Comment by skybrian

Neat! I had forgotten about that. Not entirely text-based, then.

I went looking for what primitive drawing commands it was built on, and it’s barely mentioned:

> The details of how primitive painters are implemented depend on the particular characteristics of the graphics system and the type of image to be drawn. For instance, suppose we have a procedure draw-line that draws a line on the screen between two specified points. Then we can create painters for line drawings.

That’s a pretty typical avoidance of I/O. (Also, generating static pictures is rather different than reacting to input.)