scroll bar

graphics A widget found in graphical user interfaces and

used to show and control ("scroll") which portion of a

document is currently visible in a window. A window may have

a horizontal or, most often, vertical scroll bar or both.

A vertical scroll bar is a narrow strip drawn up the side of

the window containing a "bubble" whose position in the scroll

bar represents the position of the visible part within the

whole document. By dragging the bubble with the mouse the

user can scroll the view over the entire document. Arrow

buttons are usually provided at the end(s) of the scroll bar

to allow the window to be scrolled by a small amount, e.g. one

line of text, in either direction by clicking them with the

mouse. Some programs provide a second pair of buttons for

scrolling a page at a time or some other unit. Clicking on

the scroll bar outside the bubble will either, depending on

the particular WIMP, move the bubble to that point or move

it some amount (typically a screenful) in that direction.

Different WIMP systems define different standards for

whether scroll bars appear on the left or right, top or bottom

of the window, and for their behaviour.

To reduce mouse movement, the up and down scroll buttons

should either be next to each other at one end of the scroll

bar (as in NEXTSTEP) or should reverse their effect when

clicked with the right-hand mouse button (as in the X WindowSystem and RISC OS). The fraction of the scroll bar filled

by the bubble should indicate the fraction of the document

visible in the window.

(1998-06-26)