Concentric circle generation with no gaps

Concentric.cs

    public static class Concentric
    {
        /// <summary> Enumerates the rings of a circle starting from 1 radius up to the given radius. </summary>
        public static IEnumerable<Point> EnumerateConcentric(int centerX, int centerY, int radius)
        {
            yield return new Point(centerX, centerY);
            for (var r = 1; r <= radius; ++r)
                foreach (var point in EnumerateRadius(centerX, centerY, r))
                    yield return point;
        }

        /// <summary> Enumerates the boundary of a circle at the given radius. </summary>
        public static IEnumerable<Point> EnumerateRadius(int centerX, int centerY, int radius)
        {
            // based on Tony Barrera's "4-connected" circle algorithm (gapless fast concentric circles)
            int determinant = -(radius >> 1);
            int x = 0;
            int y = radius;

            do
            {
                yield return new Point(centerX + x, centerY + y);
                yield return new Point(centerX + x, centerY - y);
                yield return new Point(centerX - x, centerY + y);
                yield return new Point(centerX - x, centerY - y);
                yield return new Point(centerX + y, centerY + x);
                yield return new Point(centerX + y, centerY - x);
                yield return new Point(centerX - y, centerY + x);
                yield return new Point(centerX - y, centerY - x);
                if (determinant <= 0)
                {
                    ++x;
                    determinant += x;
                }
                else
                {
                    --y;
                    determinant -= y;
                }
            } while (x <= y);
        }
    }