Jack E. Bresenham, 1965
Rendering in C of the algorithm in "Algorithm for Computer Control of a Digital Plotter", IBM Systems Journal 4(1)
Text reconstructed; exact original not confirmed.
In the summer of 1962 a Calcomp plotter was wired to an IBM 1401 at IBM San Jose, and Bresenham needed to make its pen draw a straight line between two points using only steps of one unit. The machine had no cheap floating point. His answer keeps a single integer error term that says whether the true line has drifted past the midpoint between two pixels, and corrects it with additions and subtractions only.
The paper gives the method as reasoning and a flow chart rather than a listing, so what hangs here is a faithful rendering, not the original text, and the placard says so. The algorithm was in production use in 1962, presented at an ACM meeting in 1963, and published in 1965. Sixty years on it is still how lines are rasterised in hardware, and it is the ancestor of a family of integer-only algorithms for circles and curves. Its beauty is that the inner loop contains nothing that a 1960s machine could not do in a single cycle.