anchor.diff:          //  Add a bit to theta (how much we're rotating the scene) and create the modelview
           //  and normal matrices.
     
  -        theta <- theta + 0.01f
  +        theta <- theta + 0.015f
           scene.CreateModelviewAndNormalMatrix(theta)
  -            
  +
           //  Clear the color and depth buffer.
  -        gl.ClearColor(0.f, 0.f, 0.f, 1.f)
  +        gl.ClearColor(1.f, 1.f, 1.f, 0.f)
           gl.Clear(OpenGL.GL_COLOR_BUFFER_BIT ||| OpenGL.GL_DEPTH_BUFFER_BIT ||| OpenGL.GL_STENCIL_BUFFER_BIT)
  +        //gl.Color(0.f,0.6f,0.8f,0.f)
  +      
  +        //gl.BlendColor(1.f,1.f,1.f,0.f)
  +        gl.Enable(OpenGL.GL_DEPTH_TEST)
  +        gl.DepthFunc(OpenGL.GL_LESS)         
               
           //  Render the scene in either immediate or retained mode.
  -        do 
  -            //axies.Render(gl, RenderMode.Render)
  -            //scene.RenderImmediateMode(gl)
  -            scene.RenderRetainedMode(gl, false)
  -
  -//        match comboRenderMode.SelectedIndex with
  -//        | 0 -> scene.RenderRetainedMode(gl, checkBoxUseToonShader.IsChecked.Value)
  -//        | 1 ->
  -//            do 
  -//                axies.Render(gl, RenderMode.Design)
  -//                scene.RenderImmediateMode(gl)
  -//        | _ -> () 
  +        axies.Render(gl, RenderMode.Design)
  +        match comboRenderModeSelectedIndex with
  +        | 0 -> scene.RenderRetainedMode(gl, checkBoxUseToonShaderIsChecked)
  +        | 1 -> gl.Color(0.f,0.6f,0.8f,0.f)
  +               scene.RenderImmediateMode(gl)
  +        | _ -> () 
           
       let OpenGLControl_OpenGLInitialized(sender : obj, args : OpenGLEventArgs) =
           
  
positive.code:         let mutable dv = new vec3()
          dv.x <- -1.5f*b*(Sin (1.5f*u))*(Cos u) - (a + b*(Cos (1.5f*u))*(Sin u))
          dv.y <- -1.5f*b*(Sin (1.5f*u))*(Sin u) + (a + b*(Cos (1.5f*u))*(Cos u))
          dv.z <- 1.5f*c*(Cos (1.5f*u))
              
          let q = glm.normalize(dv)
          let qvn = glm.normalize(new vec3(q.y, -q.x, 0.0f))
  
negative.code: 
          let positionAttribute = 0u
          let normalAttribute = 1u
          let indexAttribute = 2u
          let attributeLocations = new Dictionary<uint32, string>()
          do 
              attributeLocations.Add (positionAttribute, "Position")
              attributeLocations.Add (normalAttribute, "Normal")
              attributeLocations.Add (indexAttribute, "Index")
  
          //  Scene geometry - a trefoil knot.
          //let trefoilKnot = new TrefoilKnot()   
  