Visual Basic 2008 Tutorial

Lesson 21: RManaging Graphics -Drawing Ellipse and Circle

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We have learned how to draw rectangles with various line style in the previous lesson. Now we shall learn how to draw ellipse and circle.

24.1 Drawing Ellipse

First of all we need to understand the principal behind drawing an ellipse. The basic structure of most shapes is a rectangle, ellipse is no exception. Ellipse is an oval shape that is bounded by a rectangle, as shown below:

Therefore, you need to create a Rectangle object before you can draw an ellipse. This rectangle serves as a bounding rectangle for the ellipse. On the other hand, you can still draw an ellipse with the DrawEllipse method without first creating a rectangle. We will show you both ways.

In the first method, let say you have created a rectangle object known as myRectangle and a pen object as myPen, then you can draw an ellipse using the following statement:

      myGraphics.DrawEllipse(myPen, myRectangle)

* Assume you have also already created the Graphics object myGraphics.

The following is an example of the full code:

Example 24.1(a)

    Dim myPen As Pen

      myPen = New Pen(Drawing.Color.Blue, 5)

    Dim myGraphics As Graphics = Me.CreateGraphics

    Dim myRectangle As New Rectangle

      myRectangle.X = 10

      myRectangle.Y = 10

      myRectangle.Width = 200

      myRectangle.Height = 100

      myGraphics.DrawEllipse(myPen, myRectangle)

The output image is shown in the following figure:

The second method is using the DrawEllipse method without creating a rectangle object. Off course you still have to create the Graphics and the Pen objects. The syntax is:

      myGraphics.DrawEllipse(myPen, X,Y,Width, Height)

Where (X,Y) are the coordinates of the upper left corner of the bounding rectangle, width is the width of the ellipse and height is the height of the ellipse.

The following is an example of the full code:

Example 24.1(b)

    Dim myPen As Pen

      myPen = New Pen(Drawing.Color.Blue, 5)

    Dim myGraphics As Graphics = Me.CreateGraphics

      myGraphics.DrawEllipse(myPen, 10, 10, 200, 100)

24.2 Drawing a Circle

After you have learned how to draw an ellipse, drawing a circle becomes very simple. We use exactly the same methods used in the preceding section but modify the width and height so that they are of the same values.

The following examples draw the same circle.

Example 24.2(a)

    Dim myPen As Pen

      myPen = New Pen(Drawing.Color.Blue, 5)

    Dim myGraphics As Graphics = Me.CreateGraphics

    Dim myRectangle As New Rectangle

      myRectangle.X = 10

      myRectangle.Y = 10

      myRectangle.Width = 100

      myRectangle.Height = 100

      myGraphics.DrawEllipse(myPen, myRectangle)

Example 24.2(b)

    Dim myPen As Pen

      myPen = New Pen(Drawing.Color.Blue, 5)

    Dim myGraphics As Graphics = Me.CreateGraphics

      myGraphics.DrawEllipse(myPen, 10, 10, 100, 100)

The output image is show below:



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