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RenderRedirect Method


Render the content of the viewer to an external context.

public virtual void RenderRedirect( 
   Graphics graphics, 
   ImageViewerRenderRedirectOptions options, 
   LeadRect clipRectangle 
   virtual void RenderRedirect( 
      System::Drawing::Graphics^ graphics, 
      ImageViewerRenderRedirectOptions^ options, 
      LeadRect^ clipRectangle 



Target device context to render the content of the viewer to.


Rendering options


Clipping rectangle to use.


This method can be used to render the content of the viewer to an external context. ImageViewerPanControl uses this method to show a smaller version of the viewer in a separate external control.

To take a "snapshot" of the viewer surface to perform such operations as screen capture or printing, use RenderRedirect passing it the target context (of the printer or a bitmap).

To perform live updates for operations such as pan window, subscribe to the RedirectRender event to get notified whenever the viewer content is changed. Then call RenderRedirect to render the content of the viewer into the target device.

During the render cycle, the value of IsRenderRedirected will be set to true if this particular rendering operation is targeting an external device other than the viewer itself. If you are performing custom rendering, you can check the value of this property to apply any modification needed.


This example will mirror the content of the viewer into an external control with live updates whenever the viewer content changes.

Start with the ImageViewer example, remove all the code inside the example function (search for the "// TODO: add example code here" comment) and insert the following code:

using Leadtools; 
using Leadtools.Controls; 
using Leadtools.Codecs; 
using Leadtools.Drawing; 
using Leadtools.ImageProcessing; 
using Leadtools.ImageProcessing.Color; 
public void TestRedirectRender() 
   PictureBox control = new PictureBox(); 
   control.Width = 400; 
   control.Dock = DockStyle.Right; 
   bool renderView = false; 
   control.DoubleClick += (sender, e) => 
      renderView = !renderView; 
   control.Paint += (sender, e) => 
      Graphics graphics = e.Graphics; 
      int delta = 20; 
      LeadRect destRect = LeadRect.Create(delta, delta, control.ClientSize.Width - delta * 2, control.ClientSize.Height - delta * 2); 
      LeadRect clipRect = destRect; 
      ImageViewerRenderRedirectOptions options = new ImageViewerRenderRedirectOptions(); 
      ImageViewerItem item = null; 
      if (!renderView) 
         item = _imageViewer.Items[0]; 
      LeadRectD sourceRect; 
      if (item == null) 
         sourceRect = _imageViewer.GetViewBounds(true, false); 
         sourceRect = _imageViewer.GetItemViewBounds(item, ImageViewerItemPart.Image, false); 
         options.RenderBackgrounds = false; 
         options.RenderBorders = false; 
         options.RenderItemStates = false; 
         options.RenderShadows = false; 
         options.RenderText = false; 
      options.CreateTransform(_imageViewer, destRect, sourceRect, ControlSizeMode.FitAlways, ControlAlignment.Center, ControlAlignment.Center); 
      clipRect = options.Transform.TransformRect(sourceRect).ToLeadRect(); 
      _imageViewer.RenderRedirect(graphics, options, clipRect); 
      graphics.DrawRectangle(Pens.Black, destRect.X, destRect.Y, destRect.Width + 1, destRect.Height + 1); 
      // Now lets find out how much of the view is visible (something pan window would do) 
      LeadRectD rect; 
      if (item == null) 
         rect = _imageViewer.GetViewBounds(true, true); 
         rect = _imageViewer.GetItemViewBounds(item, ImageViewerItemPart.Image, true); 
      LeadPointD[] points = 
         LeadPointD.Create(rect.Left, rect.Top), 
         LeadPointD.Create(rect.Right, rect.Bottom) 
      double xmin = points[0].X; 
      double ymin = points[0].Y; 
      double xmax = xmin; 
      double ymax = ymin; 
      for (int i = 1; i < points.Length; i++) 
         if (points[i].X < xmin) xmin = points[i].X; 
         if (points[i].X > xmax) xmax = points[i].X; 
         if (points[i].Y < ymin) ymin = points[i].Y; 
         if (points[i].Y > ymax) ymax = points[i].Y; 
      LeadRectD bounds = LeadRectD.FromLTRB(xmin, ymin, xmax, ymax); 
      RectangleF rc = new RectangleF((float)bounds.X, (float)bounds.Y, (float)bounds.Width, (float)bounds.Height); 
      graphics.DrawRectangle(Pens.Yellow, rc.X, rc.Y, rc.Width - 1, rc.Height - 1); 
   _imageViewer.RedirectRender += (sender, e) => 

Target Platforms

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Leadtools.Controls Assembly

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© 1991-2023 LEAD Technologies, Inc. All Rights Reserved.