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)