C#

PIEBALDconsult wrote:

Or whatever, it has been a long time since high school.

System.Drawing.Graphics graphics = this.CreateGraphics();
System.Drawing.Rectangle rectangle = new System.Drawing.Rectangle(
    100, 100, 200, 200);
graphics.DrawEllipse(System.Drawing.Pens.Black, rectangle);

public partial class Form1 : Form
   {
       Rectangle SelectionRectangle = new Rectangle();
       string SelectedShape = "None";

       public Form1()
       {
           InitializeComponent();
       }

       private void Form1_MouseDown(object sender, MouseEventArgs e)
       {
           // If the current selected shape is 'Ellipse', then set the selection
           // rectangle's top-left position to mouse co-ordinates and set the width and
           // height to zero
           if (SelectedShape == "Ellipse")
           {
               SelectionRectangle.Width = 0;
               SelectionRectangle.Height = 0;
               SelectionRectangle.X = e.X;
               SelectionRectangle.Y = e.Y;
           }
       }

       private void Form1_MouseMove(object sender, MouseEventArgs e)
       {
           // If the mouse left button the pressed and the mouse is dragged, then capture
           // the mouse co-ordinates and resize the rectangle
           if (e.Button == MouseButtons.Left)
           {
               SelectionRectangle.Width = e.X - SelectionRectangle.Left; // EndPoint.X - StartPoint.Y;
               SelectionRectangle.Height = e.Y - SelectionRectangle.Top; // EndPoint.Y - StartPoint.Y;
               // ask Windows to redraw the form background
               Invalidate();
               Update();
           }
       }

       private void Form1_MouseUp(object sender, MouseEventArgs e)
       {
           // Capture the mouse position only if the current selected shape is 'Rectangle'
           // Else ignore
           if (SelectedShape == "Ellipse")
           {
               SelectionRectangle.Width = e.X - SelectionRectangle.Left; //EndPoint.X - StartPoint.X;
               SelectionRectangle.Height = e.Y - SelectionRectangle.Top; //EndPoint.Y - StartPoint.Y;
               Invalidate();
               Update();
           }

       }

       // Click 'Button2' to start drawing the ellipse
       private void button2_Click(object sender, EventArgs e)
       {
           SelectedShape = "Ellipse";
       }

       // Click 'Button2' to stop drawing the ellipse
       private void button1_Click(object sender, EventArgs e)
       {
           SelectedShape = "None";
       }

       private void Form1_Paint(object sender, PaintEventArgs e)
       {
           if ((SelectedShape == "Ellipse") && (SelectionRectangle != null))
           {
               Graphics g = e.Graphics;
               g.DrawEllipse(Pens.Black, SelectionRectangle);
               // If you do not want to draw the bounding rectangle, just comment out
               // the next line
               g.DrawRectangle(Pens.Gray, SelectionRectangle);
           }
       }