3D Computer Graphic Animation : Back-Face Culling not working properly

Question

So I've tried to do a backface culling on the cube with Visual Basic. I'm sure that the code that i wrote is right, but somehow the it's not the back face that i want.

This is the data structure

Structure TLine
    Dim p1, p2 As Integer
End Structure

Structure TLine2
    Dim p1, p2 As TPoint
End Structure

Structure TPoint
    Dim x, y, z, w As Double
End Structure

Structure TPolygon
    Dim p1, p2, p3 As Integer
End Structure

This is the function

Sub SetPoint(ByRef V As TPoint, ByVal a As Double, ByVal b As Double, ByVal c As Double, ByVal d As Double)
    V.x = a
    V.y = b
    V.z = c
    V.w = 1
End Sub

Sub SetLine(ByVal idx As Integer, ByVal p1 As Integer, ByVal p2 As Integer)
    edge(idx).p1 = p1
    edge(idx).p2 = p2
End Sub

Sub SetPolygon(ByVal idx As Integer, ByVal p1 As Integer, ByVal p2 As Integer, ByVal p3 As Integer)
    polygon(idx).p1 = p1
    polygon(idx).p2 = p2
    polygon(idx).p3 = p3
End Sub

This is the draw function

Sub draw()
    bmp = New Bitmap(400, 400)
    Dim grp As Graphics = Graphics.FromImage(bmp)
    Dim i As Integer
    Dim p As New Pen(Color.Black)

    DOP.x = 0
    DOP.y = 0
    DOP.z = -2

    For i = 0 To 11
        temp_v1.x = v(polygon(i).p2).x - v(polygon(i).p1).x
        temp_v1.y = v(polygon(i).p2).y - v(polygon(i).p1).y
        temp_v1.z = v(polygon(i).p2).z - v(polygon(i).p1).z

        temp_v2.x = v(polygon(i).p3).x - v(polygon(i).p1).x
        temp_v2.y = v(polygon(i).p3).y - v(polygon(i).p1).y
        temp_v2.z = v(polygon(i).p3).z - v(polygon(i).p1).z

        normal.x = (temp_v1.y * temp_v2.z) - (temp_v2.y * temp_v1.z)
        normal.y = (temp_v1.z * temp_v2.x) - (temp_v2.z * temp_v1.x)
        normal.z = (temp_v1.x * temp_v2.y) - (temp_v2.x * temp_v1.y)

        result = (DOP.x * normal.x) + (DOP.y * normal.y) + (DOP.z * normal.z)

        If result < 0 Then
            grp.DrawLine(p, CInt(vs(polygon(i).p1).x), CInt(vs(polygon(i).p1).y), CInt(vs(polygon(i).p2).x), CInt(vs(polygon(i).p2).y))
            grp.DrawLine(p, CInt(vs(polygon(i).p1).x), CInt(vs(polygon(i).p1).y), CInt(vs(polygon(i).p3).x), CInt(vs(polygon(i).p3).y))
            grp.DrawLine(p, CInt(vs(polygon(i).p2).x), CInt(vs(polygon(i).p2).y), CInt(vs(polygon(i).p3).x), CInt(vs(polygon(i).p3).y))
            PictureBox1.Image = bmp
        End If
    Next
    'PictureBox1.Image = bmp
End Sub

And this is the set of point and polygon in one cube

SetPoint(v(0), -1, -1, 1, 1)
    SetPoint(v(1), 1, -1, 1, 1)
    SetPoint(v(2), 1, 1, 1, 1)
    SetPoint(v(3), -1, 1, 1, 1)
    SetPoint(v(4), -1, -1, -1, 1)
    SetPoint(v(5), 1, -1, -1, 1)
    SetPoint(v(6), 1, 1, -1, 1)
    SetPoint(v(7), -1, 1, -1, 1)

    SetPolygon(0, 0, 1, 2)
    SetPolygon(1, 0, 3, 2)
    SetPolygon(2, 5, 4, 7)
    SetPolygon(3, 5, 6, 7)
    SetPolygon(4, 3, 2, 6)
    SetPolygon(5, 3, 7, 6)
    SetPolygon(6, 4, 5, 1)
    SetPolygon(7, 4, 0, 1)
    SetPolygon(8, 1, 5, 6)
    SetPolygon(9, 1, 2, 6)
    SetPolygon(10, 4, 0, 3)
    SetPolygon(11, 4, 7, 3)

This is the preview of the cube that i tried to back face culling with a rotation.

Answer 1

Back-Face culling depends on the order of your vertices on the screen. You assume that either clockwise or counterclockwise are "front" and you draw only those.

In your preview I see that you lack some of the front faces and you draw some back faces that you shouldn't. You just need to find those few broken triangles and revert their direction by swapping 2nd and 3rd vertex.