Voronoi diagram is a method of partitioning a plane into different regions based on its proximity to certain reference points. The screen capture below shows the reference points as white dots and each pixel in the image is colored based on its proximity to a reference point. A shader program is written to compute distance from each pixel to the reference points and its color is set according to the point of nearest distance.
Press 'A' for this display. A point follows cursor movement and corresponding voronoi patten.
Press 'U' for this display. Animated movement of voronoi points. 
Reference The Book of Shaders