C# - Draw line, rectangle on a Windows Form

The following code snippet show you how to draw a line and rectangle in C#.

 using System;  
 using System.Collections.Generic;  
 using System.ComponentModel;  
 using System.Data;  
 using System.Drawing;  
 using System.Linq;  
 using System.Text;  
 using System.Threading.Tasks;  
 using System.Windows.Forms;  
 namespace DrawOnWinForm  
 {  
   public partial class Form1 : Form  
   {  
     public Form1()  
     {  
       InitializeComponent();  
     }  
     System.Drawing.Pen bounderyPen;  
     System.Drawing.Pen OxOyPen;  
     System.Drawing.Pen ABPen;  
     System.Drawing.Pen CPen;  
     System.Drawing.Brush ACMBrush = Brushes.LightGray;  
     System.Drawing.Brush BCMpBrush = Brushes.LightCyan;  
     System.Drawing.Brush TextBrush = Brushes.Black;  
     Font textFont = new Font("Arial", 10);  
     Point TOPLEFT = new Point(0, 0);  
     Point BASEO = new Point(400, 400);  
     Rectangle Boundery = new Rectangle();  
     double xO = 0, yO = 0;  
     private void Form1_Load(object sender, EventArgs e)  
     {  
     }  
     int zoomX = 50;  
     int margin = 10;  
     int zoomY = 50;  
     System.Drawing.Brush brush = Brushes.White;  
     private void Form1_Paint(object sender, PaintEventArgs e)  
     {  
       Clear();  
       System.Drawing.Graphics formGraphics = this.CreateGraphics();  
       Boundery.X = margin;  
       Boundery.Y = margin;  
       Boundery.Width = this.Width - 4 * margin;  
       Boundery.Height = this.Height - Boundery.Y - margin * 5;  
       bounderyPen = new System.Drawing.Pen(System.Drawing.Color.Brown);  
       bounderyPen.Width = 2;  
       formGraphics.DrawRectangle(bounderyPen, Boundery);  
       BASEO.X = (int)(this.Width / 2);  
       BASEO.Y = this.Height - margin * 5 - 100;  
       OxOyPen = new System.Drawing.Pen(System.Drawing.Color.Blue);  
       OxOyPen.Width = 2;  
       formGraphics.DrawLine(OxOyPen, margin, BASEO.Y, Boundery.X + Boundery.Width - margin * 0, BASEO.Y);  
       formGraphics.DrawLine(OxOyPen, Boundery.X + Boundery.Width - 10 - margin * 0, BASEO.Y - 5, Boundery.X + Boundery.Width - margin * 0, BASEO.Y);  
       formGraphics.DrawLine(OxOyPen, Boundery.X + Boundery.Width - 10 - margin * 0, BASEO.Y + 5, Boundery.X + Boundery.Width - margin * 0, BASEO.Y);  
       string textTrucX = "x";  
       formGraphics.DrawString(textTrucX, textFont, TextBrush, new PointF(Boundery.X + Boundery.Width - 10 - margin * 0, BASEO.Y + 2));  
       formGraphics.DrawLine(OxOyPen, BASEO.X, this.Height - margin * 5, BASEO.X, this.Height - margin * 5 - Boundery.Height);  
       formGraphics.DrawLine(OxOyPen, BASEO.X - 5, this.Height - margin * 5 - Boundery.Height + 10, BASEO.X, this.Height - margin * 5 - Boundery.Height);  
       formGraphics.DrawLine(OxOyPen, BASEO.X + 5, this.Height - margin * 5 - Boundery.Height + 10, BASEO.X, this.Height - margin * 5 - Boundery.Height);  
       string textTrucY = "y";  
       formGraphics.DrawString(textTrucY, textFont, TextBrush, new PointF(BASEO.X - 15, this.Height - margin * 5 - Boundery.Height));  
       string textO = "O(" + xO + "," + yO + ")";  
       formGraphics.DrawString(textO, textFont, TextBrush, new PointF(ToaDoFormXZoomY(xO), ToaDoFormYZoomY(yO)));  
     }  
     private void Clear()  
     {  
       System.Drawing.Graphics formGraphics = this.CreateGraphics();  
       #region Ve Boundery  
       Rectangle screen = new Rectangle();  
       screen.X = 0;  
       screen.Y = 0;  
       screen.Width = this.Width - 1;  
       screen.Height = this.Height;  
       formGraphics.FillRectangle(brush, screen);  
       #endregion  
       formGraphics.Dispose();  
     }  
     private int ToaDoFormXZoomY(double x)  
     {  
       return (int)(BASEO.X + x * zoomY);  
     }  
     private int ToaDoFormYZoomY(double y)  
     {  
       return (int)(BASEO.Y - y * zoomY);  
     }  
     private int ToaDoFormXZoomX(double x)  
     {  
       return (int)(BASEO.X + x * zoomX);  
     }  
     private int ToaDoFormYZoomX(double y)  
     {  
       return (int)(BASEO.X - y * zoomX);  
     }  
   }  
 }  

Here is the output of the project.