How Can I Improve My Rotation3d In Wpf

<Window x:Class="WpfApplication6.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525" WindowState="Maximized">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="*"/>
            <RowDefinition Height="20"/>
        </Grid.RowDefinitions>
        <Grid x:Name="background" removed="LightGray" MouseMove="background_MouseMove" MouseDown="background_MouseDown" MouseUp="background_MouseUp"   >
            <!--<Border x:Name="border">-->
                <Viewport3D x:Name="viewport" ClipToBounds="False" >
                    <Viewport3D.Camera>
                        <OrthographicCamera x:Name="myCameraMatrix"></OrthographicCamera>
                    </Viewport3D.Camera>
                    <ModelVisual3D x:Name="model">
                        <ModelVisual3D.Content>
                            <Model3DGroup x:Name="group">
                                <AmbientLight Color="White" />
                                <DirectionalLight x:Name="directionlight" Color="White" Direction="-5,-5,-7"/>
                            </Model3DGroup>
                        </ModelVisual3D.Content>
                    </ModelVisual3D>
                </Viewport3D>
            <!--</Border>-->            
        </Grid>        
    </Grid>
</Window>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.InteropServices;
using System.Windows;
using System.Windows.Media;
using System.Windows.Media.Media3D;
using System.Diagnostics;
using System.Windows.Input;

namespace WpfCustomControlLibrary1
{
    public class MouseUtilities
    {
        public static double propangle;

        

        private FrameworkElement _eventSource;
        private Point _previousPosition2D;
        private Vector3D _previousPosition3D = new Vector3D(0, 0, 1);

        private Transform3DGroup _transform;
        public RotateTransform3D _rotateTransform;
        public ScaleTransform3D _scale = new ScaleTransform3D();
        private AxisAngleRotation3D _rotation = new AxisAngleRotation3D();
        private TranslateTransform3D _translate = new TranslateTransform3D();

        private double _rotationFactor;      
        public MouseUtilities(double rotationFactor = 1.0)
        {            
            _rotationFactor = rotationFactor;           
            _transform = new Transform3DGroup();
            _transform.Children.Add(_scale);
            _rotateTransform = new RotateTransform3D(_rotation);
            _transform.Children.Add(_rotateTransform);
            _transform.Children.Add(_translate);           
        }

        /// <summary>
        ///     A transform to move the camera or scene to the trackball's
        ///     current orientation and scale.
        /// </summary>
        public Transform3D Transform
        {
            get { return _transform; }
        }

        /// <summary>
        /// Rotation component of the transform
        /// </summary>
        public Transform3D RotateTransform
        {
            get { return _rotateTransform; }
        }

        #region Event Handling

        /// <summary>
        ///     The FrameworkElement we listen to for mouse events.
        /// </summary>
        public FrameworkElement EventSource
        {
            get { return _eventSource; }
            set
            {
                if (_eventSource != null)
                {                 
                    _eventSource.PreviewMouseDown -= this.OnMouseDown;
                    _eventSource.PreviewMouseUp -= this.OnMouseUp;
                    _eventSource.PreviewMouseMove -= this.OnMouseMove;
                    _eventSource.PreviewMouseWheel -= this.OnMouseWheel;
                }
                _eventSource = value;
                _eventSource.PreviewMouseDown += this.OnMouseDown;
                _eventSource.PreviewMouseUp += this.OnMouseUp;
                _eventSource.PreviewMouseMove += this.OnMouseMove;
                _eventSource.PreviewMouseWheel += this.OnMouseWheel;
            }
        }
        
        private void OnMouseUp(object sender, MouseEventArgs e)
        {
            Mouse.Capture(EventSource, CaptureMode.None);           
        }
       
        private void OnMouseWheel(object sender, MouseWheelEventArgs e)
        {
            Mouse.Capture(EventSource, CaptureMode.None);
            double scale = 1;
            if (e.Delta > 0 && _scale.ScaleX < 1.5)
            {
                scale = scale + 0.10;
                _scale.ScaleX *= scale;
                _scale.ScaleY *= scale;
                _scale.ScaleZ *= scale;
            }
            else if (e.Delta < 0 && _scale.ScaleX > 0.15)
            {
                scale = scale - 0.10;
                _scale.ScaleX *= scale;
                _scale.ScaleY *= scale;
                _scale.ScaleZ *= scale;
            }
        }

        private void OnMouseDown(object sender, MouseEventArgs e)
        {
            Mouse.Capture(EventSource, CaptureMode.SubTree);
            _previousPosition2D = e.GetPosition(EventSource);
            _previousPosition3D = ProjectToTrackball(EventSource.ActualWidth, EventSource.ActualHeight, _previousPosition2D);
            mouseLastPosition = new Point(_previousPosition2D.X - EventSource.ActualWidth / 2, EventSource.ActualHeight / 2 - _previousPosition2D.Y);
        }
        Point mouseLastPosition;
        private void OnMouseMove(object sender, MouseEventArgs e)
        {
           
            Point currentPosition = e.GetPosition(EventSource);
            _eventSource.RenderTransformOrigin = currentPosition;
            if (e.RightButton == MouseButtonState.Pressed)
            {
                Pan(currentPosition);
            }
            if (e.LeftButton == MouseButtonState.Pressed )
            {                
                Look(currentPosition);
            }           
            _previousPosition2D = currentPosition;
        }
                
        #endregion Event Handling
        double rotationangle;
        public static bool brotation;
        public static double xxang = 0;
        public static double xang=0;

        private void Look(Point currentPosition)
        {
            Vector3D currentPosition3D = ProjectToTrackball(EventSource.ActualWidth, EventSource.ActualHeight, currentPosition);

            if (_previousPosition3D.Equals(currentPosition3D)) return;

            Vector3D axis = Vector3D.CrossProduct(_previousPosition3D, currentPosition3D);

            rotationangle = _rotationFactor * Vector3D.AngleBetween(_previousPosition3D, currentPosition3D);

            Quaternion delta = new Quaternion(axis, -rotationangle);
           
            Quaternion q = new Quaternion(_rotation.Axis, _rotation.Angle);

            q *= delta;

            _rotation.Axis = q.Axis;
            _rotation.Angle = q.Angle;

            _previousPosition3D = currentPosition3D;
        }

        private void Pan(Point currentPosition)
        {
            Vector3D currentPosition3D = ProjectToTrackball(
                EventSource.ActualWidth, EventSource.ActualHeight, currentPosition);

            Vector change = Point.Subtract(_previousPosition2D, currentPosition);
            Vector3D changeVector = new Vector3D(change.X, change.Y, 0);
            _translate.OffsetX -= changeVector.X * .01;
            _translate.OffsetY += changeVector.Y * .01;
            _translate.OffsetZ -= changeVector.Z * .01;
            _previousPosition3D = currentPosition3D;
        }

        private Vector3D ProjectToTrackball(double width, double height, Point point)
        {
            double x = point.X / (width / 2);    // Scale so bounds map to [0,0] - [2,2]
            double y = point.Y / (height / 2);
            x = x - 1;                           // Translate 0,0 to the center
            y = 1 - y;                           // Flip so +Y is up instead of down
            double z2 = 1 - x * x - y * y;       // z^2 = 1 - x^2 - y^2
            double z = z2 > 0 ? Math.Sqrt(z2) : 0;
            return new Vector3D(x, y, z);
        }
        
    }
    
}

my xaml.cs code is here
<pre lang="c#">

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Media.Media3D;
using System.Windows.Navigation;
using System.Windows.Shapes;
using _3DTools;
using WpfCustomControlLibrary1;

namespace WpfApplication6
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        MouseUtilities trackball = new MouseUtilities();
        ScreenSpaceLines3D line = new ScreenSpaceLines3D();
        public MainWindow()
        {
            InitializeComponent();
            SetMatrixCamera();            
            trackball.EventSource = background;
            //myCameraMatrix.Transform = trackball.Transform;
            Point3D p0 = new Point3D(-0.5, 0.5, 0.5);
            Point3D p1 = new Point3D(0.5, 0.5, 0.5);
            Point3D p2 = new Point3D(-0.5, -0.5, 0.5);
            Point3D p3 = new Point3D(0.5, -0.5, 0.5);

            Point3D p4 = new Point3D(-0.5, 0.5, -0.5);//0
            Point3D p5 = new Point3D(0.5, 0.5, -0.5);//1
            Point3D p6 = new Point3D(-0.5, -0.5, -0.5);//2
            Point3D p7 = new Point3D(0.5, -0.5, -0.5);//3
            line.Points.Add(p0);
            line.Points.Add(p1);
            line.Points.Add(p2);
            line.Points.Add(p3);
            line.Points.Add(p0);
            line.Points.Add(p2);
            line.Points.Add(p3);
            line.Points.Add(p1);

            line.Points.Add(p4);//0
            line.Points.Add(p5);//1
            line.Points.Add(p6);//2
            line.Points.Add(p7);//3
            line.Points.Add(p4);//0
            line.Points.Add(p6);//2
            line.Points.Add(p7);//
            line.Points.Add(p5);//

            line.Points.Add(p0);
            line.Points.Add(p4);
            line.Points.Add(p1);
            line.Points.Add(p5);
            line.Points.Add(p2);
            line.Points.Add(p6);
            line.Points.Add(p3);
            line.Points.Add(p7);
            line.Color = Colors.Red;
            line.Thickness = 1.0;
            
            line.Transform = trackball.Transform;
            viewport.Children.Add(line);
        }

        private void SetMatrixCamera()
        {
            Point3D cameraPosition = new Point3D(0, 0, 20);
            Vector3D lookDirection = new Vector3D(0, 0, -20);
            Vector3D upDirection = new Vector3D(0, 1, 0);
            double w = 6;
            myCameraMatrix.Position = cameraPosition;
            myCameraMatrix.LookDirection = lookDirection;
            myCameraMatrix.Width = w;
            myCameraMatrix.UpDirection = upDirection;
            double zn = 1;
            double zf = 100;
            myCameraMatrix.NearPlaneDistance = zn;
            myCameraMatrix.FarPlaneDistance = zf;
        }

        private void background_MouseMove(object sender, MouseEventArgs e)
        {
            
        }
        bool isMouseDown;
        Point mouseLastPosition;
        private void background_MouseDown(object sender, MouseButtonEventArgs e)
        {
            if (e.LeftButton != MouseButtonState.Pressed) return;
            isMouseDown = true;
            Point currentPosistion = Mouse.GetPosition(viewport);
            mouseLastPosition = new Point(currentPosistion.X - viewport.ActualWidth / 2, viewport.ActualHeight / 2 - currentPosistion.Y);
        }

        private void background_MouseUp(object sender, MouseButtonEventArgs e)
        {
            isMouseDown = false;
        }
    }
}