[RESOLVED] Making a copy of a class and modifing it changes original class values PS: With ByVal

I have recently been trying to learn 3D and create a small 3DEngine.
I made the following Class:

VB.NET Code:

Public Class TriangularFace
        Private arr_Vertices(2) As PointVector
        Public Sub New(ByVal new_Vertex0 As PointVector, ByVal new_Vertex1 As PointVector, ByVal new_Vertex2 As PointVector)
            arr_Vertices(0) = new_Vertex0 : arr_Vertices(1) = new_Vertex1 : arr_Vertices(2) = new_Vertex2
        End Sub
        Public Sub New(ByVal new_Vertices() As PointVector)
            If new_Vertices.Length <> 3 Then
                Throw New Exception("The array does not have the proper size for a triangular face.")
            Else
                arr_Vertices = new_Vertices
            End If
        End Sub
        Public Property Vertex_0 As PointVector
            Get
                Return arr_Vertices(0)
            End Get
            Set(ByVal new_Vertex0 As PointVector)
                arr_Vertices(0) = new_Vertex0
            End Set
        End Property
        Public Property Vertex_1 As PointVector
            Get
                Return arr_Vertices(1)
            End Get
            Set(ByVal new_Vertex1 As PointVector)
                arr_Vertices(1) = new_Vertex1
            End Set
        End Property
        Public Property Vertex_2 As PointVector
            Get
                Return arr_Vertices(2)
            End Get
            Set(ByVal new_Vertex2 As PointVector)
                arr_Vertices(2) = new_Vertex2
            End Set
        End Property
    End Class

The issue is that assuming I make a new Triangle based on the values of an existing triangle and then change it's values, the original triangle will also see it's values modified:

VB.NET Code:

Private Sub PictureBox1_Paint(sender As Object, e As PaintEventArgs) Handles PictureBox1.Paint
        Dim GFX As Graphics = e.Graphics
 
        For Each Triangle As Temp.TriangularFace In Cube.Faces
 
            MsgBox("Original = " & Triangle.Vertex_0.Z & " " & Triangle.Vertex_1.Z & " " & Triangle.Vertex_2.Z) 
            Dim ZFixTriangle As New Temp.TriangularFace(Triangle.Vertex_0, Triangle.Vertex_1, Triangle.Vertex_2) 'These two lines affect the z values for PointVectors
            ZFixTriangle.Vertex_0.Z += 3 : ZFixTriangle.Vertex_1.Z += 3 : ZFixTriangle.Vertex_2.Z += 3               'In the "Triangle" variable and not only "ZFixTriangle"
            MsgBox("New = " & ZFixTriangle.Vertex_0.Z & " " & ZFixTriangle.Vertex_1.Z & " " & ZFixTriangle.Vertex_2.Z)
 
        Next
End Sub

Here is the PointVector Class if needed:

VB.NET Code:

Public Class PointVector
        Private v_X, v_Y, v_Z, v_W As Single
        Public Sub New(ByVal X As Single, ByVal Y As Single, ByVal Z As Single)
            v_X = X : v_Y = Y : v_Z = Z : v_W = 1
        End Sub
        Public Property X As Single
            Get
                Return v_X
            End Get
            Set(ByVal new_X As Single)
                v_X = new_X
            End Set
        End Property
        Public Property Y As Single
            Get
                Return v_Y
            End Get
            Set(ByVal new_Y As Single)
                v_Y = new_Y
            End Set
        End Property
        Public Property Z As Single
            Get
                Return v_Z
            End Get
            Set(ByVal new_Z As Single)
                v_Z = new_Z
            End Set
        End Property
        Public Property W As Single
            Get
                Return v_W
            End Get
            Set(ByVal new_W As Single)
                v_W = new_W
            End Set
        End Property
    End Class

Your Vertex properties are of type PointVector... but PointVector is a class, so when you assign a value of PointVector to a variable/property/etc you actually assign a pointer to the same item - not a copy.

That means in the line you create ZFixTriangle, you are actually linking it to the instance you passed in (so Triangle.Vertex_0 etc).


What you need to do is create a Clone of the instances instead, which you can do by creating a method for that in the PointVector class, eg:

Code:

---

Public Function Clone() as PointVector
    Dim clonedInstance as New PointVector(v_X, v_Y, v_Z)
    clonedInstance.W = v_W
    Return clonedInstance
End Function

---

...and then call this either in the line that initialises ZFixTriangle, or within the constructor for TriangularFace.

Thank you sir, simple and accurate answer making it an easy fix for me :)