UI will appear if user press "ESC" while using take control the ruler.

When user launch the game and press "C" to take control of the ruler. After that press "ESC". Notice that UI will appear if user press "ESC" while using take control the ruler. User still able to control the ruler using keyboard button "W" "A" "S" "D", but the mouse function change to the UI mode.

Please see the attachment for more details in this link.