FloodFill fix 3

        public static void FloodFill(PixelManipulator manipulator, Point position, Pixel targetColor, Pixel replaceColor, byte threshold)
        {
            unchecked
            {
                manipulator.Position = position;

                if (!manipulator.Current.Similar(targetColor, threshold))
                    return;

                Queue<Point> q = new Queue<Point>((manipulator.Width * manipulator.Height));
                q.Enqueue(manipulator.Position);
                HashSet<Point> visitedNodes = new HashSet<Point>();

                while (q.Count > 0)
                {
                    Point n = q.Dequeue();
                    if (n.X < 0 || n.Y < 0 || n.X >= manipulator.Width || n.Y >= manipulator.Height || visitedNodes.Contains(n))
                    {
                        continue;
                    }

                    visitedNodes.Add(n);
                    manipulator.Position = n;
                    if (!manipulator.Current.Similar(targetColor, threshold))
                    {
                        continue;
                    }

                    manipulator.Current = replaceColor;
                    q.Enqueue(new Point(n.X - 1, n.Y)); //Left
                    q.Enqueue(new Point(n.X + 1, n.Y)); //Right
                    q.Enqueue(new Point(n.X, n.Y - 1)); //Top
                    q.Enqueue(new Point(n.X, n.Y + 1)); //Bottom
                }
            }
        }