate", mjMESH_BUILTIN_PLATE}
+};
+
+
 // flexcomp type
 const mjMap fcomp_map[mjNFCOMPTYPES] = {
   {"grid",        mjFCOMPTYPE_GRID},
@@ -1539,6 +1553,21 @@ void mjXReader::OneMesh(XMLElement* elem, mjsMesh* mesh, const mjVFS* vfs) {
     }
   }
 
+  // read builtin options
+  if (MapValue(elem, "builtin", &n, meshbuiltin_map, meshbuiltin_sz)) {
+    std::vector<double> params;
+    int nparams = ReadVector(elem, "params", params, text, /*required*/ true);
+    if (file) {
+      throw mjXError(elem, "builtin cannot be used with a mesh file");
+    }
+    if (!mesh->uservert->empty()) {
+      throw mjXError(elem, "builtin mesh cannot be used with user vertex data");
+    }
+    if (mjs_makeMesh(mesh, (mjtMeshBuiltin)n, params.data(), nparams)) {
+      throw mjXError(elem, mjs_getError(spec));
+    }
+  }
+
   // write error info
   mjs_setString(mesh->info, ("line " + std::to_string(elem->GetLineNum())).c_str());
 }