Input Techniques

Input Techniques

INPUT OF GRAPHICAL DATA

Two possible ways to see input devices:

•         as a physical device – keyboard, mouse, trackball,  etc.

•         as a logical device – from a programmer perspective – with specified functionality, in graphics more complex

•         the separation of physical and logical levels enable us to make programs more flexible, independent from the actual physical device

Physical input devices:

pointing device – allows to indicate position & send signals/interrupts to the computer – relative/absolute positioning

•        keyboard device   – almost

          physical keyboard – returns

          character codes to a program

Absolute positioning:

•        data tablets

•        light pen

•        joystick – variable-sensitivity

          device & haptic device

•        spaceball – up-down, left-right,

          front-back & 3 independent

          twists

Logical Input Devices

Some APIs (PHIGS, GKS, Direct xx) supports 6 classes of logical input devices – OpenGL does not take this approach

•         Two older APIs (GKS, PHIGS) defined six types of logical input

Locator: return a position

Pick: return ID of an object

Keyboard: return strings of characters

Stroke: return array of positions

Valuator: return floating point number

Choice: return one of n items

Input Modes

•         Input devices contain a trigger which can be used to send a signal to the operating system

Button on mouse

Pressing or releasing a key

•         When triggered, input devices return information (their measure) to the system

Mouse returns position information

Keyboard returns ASCII code

Request Mode

•         Input provided to program only when user triggers the device

•         Typical of keyboard input

Can erase (backspace), edit, correct until enter (return) key (the trigger) is depressed

Event Mode

•         Most systems have more than one input device, each of which can be triggered at an arbitrary time by a user

•         Each trigger generates an event whose measure is put in an event queue which can be examined by the user program

Event Types

•         Window: resize, expose, iconify

•         Mouse: click one or more buttons

•         Motion: move mouse

•         Keyboard: press or release a key

•         Idle: nonevent

Define what should be done if no other event is in queue