Visual Basic 2012 Lesson 23– Managing Graphics -Drawing Ellipse and Circle

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[Lesson 22] << [CONTENTS] >> [Lesson 24]

We have learned how to draw rectangles with various line styles in Visual Basic 2012 in the previous lesson. 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 2012. The basic structure of most shapes is a rectangle, an ellipse is no exception. Ellipse is an oval shape that is bounded by a rectangle, as shown below:
Visual Basic 2012Therefore, 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 finish the job. On the other hand, we can also draw an ellipse with the DrawEllipse method without first creating a rectangle. We shall show you both methods.

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 figure:

Visual Basic 2012



The second method is using the DrawEllipse method without creating a rectangle object. Of 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 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:





[Lesson 22] << [CONTENTS] >> [Lesson 24]

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