I think I will use the same method as I do for Bézier curves to step along the circumference.
Another generalisation I had to make from the circle code is with respect to the normal. For a circle of radius r, centred on the origin, and parameterised by angle θ, a point on the circle is (r cos θ, r sin θ). And the normal is exactly the same: the point vector is normal to the circle.
For an ellipse, this is not the case. For an ellipse with half-dimensions a and b, centred on the origin, and parameterised by angle θ, a point on the ellipse is (a cos θ, b sin θ). But the normal is (b cos θ, a sin θ).
(Of course, the ellipse form degenerates to the circle form when a = b.)