Chapter 23 – Managing Graphics -Drawing Ellipse and Circle

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We have learned how to draw rectangles with various line styles in Visual Basic 2010. Now we shall learn how to draw ellipse and circle.
23.1 Drawing Ellipse
First of all we need to understand the principle behind drawing an ellipse in Visual Basic 2010. 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, we need to create a Rectangle object before we can draw an ellipse. This rectangle serves as a bounding rectangle for the ellipse. We still need to use the DrawEllipse method to complete the job. On the other hand, we can alaso draw an ellipse with the DrawEllipse method without first creating a rectangle. We shall illustrates 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 23.1(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 diagram:

The second method is using the DrawEllipse method without creating a rectangle object. Offcourse 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 23.1(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)
23.2 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 23.2(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 23.2(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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