WPF Interactive 2D Drawing

<Window x:Class="WpfApplication21.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Interactive 2D Drawing" Height="400" Width="400">
<Window.Resources>
<SolidColorBrush x:Key="MyGrayGridBrush" Color="YellowGreen"/>
</Window.Resources>
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition/>
</Grid.RowDefinitions>
 
<ToolBarTray Grid.Row="0">
<ToolBar>
    <RadioButton x:Name="rbSquare" 
        IsChecked="True" ToolTip="Add Square">
        <Rectangle Width="15" Height="15" 
            Stroke="Blue" Fill="LightBlue"/>
    </RadioButton>
 
    <RadioButton x:Name="rbRectangle" 
        IsChecked="False" ToolTip="Add Rectangle">
        <Rectangle Width="20" Height="12"  
            Stroke="Blue" Fill="LightBlue"/>
    </RadioButton>
 
    <RadioButton x:Name="rbCircle" 
        IsChecked="False" ToolTip="Add Circle">
        <Ellipse Width="18" Height="18" 
                    Stroke="Blue" Fill="LightBlue"/>
    </RadioButton>
 
    <RadioButton x:Name="rbEllipse"  
        IsChecked="False" ToolTip="Add Ellipse">
        <Ellipse Width="22" Height="15" 
                    Stroke="Blue" Fill="LightBlue"/>
    </RadioButton>
 
    <RadioButton x:Name="rbCombine"  
        IsChecked="False" ToolTip="Combine shapes">
        <Path Fill="LightBlue" Stroke="Blue">
            <Path.Data>
                <CombinedGeometry>
                    <CombinedGeometry.Geometry1>
                        <EllipseGeometry  
                            RadiusX="8" 
                            RadiusY="8" 
                            Center="8,8"/>
                    </CombinedGeometry.Geometry1>
                    <CombinedGeometry.Geometry2>
                        <EllipseGeometry 
                            RadiusX="8" 
                            RadiusY="8" 
                            Center="20,8"/>
                    </CombinedGeometry.Geometry2>
                </CombinedGeometry>
            </Path.Data>
        </Path>
    </RadioButton>
 
    <RadioButton x:Name="rbSelect"  
        IsChecked="False" ToolTip="Select/Move">
        <Polygon  
        Points="6 1,10 1,10 10,14 10,8 16,2 10,6 10"  
            Fill="LightBlue" Stroke="Blue">
            <Polygon.RenderTransform>
                <RotateTransform CenterX="8" 
                                    CenterY="8" 
                                    Angle="225"/>
            </Polygon.RenderTransform>
        </Polygon>
    </RadioButton>
 
    <RadioButton x:Name="rbDelete"  
        IsChecked="False" ToolTip="Delete">
        <Grid>
            <Line X1="2" Y1="2" X2="14"  
                    Y2="14" Stroke="Blue"/>
            <Line X1="2" Y1="14" X2="14"  
                    Y2="2" Stroke="Blue"/>
        </Grid>
    </RadioButton>
</ToolBar>
</ToolBarTray>
 
<Viewbox Stretch="Uniform" Grid.Row="1">
<Border Margin="5" BorderBrush="Black" 
        BorderThickness="1" Grid.Row="1" 
        HorizontalAlignment="Left">
    <Canvas Name="canvas1" Width="400" 
            Height="345" ClipToBounds="True" 
Background="{StaticResource MyGrayGridBrush}" 
MouseLeftButtonDown="OnMouseLeftButtonDown" 
MouseLeftButtonUp="OnMouseLeftButtonUp"  
MouseMove="OnMouseMove"/>
</Border>
</Viewbox>
</Grid>
</Window> 

public partial class MainWindow : Window
{
private List<Path> paths = new List<Path>();
private Point startPoint = new Point();
private Shape rubberBand = null;
Point currentPoint = new Point();
private bool isDragging = false;
private bool isDown = false;
private Path originalElement = new Path();
private Path movingElement = new Path();
private Path path1 = new Path();
private Path path2 = new Path();
private SolidColorBrush fillColor =
                        new SolidColorBrush();
private SolidColorBrush borderColor =
                        new SolidColorBrush();
private SolidColorBrush selectFillColor =
                        new SolidColorBrush();
private SolidColorBrush selectBorderColor =
                        new SolidColorBrush();
 
public MainWindow()
{
    InitializeComponent();
 
    fillColor.Color = Colors.LightGray;
    fillColor.Opacity = 0.5;
    borderColor.Color = Colors.Gray;
    selectFillColor.Color = Colors.LightCoral;
    selectFillColor.Opacity = 0.5;
    selectBorderColor.Color = Colors.Red;
}
 
private void OnMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
    if (!canvas1.IsMouseCaptured)
    {
        startPoint = e.GetPosition(canvas1);
        canvas1.CaptureMouse();
 
        if (rbCombine.IsChecked == true)
        {
            SetCombineShapes(e);
        }
        else if (rbSelect.IsChecked == true)
        {
            if (canvas1 == e.Source)
                return;
            isDown = true;
            originalElement = (Path)e.Source;
            e.Handled = true;
        }
        else if (rbDelete.IsChecked == true)
        {
            originalElement = (Path)e.Source;
            DeleteShape(originalElement);
        }
    }
}
 
private void OnMouseLeftButtonUp(object sender, MouseButtonEventArgs e)
{
    if (rbSquare.IsChecked == true)
        AddSquare(startPoint, currentPoint);
    else if (rbRectangle.IsChecked == true)
        AddRectangle(startPoint, currentPoint);
    else if (rbCircle.IsChecked == true)
        AddCircle(startPoint, currentPoint);
    else if (rbEllipse.IsChecked == true)
        AddEllipse(startPoint, currentPoint);
 
    if (rubberBand != null)
    {
        canvas1.Children.Remove(rubberBand);
        rubberBand = null;
        canvas1.ReleaseMouseCapture();
    }
 
    if (rbSelect.IsChecked == true)
    {
        if (isDown)
        {
            DragFinishing(false);
            e.Handled = true;
        }
    }
}
 
private void AddSquare(Point point, Point currentPoint1)
{
    Path path = new Path();
    path.Fill = fillColor;
    path.Stroke = borderColor;
    RectangleGeometry rg = new RectangleGeometry();
    double width = Math.Abs(point.X - currentPoint1.X);
    double height = Math.Abs(point.Y - currentPoint1.Y);
    double left = Math.Min(point.X, currentPoint1.X);
    double top = Math.Min(point.Y, currentPoint1.Y);
    double side = width;
    if (width > height)
        side = height;
    rg.Rect = new Rect(left, top, side, side);
    path.Data = rg;
    paths.Add(path);
    canvas1.Children.Add(paths[paths.Count - 1]);
}
 
private void AddRectangle(Point point, Point currentPoint1)
{
    Path path = new Path();
    path.Fill = fillColor;
    path.Stroke = borderColor;
    RectangleGeometry rg = new RectangleGeometry();
    double width = Math.Abs(point.X - currentPoint1.X);
    double height = Math.Abs(point.Y - currentPoint1.Y);
    double left = Math.Min(point.X, currentPoint1.X);
    double top = Math.Min(point.Y, currentPoint1.Y);
    rg.Rect = new Rect(left, top, width, height);
    path.Data = rg;
    paths.Add(path);
    canvas1.Children.Add(paths[paths.Count - 1]);
}
 
private void AddCircle(Point point, Point currentPoint1)
{
    Path path = new Path();
    path.Fill = fillColor;
    path.Stroke = borderColor;
    EllipseGeometry eg = new EllipseGeometry();
    double width = Math.Abs(point.X - currentPoint1.X);
    double height = Math.Abs(point.Y - currentPoint1.Y);
    double left = Math.Min(point.X, currentPoint1.X);
    double top = Math.Min(point.Y, currentPoint1.Y);
    double side = width;
    if (width > height)
        side = height;
    eg.Center = new Point(left + side / 2,
        top + side / 2);
    eg.RadiusX = side / 2;
    eg.RadiusY = side / 2;
    path.Data = eg;
    paths.Add(path);
    canvas1.Children.Add(paths[paths.Count - 1]);
}
 
private void AddEllipse(Point point, Point currentPoint1)
{
    Path path = new Path();
    path.Fill = fillColor;
    path.Stroke = borderColor;
    EllipseGeometry eg = new EllipseGeometry();
    double width = Math.Abs(point.X - currentPoint1.X);
    double height = Math.Abs(point.Y - currentPoint1.Y);
    double left = Math.Min(point.X, currentPoint1.X);
    double top = Math.Min(point.Y, currentPoint1.Y);
    eg.Center = new Point(left + width / 2,
        top + height / 2);
    eg.RadiusX = width / 2;
    eg.RadiusY = height / 2;
    path.Data = eg;
    paths.Add(path);
    canvas1.Children.Add(paths[paths.Count - 1]);
}
 
private void DragFinishing(bool cancel)
{
    Mouse.Capture(null);
    if (isDragging)
    {
        if (!cancel)
        {
            currentPoint = Mouse.GetPosition(canvas1);
            TranslateTransform tt0 = new TranslateTransform();
            TranslateTransform tt = new TranslateTransform();
            tt.X = currentPoint.X - startPoint.X;
            tt.Y = currentPoint.Y - startPoint.Y;
            Geometry geometry =
                        (RectangleGeometry)new RectangleGeometry();
 
            string s = originalElement.Data.ToString();
 
            if (s == "System.Windows.Media.EllipseGeometry")
                geometry = (EllipseGeometry)originalElement.Data;
            else if (s == "System.Windows.Media.RectangleGeometry")
                geometry = (RectangleGeometry)originalElement.Data;
            else if (s == "System.Windows.Media.CombinedGeometry")
                geometry = (CombinedGeometry)originalElement.Data;
 
            if (geometry.Transform.ToString() != "Identity")
            {
                tt0 = (TranslateTransform)geometry.Transform;
                tt.X += tt0.X;
                tt.Y += tt0.Y;
            }
            geometry.Transform = tt;
            canvas1.Children.Remove(originalElement);
            originalElement = new Path();
            originalElement.Fill = fillColor;
            originalElement.Stroke = borderColor;
            originalElement.Data = geometry;
            canvas1.Children.Add(originalElement);
        }
 
        canvas1.Children.Remove(movingElement);
        movingElement = null;
    }
    isDragging = false;
    isDown = false;
}
 
private void OnMouseMove(object sender, MouseEventArgs e)
{
    if (canvas1.IsMouseCaptured)
    {
        currentPoint = e.GetPosition(canvas1);
        if (rubberBand == null)
        {
            rubberBand = new Rectangle();
            rubberBand.Stroke = Brushes.LightCoral;
            rubberBand.StrokeDashArray =
                new DoubleCollection(new double[] { 4, 2 });
            if (rbSquare.IsChecked == true ||
                rbRectangle.IsChecked == true ||
                rbCircle.IsChecked == true ||
                rbEllipse.IsChecked == true)
            {
                canvas1.Children.Add(rubberBand);
 
            }
        }
 
        double width = Math.Abs(
            startPoint.X - currentPoint.X);
        double height = Math.Abs(
            startPoint.Y - currentPoint.Y);
        double left = Math.Min(
            startPoint.X, currentPoint.X);
        double top = Math.Min(
            startPoint.Y, currentPoint.Y);
 
        rubberBand.Width = width;
        rubberBand.Height = height;
        Canvas.SetLeft(rubberBand, left);
        Canvas.SetTop(rubberBand, top);
 
        if (rbSelect.IsChecked == true)
        {
            if (isDown)
            {
                if (!isDragging && Math.Abs(currentPoint.X - startPoint.X) >
                    SystemParameters.MinimumHorizontalDragDistance &&
                    Math.Abs(currentPoint.Y - startPoint.Y) >
                    SystemParameters.MinimumVerticalDragDistance)
                    DragStarting();
                if (isDragging)
                    DragMoving();
            }
        }
    }
}
 
private void DragMoving()
{
    currentPoint = Mouse.GetPosition(canvas1);
    TranslateTransform tt = new TranslateTransform();
    tt.X = currentPoint.X - startPoint.X;
    tt.Y = currentPoint.Y - startPoint.Y;
    movingElement.RenderTransform = tt;
}
 
private void DragStarting()
{
    isDragging = true;
    movingElement = new Path();
    movingElement.Data = originalElement.Data;
    movingElement.Fill = selectFillColor;
    movingElement.Stroke = selectBorderColor;
    canvas1.Children.Add(movingElement);
}
 
private void DeleteShape(Path path)
{
    path.Stroke = selectBorderColor;
    string msg =
        "Do you really want to delete this shape?";
    string title = "Delete Shape?";
    MessageBoxButton buttons = MessageBoxButton.YesNo;
    MessageBoxImage icon = MessageBoxImage.Warning;
    MessageBoxResult result =
        MessageBox.Show(msg, title, buttons, icon);
    if (result == MessageBoxResult.Yes)
        canvas1.Children.Remove(path);
    else
    {
        path.Stroke = borderColor;
        return;
    }
}
 
private void SetCombineShapes(MouseButtonEventArgs e)
{
    if (path1.Name != "path1Selected")
    {
        path1 = (Path)e.Source;
        path1.Cursor = Cursors.Hand;
        path1.Stroke = selectBorderColor;
        path1.Name = "path1Selected";
    }
    else
    {
        if (path2 != null)
        {
            path2.Stroke = borderColor;
            path2.Cursor = Cursors.Arrow;
        }
        path2 = (Path)e.Source;
        path2.Cursor = Cursors.Hand;
        path2.Stroke = selectBorderColor;
 
        ContextMenu cm = new ContextMenu();
        path2.ContextMenu = cm;
        MenuItem mi = new MenuItem();
        mi.Header = "Union";
        mi.Click +=
            new RoutedEventHandler(Union_Click);
        cm.Items.Add(mi);
        mi = new MenuItem();
        mi.Header = "Xor";
        mi.Click +=
            new RoutedEventHandler(Xor_Click);
        cm.Items.Add(mi);
        mi = new MenuItem();
        mi.Header = "Intersect";
        mi.Click +=
            new RoutedEventHandler(Intersect_Click);
        cm.Items.Add(mi);
        mi = new MenuItem();
        mi.Header = "Exclude";
        mi.Click +=
            new RoutedEventHandler(Exclude_Click);
        cm.Items.Add(mi);
    }
}
 
private void Union_Click(
    object sender, RoutedEventArgs e)
{
    CombineShapes(path1, path2, "Union");
    path1.Name = "";
}
 
private void Xor_Click(object sender,
    RoutedEventArgs e)
{
    CombineShapes(path1, path2, "Xor");
    path1.Name = "";
}
 
private void Intersect_Click(object sender,
    RoutedEventArgs e)
{
    CombineShapes(path1, path2, "Intersect");
    path1.Name = "";
}
 
private void Exclude_Click(object sender,
    RoutedEventArgs e)
{
    CombineShapes(path1, path2, "Exclude");
    path1.Name = "";
}
 
private void CombineShapes(Path p1, Path p2, string s)
{
    Path myPath = new Path();
    myPath.Fill = fillColor;
    myPath.Stroke = borderColor;
    CombinedGeometry cg = new CombinedGeometry();
 
    if (s == "Union")
        cg.GeometryCombineMode =
            GeometryCombineMode.Union;
    else if (s == "Xor")
        cg.GeometryCombineMode =
            GeometryCombineMode.Xor;
    else if (s == "Intersect")
        cg.GeometryCombineMode =
            GeometryCombineMode.Intersect;
    else if (s == "Exclude")
        cg.GeometryCombineMode =
            GeometryCombineMode.Exclude;
    cg.Geometry1 = p1.Data;
    cg.Geometry2 = p2.Data;
    myPath.Data = cg;
    paths.Add(myPath);
    canvas1.Children.Add(paths[paths.Count - 1]);
    canvas1.Children.Remove(p1);
    canvas1.Children.Remove(p2);
}
}

reference : Practical WPF Graphics Programming