If you dig into Adafruit’s GFX library a bit — the drawing library that provides the backbone for most of our displays! — you’ll noticed a reference to Bresenham in the various line or circle functions. Jack Bresenham came up with a simple, efficient way to draw a straight line between two given points, and you come across it a lot on small resource limited embedded systems. Wikipedia has a good article on it, but if you’re interested in line drawing algorithms in general, this power point presentation does a good job of explaining how it really works. Once you understand Bresenham lines, you might want to dig a bit deeper and look at ‘Wu Lines‘ which add high-speed anti-aliasing to the line drawing equation.