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In computer graphics and television, scrolling or text crawling is the act of sliding a horizontal or vertical presentation of content, such as text, drawings, or images, across a screen or display window. Scrolling is often used to show reams of data longer than the viewport. The word scroll is derived from the way in which people read scrolls of paper, by rolling up the top of the page and allowing objects lower on the page to move up.
On a computer, scrolling may be performed by software running on a computer's CPU, or it may be done by performing some operation on a dedicated 2D computer graphics chip.
In a WIMP-style graphical user interface, scrolling is done with the help of a scrollbar or using keyboard shortcuts, often the arrow keys. Scrolling is often a key feature in text user interfaces and command line interfaces, though some older computer terminals used a paging mode instead, akin to flipping through a series of pages in a book, usually using the PgUp/PgDn keys. Modern computer mice may also have a scroll wheel, which scrolls text vertically when rolled.
There are also more advanced scrolling functionalities available with the mouse, though they vary widely between different pieces of software. Most scroll wheels can be pressed down, functioning like a button. Depending on the software, this typically allows scrolling in both the horizontal and vertical directions by dragging in the direction desired; when the mouse is moved to the original position, scrolling stops. A few scroll wheels can also be tilted, scrolling horizontally in one direction until released. Software like Adobe Reader can also be scrolled with the hand tool. In this case, the document is dragged and moved around like a piece of paper.
If any content is too wide to fit on a display, horizontal scrolling is often required to view all of it. For text, this is often considered impractical and annoying, as the user must scroll back and forth in two dimensions, instead of just up and down. Such a problem is very common on certain websites. However, in other applications, like graphics and spreadsheets, horizontal scrolling is useful and necessary.
Scrolling texts, also referred to as scrolltexts or scrollers, were an integral feature of the majority of the demos written for home computers in the 1980s. They were particularly important in crack intros programmed by software crackers, where they were used to convey messages between groups involved in the activity.
Many scrollers were plain horizontal scrollers, but demo coders also paid a lot of attention in finding new and different types of scrolling. The characters could, for example, continuously alter their shape, take unusual flying paths or incorporate color effects such as raster bars.
Scrolling is commonly used to display the credits at the end of television shows.
Scrolling is also used in television news when a news ticker is employed, scrolling news stories horizontally across the bottom of the screen.
In computer and video games, scrolling of a playing field allows the player to control an object in a large contiguous area. Super Bug pioneered this method. Parallax scrolling, which was first featured in Moon Patrol, involves several semi-transparent layers, which scroll on top of each other at varying rates in order to give the illusion of depth.
A previously much used alternative to video game scrolling is the flip-screen method.