i am trying to create "PaintBrush" short of project.... but after creating a line/circle/rectangle, when i want to create another line/circle/rectangle.. then it removes my last line/circle/rectangle......

here is my code.......
using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.Windows.Forms;

namespace Testing_Project
{
/// <summary>
/// Summary description for DrawForm.
/// </summary>
public class DrawForm : System.Windows.Forms.Form
{
private System.Windows.Forms.Panel pnlTool;
private System.Windows.Forms.Button button3;
private System.Windows.Forms.Button button2;
private System.Windows.Forms.Button button1;
private System.Windows.Forms.ImageList imageList1;
private System.ComponentModel.IContainer components;
private Graphics gB;
private Pen pen;
private Bitmap bitmap;
private int x0, y0, x, y;
private int cx, cy;
private bool blDrag = false;
private System.Windows.Forms.Label lblMsg;
private int DrawMode=1;

public DrawForm()
{
//
// Required for Windows Form Designer support
//
InitializeComponent();

//
// TODO: Add any constructor code after InitializeComponent call
//
SetStyle(ControlStyles.UserPaint, true);
SetStyle(ControlStyles.AllPaintingInWmPaint, true);
SetStyle(ControlStyles.DoubleBuffer, true);
}

/// <summary>
/// Clean up any resources being used.
/// </summary>
protected override void Dispose( bool disposing )
{
if( disposing )
{
if(components != null)
{
components.Dispose();
}
}
base.Dispose( disposing );
}

#region Windows Form Designer generated code
/// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
private void InitializeComponent()
{
this.components = new System.ComponentModel.Container();
System.Resources.ResourceManager resources = new System.Resources.ResourceManager(typeof(DrawForm));
this.pnlTool = new System.Windows.Forms.Panel();
this.button3 = new System.Windows.Forms.Button();
this.imageList1 = new System.Windows.Forms.ImageList(this.components);
this.button2 = new System.Windows.Forms.Button();
this.button1 = new System.Windows.Forms.Button();
this.lblMsg = new System.Windows.Forms.Label();
this.pnlTool.SuspendLayout();
this.SuspendLayout();
//
// pnlTool
//
this.pnlTool.BackColor = System.Drawing.SystemColors.Control;
this.pnlTool.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
this.pnlTool.Controls.Add(this.button3);
this.pnlTool.Controls.Add(this.button2);
this.pnlTool.Controls.Add(this.button1);
this.pnlTool.Location = new System.Drawing.Point(0, 0);
this.pnlTool.Name = "pnlTool";
this.pnlTool.Size = new System.Drawing.Size(72, 368);
this.pnlTool.TabIndex = 0;
//
// button3
//
this.button3.BackColor = System.Drawing.Color.FloralWhite;
this.button3.FlatStyle = System.Windows.Forms.FlatStyle.Flat;
this.button3.ImageIndex = 2;
this.button3.ImageList = this.imageList1;
this.button3.Location = new System.Drawing.Point(14, 72);
this.button3.Name = "button3";
this.button3.Size = new System.Drawing.Size(40, 21);
this.button3.TabIndex = 3;
this.button3.Click += new System.EventHandler(this.button3_Click);
//
// imageList1
//
this.imageList1.ImageSize = new System.Drawing.Size(16, 16);
this.imageList1.ImageStream = ((System.Windows.Forms.ImageListStreamer)(resources.GetObject("imageList1.ImageStream")));
this.imageList1.TransparentColor = System.Drawing.Color.Silver;
//
// button2
//
this.button2.BackColor = System.Drawing.Color.FloralWhite;
this.button2.FlatStyle = System.Windows.Forms.FlatStyle.Flat;
this.button2.ImageIndex = 1;
this.button2.ImageList = this.imageList1;
this.button2.Location = new System.Drawing.Point(14, 48);
this.button2.Name = "button2";
this.button2.Size = new System.Drawing.Size(40, 21);
this.button2.TabIndex = 2;
this.button2.Click += new System.EventHandler(this.button2_Click);
//
// button1
//
this.button1.BackColor = System.Drawing.Color.FloralWhite;
this.button1.FlatStyle = System.Windows.Forms.FlatStyle.Flat;
this.button1.ImageIndex = 0;
this.button1.ImageList = this.imageList1;
this.button1.Location = new System.Drawing.Point(14, 24);
this.button1.Name = "button1";
this.button1.Size = new System.Drawing.Size(40, 21);
this.button1.TabIndex = 1;
this.button1.Click += new System.EventHandler(this.button1_Click);
//
// lblMsg
//
this.lblMsg.Location = new System.Drawing.Point(72, 344);
this.lblMsg.Name = "lblMsg";
this.lblMsg.Size = new System.Drawing.Size(424, 16);
this.lblMsg.TabIndex = 1;
//
// DrawForm
//
this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);
this.BackColor = System.Drawing.SystemColors.ActiveCaptionText;
this.ClientSize = new System.Drawing.Size(504, 365);
this.Controls.Add(this.lblMsg);
this.Controls.Add(this.pnlTool);
this.Name = "DrawForm";
this.Text = "DrawForm";
this.MouseDown += new System.Windows.Forms.MouseEventHandler(this.DrawForm_MouseDown);
this.Load += new System.EventHandler(this.DrawForm_Load);
this.MouseUp += new System.Windows.Forms.MouseEventHandler(this.DrawForm_MouseUp);
this.Paint += new System.Windows.Forms.PaintEventHandler(this.DrawForm_Paint);
this.MouseMove += new System.Windows.Forms.MouseEventHandler(this.DrawForm_MouseMove);
this.pnlTool.ResumeLayout(false);
this.ResumeLayout(false);

}
#endregion

/// <summary>
/// The main entry point for the application.
/// </summary>

[STAThread]
static void Main()
{
Application.Run(new DrawForm());
}

private void DrawForm_Load(object sender, System.EventArgs e)
{
Size size = SystemInformation.PrimaryMonitorMaximizedWindowSize;
bitmap = new Bitmap(size.Width, size.Height);
gB = Graphics.FromImage(bitmap);
// Color bgColor=this.BackColor;
// gB.Clear(bgColor);
// gB.Dispose();
}

private void DrawForm_MouseDown(object sender, System.Windows.Forms.MouseEventArgs e)
{
Point p=new Point(e.X,e.Y);
//p.X=e.X;
//p.Y=e.Y;
x0=p.X;
y0=p.Y;
blDrag = true;
}

private void DrawForm_MouseMove(object sender, System.Windows.Forms.MouseEventArgs e)
{
Point p=new Point(e.X,e.Y);
//p.X=e.X;
//p.Y=e.Y;
x=p.X;
y=p.Y;
cx=x-x0;
cy=y-y0;
if(blDrag)
{
Invalidate();
}
}

private void DrawForm_MouseUp(object sender, System.Windows.Forms.MouseEventArgs e)
{
cx=x-x0;
cy=y-y0;
//pen=new Pen(Color.Blue);
//try
//{
// if (DrawMode==1)
// {
// gB.DrawLine(pen,x0,y0,x,y);
// }
blDrag = false;
// pen.Dispose();
//}
//catch(Exception er)
//{
// lblMsg.Text = er.Message +"//" + er.Source;
//}
}

private void button1_Click(object sender, System.EventArgs e)
{
DrawMode=1;
}

private void button2_Click(object sender, System.EventArgs e)
{
DrawMode=2;
}

private void button3_Click(object sender, System.EventArgs e)
{
DrawMode=3;
}

private void DrawForm_Paint(object sender, System.Windows.Forms.PaintEventArgs e)
{
gB=e.Graphics;
pen=new Pen(Color.Blue);
if (blDrag)
{
if (DrawMode==1)
{
gB.DrawLine(pen,x0,y0,x,y);
}
else if (DrawMode==2)
{
gB.DrawEllipse(pen, x0, y0, cx, cy);
}
else if (DrawMode==3)
{
gB.DrawRectangle(pen, x0, y0, cx, cy);
}
}
pen.Dispose();
}
}
}


do you have any suggestion/code to help me out.......