Lesson 25 : Drawing Polygon and Pie

In this Lesson, we will learn how to draw polygon and pie

25.1: Drawing a Polygon using the DrawPolygon method

Polygon is a closed plane figure bounded by three or more straight sides. In order to draw a polygon on the screen, we need to define the coordinates of all the points (also known as vertices) that joined up to form the polygon.

The syntax to defines the points of a polygon with vertices A1, A2, A3, A4…….An is as follows

Dim A1 As New Point(X1,Y1)
Dim A2 As New Point(X2,Y2)
Dim A3 As New Point(X3,Y3)
.
.

Dim An as New Point(Xn,Yn)

After declaring the points, we need to define a point structure that group all the points together using the following syntax:

Dim myPoints As Point() = {A1, A2, A3,....,An}

.Finally, create the graphics object and use the DrawPolygon method to draw the polygon using the following syntax:

Dim myGraphics As Graphics = Me.CreateGraphics
 myGraphics.DrawPolygon(myPen, myPoints)

where myPen is the Pen object created using the following syntax:

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

Example 25.1: Drawing a Triangle

A triangle is a polygon with three vertices. Here is the sample code:

Dim myPen As Pen
Dim A As New Point(10, 10)
Dim B As New Point(100, 50)
Dim C As New Point(60, 150)
Dim myPoints As Point() = {A, B, C}
 myPen = New Pen(Drawing.Color.Blue, 5)
Dim myGraphics As Graphics = Me.CreateGraphics
 myGraphics.DrawPolygon(myPen, myPoints)

Running the program produces the image as shown in Figure 25.1

Figure 25.1

Example 25.2: Drawing a Quadrilateral

A quadrilateral is a polygon consist of four sides, so you need to define four vertices. The following is the code:

Dim myPen As Pen
Dim A As New Point(10, 10)
Dim B As New Point(100, 50)
Dim C As New Point(120, 150)
Dim D As New Point(60, 200)
Dim myPoints As Point() = {A, B, C, D}
 myPen = New Pen(Drawing.Color.Blue, 5)
Dim myGraphics As Graphics = Me.CreateGraphics
 myGraphics.DrawPolygon(myPen, myPoints)

The output image is as shown in Figure 25.2

Figure 25.2

25.2: Drawing Pie

In order to draw a pie, you can use the DrawPie method of the graphics object. As usual, you need to create the Graphics and the Pen objects. The syntax for drawing a pie is:

myGraphics.DrawPie(myPen, X, Y, width,height, StartAngle, SweepAngle)

Where X and Y are the coordinates the bounding rectangle, other arguments are self-explanatory. Both StartAngle and SweepAngle are measured in degree. SweepAngle can take possible or negative values. If the value is positive, it sweeps through clockwise direction while negative means it sweep through anticlockwise direction.

Example 25.3: Drawing a pie that starts with 0 degree and sweep clockwise through 60 degree.

Dim myPen As Pen
 myPen = New Pen(Drawing.Color.Blue, 5)
Dim myGraphics As Graphics = Me.CreateGraphics
 myGraphics.DrawPie(myPen, 50,50, 150,150,0,60)

The output image is as shown in Figure 25.3

Figure 25.3