3.1. Input Types.   

Typically these inputs come under the headings of LOCATOR, VALUATOR, PICK, CHOICE, STRING and STROKE input. 


LOCATOR:   inputs a position (x,y) typically via crosshairs.


PICK:      identifies a displayed object NOT just an (x,y).

          PICK picks a whole object that is normally associated with a

          segment via a lightpen (see later section).


CHOICE:    selects from a set of alternatives:

          i.e. integer value from buttons on a box

          or via a menu selection with lightpen, crosshair or digitiser.


VALUATOR:  inputs a value (real or integer) perhaps from a dial

          or from a keyboard.


STRING:    input a string of characters from the keyboard perhaps

          for labelling or a filename.


STROKE:    sequence of (x,y) pairs. Normally from a digitiser and is

          similar to multiple LOCATOR calls.

The Graphical Kernel System (GKS) supports these types of inputs from a workstation. (GKS supports these types of input in three different modes - REQUEST, SAMPLE and EVENT.) In a later section we will look at the devices such as the digitiser or lightpen that could produce these types of input.

Typically interactive devices are used in conjunction with a graphics cursor which tracks the physical cursor: a small cross-hair on the screen following the movement of the pen on a digitiser or the deflection / movement of a trackball, joystick, etc. This tracking and positioning can then be used to pick an object or position the cursor for the next graphics action - draw, delete, shade, etc.

To handle the different types of device we may require special software and/or special hardware to enable good interactive work to be done: quick response of the graphics cursor to the input.

A GKS workstation has only one output device but may have many input devices. For example the Tektronix T4010 with keyboard (VALUATOR, STRING), crosshairs (CHOICE, LOCATOR) and a digitiser (STROKE, CHOICE) would be an adequate, if not archaic, workstation.