C#做的画板 问题请教！！

想用C#做个画板的小程序 不知道为什么不能画出画来 是我的鼠标事件没写对么 没有报错 但是鼠标不能画画
下面是form.cs 请各位帮忙看看 感激不尽
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.IO;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;
namespace WindowsFormsApplication2
{
    public partial class Form1 : Form
    {
        private Shape current;
        private bool isDown;
        private Bitmap bmp, bmp1;
        private List <Shape >shapes=new List<Shape> ();
        private ShapeType type = ShapeType.Line;
        private bool isTrail;
        private FileInfo currentFile;
        private static string openFileName = "";
        private static int lineWidth = 1;        public Form1()
        {
            InitializeComponent();
            bmp = new Bitmap(pictureBox1 .Width ,pictureBox1 .Height );
            bmp1 = new Bitmap(pictureBox1 .Width ,pictureBox1 .Height );
            current = new MyLine();
            this.button12.BackColor = Color.Black;
        }        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            Graphics grfx = e.Graphics;
            grfx.DrawImage(bmp ,0,0);
        }
        private void button1_Click(object sender, EventArgs e)
        {
            isTrail = true;
            type = ShapeType.Line;
        }        private void button2_Click(object sender, EventArgs e)
        {
            isTrail = false ;
            type = ShapeType.Line;        }        private void button3_Click(object sender, EventArgs e)
        {
            isTrail = false;
            type = ShapeType.Rect ;
        }        private void button5_Click(object sender, EventArgs e)
        {
            isTrail = false;
            type = ShapeType.Ellipse ;
        }        private void button4_Click(object sender, EventArgs e)
        {
            isTrail = false;
            type = ShapeType.FilledRect ;
        }        private void button6_Click(object sender, EventArgs e)
        {
            isTrail = false;
            type = ShapeType.FilledEllipse ;
        }        private void button7_Click(object sender, EventArgs e)
        {
            isTrail = false;
            type = ShapeType.CircleRect;
        }        private void button13_Click(object sender, EventArgs e)
        {
            this.button12.BackColor = this.button13.BackColor;
        }        private void button14_Click(object sender, EventArgs e)
        {
            this.button12.BackColor = this.button14.BackColor;
        }        private void button15_Click(object sender, EventArgs e)
        {
            this.button12.BackColor = this.button15.BackColor;
        }        private void button16_Click(object sender, EventArgs e)
        {
            this.button12.BackColor = this.button16.BackColor;
        }        private void button17_Click(object sender, EventArgs e)
        {
            this.button12.BackColor = this.button17.BackColor;
        }        private void button18_Click(object sender, EventArgs e)
        {
            this.button12.BackColor = this.button18.BackColor;
        }        private void button19_Click(object sender, EventArgs e)
        {
            if (colorDialog1.ShowDialog() == DialogResult.OK)
            {
                this.button12.BackColor = colorDialog1.Color;
            }
        }        private void button9_Click(object sender, EventArgs e)
        {
            lineWidth = 1;
        }        private void button10_Click(object sender, EventArgs e)
        {
            lineWidth = 2;
        }        private void button11_Click(object sender, EventArgs e)
        {
            lineWidth = 3;
        }
        private void pictureBox1_MouseDown(object sender, MouseEventArgs  e)
        {
            if (e.Button == MouseButtons.Left)
            {
                isDown = true;
                current = ShapeFactory.CreateShape(type);
                current.First = e.Location;
                
            }
        }
        private void pictureBox1_MouseMove(object sender, MouseEventArgs e)
        {
            if (isDown )
            {
                if (!isTrail)
                {
                    DrawShape(e.Location);
                }
                else
                {
                    DrawTrail(e.Location);
                }
                Graphics grfx = pictureBox1.CreateGraphics();
                if (shapes.Count != 0)
                {
                    grfx.DrawImage(bmp, 0, 0);
                }
                grfx.Dispose();
            }
            
            
        }
        private void DrawTrail(Point point)
        {
            Graphics grfx = pictureBox1.CreateGraphics();
            current.Last = point;
            current.ForeColor = this.button12.BackColor;
            current.PenWidth = lineWidth;
            current.Draw(grfx );
            Graphics img = Graphics.FromImage(bmp);
            current.Draw(img) ;            shapes.Add(current);
            current = ShapeFactory.CreateShape(type );
            current.First = point;            grfx.Dispose();
            img.Dispose();
        }
        private void DrawShape(Point point)
        {
            Graphics grfx = pictureBox1.CreateGraphics();
            if (!current.Last.Equals(Point.Empty))
            {
                current.ForeColor = pictureBox1.BackColor;
                current.PenWidth = lineWidth;
                current.Draw(grfx);
            }            current.Last = point;
            current.ForeColor = this.button12.BackColor;
            current.PenWidth = lineWidth;
            current.Draw(grfx );            grfx.Dispose();        }
        private void pictureBox1_MouseUp(object sender, MouseEventArgs e)
        {
            isDown = false;
            if (!current.Last.Equals(Point.Empty))
            {
                Graphics img = Graphics.FromImage(bmp);
                current.Draw(img);
                shapes.Add(current);
            }
            current = null;
 
        }        private void button8_Click(object sender, EventArgs e)
        {
            Graphics g = pictureBox1.CreateGraphics();
            g.Clear(pictureBox1 .BackColor );
            g.Dispose();            bmp = new Bitmap(pictureBox1 .Width ,pictureBox1 .Height );
        }        private void Form1_Load(object sender, EventArgs e)
        {        }        private void openFileDialog1_FileOk(object sender, CancelEventArgs e)
        {        }        private void pictureBox1_Click(object sender, EventArgs e)
        {        }        private void 文件保存ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            if (File.Exists(openFileName))
            {
                currentFile = new FileInfo(openFileName);
                bmp.Save(currentFile.FullName);
            }
            else
            {
                if (saveFileDialog1.ShowDialog() == DialogResult.OK)
                {
                    currentFile = new FileInfo(saveFileDialog1 .FileName );
                    bmp.Save(currentFile.FullName);
                }
            }
        }    }
}