程序代码：

using System;
using System.Collections.Generic;
using using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Drawing.Drawing2D;

namespace MyPaint
{
    public partial class MainForm : Form
    {
        DrawTool currentTool;
        Image image;
        Matrix matrix;

        string path = null;
        public Matrix Matrix
        {
            get { return matrix; }
            set { matrix = value; }
        }
        /// <summary>
        /// 获取当前图像
        /// </summary>
        public Image Image
        {
            get { return image; }
        }
       
        OpenFileDialog opdlg = new OpenFileDialog();
        SaveFileDialog sfdlg = new SaveFileDialog();
        public MainForm()
        {
            InitializeComponent();
            matrix = new Matrix();
            CreateTools();
            currentTool = null;
            sfdlg.Filter = opdlg.Filter = "位图文件(*.bmp)|*.bmp||";
            NewFile();
        }
        //创建要使用的工具
        private void CreateTools()
        {
            DrawTool[] tools = new DrawTool[]{new Zoom(), new MyPen()};
            int x, y, c;
            x = y = c = 0;
            foreach (DrawTool tool in tools)
            {
                RadioButton rb = new RadioButton();
                pnlTools.Controls.Add(rb);
                rb.Appearance = Appearance.Button;
                rb.FlatStyle = FlatStyle.Flat;
                rb.Image = tool.ToolImage;
                rb.TextImageRelation = TextImageRelation.Overlay;
                rb.Left = x;
                rb.Top = y;
                rb.AutoSize = false;
                rb.Width = 32;
                rb.Height = 32;
                rb.Tag = tool;
                if (c++ % 2 > 0) //换行
                {
                    x = 0;
                    y = rb.Bottom + 3;
                }
                else
                {
                    x = rb.Right + 3;
                }
                rb.CheckedChanged += new EventHandler(ToolButtonChange);
            }
        }

        void ToolButtonChange(object sender, EventArgs e)
        {
            RadioButton rb = sender as RadioButton;
            if (!rb.Checked) return;
            if (currentTool != null) currentTool.Clear(this);
            currentTool = rb.Tag as DrawTool;
            pnlPaint.Cursor = currentTool.ToolCursor;
            pnlPaint.Refresh();
        }
        /// <summary>
        /// 绘制图像
        /// </summary>
        public void PaintImage()
        {
            Graphics g = pnlPaint.CreateGraphics();
            g.PageUnit = GraphicsUnit.Pixel;
            g.Transform = matrix;
            g.DrawImage(image, 0, 0);
            pnlPaint.Size = g.ClipBounds.Size.ToSize();
            g.Dispose();
        }
        private void pnlPaint_Paint(object sender, PaintEventArgs e)
        {
            PaintImage();
        }
        private void NewFile()
        {
            path = null;
            image = new Bitmap(640, 480);
            Graphics g = Graphics.FromImage(image);
            g.Clear(Color.White);
            g.Dispose();
        }
        private void OnNewFile(object sender, EventArgs e)
        {
            NewFile();
        }

        private void OpenFile(object sender, EventArgs e)
        {
            if (opdlg.ShowDialog(this) != DialogResult.OK) return;
            image = Image.FromFile(opdlg.FileName);
            pnlPaint.Refresh();
        }

        private void pnlPaint_MouseClick(object sender, MouseEventArgs e)
        {
            if (currentTool == null) return;
            Graphics g = pnlPaint.CreateGraphics();
            pnlPaint.Cursor = currentTool.ToolCursor;
            currentTool.OnMouseClick(this, e);
            g.Dispose();
            pnlPaint.Refresh();
        }

        private void MainForm_KeyDown(object sender, KeyEventArgs e)
        {
            if (currentTool != null)
            {
                currentTool.OnKeyDown(this, e);
            }
        }

        private void MainForm_KeyUp(object sender, KeyEventArgs e)
        {
            if (currentTool != null)
            {
                currentTool.OnKeyUp(this, e);
            }
        }

        private void pnlPaint_MouseMove(object sender, MouseEventArgs e)
        {
            if (currentTool != null)
            {
                currentTool.OnMouseMove(this, e);
            }
        }

        private void OnSave(object sender, EventArgs e)
        {
            if (path == null)
                OnSaveAs(null, null);
            else
                image.Save(path);

        }

        private void OnSaveAs(object sender, EventArgs e)
        {
            if (sfdlg.ShowDialog(this) != DialogResult.OK) return;
            path = sfdlg.FileName;
            OnSave(null, null);
        }

    }
}