# GDI Draw curve

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.
###### Who is Participating?

Commented:
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

Commented:
Did you look at the DrawArc method?

Bob
0

Author Commented:
Yes I did, but how do I determine the arc for the rest of the coordinates because they all depend upon each other
0

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

Bob
0

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

Commented:
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 Commented:
Ummm, I have no idea what you mean RonaldBiemans
0

Commented:
Do you want the curve to look smooth or chunky?

Bob
0

Commented:
0

Commented:
TheLearnedOne said it (Smooth or Chuncky)
0

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

Bob
0

Author Commented:
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

Author Commented:
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

Commented:
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 Commented:
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 Commented:
I don't understand it, but it works.

Thanks RonaldBiemans, you are truely an expert.

And thanks to TheLearnedOne too.
0

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

Bob
0

Author Commented:
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
Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.