Computer Programming Concepts and Visual Basic David I. Schneider

278 Computer Programming Concepts and Visual Basic
FIGURE 9-18 (a) Arc of a Circle and (b) Sector of a Circle
A special case occurs when a is 0. The expression –a * c will be zero rather than a negative
number. As a result, Visual Basic does not draw the horizontal radius line associated
with a = 0. In order to create a sector that has the horizontal radius line as one of its edges,
use a small number such as .0000001 for a.
EXAMPLE 2
Write a program to draw a sector whose sides are a horizontal radius line and the radius line that is 40
percent of the way around the circle.
SOLUTION:
The following program draws the sector with its center at the center of the picture box. The radius was
arbitrarily chosen to be 2 and the picOutput.Scale statement was chosen so that the circle would be fairly
large. The output displayed in the picture box is shown in Figure 9-19.
Private Sub cmdDraw_Click()
Dim c As Single
picOutput.Cls
picOutput.Scale (-3, 3)-(3, -3) ‘Specify coordinate system
c = 2 * 3.14159
a = .0000001
b = .4
‘Draw sector with radius lines corresponding to 0 and .4
picOutput.Circle (0, 0), 2, , -a * c, -b * c
End Sub
FIGURE 9-19 Display from Example 2
A sector can be “painted” using any of the patterns shown in Figure 9-20. Which pattern
is used to fill a sector is determined by the value of the FillStyle property. The default value
of this property is 1 for transparent. Thus, by default, the interior of a sector is not painted.
FIGURE 9-20 Fill Patterns