I’ve completed the first cut of the WebGL code for lesson 16; its code still needs significant tidying before I write it up, but I think it looks pretty much right. If you have a WebGL browser (here’s how to get one), click the link in the last sentence, and if you don’t, here’s a YouTube video:
The point of this lesson is to introduce rendering to textures — that is, the process of rendering one WebGL scene into a texture that you can then use in another scene. Directly, render-to-texture is a nice way of producing demos like this. But indirectly, it’s much more useful: it’s the basis of two of the most popular suggestions people made when I asked the other day what I should write tutorials about next, picking and shadows. So lesson 16 will teach a technique that will be incredibly useful later on; don’t miss it!