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ImageViewerVirtualizer Class

Summary

Support for loading large amount of items in an ImageViewer.

Syntax
C#
C++
public abstract class ImageViewerVirtualizer 
vb[VB Syntax] 
Public MustInherit Class ImageViewerVirtualizer 
public ref class ImageViewerVirtualizer abstract 
Remarks

The ImageViewerVirtualizer provide support for handling large amount of image data in an ImageViewer by loading and unloading item data on demand with full control for rendering place-holders and controlling the number of items to cache in memory.

For detailed information, refer to Image Viewer Virtualizer.

Example
C#
using Leadtools; 
using Leadtools.Controls; 
using Leadtools.Codecs; 
using Leadtools.Drawing; 
 
 
public void ImageViewerVirtualizer_Example() 
{ 
   string imageFileName = GetExampleImageFile(); 
 
   // Create a new form to test out virtualizer 
   MyForm form = new MyForm(imageFileName); 
   form.ShowDialog(); 
} 
 
private static string GetExampleImageFile() 
{ 
   string imageFileName = Path.Combine(LEAD_VARS.ImagesDir, "ImageViewerVirtualizerExample.tif"); 
 
   // Check if it is previously created, return it 
   if (File.Exists(imageFileName)) 
      return imageFileName; 
 
   // Create an image that has many pages, we will use that for out testing 
   const int pageCount = 100; 
   const int imageWidth = 800; 
   const int imageHeight = 800; 
 
   var rc = new Rectangle(0, 0, imageWidth, imageHeight); 
 
   using (RasterCodecs codecs = new RasterCodecs()) 
   using (Font font = new Font(FontFamily.GenericMonospace, 80)) 
   { 
      for (int page = 1; page <= pageCount; page++) 
      { 
         using (RasterImage image = RasterImage.Create(imageWidth, imageHeight, 24, 96, RasterColor.FromKnownColor(RasterKnownColor.White))) 
         { 
            IntPtr hdc = RasterImagePainter.CreateLeadDC(image); 
            using (Graphics graphics = Graphics.FromHdc(hdc)) 
            { 
               graphics.DrawRectangle(Pens.Blue, 0, 0, rc.Width - 1, rc.Height - 1); 
               TextRenderer.DrawText(graphics, "Page " + page.ToString(), font, rc, Color.Red, TextFormatFlags.HorizontalCenter | TextFormatFlags.VerticalCenter); 
            } 
            RasterImagePainter.DeleteLeadDC(hdc); 
 
            codecs.Save(image, imageFileName, RasterImageFormat.TifLzw, 0, 1, -1, -1, page == 1 ? CodecsSavePageMode.Overwrite : CodecsSavePageMode.Append); 
         } 
      } 
   } 
 
   return imageFileName; 
} 
 
 
// Custom Virtualizer 
public class MyVirtualizer : ImageViewerVirtualizer 
{ 
   private string _imageFileName; 
   public MyVirtualizer(string imageFileName) : 
      base() 
   { 
      _imageFileName = imageFileName; 
      // We will load 4 items at a time 
      this.MaximumItems = 4; 
   } 
 
   protected override object LoadItem(ImageViewerItem item) 
   { 
      // Load a page, the page number is the item index + 1, but it 
      // could be anything in your application, for example 
      // using ImageViewerItem.Tag to store the necessary data to identity this item 
      int pageNumber = this.ImageViewer.Items.IndexOf(item) + 1; 
      using (RasterCodecs codecs = new RasterCodecs()) 
      { 
         return codecs.Load(_imageFileName, pageNumber); 
      } 
   } 
 
   protected override void SaveItem(ImageViewerItem item, object data) 
   { 
      // Nothing to do in this application, just log it. 
      // If save is required, then this is the place to do it 
      int pageNumber = this.ImageViewer.Items.IndexOf(item) + 1; 
      System.Diagnostics.Debug.WriteLine("SaveItem for page {0} is called"); 
   } 
 
   protected override void DeleteItem(ImageViewerItem item, object data) 
   { 
      // Dispose the image 
      RasterImage image = data as RasterImage; 
      if (image != null) 
         image.Dispose(); 
   } 
 
   protected override void RenderItemPlaceholder(ImageViewerRenderEventArgs e) 
   { 
      // Render the place holder for this page 
      int pageNumber = this.ImageViewer.Items.IndexOf(e.Item) + 1; 
      LeadMatrix transform = this.ImageViewer.GetItemImageTransform(e.Item); 
 
      Graphics graphics = e.PaintEventArgs.Graphics; 
 
      // Render the message at 0,0 in this item transformation 
      LeadPointD pt = LeadPointD.Create(0, 0); 
      pt = transform.Transform(pt); 
      string message = string.Format("Loading page {0}...", pageNumber); 
      graphics.DrawString(message, this.ImageViewer.Font, Brushes.Black, (float)pt.X, (float)pt.Y); 
   } 
} 
 
// Form to test the virtualizer 
class MyForm : Form 
{ 
   public MyForm(string imageFileName) 
   { 
      _imageFileName = imageFileName; 
   } 
 
   private ImageViewer _imageViewer; 
   private string _imageFileName; 
 
   protected override void OnLoad(EventArgs e) 
   { 
      // Create a new image viewer with vertical layout 
      _imageViewer = new ImageViewer(new ImageViewerVerticalViewLayout { Columns = 1 }); 
      _imageViewer.BackColor = Color.Bisque; 
      _imageViewer.Dock = DockStyle.Fill; 
 
      // Add pan zoom interactive mode 
      _imageViewer.InteractiveModes.Add(new ImageViewerPanZoomInteractiveMode()); 
 
      this.Controls.Add(_imageViewer); 
      _imageViewer.BringToFront(); 
 
      // Add empty items, each one with the correct size but with 
      using (RasterCodecs codecs = new RasterCodecs()) 
      { 
         int pageCount; 
         LeadSize pageSize; 
         LeadSizeD pageResolution; 
 
         using (CodecsImageInfo info = codecs.GetInformation(_imageFileName, true)) 
         { 
            pageCount = info.TotalPages; 
            pageSize = LeadSize.Create(info.Width, info.Height); 
            pageResolution = LeadSizeD.Create(info.XResolution, info.YResolution); 
         } 
 
         _imageViewer.BeginUpdate(); 
         for (int page = 1; page <= pageCount; page++) 
         { 
            // no image data, the virtualizer will take care of loading the pages and rendering them 
            ImageViewerItem item = new ImageViewerItem(); 
            item.ImageSize = pageSize; 
            item.Resolution = pageResolution; 
            _imageViewer.Items.Add(item); 
         } 
         _imageViewer.EndUpdate(); 
      } 
 
      // Finally, set our virtualizer so it can start working 
      _imageViewer.Virtualizer = new MyVirtualizer(_imageFileName); 
 
      // Run the demo, use pan (drag) and zoom (CTRL-CLICK and drag) to show the items 
      // Note how they get loaded when they are in view 
      // Change the number of MaximumItems to see its effect. 
 
      base.OnLoad(e); 
   } 
} 
 
static class LEAD_VARS 
{ 
   public const string ImagesDir = @"C:\LEADTOOLS22\Resources\Images"; 
} 
Requirements

Target Platforms

Help Version 22.0.2022.4.4
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Leadtools.Controls Assembly

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© 1991-2022 LEAD Technologies, Inc. All Rights Reserved.