To apply the midpoint method, we define
(a) ?circle(x, y)= x ^2+ y ^2-? r?^2
(b) ?circle(x, y)= x+ y ^2-? r?^2
(c) ?circle(x, y)= x ^2– y ^2-? r?^2
(d) ?circle(x, y)= x^2+ y ^2-? z?^2
This question was addressed to me in an interview for job.
My question comes from Line Filling Algorithms topic in chapter Graphics Primitives of Computer Graphics