Most books would have you believe that the development of line drawing algorithms ended with Bresenham's famous algorithm. But there has been some signifcant work since then. The following 2-step algorithm, developed by Xiaolin Wu, is a good example. The interesting story of this algorithm's development is discussed in an article that appears in Graphics Gems I by Brian Wyvill.

The two-step algorithm takes the interesting approach of treating line drawing as a automaton, or finite state machine. If one looks at the possible configurations that the next two pixels of a line, it is easy to see that only a finite set of possiblities exist.

The two-step algorithm also exploits the symmetry of line-drawing by simultaneously drawn from both ends towards the midpoint.

The code, which is here, is a bit long to show an a slide.