On latest Samsung galaxy products, phone and tablet, the user interface allows the "navigation bar" to be hidden and use swipes or show a bottom row of system icons with buttons for return functions. In drawing mode, the pallet picks are displayed underneath the navigation bar of system icons and buttons. Or said another way, topodroid requires the user to use a hidden bar with swipes. Using swipes can be difficult with thick device cases that cover the device's edge.
The drawing icons need to optionally in a dropdown menu or the icon bar move up one row if the user has decided to place system functions on the bottom row.
Garry Petrie