public MainPage()
    {
      InitializeComponent();

      m_timeCounter = new Timer(16);
      m_timeCounter.Elapsed += FrameTimeElapsed;
      m_timeCounter.Start();

      m_ogl = new OpenGLView();
      m_ogl.HeightRequest = Forms.Context.Resources.DisplayMetrics.HeightPixels;
      m_ogl.WidthRequest  = Forms.Context.Resources.DisplayMetrics.WidthPixels;
      m_ogl.HasRenderLoop = true;

      m_ogl.OnDisplay = (r) =>
      {
        if (!m_init)
        {
          InitOpengl((int)m_ogl.HeightRequest, (int)m_ogl.WidthRequest);
          m_init = true;
        }

        GL.ClearColor(System.Drawing.Color.CornflowerBlue);
        GL.Clear(ClearBufferMask.ColorBufferBit | ClearBufferMask.DepthBufferBit);
        GL.Viewport(0, 0, m_vpWidth, m_vpHeight);

        float ratio = (float)m_vpWidth / m_vpHeight;
        m_projMatrix = Matrix4.CreateOrthographic(-ratio, ratio, -1, 1);
        m_viewMatrix = Matrix4.LookAt(-Vector3.UnitZ, Vector3.Zero, Vector3.UnitY);
        m_mvpMatrix  = m_projMatrix * m_viewMatrix;
        Vector4 value = Vector4.Transform(new Vector4(0, 0, 0, 1), m_mvpMatrix);

        foreach (ShaderProgram shader in m_shaderPrograms)
        {
          GL.UseProgram(shader.ShaderProgramId);
          shader.CallAttributeLocationDataFuncs();
          shader.CallUniformLocationDataFuncs();
          shader.ShaderUseFunc();
          GL.Finish();
        }
      };

      StackLayout stackLayout = Content as StackLayout;
      stackLayout.Children.Add(m_ogl);
    }