C# GDI 绘图 滚动的轮子

刚开始学习C#，试着做一个动画，滚动的轮子。实在不会写，费了很大劲。
大学时候学习计算机图形学，用的Turbo C，现在的电脑运行不了TC的绘图。

lunzi.gif

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Windows.Forms;
using System.Timers;

namespace WinSDITest
{
    
    /// <summary>
    /// Description of MainForm.
    /// </summary>
    public partial class MainForm : Form
    {
        //Timer不要声明成局部变量，否则会被GC回收
        private static System.Timers.Timer aTimer;
        
        private static int centerX = 50;
        private static int centerY = 250;
        private static double a = 0.0;
        private static int r = 50;
        private static int step = 15;
        
        private static Graphics g;
        private static Pen pen;
        private static Point n1;
        private static Point n2;
            
        public MainForm()
        {
            //
            // The InitializeComponent() call is required for Windows Forms designer support.
            //
            InitializeComponent();
            
            //
            // TODO: Add constructor code after the InitializeComponent() call.
            //
            
            //实例化Timer类，设置间隔时间为10000毫秒； 
            aTimer = new System.Timers.Timer(10000);

            //注册计时器的事件
            aTimer.Elapsed += new ElapsedEventHandler(OnTimedEvent);

            //设置时间间隔为2秒（2000毫秒），覆盖构造函数设置的间隔
            aTimer.Interval = 200;

            //设置是执行一次（false）还是一直执行(true)，默认为true
            aTimer.AutoReset = true;

            //开始计时
            //aTimer.Enabled = true;
        
            g = this.CreateGraphics();//创建GDI对像
            pen = new Pen(Brushes.Red);//创建画笔(颜色)
            
            Point n1 = new Point(50, 250);
            Point n2 = new Point(50, 250);
        }
        
        //指定Timer触发的事件
        private static void OnTimedEvent(object source, ElapsedEventArgs e)
        {
            g.Clear(Color.White);
            
            g.DrawLine(pen, 0, 300, 1000,300);
            g.DrawEllipse(pen, centerX - r,200,100,100);
            
            n1.X = centerX + (int)(r* Math.Cos(a));
            n1.Y = centerY + (int)(r* Math.Sin(a));
            n2.X = centerX + (int)(r* Math.Cos(a+Math.PI));
            n2.Y = centerY + (int)(r* Math.Sin(a+Math.PI));
            g.DrawLine(pen, n1, n2);
            
            
            n1.X = centerX + (int)(r* Math.Cos(a+Math.PI/3));
            n1.Y = centerY + (int)(r* Math.Sin(a+Math.PI/3));
            n2.X = centerX + (int)(r* Math.Cos(a+Math.PI + Math.PI/3));
            n2.Y = centerY + (int)(r* Math.Sin(a+Math.PI + Math.PI/3));
            g.DrawLine(pen, n1, n2);
            
            
            n1.X = centerX + (int)(r* Math.Cos(a+Math.PI*2/3));
            n1.Y = centerY + (int)(r* Math.Sin(a+Math.PI*2/3));
            n2.X = centerX + (int)(r* Math.Cos(a+Math.PI+Math.PI*2/3));
            n2.Y = centerY + (int)(r* Math.Sin(a+Math.PI+Math.PI*2/3));
            g.DrawLine(pen, n1, n2);
            
            centerX +=step;
            a += step/50.0;
            
            if(centerX >= 1000)
            {
                centerX = 0;
                //aTimer.Enabled = false;
                //pen.Dispose();  
                //g.Dispose();
            }
        }
    
        void Button1Click(object sender, EventArgs e)
        {
            if(button1.Text == "停止")
            {
                aTimer.Enabled = false;
                button1.Text = "开始";
            }
            else
            {
                button1.Text = "停止";
                //centerX = 50;
                aTimer.Enabled = true;
            }
        }
    }
}