Invalidate Method

using Leadtools; 
using Leadtools.Codecs; 
using Leadtools.Controls; 
 
//method to listen to transform Change Event 
[TestClass] 
void TransformExample() 
{ 
   //listen to Transform Change event 
   _viewer.TransformChanged += _Viewer_TransformChanged; 
} 
//event handler method 
[TestClass] 
void _Viewer_TransformChanged(object sender, EventArgs e) 
{ 
   //  clear imageViewer InteractiveMode canvas from all objects 
   _viewer.InteractiveModeCanvas.Children.Clear(); 
 
 
   //Fixed Rectangle  
   LeadRectD rc1 = LeadRectDHelper.Create(20, 20, 50, 50); 
 
   LeadMatrix matrix = new LeadMatrix(_viewer.Transform.M11, _viewer.Transform.M12, 
         _viewer.Transform.M21, _viewer.Transform.M22, 
         _viewer.Transform.OffsetX, _viewer.Transform.OffsetY); 
 
   //transformed Rectangle Rectangle  
   LeadRectD rc2 = matrix.TransformRect(rc1); 
 
 
   // add the fixed blue rectangle at 50, 50 (do not use the viewer transform) 
   Rectangle rect = new Rectangle 
   { 
      Width = rc1.Width, 
      Height = rc1.Height, 
      Fill = new SolidColorBrush(Windows.UI.Color.FromArgb(255, 0, 0, 255)), 
   }; 
 
   // Draw the red rectangle. This will be at 50, 50 as well, but will scroll and zoom 
   // with the viewer 
   Rectangle rect2 = new Rectangle 
   { 
      Width = rc2.Width, 
      Height = rc2.Height, 
      Fill = new SolidColorBrush(Windows.UI.Color.FromArgb(255, 0, 255, 0)), 
   }; 
 
 
   Canvas.SetLeft(rect, rc1.X); 
   Canvas.SetTop(rect, rc1.Y); 
 
   Canvas.SetLeft(rect2, rc2.X); 
   Canvas.SetTop(rect2, rc2.Y); 
 
   //add the two rectangles to interactive service canvas 
   _viewer.InteractiveModeCanvas.Children.Add(rect); 
   _viewer.InteractiveModeCanvas.Children.Add(rect2); 
}