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GDI Draw curve

Posted on 2004-09-02
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Last Modified: 2008-01-09
Hi experts,

I have an Array that contains x and y coordinates. I need to draw a curve
through those coordinates. But I have no idea how to do that , I tried using bezier curves but that didn't seem to work.

I'm a vb.net newbe so be gentle

K.
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Question by:Strategus
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Expert Comment

by:Bob Learned
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Did you look at the DrawArc method?

Bob
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Author Comment

by:Strategus
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Yes I did, but how do I determine the arc for the rest of the coordinates because they all depend upon each other
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Expert Comment

by:Bob Learned
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I'm sorry (senior moment).  Look at the Graphics.DrawCurve method--one of the overloaded methods takes an array of points:

Overloads Public Sub DrawCurve(Pen, Point())

Bob
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Author Comment

by:Strategus
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I'll give it a try, thanks TheLearnedOne.
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Expert Comment

by:RonaldBiemans
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Hi Strategus, do you want to draw a S-Curve, if so drawCurve won't do the trick because it is a cardinal spline,
for an s -curve you need a cubic spline.
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by:Strategus
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Ummm, I have no idea what you mean RonaldBiemans
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Expert Comment

by:Bob Learned
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Do you want the curve to look smooth or chunky?

Bob
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by:Bob Learned
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Expert Comment

by:RonaldBiemans
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TheLearnedOne said it (Smooth or Chuncky)
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Expert Comment

by:Bob Learned
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I like my peanut butter chunky, but I like my curves smooth :)

Bob
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Author Comment

by:Strategus
Comment Utility
Ok, Smooth then because the drawcurve didn't give me the required result. Well it gave Me the required result but not for the one I'm making it for :-)
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Accepted Solution

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RonaldBiemans earned 500 total points
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Ok, try this, I needed something simular a while back and this worked (I'm drawing on a panel here)

 Dim x(4) As Single
    Dim y(4) As Single
    Dim y2() As Single
    Dim yout As Single
    Dim ron As Graphics

    Private Sub spline(ByVal x() As Single, ByVal y() As Single, ByVal n As Integer, ByVal yp1 As Single, ByVal ypn As Single)
        Dim i, k As Integer
        Dim p, qn, sig, un, u() As Single

        ReDim y2(n)
        ReDim u(n)

        If yp1 > 9.9E+29 Then
            y2(0) = u(0) = 0.0
        Else
            y2(0) = -0.5
            u(0) = (3.0 / (x(1) - x(0))) * ((y(1) - y(0)) / (x(1) - x(0)) - yp1)
        End If

        For i = 1 To n - 1
            sig = (x(i) - x(i - 1)) / (x(i + 1) - x(i - 1))
            p = sig * y2(i - 1) + 2
            y2(i) = (sig - 1) / p
            u(i) = (y(i + 1) - y(i)) / (x(i + 1) - x(i)) - (y(i) - y(i - 1)) / (x(i) - x(i - 1))
            u(i) = (6 * u(i) / (x(i + 1) - x(i - 1)) - sig * u(i - 1)) / p
        Next i

        If ypn > 9.9E+29 Then
            qn = un = 0.0
        Else
            qn = 0.5
            un = (3.0 / (x(n) - x(n - 1))) * (ypn - (y(n) - y(n - 1)) / (x(n) - x(n - 1)))
        End If

        y2(n) = (un - qn * u(n - 1)) / (qn * y2(n - 1) + 1)
        For k = n - 1 To k >= 1 Step -1
            y2(k) = y2(k) * y2(k + 1) + u(k)

        Next


    End Sub

    Private Function splint(ByVal xa() As Single, ByVal ya() As Single, ByVal y2a() As Single, ByVal n As Integer, ByVal x As Single)
        Dim klo, khi, k As Integer
        Dim h, b, a As Single

        klo = 0
        khi = n
        Do While khi - klo > 1
            k = khi + klo >> 1

            If xa(k) > x Then
                khi = k
            Else
                klo = k
            End If
        Loop
        h = xa(khi) - xa(klo)
        a = (xa(khi) - x) / h
        b = (x - xa(klo)) / h
        yout = a * ya(klo) + b * ya(khi) + ((a ^ 3 - a) * y2a(klo) + (b ^ 3 - b) * y2a(khi)) * (h ^ 2) / 6

        Return yout
    End Function

    Private Sub spline_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        x(0) = 100
        x(1) = 200
        x(2) = 300
        x(3) = 400
        x(4) = 500

        y(0) = 300
        y(1) = 330
        y(2) = 200
        y(3) = 300
        y(4) = 200

        spline(x, y, 4, 0, 0)

    End Sub

    Private Sub Panel1_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles Panel1.Paint
        Dim Xrange As Single
        Dim Yrange As Single

        Xrange = Panel1.Width / (x(4) + 100)
        Yrange = Panel1.Height / (y(1) + 100)

        ron = Panel1.CreateGraphics
        For br As Single = x(0) To 500 Step 0.1
            ron.DrawRectangle(New Pen(Color.Black), br * Xrange, splint(x, y, y2, 4, br) * Yrange, 1, 1)
            For bf As Integer = 0 To x.GetUpperBound(0)
                ron.FillEllipse(New System.Drawing.SolidBrush(Color.Black), x(bf) * Xrange, y(bf) * Yrange, 5, 5)
            Next
        Next
    End Sub
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Author Comment

by:Strategus
Comment Utility
GULP, I though I asked to be gentle :-).

Can I just cut and paste this ? Because I don't think I have the brainpower to figure this out.

Do you have any friends ? ;-)
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Expert Comment

by:RonaldBiemans
Comment Utility
Yes, you can cut and paste this, you just need a panel on your form (panel1)

and you ofcourse you need to adjust the x and y declarations to the number of point you have

Dim x(4) As Single
Dim y(4) As Single

and fill them with your own coordinates.

Want do you mean if I have any friends
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Author Comment

by:Strategus
Comment Utility
Ok I'll give it a try.

And what I meant was, if you can figure out these things you won't have much spare time or your brilliant . ;-)
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Author Comment

by:Strategus
Comment Utility
I don't understand it, but it works.

Thanks RonaldBiemans, you are truely an expert.

And thanks to TheLearnedOne too.
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Expert Comment

by:Bob Learned
Comment Utility
You know, if you really want to thank, then you can think about splitting points.  I am working stiff, too:)

Bob
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Author Comment

by:Strategus
Comment Utility
Sorry TheLearnedOne, this was my first question here on EE and I'm not quite familiar with the way things work here. I will do better next time :)
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