Scrollbar

A scrollbar is an interaction technique or widget in which continuous text, pictures, or any other content can be scrolled in a predetermined direction (up, down, left, or right) on a computer display, window, or viewport so that all of the content can be viewed, even if only a fraction of the content can be seen on a device's screen at one time. It offers a solution to the problem of navigation to a known or unknown location within a two-dimensional information space. It was also known as a handle in the very first GUIs. They are present in a wide range of electronic devices including computers, graphing calculators, mobile phones, and portable media players. The user interacts with the scrollbar elements using some method of direct action, the scrollbar translates that action into scrolling commands, and the user receives feedback through a visual updating of both the scrollbar elements and the scrolled content.

Although scrollbar designs differ throughout their history, they usually appear on one or two sides of the viewing area as long rectangular areas containing a bar (or thumb) that can be dragged along a trough (or track) to move the body of the document. This can be placed vertically, horizontally, or both in the window depending on which direction the content extends past its boundaries. Two arrows are often included on either end of the thumb or trough for more precise adjustments. The "thumb" has different names in different environments: on the Mac OS X 10.4 it is called a "scroller"; 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"; in certain environments where browsers use agnostic language to the scrollbar terminology, the thumb is referred to as the 'pea' for vertical movement of the bar and still use 'puck' for horizontal movement.

Additional functions may be found, such as zooming in/out or various application-specific tools. Depending on the GUI, the size of the thumb can be fixed or variable in size; in the later case of proportional thumbs, its length would indicate the size of the window in relation to the size of the whole document, indicated by the full track. While proportional thumbs were available in several GUIs, including GEM, AmigaOS and PC/GEOS, even in the mid 1980s, Microsoft did not implement them until Windows 95. A proportional thumb that completely fills the trough indicates that the entire document is being viewed, at which point the scrollbar may temporarily become hidden. The proportional thumb can also sometimes be adjusted by dragging its ends, such as in Sony Vegas, a non-linear video editing software package. 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 scrollbar should be distinguished from a slider which is another visually similar yet functionally different object. The slider is used to change values, but does not change the display or move the area that is shown as a scrollbar does.

In 1974, moving the cursor to the left margin while using Bravo changed its shape to a double-headed arrow to allow for scrolling. Pressing the left or top red button scrolled the content up, and the line next to the cursor went to the top of the window. Pressing the right or bottom blue button scrolled the content down, and the line at the top of the window went down to the cursor. Holding down the middle yellow button changed the cursor to a thumb, allowing for jumping to that percentage of the document with an indicator of current placement.

In 1977, Smalltalk included a stable scrollbar on the left side of the focus window. Clicking at the right half of the scrollbar moved the content up, and the left half moved the content down. The center thumb of the bar could be dragged smoothly and showed the percentage of the content visible; the first proportional scroll bar.

In 1980, Interlisp had a scrollbar that appeared on the left side of the window as the cursor moved towards the left. The bar's shaded thumb showed the percentage of content visible and was controlled by the middle button. The left button scrolled up to move the selected position to the top edge of the window, and the right button scrolled down to move the top edge of the window to the selected position.

Between 1981 and 1982, the Xerox Star moved the scrollbar to the right to get it out of the way and reduce visual clutter. Scroll arrows pointed inwards in the direction the content would move based on user studies, and + and – buttons allowed for scrolling by pages. The thumb was a fixed size diamond, independent of how much of document is visible. Clicking in the thumb elevator region would jump to that part of document.