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Chapter: Graphics and Multimedia - Output Primitives

Input Techniques

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

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


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