I made the live shader editor myself. It uses CodeMirror to display the code, and a webgl canvas for the preview.
Took some work to support having lots of editors on the page. If you do the naïve thing and create a webgl canvas for every one and instantiate all CodeMirror editors at page load time, the whole page would freeze for several seconds. So I create the editors as they are about to be scrolled into view. I also create only one webgl canvas, and when a preview is paused I cache the preview to an img, and move the canvas to the newly active editor instance.
Took some work to support having lots of editors on the page. If you do the naïve thing and create a webgl canvas for every one and instantiate all CodeMirror editors at page load time, the whole page would freeze for several seconds. So I create the editors as they are about to be scrolled into view. I also create only one webgl canvas, and when a preview is paused I cache the preview to an img, and move the canvas to the newly active editor instance.