GDI+ Shapes: Ellipses and Circles

Because an ellipse can fit in a rectangle, in GDI+ programming, an ellipse is defined with regards to a rectangle it would fit in. To draw an ellipse, you can use the Graphics.DrawEllipse() method that comes in four versions whose syntaxes are:

public void DrawEllipse(Pen pen,
		     Rectangle rect);
public void DrawEllipse(Pen pen,
		     RectangleF rect);
public void DrawEllipse(Pen pen,
		     int x,
		     int y,
		     int width,
		     int height);
public void DrawEllipse(Pen pen,
		     float x,
		     float y,
		     float width,
		     float height);

The arguments of this method play the same roll as those of the Graphics.DrawRectangle() method:

Here is an example:

private void Exercise_Paint(object sender, PaintEventArgs e)
{
        Pen penCurrent = new Pen(Color.Red);

        e.Graphics.DrawEllipse(penCurrent, new Rectangle(20, 20, 226, 144));
}

1. Start a new Windows Application named RotatingCircles1
2. Double-click middle of the form and change the file as follows:
   

   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;
   
   namespace RotatingCircles1
   {
       public partial class Form1 : Form
       {
           Graphics graphDrawingArea;
           Bitmap bmpDrawingArea;
   
           public Form1()
           {
               InitializeComponent();
           }
   
           private void Form1_Load(object sender, EventArgs e)
           {
               bmpDrawingArea = new Bitmap(Width, Height);
               graphDrawingArea = Graphics.FromImage(bmpDrawingArea);
           }
       }
   }

3. From the Components section of the Toolbox, click Timer and click the form
4. In the Properties window, change the following values:
   Enabled: True
   Interval: 20
5. Under the form, double-click the timer1 object and make the following changes:
   

   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;
   
   namespace RotatingCircles1
   {
       public partial class Form1 : Form
       {
           Graphics graphDrawingArea;
           Bitmap bmpDrawingArea;
           static int mainRadius = 10;
           static int smallRadius = 5;
           static bool isMax;
           static bool smallRadiusMax;
   
           public Form1()
           {
               InitializeComponent();
           }
   
           private void Form1_Load(object sender, EventArgs e)
           {
               bmpDrawingArea = new Bitmap(Width, Height);
               graphDrawingArea = Graphics.FromImage(bmpDrawingArea);
           }
   
           void DrawCentralCircle(int CenterX, int CenterY, int Radius)
           {
               int start = CenterX - Radius;
               int end = CenterY - Radius;
               int diam = Radius * 2;
   
               graphDrawingArea.DrawEllipse(new Pen(Color.Blue),
                             start, end, diam, diam);
           }
   
           void DrawCornerCircle(int CenterX, int CenterY, int Radius)
           {
               int start = CenterX - Radius;
               int end = CenterY - Radius;
               int diam = Radius * 2;
   
               graphDrawingArea.DrawEllipse(new Pen(Color.Red),
                             start, end, diam, diam);
           }
   
           private void timer1_Tick(object sender, EventArgs e)
           {
               Graphics graph = Graphics.FromHwnd(this.Handle);
   
               int centerX = ClientRectangle.Width / 2;
               int centerY = ClientRectangle.Height / 2;
   
               if (isMax == true)
                   mainRadius--;
               else
                   mainRadius++;
   
               if (mainRadius > (ClientRectangle.Height / 2))
                   isMax = true;
               if (mainRadius < 10)
                   isMax = false;
   
               if (smallRadiusMax == true)
                   smallRadius--;
               else
                   smallRadius++;
   
               if (smallRadius > 240)
                   smallRadiusMax = true;
               if (smallRadius < 5)
                   smallRadiusMax = false;
   
               // Central
               DrawCentralCircle(centerX, centerY, mainRadius);
               // Top-Left
               DrawCornerCircle(centerX / 2, centerY / 2, smallRadius);
               // Top-Right
               DrawCornerCircle(centerX + (centerX / 2), centerY / 2, smallRadius);
               // Bottom-Left
               DrawCornerCircle(centerX / 2, centerY + (centerY / 2), smallRadius);
               // BottomRight
               DrawCornerCircle(centerX + (centerX / 2),
                        centerY + (centerY / 2), smallRadius);
   
               graph.DrawImage(bmpDrawingArea, 0, 0);
           }
       }
   }

6. Execute the application to see the result
7. Close the form