Copy texture coordinates from OBJ into flex. Fixes #2464.

PiperOrigin-RevId: 732109960
Change-Id: I506b3540ab5d489ce8f10d0c473919611ccb654a

src/user/user_flexcomp.cc

@@ -413,6 +413,7 @@ bool mjCFlexcomp::Make(mjsBody* body, char* error, int error_sz) {
   mjs_setString(pf->name, name.c_str());
   mjs_setInt(pf->elem, element.data(), element.size());
   mjs_setFloat(pf->texcoord, texcoord.data(), texcoord.size());
+  mjs_setInt(pf->facetexcoord, facetexcoord.data(), facetexcoord.size());
   if (!centered) {
     mjs_setDouble(pf->vert, point.data(), point.size());
   }
@@ -1055,6 +1056,11 @@ bool mjCFlexcomp::MakeMesh(mjCModel* model, char* error, int error_sz) {
     point[i] = (double) mesh.Vert(i);
   }
 
+  if (mesh.HasTexcoord()) {
+    texcoord = mesh.Texcoord();
+    facetexcoord = mesh.FaceTexcoord();
+  }
+
   // copy faces or create 3D mesh
   if (def.spec.flex->dim == 2) {
     element = mesh.Face();