How to create submenus (or multiple command UIs)

从 issue 中展示的 Command UI callback 以及 ImGui::InputInt 和 ImGui::Button 的用法开始。确定如何让持久化的半径输入框或独立子菜单在多次 callback 调用之间保持可见，并定义应将哪种交互视为完成；issue 未指定任何文件或测试。

I have some UI

Everything into the Command UI is a Imgui::Button inside the callback

    ImGui::InputInt("Radius", &radius);

    ImGui::SameLine();

    //
    // Button
    if (ImGui::Button("Max Curvature"))
    {
        // get mesh
        polyscope::registerSurfaceMesh("mesh", V, F);
        
        // Compute curvature directions via quadric fitting
        MatrixXd PD1, PD2;
        VectorXd PV1, PV2;
        std::vector<Index> bv = {};
        
        igl::principal_curvature(V, F, PD1, PD2, PV1, PV2, bv, radius);
        
        polyscope::getSurfaceMesh("mesh")
            ->addVertexScalarQuantity("Max Curvature", PV1,
                                      polyscope::DataType::SYMMETRIC);
        
    }

pretty standard. Now I'd like to add the "radius" input inside the button scope, so that when I press the button all the relevant data is presented to the user.
Of course, if I simply put the input widget code inside the button one the input widget is just show for an instant then deleted, as the callback runs over and over.
The best option would be to create a separate sub-UI, possibly opening down below the command UI itself. Or to create multiple command UIs.
Is there a way?
Thank you