System.Timer.Timer的lock争用问题

[__Meow]

好奇Win8的Loading动画，故尝试winform实现之。现在的问题是多个线程(Timer)共用一个Graphics对象(lock)，出现了争用引起的错位问题，废话不多，上Code……

//辅助类
static class Common
    {
        //圆心
        public static Point CenterPoint = new Point(25, 25);
        //包围矩形
        public static Rectangle Rect = new Rectangle(0, 0, 50, 50);

        //绘图委托
        public delegate void DrawDelegate();

        //最慢速临界角度
        public const int slowAngle_1 = 315;
        public const int slowAngle_2 = 135;

        //最快速临界角度
        public const int quickAngle_1 = slowAngle_1 + 90 - 360;
        public const int quickAngle_2 = slowAngle_2 + 90;

        /// <summary>
        /// 根据半径、角度求圆上坐标
        /// </summary>
        /// <param name="radius">半径</param>
        /// <param name="angle">角度</param>
        /// <returns>坐标</returns>
        public static Point GetDotLocationByAngle(int radius, int angle)
        {
            int x, y;

            x = (int)(CenterPoint.X + radius * Math.Cos(angle * Math.PI / 180));
            y = (int)(CenterPoint.Y + radius * Math.Sin(angle * Math.PI / 180));

            return new Point(x, y);
        }
    }

//窗体类
public partial class Form1 : Form
    {
        Dot[] dots = new Dot[5];

        //当前活动点索引(用于辅助支持线程同步)
        //public static int CurrentDotIndex = 0;

        //public static object lockobj = new object();

        public Form1()
        {
            InitializeComponent();

            for (int i = 0; i < dots.Length; ++i)
            {
                dots[i] = new Dot(i, this.CreateGraphics());
            }
        }

        /// <summary>
        /// 变更活动点
        /// </summary>
        //public static void NextDot()
        //{
        //    lock (lockobj)
        //    {
        //        if (CurrentDotIndex < 4)
        //            ++CurrentDotIndex;
        //        else
        //            CurrentDotIndex = 0;
        //    }
        //}

        private void button1_Click(object sender, EventArgs e)
        {
            for (int i = 0; i < dots.Length; ++i)
            {
                dots[i].Start();
            }
        }
        
    }//end of class Form1

/// <summary>
    /// 表示一个“点”
    /// </summary>
    internal sealed class Dot
    {
        readonly int m_index;
        /// <summary>
        /// 点位于点数组中的索引(0~4)
        /// </summary>
        public int Index
        {
            get { return m_index; }
        }

        bool m_isVisible;
        /// <summary>
        /// 是否可见
        /// </summary>
        public bool IsVisible
        {
            get { return m_isVisible; }
            set { m_isVisible = value; }
        }

        //点坐标
        Point m_location;
        //角度
        int m_angle;
        //定时器
        System.Timers.Timer m_tmr;
        //图形
        Graphics m_graphics;

        /// <summary>
        /// 构造点
        /// </summary>
        /// <param name="index">点位于点数组中的索引(0~4)</param>
        /// <param name="g">图形</param>
        public Dot(int index, Graphics g)
        {
            if (index < 0 || index > 4)
                throw new IndexOutOfRangeException("索引必须在0~4之间");

            m_index = index;
            m_isVisible = false;
            m_tmr = new System.Timers.Timer(30);
            m_tmr.Elapsed += m_tmr_Elapsed;
            m_graphics = g;
            m_angle = 312 - m_index * 12;
        }

        void m_tmr_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
        {
            //if (this.InvokeRequired)
            //{
            //    DrawDelegate draw = Draw;
            //    this.BeginInvoke(draw);
            //}

            Console.WriteLine(m_tmr.Interval);

            //if (Form1.CurrentDotIndex == m_index)
            //{
                //Common.DrawDelegate drawdele = Draw;
                //drawdele();
                Draw();

                m_angle = m_angle >= 356 ? 0 : m_angle + 4;

                #region ChangeTimerInterval

                if (m_angle >= Common.slowAngle_1 || m_angle < Common.quickAngle_1)//因涉及到359变0，此处为||而不是&&
                {
                    if (m_tmr.Interval > 2)
                    {
                        m_tmr.Interval -= 2;
                    }
                    else if (m_tmr.Interval > 0.1)
                    {
                        m_tmr.Interval -= 0.1;
                    }
                    else if (m_tmr.Interval > 0.01)
                    {
                        m_tmr.Interval -= 0.01;
                    }
                    else if (m_tmr.Interval > 0.001)
                    {
                        m_tmr.Interval -= 0.001;
                    }
                }
                else if (m_angle >= Common.quickAngle_1 && m_angle < Common.slowAngle_2)
                {
                    if (m_tmr.Interval < 30)
                    {
                        ++m_tmr.Interval;
                    }
                }
                else if (m_angle >= Common.slowAngle_2 && m_angle < Common.quickAngle_2)
                {
                    if (m_tmr.Interval > 2)
                    {
                        m_tmr.Interval -= 2;
                    }
                    else if (m_tmr.Interval > 0.1)
                    {
                        m_tmr.Interval -= 0.1;
                    }
                    else if (m_tmr.Interval > 0.01)
                    {
                        m_tmr.Interval -= 0.01;
                    }
                    else if (m_tmr.Interval > 0.001)
                    {
                        m_tmr.Interval -= 0.001;
                    }
                }
                else if (m_angle >= Common.quickAngle_2 && m_angle < Common.slowAngle_1)
                {
                    if (m_tmr.Interval < 30)
                    {
                        ++m_tmr.Interval;
                    }
                }
                #endregion

            //    Form1.NextDot();
            //}
        }

        public void Start()
        {
            if (!m_tmr.Enabled)
                m_tmr.Start();
        }

        public void Stop()
        {
            if (m_tmr.Enabled)
                m_tmr.Stop();
        }

        /// <summary>
        /// 绘制
        /// </summary>
        private void Draw()
        {
            lock (m_graphics)
            {
                Rectangle rect = new Rectangle(m_location, new Size(3, 3));

                //m_graphics.DrawEllipse(Pens.RoyalBlue, rect);
                m_graphics.FillEllipse(Brushes.RoyalBlue, rect);//Erase last frame

                m_location = Common.GetDotLocationByAngle(25, m_angle); 

                rect = new Rectangle(m_location, new Size(3, 3));
                m_graphics.FillEllipse(Brushes.White, rect);
            }
        }
        
    }//end of class Dot

我用一个Dot对象表示一个“点”，每个Dot有自己的timer，但共用一个由窗体创建的Graphics，线程争用问题导致点的顺序会乱，求各位大神给个解决方案……万谢……
PS：各位大神可以新建个winform运行下，错位在转一圈之后就很明显了

[__Meow]

自己顶，求大神指点……

[__Meow]

不要沉啊………………不要沉啊………………

[__Meow]

自己顶起啊………………

[MX_小市民]

我了个去啊，我也要帮咖啡胸顶起，顶起，顶起，顶起，顶起，顶起，顶起，顶起，顶起