This is done with a scope, taken from the original by johnengineer.com and reported on adafruit. He gets the credit for the very nice and simple Atmel PWM setup. The integrator is fairly standard though.
The GT 2500 Logo vector processor was a desk-sized unit and it would eventually cause Logo to give the error "TOO MANY LINES!" This turned out to be a blessing as kids never had to worry about stop rules in their recursive procedures!
Later the TI 99/4 used tiles instead of bitmap graphics, and it gave the error "OUT OF TILES!" to similar effect.
Logo for the Apple II didn't run out of lines or tiles, nor did the C64 Logo or Mac Logo, or the various implementations that Brian Harvey did before.
The hard part was already there. I just added turtle graphics. turtle.ino