My first experience with metaballs was in 3D as a feature in Truespace (https://en.wikipedia.org/wiki/TrueSpace https://en.wikipedia.org/wiki/TrueSpace) where t

My first experience with metaballs was in 3D as a feature in Truespace (https://en.wikipedia.org/wiki/TrueSpace https://en.wikipedia.org/wiki/TrueSpace) where they were used for modeling. In order to render a surface you have to either use a contouring algorithm like marching cubes to generate a mesh like the above three.js demo, or raytrace or raymarch them. Because metaballs describe a distance function, its really easy to use SDF raymarching and there is a whole category dedicated to metaball shaders on shader toy (https://www.shadertoy.com/results?query=tag%3Dmetaballs https://www.shadertoy.com/results?query=tag%3Dmetaballs).