9.4 Physical Controllers
Physical controllers such as buttons and switches offer a lightweight solution for performing system control, analogous to function keys in desktop systems.
Buttons and switches are a direct way of changing a mode in an application. In contrast to using a pointing device to select, for example, an item from a menu, the physical controller allows the user to directly switch the mode between different states. Examples of well-known techniques are the function keys on a keyboard or buttons on a gaming device to which functions can be assigned. Gamers, for instance, often toggle between weapons in first-person shooters by pressing specific buttons.
9.4.2 Design and implementation issues
Buttons and switches can provide a useful and straightforward system control method; however, there are a number of issues that should be noted.
Placement and Form
When built-in controllers are used, you should carefully validate their placement and the potential need for regrasping a device to access the button, as discussed in section 9.2.1. While some devices are designed carefully from this perspective (e.g., Figure 9.2), other devices may have controllers placed at locations that are less accessible. Furthermore, devices such as tablets or phones often have very flat buttons that may be difficult to reach and control, making system control in handheld AR applications tricky to perform. Thus, it is not only the placement but also the physical form and quality (robustness) of buttons and switches that should be considered carefully.
Figure 9.2 A Thrustmaster flight joystick deploying numerous switches and buttons. (© Guillemot Corporation S.A. All rights reserved. Thrustmaster® is a registered trademark of Guillemot Corporation S.A.)
These controllers are often used eyes-off: finding the right controller can be achieved using proprioceptive feedback but also through the feel of a button when different controllers are located close to each other. When designing new devices or extending existing devices, it is important to carefully evaluate different variants.
Representation and Structure
Buttons and switches are not connected to any menu-like structure. Rather, their structure is based on the placement of buttons and their interrelationship. Button locations on many devices are more often defined by accessibility (ergonomic placement) than by functional structure. This means that mode feedback changes should be clearly communicated to the user, possibly through multiple sensory modalities. It may also make sense to place a small label or pictogram on the button itself to indicate its usage, allowing the user to visually explore the functionality of the buttons before operation.
9.4.3 Practical Application
Buttons and switches are highly useful in a number of situations, in particular when users need to switch frequently between functions. These function keys can be lightweight, quick, and straightforward if users know where to find each button and what it does. However, they can be a burden too when mode change is not clearly communicated, buttons are badly positioned, or there is an unknown functional mapping. In applications that are used for short durations by inexperienced users, function keys may be very useful, but only with a small functional space. For example, for public systems in theme parks, a very limited number of buttons can be easily understood and matched to simple tasks in the system. If users have the time and motivation to learn more complicated sets of functions, this may come with a great increase in performance. Game interfaces are a great example: gamers with prolonged experience with specific button layouts can achieve incredible speeds in performing system control actions. Finally, physical controllers can also be used for symbolic input, as buttons can be directly assigned to certain letters or numbers.