@RobFarely74 said "I'm sure there's some clever maths doable, whereby you'd calculate the circumference and then work out the amount of degrees you need to increment by. But you'd still be writing pixels that you've already written." So I remixed this project to show two things (1) No pixel re-writing - within one screen refresh, entire circle has been drawn. (2) No math at all.
Thanks to @RobFarely74 for the original project.