Raymarching
A 3D rendering technique where the camera "walks" through space in small steps until it hits a surface — compact enough to fit in a tiny shader program.
Raymarching renders 3D scenes without storing polygons or complex geometry. Instead, objects are defined mathematically, and the algorithm steps through space from the camera for each pixel, testing the distance to the nearest surface until it either hits something or travels far enough to miss. This allows wildly complex fractal shapes, volumetric effects, and impossible geometries — all in a few hundred bytes of shader code. The technique became popular in the demoscene around the 2000s as a way to create visually complex worlds without the polygon overhead of traditional 3D rendering.