The marching ants effect is an animation technique often found in selection tools of computer graphics

Computer graphics

Computer graphics are graphics created using computers and, more generally, the representation and manipulation of image data by a computer with help from specialized software and hardware....

 programs. It helps the user to distinguish the selection border from the image background by animating the border. The border is a dotted or dashed line where the dashes seem to slowly walk sideways and up and down. This creates an illusion of ants marching in line as the black and white parts of the line start to move. Some prefer the term marquee selection, as effect resembles the chaser lights of a marquee

Marquee (sign)

A marquee is most commonly a structure placed over the entrance to a hotel or theatre. It has signage stating either the name of the establishment or, in the case of theatres, the play or movie and the artist appearing at that venue...

, and this term can be considered a synonym. Popular graphics programs, such as Gimp

GIMP

GIMP is a free software raster graphics editor. It is primarily employed as an image retouching and editing tool and is freely available in versions tailored for most popular operating systems including Microsoft Windows, Apple Mac OS X, and Linux.In addition to detailed image retouching and...

 and Adobe Photoshop, implement their selection tools using the marching ants effect. The technique was first widely used by the MacPaint

MacPaint

MacPaint was a bitmap-based graphics painting software program developed by Apple Computer and released with the original Macintosh personal computer on January 22, 1984. It was sold separately for US$195 with its word processor counterpart, MacWrite. MacPaint was notable because it could generate...

 program developed by Bill Atkinson

Bill Atkinson

Bill Atkinson is an American computer engineer and photographer. Atkinson worked at Apple Computer from 1978 to 1990. He received his undergraduate degree from the University of California, San Diego, where Apple Macintosh developer Jef Raskin was one of his professors...

.

The easiest way to achieve this animation is by drawing the selection using a pen pattern that contains diagonal lines. If the selection outline is only one pixel thick, the slices out of the pattern will then look like a dashed line, and the animation can easily be achieved by simply shifting the pattern one pixel sideways and redrawing the outline. The method has the disadvantage of not looking like marching ants with selection borders that aren't parallel to the coordinate axes.

Origin of this idea

With the selection problem in mind, Bill Atkinson went to his favorite pub in Los Gatos. Something on the wall caught his attention. It was the "Hamm's" beer sign. The beer sign was composed of a kind of animated waterfall. Water seemed to flow down the waterfall into the lake. Bill figured that this effect could solve his problem because it is easily recognizable.

He implemented the idea and showed it to Rod Perkins from the Lisa

Apple Lisa

The Apple Lisa—also known as the Lisa—is a :personal computer designed by Apple Computer, Inc. during the early 1980s....

team, who told Bill the effect reminded him of "marching ants".

External links

• Fun with marching ants describes another scheme for generating the marching ants pattern