| Tutorials > VSDraw Tutorial - Chart > Step 2: Drawing Pie Charts |
To draw a pie chart, we will start with some random data, and then call a general-purpose pie drawing routine. Double-click on the Pie Chart button and add the following code to the cmdPie_Click event handler:
| Example Title |
Copy Code
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Private Sub cmdPie_Click() ' set up chart data in variant array: ' col 0 has values, col 1 has labels, and ' col 2 has colors ' negative values create exploded slices Dim cd(2, 6) cd(0, 0) = 30: cd(1, 0) = "Phone" cd(0, 1) =-65: cd(1, 1) = "Payroll" cd(0, 2) = 42: cd(1, 2) = "Equipment" cd(0, 3) = 24: cd(1, 3) = "Rent" cd(0, 4) =-52: cd(1, 4) = "Advertising" cd(0, 5) = 12: cd(1, 5) = "Production" cd(0, 6) = 22: cd(1, 6) = "Other" cd(2, 0) = vbRed cd(2, 1) = vbBlue cd(2, 2) = vbGreen cd(2, 3) = vbYellow cd(2, 4) = vbCyan cd(2, 5) = vbMagenta cd(2, 6) = vbBlack ' draw chart vd.FontName = "Tahoma" DrawPieChart vd, cd, _ "Expense Report - March 1999" & vbCrLf & _ "(values in 1,000 US$)" End Sub |
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The routine sets up a variant array with some values, labels and colors, and then calls the DrawPieChart routine.
DrawPieChart is a generic pie-chart routine for the VSDraw control. It is not trivial code, but it is not very difficult either. You should be able to understand what it does and to customize it without trouble.
Here is the DrawPieChart routine (it is pretty long, so we suggest you copy it to the clipboard and paste into your project rather than typing it):
| Example Title |
Copy Code
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|---|---|
Sub DrawPieChart(vd As VSDraw, _
ByRef ChartData(), _
tit$)
Const Pi = 3.1416
Const Radius = 500
Dim i%, arc#, start#, tot#, a#, cx#, cy#
With vd
'---------------------------------------------
' clear control
.Clear
'---------------------------------------------
' setup scale based on pie radius
' use negative ScaleHeight so positive is up
.ScaleWidth = 2.75 * Radius
.ScaleLeft = 0
.ScaleHeight = -.ScaleWidth
.ScaleTop = .ScaleWidth
'---------------------------------------------
' calculate total value to scale pie slices
For i = 0 To UBound(ChartData, 2)
tot = tot + Abs(ChartData(0, i))
Next
'---------------------------------------------
' set up to draw pie slices
.PenColor = vbBlack
.PenWidth = 0
.PenStyle = psSolid
.BrushStyle = bsSolid
'---------------------------------------------
' draw shadow slices in gray
.BrushColor = RGB(90, 90, 90)
For i = 0 To UBound(ChartData, 2)
' calculate arc
arc = Abs(ChartData(0, i)) / tot * 2 * Pi
a = start + arc / 2
' get slice origin
cx = .ScaleWidth / 2 + Radius / 20
cy = .ScaleWidth / 2 + Radius / 20
' explode slices with negative amounts
If ChartData(0, i) < 0 Then
cx = cx + Radius / 10 * Cos(a)
cy = cy + Radius / 10 * Sin(a)
End If
' draw slice
If arc > 0 Then
.DrawCircle cx, cy, Radius, start, start + arc
End If
' update start
start = start + arc
Next
'---------------------------------------------
' draw real slices in given colors
start = 0
For i = 0 To UBound(ChartData, 2)
' set color
.BrushColor = ChartData(2, i)
' calculate arc
arc = Abs(ChartData(0, i)) / tot * 2 * Pi
a = start + arc / 2
' get slice origin
cx = .ScaleWidth / 2
cy = .ScaleWidth / 2
' explode slices with negative amounts
If ChartData(0, i) < 0 Then
cx = cx + Radius / 10 * Cos(a)
cy = cy + Radius / 10 * Sin(a)
End If
' draw slice
If arc > 0 Then
.DrawCircle cx, cy, Radius, start, start + arc
End If
' update start
start = start + arc
Next
'---------------------------------------------
' set up to draw slice labels
.TextAlign = tadCenter
.TextColor = vbWhite
.FontBold = True
.FontSize = Radius / 10
'---------------------------------------------
' draw slice labels
start = 0
For i = 0 To UBound(ChartData, 2)
' calculate arc
arc = Abs(ChartData(0, i)) / tot * 2 * Pi
a = start + arc / 2
' get slice origin
cx = .ScaleWidth / 2
cy = .ScaleWidth / 2
' explode slices with negative amounts
If ChartData(0, i) < 0 Then
cx = cx + Radius / 10 * Cos(a)
cy = cy + Radius / 10 * Sin(a)
End If
' draw label
If arc > 0 Then
a = start + arc / 2
.X1 = cx + Radius * 2 / 3 * Cos(a)
.Y1 = cy + Radius * 2 / 3 * Sin(a) + .FontSize
.Text = ChartData(1, i) & vbCrLf & _
Abs(ChartData(0, i))
End If
' update start
start = start + arc
Next
'---------------------------------------------
' draw chart title
.X1 = .ScaleWidth / 2
.Y1 = .ScaleTop + .ScaleHeight + .FontSize * 2.5
.TextColor = vbBlack
.Text = tit
End With
End Sub
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