Replace meshid and hfieldid with mjCMesh and mjCHField pointers in mjCGeom.

PiperOrigin-RevId: 597279837
Change-Id: I45ca00c70c13cd5bddb3385a0c60388fb166527c

src/xml/xml_native_reader.cc

@@ -1525,8 +1525,8 @@ void mjXReader::OneGeom(XMLElement* elem, mjCGeom* pgeom) {
   ReadAttr(elem, "solimp", mjNIMP, pgeom->solimp, text, false, false);
   ReadAttr(elem, "margin", 1, &pgeom->margin, text);
   ReadAttr(elem, "gap", 1, &pgeom->gap, text);
-  ReadAttrTxt(elem, "hfield", pgeom->hfield);
-  ReadAttrTxt(elem, "mesh", pgeom->mesh);
+  ReadAttrTxt(elem, "hfield", pgeom->hfieldname);
+  ReadAttrTxt(elem, "mesh", pgeom->meshname);
   ReadAttr(elem, "fitscale", 1, &pgeom->fitscale, text);
   ReadAttrTxt(elem, "material", pgeom->material);
   ReadAttr(elem, "rgba", 4, pgeom->rgba, text);

src/xml/xml_native_writer.cc

@@ -347,7 +347,7 @@ void mjXWriter::OneGeom(XMLElement* elem, mjCGeom* pgeom, mjCDef* def) {
 
     // mesh geom
     if (pgeom->type==mjGEOM_MESH || pgeom->type==mjGEOM_SDF) {
-      mjCMesh* pmesh = model->meshes[pgeom->meshid];
+      mjCMesh* pmesh = pgeom->mesh;
 
       // write pos/quat if there is a difference
       if (!SameVector(pgeom->pos, pmesh->GetPosPtr(pgeom->typeinertia), 3) ||
@@ -403,10 +403,10 @@ void mjXWriter::OneGeom(XMLElement* elem, mjCGeom* pgeom, mjCDef* def) {
 
   // hfield and mesh attributes
   if (pgeom->type==mjGEOM_HFIELD) {
-    WriteAttrTxt(elem, "hfield", pgeom->hfield);
+    WriteAttrTxt(elem, "hfield", pgeom->hfieldname);
   }
   if (pgeom->type==mjGEOM_MESH || pgeom->type==mjGEOM_SDF) {
-    WriteAttrTxt(elem, "mesh", pgeom->mesh);
+    WriteAttrTxt(elem, "mesh", pgeom->meshname);
   }
 
   // userdata

src/xml/xml_urdf.cc

@@ -573,7 +573,7 @@ mjCGeom* mjXURDF::Geom(XMLElement* geom_elem, mjCBody* pbody, bool collision) {
     // set fields
     pmesh->set_file(meshfile);
     pmesh->name = meshname;
-    pgeom->mesh = meshname;
+    pgeom->meshname = meshname;
     pmesh->set_scale(meshscale);
   }