This document discusses different types of input devices used in graphics programs. It describes six logical device classifications - locator, stroke, string, valuator, choice, and pick devices. Locator devices input coordinate positions, stroke devices record sequences of coordinates, string devices input text, valuator devices set parameter values, choice devices select menu options, and pick devices select parts of an image. Examples of physical devices that can be used for each logical device type are provided. Approaches for uniquely identifying picked objects include distance calculations and highlighting potentially selected objects.

1. S.RAJAPRIYA
Assistant Professor of IT
rajapriya@vvvcollege.org

2.  Graphics programs use several kinds of input
data.
 Picture specification need values for
Coordinate positions
Character string parameters
Scalar values for transformation
Menu options
Identification of picture parts

3.  There are six logical device classification used
by PHIGS and GKS.
LOCATOR devices
STROKE devices
STRING devices
VALUATOR devices
CHOICE devices
PICK devices

4.  A device for specifying a coordinate
position(x,y)
 Positioning the screen cursor at some
location in a displayed scene
 Example of physical device: mouse, trackball,
space-ball, thumbwheels,dials etc.,
 Keyboards can be used for locator input in
several device.
 Light pens have also been used.

5.  To input a sequence of coordinate positions
 Physical device for generating locator input
 Translate continuous movement of cursor
positioning device, such as mouse, into a
series of input coordinate values
 The graphics tablet is one of the more
common stroke device.
 Button activation can be used to place the
tablet in continuous mode

6.  Primary physical device used for string input
– keyboard.
 Used for picture or graph labelling in
computer-graphics applications

7.  To set the scalar value for geometric
transformations, viewing parameters and
illumination parameters
 Also used for setting physical parameter such as
temperature, voltage levels, stress factors,etc.,
 Example of physical device:
a panel of control dials, joystick, tablet
 Other technique for providing valuator input:
Display the graphical representation of
sliders, buttons, rotating scales and menu on the
video monitor

8.  Menus, typically used in graphics programs to select
processing options, parameterValues and object shape
 Cursor positioning device are commonly choice device for
a selecting menu
 Determine a menu item is selected by the cursor position
(x,y) :
•For a menu item with vertical and horizontal boundaries
(xmin,xmax,ymin,ymax)
•If the cursor position satisfy the condition
xmin<=x<=xmax ymin<=y<=ymax
•The menu is selected with the cursor position
• The other choice devices are keyboard an voice entry.

9.  To select a part of a scene that is to be
transformed or edited in some way
 Picking can be performed by positioning the
screen cursor and pressing a button or key to
record the pixel coordinates
 Example of physical device: mouse, joystick,
keyboard
 Other pick methods include highlighting
schemes, selecting object by name or a
combination of methods

10.  Coordinate-extent tests do not uniquely identify a pick
object
 Approach 1:Compute the distances from the pick position to
individual line segments
 Calculate the perpendicular distance squared from a pick
position to the line position to the line
 For a line segment with endpoints (x1, y1) , (x2, y2),the
perpendicular distance squared from a pick position (x, y) is

11.  Approach 2:
 Associate a pick window with a selected cursor position–the
pick window is centered on the cursor position
 Example: A pick window with center (x,y), width w and
height h
Highlighting
 other method used to facilitate picking
 other method used to facilitate picking successively highlight
those objects whose coordinate extent overlap a pick
position (or pick window)
 user could issue accept or reject action after the object is
highlighted