vb.net opengl - Hidden Line/Surface Removal

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VB

OpenGL

Hello Everyone,

I am a newbie to Opengl and I am using Tao framework in opengl.

I have read about hidden lien removal etc on various internet links but, I am not clear about the process.

Can some one please help me in understanding the process?

I have a simple starter code here:

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Dim hDC = Me.CreateGraphics.GetHdc
        glf.EnableOpenGL(hDC)

        Me.Show()
        Application.DoEvents()
        Dim z = -10.0F


        Gl.glShadeModel(Gl.GL_SMOOTH)
        Gl.glClearColor(0.0F, 0.0F, 0.0F, 0.0F)
        Gl.glClearDepth(1.0F)
        Gl.glEnable(Gl.GL_DEPTH_TEST)
        Gl.glDepthFunc(Gl.GL_LEQUAL)
        Gl.glHint(Gl.GL_PERSPECTIVE_CORRECTION_HINT, Gl.GL_NICEST)

        Gl.glMatrixMode(Gl.GL_PROJECTION)
        Gl.glLoadIdentity()
        Glu.gluPerspective(45.0F, Me.Width / Me.Height, 0.1, 1000)
        Gl.glMatrixMode(Gl.GL_MODELVIEW)
        Gl.glLoadIdentity()

        Gl.glClear(Gl.GL_DEPTH_BUFFER_BIT)
        Gl.glClear(Gl.GL_COLOR_BUFFER_BIT)Gl.glPushMatrix()
        Gl.glPushMatrix()
       'drawSquare()
        drawTriangle()
        Gl.glPopMatrix()
        Gl.glFlush()
        Gdi.SwapBuffers(hDC)
End Sub
 Public Function drawSquare()
        Dim z As Single = -5.0F
        Gl.glBegin(Gl.GL_POLYGON)
        Gl.glVertex3f(-1.0F, 1.0F, z)
        Gl.glVertex3f(1.0F, 1.0F, z)
        Gl.glVertex3f(1.0F, -1.0F, z)
        Gl.glVertex3f(-1.0F, -1.0F, z)
        Gl.glEnd()
        Return 0
    End Function

    Public Function drawTriangle()
        Dim z As Single = -4.0F
        Gl.glBegin(Gl.GL_POLYGON)
        'Gl.glColor3f(0.5F, 0.5F, 0.5F)
        Gl.glVertex3f(0.0F, 0.0F, z)
        Gl.glVertex3f(1.0F, 1.0F, z)
        Gl.glVertex3f(1.0F, -1.0F, z)
        Gl.glEnd()
        Return 0
    End Function

Now this code initializes the opengl window and makes a square and a triangle.
What I want to do is:
get the part of Square which is not overlapped by the triangle.

Can some one please guide me through this?

Thanks in advance,
Videep