Code

diagram.AllowInplaceEdit = false;

void OnNodeDoubleClicked(object sender, NodeEventArgs e)
{
	var overlay = diagram.Factory.CreateShapeNode(e.Node.Bounds);
	overlay.Text = "description text here";
	overlay.Brush = Brushes.Transparent;
	overlay.RotateText = true;

	var center = overlay.GetCenter();
	overlay.ResizeToFitText(FitSize.KeepHeight);
	overlay.ResizeToFitText(FitSize.KeepWidth);
	overlay.Move(
		center.X - overlay.Bounds.Width / 2,
		center.Y - overlay.Bounds.Height / 2);
	overlay.RotationAngle = 45;
} 

Code

var newBounds = new Rect(centerX - width / 2, centerY - height / 2, width, height);
rectangle1Node.Bounds = newBounds;
 

Code

// event handler of diagram's DoubleClicked event
void OnDiagramDoubleClicked(object sender, DiagramEventArgs e)
{
	// hold down the Ctrl key + double-click
	if (Keyboard.Modifiers == ModifierKeys.Control)
	{
		var cx = e.MousePosition.X;
		var cy = e.MousePosition.Y;

		rectangle1 = diagram.Factory.CreateShapeNode(
			cx - width / 2, cy - height / 2, width, height,
			Shapes.Rectangle);

		rectangle1.Brush = Brushes.Transparent;
		rectangle1.Stroke = Brushes.Green;
	}
}

// event handler of button's Click event
void button1_Click(object sender, RoutedEventArgs e)
{
	//  rectangle 2 produced by clicking the button
	if (rectangle1 != null)
	{
		var cx = rectangle1.GetCenter().X;
		var cy = rectangle1.GetCenter().Y;

		rectangle2 = diagram.Factory.CreateShapeNode(
			cx - width2 / 2, cy - height2 / 2, width2, height2,
			Shapes.Rectangle);

		rectangle2.Brush = Brushes.Transparent;
		rectangle2.Stroke = Brushes.Orange;
		rectangle2.StrokeDashStyle = DashStyles.Dot;

		// let user draw rectangle3
		diagram.Behavior = Behavior.DrawShapes;
	}
}

// event handler of diagram's InitializeNode event
void OnInitializeNode(object sender, NodeEventArgs e)
{
	rectangle3 = e.Node as ShapeNode;
	if (rectangle3 != null)
	{
		rectangle3.Shape = Shapes.Rectangle;
		rectangle3.Brush = Brushes.Transparent;
		rectangle3.Stroke = Brushes.Blue;
	}
}

ShapeNode rectangle1;
ShapeNode rectangle2;
ShapeNode rectangle3;

// parse these from your text boxes instead
double width = 150;
double height = 150;
double width2 = 80;
double height2 = 80; 

Code

if (Diagram.GetNodesAt(mousePosition).Count >= 2)
    // multiple nodes
 

Code

double DistToRect(Point point, Rect rect)
{
    var v = new[]
    {
        new Point(rect.Left, rect.Top),
        new Point(rect.Right, rect.Top),
        new Point(rect.Right, rect.Bottom),
        new Point(rect.Left, rect.Bottom),
    };
    double minDist = double.MaxValue;
    for (var i = 0; i < 4; i++)
    {
        var v1 = v[i];
        var v2 = v[(i + 1) % 4];
        var dist = Utilities.DistToLineSegment(point, v1, v2);
        if (dist < minDist)
            minDist = dist;
    }
    return minDist;
}

DiagramNode NearestRect(Point point)
{
    DiagramNode nearest = null;
    double minDist = double.MaxValue;
    foreach (var node in diagram.Nodes)
    {
        var dist = DistToRect(point, node.Bounds);
        if (dist < minDist)
        {
            minDist = dist;
            nearest = node;
        }
    }
    return nearest;
}