Designing control in games is challenging in any case, however it is even harder on mobile devices, where our capabilities are very limited by the size of the device.
In the event that our game requires the use of a screen controller, the first challenge is to place it so that it is easy to use and that no button can be pressed by accident. Control with the display controller has one main advantage: the player does not obstruct the view of the fingers. This is a big problem for games that require clicking objects across the entire display surface. This is of course not a problem in games that are not focused on the action. However, in high-speed games, requiring immediate response screen obscuration can have bad consequences for the player and lead to his frustration.
Due to the limited space, the control must be designed to be as simple and effective as possible. Often you should look for solutions that can simplify the game. It seems that the complexity of control in games for mobile devices is one of the most important factors influencing the success of the game. Most games for phones and tablets are extremely simple. It often comes down to support two or three buttons, or clicking something on the screen.