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| Title | Let the user draw a Bezier curve in VB .NET |
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| Description | This example shows how to let the user draw a Bezier curve in VB .NET. When the user clicks four points, the program draws the Bezier curve defined by them. |
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| Keywords | Bezier, Bezier curve, curve, VB.NET |
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| Categories | VB.NET, Graphics |
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If the program already had four points, the program's MouseDown event handler clears the previous Bezier curve. The event handler then saves the new point and redraws the data.
Subroutine Redraw draws the data. If the program has saved four points, the routine uses he Graphics object's DrawBezier method to draw the curve defined by the points. Then it draws boxes around the points it has so you can see them.
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Private m_Points(3) As Point
Private m_MaxPoint As Integer = -1
Private Sub Form1_MouseDown(ByVal sender As Object, ByVal e _
As System.Windows.Forms.MouseEventArgs) Handles _
MyBase.MouseDown
If m_MaxPoint = 3 Then
Me.CreateGraphics.Clear(Me.BackColor)
m_MaxPoint = 0
Else
m_MaxPoint += 1
End If
m_Points(m_MaxPoint).X = e.X
m_Points(m_MaxPoint).Y = e.Y
Redraw(Me.CreateGraphics)
End Sub
Private Sub Form1_Paint(ByVal sender As Object, ByVal e As _
System.Windows.Forms.PaintEventArgs) Handles _
MyBase.Paint
Redraw(e.Graphics)
End Sub
Private Sub Redraw(ByVal gr As Graphics)
If m_MaxPoint = 3 Then
' Draw the Bezier curve.
gr.DrawBezier(Pens.Black, _
m_Points(0), m_Points(1), _
m_Points(2), m_Points(3))
End If
' Draw the control points.
For i As Integer = 0 To m_MaxPoint
Dim rect As New Rectangle( _
m_Points(i).X - 2, m_Points(i).Y - 2, 5, 5)
gr.FillRectangle(Brushes.White, rect)
gr.DrawRectangle(Pens.Black, rect)
Next i
End Sub
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