41ms to draw a single quad seems incredibly slow, even on ancient hardware - I recall being able to do drawing quite a lot faster than that to a crt even on an old 4MHz z80 cpu in the 1980s.

Is the slowness maybe from the IO to the display or maybe something else?

> You may wonder why I didn't just write a routine to plot filled triangles, and then draw quadrilaterals as two adjacent triangles. The answer is that with the libraries that support exclusive-OR plotting this results in a visible line between the two triangles, because that line is drawn twice; having a dedicated routine to plot quadrilaterals avoids this. In addition, this routine is faster.

I guess the Sega Saturn was on to something, then.

All of this blog's posts are elegant, well-researched, and fun — I'm a big fan. It's amazing what sorts of functionality he squeezes out of 8-bit and other small microcontrollers.