There's an even simpler algorithm if you're fine with "close enough" circles: https://news.ycombinator.com/item?id=15266331

I love Yurichev's books on assembly language, and he gives them away (CC-BY-4.0).

https://beginners.re/

You can always try Bresenham’s circle drawing algorithm.

With the error initialized to zero, this algorithm will always step immediately after drawing the first pixel, which will cause that pixel to "stick out".

  y += 1;          // y == 1
  err += 2*y + 1;  // err == 3
  x -= 1;          // x == radius-1
  err -= 2*x + 1;  // err == 2-(2*(radius-1))

And you don't need calculus to come up with the algorithm, just simple high school algebra: (x+1)² - x² = 2x + 1.

> It requires only additions, subtractions and bit shifts: 2x is the same as x<<1, of course. It also requires only integer arithmetic.

Does any of this mean anything in JS, where AFAIK there are no real ints? 2x is an fpu operation under the hood, and not a bit shift.

This is how we did it on the C64, back in the 80's :-D