Event generating hardware

Event devices can be categorized as relative locator, absolute locator, or string. The event(FP) manual page lists the defined constants that represent these classes. Most mice and trackballs are examples of relative locator devices. They are termed ``relative'' devices because the mouse generates events when it is moved relative to its previous position. The motion of the mouse generates the events, not the final position of the mouse. Relative locations are reported as signed 32-bit quantities. Bit-pads and light pens are absolute locator devices. The pens are used on a sensitive pad, and the events are generated by the absolute position of the pen on the pad, not the relative motion of the pen. Absolute locations are reported as unsigned 32-bit quantities. The keyboard is a string graphics input device. This means that the events will be generated by pressing a key on the keyboard, such as an arrow key. Some devices can operate in multiple modes. For example, some mice can function in bitpad mode with the appropriate bitpad software.

Many event devices have buttons; others do not. Three-button devices are viewed as having a left button, a middle button, and a right button. Two-button devices do not have a middle button. One-button devices have only a middle button. Bits representing buttons are set to 1 when the button is depressed. Up to eight buttons can be read at a time. The event(FP) manual page lists macros used to identify buttons.