The Raster bar, also known as Copper bar, is a very popular graphics effect seen on many of the personal computers in the 80’s through 90’s era.

It was widely used in video games and especially graphics demos. Here is a link to the wikipedia article for more detail,

It is accomplished by changing the background color in-between scan lines being drawn on the monitor/screen. This requires  accessing the video controller hardware directly and changing appropriate registers as well as a way to time it precisely with the screen being drawn.

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