Shadertoy.com is a cross-browser online community and tool for creating and sharing shaders through WebGL, used both for learning and teaching 3D computer graphics in a web browser.
https://en.wikipedia.org/wiki/Shadertoy
https://www.shadertoy.com/
https://gamedevelopment.tutsplus.com/tutorials/a-beginners-guide-to-coding-graphics-shaders--cms-23313