is a graphical widget
in a GUI
with which continuous text, pictures or anything else can be scrolled
including time in video applications, i.e., viewed even if it does not fit into the space in a computer display
, or viewport.
Usually designed as a long rectangular area on one or two sides of the viewing area, containing a bar (or thumb) that can be dragged along a trough (or track) to move the body of the document as well as two arrows on either end for precise adjustments. The "thumb" has different names in different environments: on the Macintosh it is called a "thumb" on the Java platform it is called "thumb" or "knob"; Microsoft's .NET documentation refers to it as "scroll box" or "scroll thumb"; in other environments it is called "elevator", "quint", "puck", "wiper" or "grip". Additional functions may be found, such as zooming in/out or various application-specific tools. The thumb can also sometimes be adjusted by dragging its ends. In this case it would adjust both the position and the zooming of the document, where the size of the thumb represents the degree of zooming applied. A thumb that completely fills the trough indicates that the entire document is being viewed, at which point the scrollbar may temporarily become hidden.
Scrollbars can be seen as a computer representation of a thumb, with which you thumb through pages of documents.
A scrollbar should be distinguished from a slider which is another widget that works in a similar fashion, the difference being that the slider is used to change values, and does not change the display or move the area that is shown.
While dragging the thumb is historically the traditional way of manipulating the widget, a scroll wheel
may also be used. In addition, the arrow buttons may be clicked to scroll a small amount, or the trough above or below the thumb for a larger amount. Sometimes, both arrow buttons appear next to each other for quick, precise manipulation without having to drag the thumb or move the mouse great distances to the other arrow; one of them may also be duplicated so as to show at both ends of the bar, providing familiarity for those used to both separate and adjacent buttons.
Another system for manipulating them is to look at which mouse button was pressed. For instance, a left-click might cause it to scroll down, while a right click would scroll up, and the middle button could be used to place the thumb precisely. This form requires less fine motor skills, although it requires a multi-button mouse, and possibly a greater degree of GUI literacy.
Special scroll-bar like widgets allow panning around a two dimensional space by simply moving a single rectangle in any direction on the plane. For example the GtkScrollpane is implemented in the text viewers gv and ghostview
Another example for simultaneous two-dimensional scrolling is an alignment program for protein sequences
Initially, the horizontal scroll-bar looks like a conventional one. But then the scroll-bar offers three additional features:
- It provides an overview of the entire scene.
- The height can be enlarged.
- The knob can not only be moved left and right but also up and down for vertical scrolling.
The ability and specific methods needed to customize the look and function of scrollbars
can vary significantly based on which operating system
or software application
you are attempting to customize. The most commonly used method of altering the look-and-feel of the scrollbar in Web pages
is to use a set of non-standardized CSS
directives which at the time of this writing were only supported by Microsoft Internet Explorer
versions 5.x or higher.
An example of customization is the Find feature in Google Chrome. Chrome places marks in the trough of the vertical scroll bar to indicate the places where it found the term the user is searching for.