A program with the same approximate purpose as a kaleidoscope: to make pretty pictures. Famous display hacks include munching squares, smoking clover, the BSD Unix "rain(6)" program, "worms(6)" on miscellaneous Unixes, and the X "kaleid(1)" program. Display hacks can also be implemented without programming by creating text files containing numerous escape sequences for interpretation by a video terminal; one notable example displayed, on any VT100, a Christmas tree with twinkling lights and a toy train circling its base. The hack value of a display hack is proportional to the aesthetic value of the images times the cleverness of the algorithm divided by the size of the code. Synonym psychedelicware.

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