Add built-in sphere mesh.

PiperOrigin-RevId: 791162850
Change-Id: I573a414727e79f1a495e0f2282b2faff48ab3443

python/mujoco/specs.cc

@@ -1014,6 +1014,15 @@ PYBIND11_MODULE(_specs, m) {
       },
       py::arg("resolution") = std::array<int, 2>{0, 0},
       py::arg("fov") = std::array<double, 2>{0, 0}, py::arg("gamma") = 0);
+  mjsMesh.def(
+      "make_sphere",
+      [](raw::MjsMesh* self, int subdivision) {
+        double params[1] = {static_cast<double>(subdivision)};
+        if (mjs_makeMesh(self, mjMESH_BUILTIN_SPHERE, params, 1)) {
+          throw pybind11::value_error(mjs_getError(mjs_getSpec(self->element)));
+        }
+      },
+      py::arg("subdivision"));
   mjsMesh.def(
       "make_hemisphere",
       [](raw::MjsMesh* self, int subdivision) {

python/mujoco/specs_test.py

@@ -499,12 +499,16 @@ class SpecsTest(absltest.TestCase):
     mesh = spec.add_mesh(name='hemisphere')
     mesh.make_hemisphere(subdivision=4)
 
+    mesh = spec.add_mesh(name='sphere')
+    mesh.make_sphere(subdivision=2)
+
     model = spec.compile()
-    self.assertEqual(model.nmesh, 4)
+    self.assertEqual(model.nmesh, 5)
     self.assertEqual(model.mesh_vertnum[0], 25 * 25)
     self.assertEqual(model.mesh_vertnum[1], 10)
     self.assertEqual(model.mesh_vertnum[2], 7)
     self.assertEqual(model.mesh_vertnum[3], 2 * (4 + 1) * (4 + 2) + 2)
+    self.assertEqual(model.mesh_vertnum[4], 2 + 10 * 4**2)
 
   def test_compile_errors_with_line_info(self):
     spec = mujoco.MjSpec()