OpenGL Shaders
I presented at my local makerspace on this topic on April 24, 2014. I had recently discovered shaders, and became fascinated by how they turn code and math into art. But the also turn the the classic rendering model on its head: instead of rendering an object into pixels, you ask a program what color this pixel right here is.
This presentation explains the basics of how it works and each code example has a real WebGL shader animating that very code.