Despite seeing code early in the series, didn't see any code that would actually put pixels on a screen, or even to write a static image into a file, at least not within the first 6 or 7 units. Somewhere around that point there is some reference to OpenGL, so presumably you could start to brighten patches of screen at that point?

Offering this as constructive criticism - the tutorials could be more engaging if the student could follow along and cause things to happen directly on the screen. It'd be awesome to organize the 1st unit as more than just confirming one has a compiler, to take it all the way to a kind of "hello, pixels".