There is a recent trend of coding with an overlay editor on top of the live result, changing as the code gets written and modified. I suspect it originates on one hand from the work of the folks at Sexy Visuals and some of the videos Iñigo Quilez has been publishing demonstrating some concepts, including a basic raytracer in less than half an hour. And on the other hand, on Shader Toy (made by the same usual suspect), a web page using WebGL to allow fast GLSL shader prototyping in a browser.
It was only a question of time before someone would merge both concepts. Thus Ricardo Cabello (often known as Mr Doob) sparked off a lot of effervescence when he published his GLSL Sandbox. People would try many things, give feedback and advices, someone would quickly come up with a gallery… But after various toy experiments by various people, IQ would come back and make waves with his procedural apple. He also published another live coding video, showing how it was made.