Ray marching / Distance Fields

Might be similar to https://github.com/CodingRainbow/Rainbow-Topics/issues/14 (ray marching, marching cubes, ray casting, ray tracing... what is the difference?)

Mind was blown by this talk: [NVScene 2015 Session: How to Create Content with Signed Distance Functions (Johann Korndorfer)](https://www.youtube.com/watch?v=s8nFqwOho-s)
but there's an assumption that the viewer knows some basic things about GLSL

ref:
http://iquilezles.org/www/articles/distfunctions/distfunctions.htm
http://www.iquilezles.org/www/articles/terrainmarching/terrainmarching.htm
http://www.viz.tamu.edu/faculty/ergun/research/implicitmodeling/papers/sm99.pdf
http://www.hugi.scene.org/online/hugi37/hugi%2037%20-%20coding%20adok%20on%20ray%20casting,%20ray%20tracing,%20ray%20marching%20and%20the%20like.htm

Start by comparing the linked related issue and the referenced ray-marching, terrain-marching, and implicit-modeling resources. Define the intended educational scope, including how ray marching, marching cubes, ray casting, ray tracing, signed distance functions, and GLSL should be covered. Done means the project has an agreed topic specification and implementation or content location.

Scritto dal modello di indicizzazione a partire dal testo della issue.