RenderItemPlaceholder Method (ImageViewerVirtualizer)

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"; 
}