Enable reading textures from spec in Python

PiperOrigin-RevId: 842151742
Change-Id: I477d118cc7e2385d29b395b192fa89e9facb9c3e

python/mujoco/specs.cc

@@ -134,6 +134,41 @@ void DefineArray(py::module& m, const std::string& typestr) {
       }, py::keep_alive<0, 1>(), py::return_value_policy::reference_internal);
 };
 
+// Specialization for std::byte to convert to int for Python iteration
+template <>
+void DefineArray<std::byte>(py::module& m, const std::string& typestr) {
+  using Class = MjTypeVec<std::byte>;
+  py::class_<Class>(m, typestr.c_str())
+      .def(
+          py::init([](std::byte* data, int size) { return Class(data, size); }))
+      .def("__getitem__",
+           [](Class& v, int i) -> int {
+             if (i < 0 || i >= v.size) {
+               throw py::index_error("Index out of range.");
+             }
+             return static_cast<int>(v.ptr[i]);
+           })
+      .def("__setitem__",
+           [](Class& v, int i, int c) {
+             if (i < 0 || i >= v.size) {
+               throw py::index_error("Index out of range.");
+             }
+             if (c < 0 || c > 255) {
+               throw py::value_error("Value out of range [0, 255].");
+             }
+             v.ptr[i] = static_cast<std::byte>(c);
+           })
+      .def("__len__", [](Class& v) { return v.size; })
+      .def(
+          "__iter__",
+          [](Class& v) {
+            return py::make_iterator(
+                reinterpret_cast<unsigned char*>(v.ptr),
+                reinterpret_cast<unsigned char*>(v.ptr + v.size));
+          },
+          py::keep_alive<0, 1>(), py::return_value_policy::reference_internal);
+};
+
 py::list FindAllImpl(raw::MjsBody& body, mjtObj objtype, bool recursive) {
   py::list list;
   raw::MjsElement* el = mjs_firstChild(&body, objtype, recursive);