public void Shutdown()
        {
            // Release the light object.
            Light = null;
            // Release the camera object.
            Camera = null;

            // Release the Second Cube model object.
            CubeModel2?.Shutdown();
            CubeModel2 = null;
            // Release the Third Cube model object.
            CubeBumpMapModel3?.Shutdown();
            CubeBumpMapModel3 = null;
            // Release the First cube model object.
            CubeModel1?.Shutdown();
            CubeModel1 = null;
            // Release the shader manager object.
            ShaderManager?.ShutDown();
            ShaderManager = null;
            // Release the Direct3D object.
            D3D?.ShutDown();
            D3D = null;
        }