Solved

# 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.
0
Question by:Strategus
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18 Comments

LVL 96

Expert Comment

Did you look at the DrawArc method?

Bob
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Author Comment

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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LVL 96

Expert Comment

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
0

Author Comment

I'll give it a try, thanks TheLearnedOne.
0

LVL 25

Expert Comment

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.
0

Author Comment

Ummm, I have no idea what you mean RonaldBiemans
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LVL 96

Expert Comment

Do you want the curve to look smooth or chunky?

Bob
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LVL 96

Expert Comment

0

LVL 25

Expert Comment

TheLearnedOne said it (Smooth or Chuncky)
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LVL 96

Expert Comment

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

Bob
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Author Comment

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 :-)
0

LVL 25

Accepted Solution

RonaldBiemans earned 500 total points
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
0

Author Comment

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 ? ;-)
0

LVL 25

Expert Comment

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
0

Author Comment

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 . ;-)
0

Author Comment

I don't understand it, but it works.

Thanks RonaldBiemans, you are truely an expert.

And thanks to TheLearnedOne too.
0

LVL 96

Expert Comment

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

Bob
0

Author Comment

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 :)
0

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