triangulate with glu

I'm trying to triangulate some polygons. It's not easy to use the GL Utility library (glu32.dll) from VB, but I guess you could write a dll in C/C++ that acts as a wrapper. I have very little experience in that area, would anyone like to help me? I know how it should work in theory and there is a good example of c-code at:

http://graphicsbb.itgo.com/solutions/extrude.html

I would like to put that code (the triangulation-part) into a c/c++ dll so that it is accessible from VB.

Any help and directsion is appreciated!

Recruitment to have somebody develop you a DLL is not permitted on this site.

Here in the Interface & Graphics forum however, you may find somebody with experience in developing a solution that can assist you in providing direction.

Recruitment to have somebody develop you a DLL is not permitted on this site.

Here in the Interface & Graphics forum however, you may find somebody with experience in developing a solution that can assist you in providing direction.

Sorry, I did not mean to recruite someone to create a DLL for me, I meant to ask for help in as in 'how do you create a dll' in c/c++ for use in vb. Thats why I asked for help and directions. Sorry about not being crystal clear. If I only wanted a dll, I would just post at rentacoder... :) But I want to learn how to do it myself.

Hi again, I'm back with some working code. The function 'triangulate' takes a polygon in the form of an array of points (as doubles), triangulates the polygon and returns a new array where the triangles are stored as three points following each other.

It is the CombineCB function (which is used for self-intersecting polygons) that I don't know how to write, I have looked at many examples but the ones I have tried have made errors in the resulting list of triangles.


Option Explicit

Private Type VERTEX
x As Double
y As Double
z As Double
End Type

Public Type POINTAPI_DOUBLE
x As Double
y As Double
End Type

Private Mode&
Private tesspoints(0 To 2) As Long
Private triangles() As Long
Private index As Long
Private TIndex As Long
Private Poly() As VERTEX

Declare Sub CopyToDoubleFromPtr Lib "kernel32" Alias "RtlMoveMemory" (Dest#, ByVal PtrSrc&, ByVal length&)

Public Function triangulate(polypoint() As POINTAPI_DOUBLE) As POINTAPI_DOUBLE()

Dim tobj&
Dim i As Long

TIndex = 0

tobj = gluNewTess
gluTessCallback tobj, GLU_TESS_BEGIN, AddressOf glBeginCB
gluTessCallback tobj, GLU_TESS_END, AddressOf glEndCB
gluTessCallback tobj, GLU_TESS_ERROR, AddressOf glErrorCB
gluTessCallback tobj, GLU_TESS_VERTEX, AddressOf glVertex3dvCB
'gluTessCallback tobj, GLU_TESS_COMBINE, AddressOf CombineCB

ReDim Poly(0 To UBound(polypoint) - 1) As VERTEX

For i = 0 To UBound(Poly)
Poly(i).x = polypoint(i).x
Poly(i).y = polypoint(i).y
Poly(i).z = 0
Next

Dim id() As Double
ReDim id(0 To UBound(Poly)) As Double

ReDim triangles(0 To UBound(Poly) * 3) As Long

gluTessBeginPolygon tobj, 0&
gluTessBeginContour tobj
For i = 0 To UBound(Poly)
id(i) = i
gluTessVertex tobj, Poly(i).x, id(i)
Next
gluTessEndContour tobj
gluTessEndPolygon tobj

Dim retur() As POINTAPI_DOUBLE
ReDim retur(0 To TIndex - 1) As POINTAPI_DOUBLE

For i = 0 To TIndex - 1
retur(i).x = Poly(triangles(i)).x
retur(i).y = Poly(triangles(i)).y
Next

triangulate = retur

End Function

Sub glBeginCB(ByVal which&)
Dim S$
glBegin which
Mode = which
index = 0
End Sub

Sub glEndCB()
glEnd
End Sub

Sub glErrorCB(ByVal errorCode&) '???
Dim estring$, S$
estring = gluErrorString(errorCode)
Debug.Print "Tessellation Error: " & estring
Select Case errorCode
Case GLU_TESS_MISSING_BEGIN_POLYGON
Debug.Assert 0
Case GLU_TESS_MISSING_END_POLYGON
Debug.Assert 0
Case GLU_TESS_MISSING_BEGIN_CONTOUR
Debug.Assert 0
Case GLU_TESS_MISSING_END_CONTOUR
Debug.Assert 0
Case GLU_TESS_COORD_TOO_LARGE
Debug.Assert 0
Case GLU_TESS_NEED_COMBINE_CALLBACK
Debug.Assert 0
Case errorCode >= GLU_TESS_ERROR1 And errorCode <= GLU_TESS_ERROR8
'10151-10158
Debug.Assert 0
Case Else
Debug.Assert 0
End Select
Stop
End Sub

Sub glVertex3dvCB(ByRef arg#)
glVertex3dv arg

tesspoints(index) = arg
index = index + 1

Select Case Mode
Case 4
If index = 3 Then
triangles(TIndex) = tesspoints(0)
TIndex = TIndex + 1
triangles(TIndex) = tesspoints(1)
TIndex = TIndex + 1
triangles(TIndex) = tesspoints(2)
TIndex = TIndex + 1
index = 0
End If
Case 5
If index = 3 Then
If (Not (index And &H1)) Then
triangles(TIndex) = tesspoints(0)
TIndex = TIndex + 1
triangles(TIndex) = tesspoints(1)
TIndex = TIndex + 1
triangles(TIndex) = tesspoints(2)
TIndex = TIndex + 1
Else
triangles(TIndex) = tesspoints(1)
TIndex = TIndex + 1
triangles(TIndex) = tesspoints(2)
TIndex = TIndex + 1
triangles(TIndex) = tesspoints(0)
TIndex = TIndex + 1
End If
tesspoints(0) = tesspoints(1)
tesspoints(1) = tesspoints(2)
index = 2
End If
Case 6
If index = 3 Then
triangles(TIndex) = tesspoints(0)
TIndex = TIndex + 1
triangles(TIndex) = tesspoints(1)
TIndex = TIndex + 1
triangles(TIndex) = tesspoints(2)
TIndex = TIndex + 1
tesspoints(1) = tesspoints(2)
index = 2
End If
End Select

End Sub


This is one example of the CombineCB that I have used:


Sub CombineCB(Coords As VERTEX, ByVal vdata&, ByVal weight&, ByRef OutData&)

Dim cv As Long

cv = UBound(Poly) + 1

ReDim Preserve Poly(0 To cv) As VERTEX

Poly(cv).x = Coords.x
Poly(cv).y = Coords.y
Poly(cv).z = 0

OutData = VarPtr(cv)

ReDim Preserve triangles(0 To UBound(triangles) + 3) As Long

End Sub


Please help me, I'm stuck!

You need a reference to vbogl.tbl from http://home.pacific.net.hk/~edx/tlb.htm

Here is some code for a polygon that works:

Private Sub cmdTest_Click()

Dim polypoint(0 To 8) As POINTAPI_DOUBLE

polypoint(0).x = 10
polypoint(0).y = 0

polypoint(1).x = 40
polypoint(1).y = 0

polypoint(2).x = 40
polypoint(2).y = 10

polypoint(3).x = 15
polypoint(3).y = 10

polypoint(4).x = 15
polypoint(4).y = 30

polypoint(5).x = 40
polypoint(5).y = 30

polypoint(6).x = 40
polypoint(6).y = 40

polypoint(7).x = 10
polypoint(7).y = 40

polypoint(8).x = 10
polypoint(8).y = 0

Dim triangles() As POINTAPI_DOUBLE

triangles = triangulate(polypoint)

Dim i As Integer

For i = 0 To UBound(triangles) Step 3
MsgBox triangles(i).x & "," & triangles(i).y & " / " & triangles(i + 1).x & "," & triangles(i + 1).y & " / " & triangles(i + 2).x & "," & triangles(i + 2).y
Next

End Sub

Heureka! It works! I found the bug! I now have a complete working version of this triangulator/tesselator which is extremely fast compared to native vb such as the Delauney algorithm.

I'm looking for the same thing as you do, can you send me the correct code, also of combineCB? Is it also possible to make a hole in a polygon with this code?