I have a problem with my Visual Basic 6.0 program. It is a simple program: just drag & drop a picturebox into your object window, then copy and paste the code below into your code window. You may have to fix the code a bit to eliminate unwanted carriage returns (due to this message board). Then run the program.

The program is supposed to orbit a point-object in a circular path around the origin. Instead it follows a figure-eight path! Can anyone fix this?

' Code to Orbit point-object through incremental angles in 3D space.
Dim pi As Double

' Initialize window.
Private Sub form_activate()
pi = 4 * Atn(1)
Form1.WindowState = vbMaximized
Picture1.AutoRedraw = True
Picture1.Width = 9855
Picture1.Height = 6375
Picture1.ScaleMode = vbPixels
Picture1.ScaleWidth = 640
Picture1.ScaleHeight = 480
Form1.Refresh
Call LineTest
End Sub

' Defines point-object position, increments angles, calls the rotate function, and draws the result.
Private Sub LineTest()
Dim Vx(1) As Variant
Dim Vy(1) As Variant
Dim Vz(1) As Variant
Dim Px(1) As Variant
Dim Py(1) As Variant
Dim Pz(1) As Variant

' Defines the original vector position of the point-object.
Vx(1) = 0
Vy(1) = 200
Vz(1) = 0

' Loop to increment rotation angles.
For i = 0 To 360
anglex = i ' Angle for rotation around the x-axis.
angley = 0 ' Angle for rotation around the y-axis.
anglez = 0 ' Angle for rotation around the z-axis.
Call Rotate(1, anglex, angley, anglez, Vx(), Vy(), Vz(), Px(), Py(), Pz())

' Draws line from origin to rotated point-object.
Picture1.Cls
Picture1.DrawWidth = 2
If Pz(1) < 0 Then
Picture1.Line (Picture1.ScaleWidth / 2, Picture1.ScaleHeight / 2)-(Pz(1) + Picture1.ScaleWidth / 2, Py(1) + Picture1.ScaleHeight / 2), RGB(255, 0, 0)
Else
Picture1.Line (Picture1.ScaleWidth / 2, Picture1.ScaleHeight / 2)-(Pz(1) + Picture1.ScaleWidth / 2, Py(1) + Picture1.ScaleHeight / 2), RGB(0, 0, 0)
End If

' Prints text showing object coordinates.
Picture1.CurrentX = Pz(1) + Picture1.ScaleWidth / 2 + 10
Picture1.CurrentY = Py(1) + Picture1.ScaleHeight / 2
Picture1.Print "P( " & Int(Px(1)) & " , " & Int(Py(1)) & " , " & Int(Pz(1)) & " )"
Picture1.CurrentX = 0
Picture1.CurrentY = 0
Picture1.Print "Rotation angle around x-axis = " & anglex
Picture1.Print "Rotation angle around y-axis = " & angley
Picture1.Print "Rotation angle around z-axis = " & anglez
Picture1.Print "P( " & Int(Px(1)) & " , " & Int(Py(1)) & " , " & Int(Pz(1)) & " )"
Picture1.CurrentX = Picture1.ScaleWidth / 2 - 45
Picture1.CurrentY = Picture1.ScaleHeight / 2 - 10
Picture1.Print "( 0,0,0 )"

' Draws axes defining yz-plane.
Picture1.Line (10, Picture1.ScaleHeight - 30)-(10, Picture1.ScaleHeight - 70), RGB(0, 0, 0)
Picture1.CurrentY = Picture1.ScaleHeight - 85
Picture1.Print "Y"
Picture1.Line (10, Picture1.ScaleHeight - 30)-(50, Picture1.ScaleHeight - 30), RGB(0, 0, 0)
Picture1.Print "Z"
Picture1.Refresh
Next i
End Sub

' Black Box Subroutine that Rotates and Returns Duplicate Vertices (Avoids Modification Of Original).
Public Sub Rotate(ByVal nodeCount As Single, ByVal anglex As Single, ByVal angley As Single, ByVal anglez As Single, ByRef Inputx() As Variant, ByRef Inputy() As Variant, ByRef Inputz() As Variant, ByRef Outputx() As Variant, ByRef Outputy() As Variant, ByRef Outputz() As Variant)
Dim ThetaRadX As Double, ThetaRadY As Double, ThetaRadZ As Double 'rotation angles in radians
Dim Rotatx(3, 3) As Double, Rotaty(3, 3) As Double, Rotatz(3, 3) As Double 'axial rotation matrices
Dim Resultant(3, 3) As Double 'resultant rotation matrix
' Converts Angles to Radians.
ThetaRadX = anglex * pi / 180
ThetaRadY = angley * pi / 180
ThetaRadZ = anglez * pi / 180
' Matrix for Rotation around the x-axis.
Rotatx(1, 1) = 1: Rotatx(1, 2) = 0: Rotatx(1, 3) = 0
Rotatx(2, 1) = 0: Rotatx(2, 2) = Cos(ThetaRadX): Rotatx(2, 3) = -Sin(ThetaRadX)
Rotatx(3, 1) = 0: Rotatx(3, 2) = Sin(ThetaRadX): Rotatx(3, 3) = Cos(ThetaRadX)
' Matrix for Rotation around the y-axis.
Rotaty(1, 1) = Cos(ThetaRadY): Rotaty(1, 2) = 0: Rotaty(1, 3) = Sin(ThetaRadY)
Rotaty(2, 1) = 0: Rotaty(2, 2) = 1: Rotaty(2, 3) = 0
Rotaty(3, 1) = -Sin(ThetaRadY): Rotaty(3, 2) = 0: Rotaty(3, 3) = Cos(ThetaRadY)
' Matrix for Rotation around the z-axis.
Rotatz(1, 1) = Cos(ThetaRadZ): Rotatz(1, 2) = -Sin(ThetaRadZ): Rotatz(1, 3) = 0
Rotatz(2, 1) = Sin(ThetaRadZ): Rotatz(2, 2) = Cos(ThetaRadZ): Rotatz(2, 3) = 0
Rotatz(3, 1) = 0: Rotatz(3, 2) = 0: Rotatz(3, 3) = 1
' Resultant Matrix for Rotation Operation.
For i = 1 To 3
For j = 1 To 3
Resultant(i, j) = Rotaty(i, 1) * Rotatz(1, j) + Rotaty(i, 2) * Rotatz(2, j) + Rotaty(i, 3) * Rotatz(3, j)
Next j
Next i
For i = 1 To 3
For j = 1 To 3
Resultant(i, j) = Rotatx(i, 1) * Resultant(1, j) + Rotatx(i, 2) * Resultant(2, j) + Rotatx(i, 3) * Resultant(3, j)
Next j
Next i
' Rotates Duplicate Vertices (Avoids Modification Of Original).
For t = 1 To nodeCount
Outputx(t) = Inputx(t) * Resultant(1, 1) + Inputy(t) * Resultant(1, 2) + Inputz(t) * Resultant(1, 3)
Outputy(t) = Inputx(t) * Resultant(2, 1) + Inputy(t) * Resultant(2, 2) + Inputz(t) * Resultant(2, 3)
Outputz(t) = Inputx(t) * Resultant(3, 1) + Inputy(t) * Resultant(3, 2) + Inputz(t) * Resultant(3, 3)
Next t
End Sub