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ImageViewerVirtualizer Class

Summary

Support for loading large amount of items in an ImageViewer

Syntax

C#
VB
C++
public abstract class ImageViewerVirtualizer
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#
VB
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(ImagesPath.Path, "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); 
   } 
} 
Imports Leadtools 
Imports Leadtools.Controls 
Imports Leadtools.Codecs 
Imports Leadtools.Drawing 
 
<TestMethod> 
Public Sub ImageViewerVirtualizer_Example() 
   Dim imageFileName As String = GetExampleImageFile() 
   ' Create a new form to test out virtualizer 
   Dim form As MyForm = New MyForm(imageFileName) 
   form.ShowDialog() 
End Sub 
 
Private Shared Function GetExampleImageFile() As String 
   Dim imageFileName As String = Path.Combine(ImagesPath.Path, "ImageViewerVirtualizerExample.tif") 
 
   ' Check if it is previously created, return it 
   If File.Exists(imageFileName) Then 
      Return imageFileName 
   End If 
 
   ' Create an image that has many pages, we will use that for out testing 
   Const pageCount As Integer = 100 
   Const imageWidth As Integer = 800 
   Const imageHeight As Integer = 800 
 
   Dim rc As New Rectangle(0, 0, imageWidth, imageHeight) 
 
   Using codecs As RasterCodecs = New RasterCodecs() 
      Using font As Font = New Font(FontFamily.GenericMonospace, 80) 
         For page As Integer = 1 To pageCount 
            Using image As RasterImage = RasterImage.Create(imageWidth, imageHeight, 24, 96, RasterColor.FromKnownColor(RasterKnownColor.White)) 
               Dim hdc As IntPtr = RasterImagePainter.CreateLeadDC(image) 
               Using graphics As 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 Or TextFormatFlags.VerticalCenter) 
               End Using 
               RasterImagePainter.DeleteLeadDC(hdc) 
 
               If page = 1 Then 
                  codecs.Save(image, imageFileName, RasterImageFormat.TifLzw, 0, 1, -1, -1, CodecsSavePageMode.Overwrite) 
               Else 
                  codecs.Save(image, imageFileName, RasterImageFormat.TifLzw, 0, 1, -1, -1, CodecsSavePageMode.Append) 
               End If 
            End Using 
         Next page 
      End Using 
   End Using 
 
   Return imageFileName 
End Function 
 
 
' Custom Virtualizer 
Public Class MyVirtualizer : Inherits ImageViewerVirtualizer 
   Private _imageFileName As String 
   Public Sub New(ByVal imageFileName As String) 
      MyBase.New() 
      _imageFileName = imageFileName 
      ' We will load 4 items at a time 
      Me.MaximumItems = 4 
   End Sub 
 
   Protected Overrides Function LoadItem(ByVal item As ImageViewerItem) As Object 
      ' 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 
      Dim pageNumber As Integer = Me.ImageViewer.Items.IndexOf(item) + 1 
      Using codecs As RasterCodecs = New RasterCodecs() 
         Return codecs.Load(_imageFileName, pageNumber) 
      End Using 
   End Function 
 
   Protected Overrides Sub SaveItem(ByVal item As ImageViewerItem, ByVal data As Object) 
      ' Nothing to do in this application, just log it. 
      ' If save is required, then this is the place to do it 
      Dim pageNumber As Integer = Me.ImageViewer.Items.IndexOf(item) + 1 
      System.Diagnostics.Debug.WriteLine("SaveItem for page {0} is called") 
   End Sub 
 
   Protected Overrides Sub DeleteItem(ByVal item As ImageViewerItem, ByVal data As Object) 
      ' Dispose the image 
      Dim image As RasterImage = TryCast(data, RasterImage) 
      If Not image Is Nothing Then 
         image.Dispose() 
      End If 
   End Sub 
 
   Protected Overrides Sub RenderItemPlaceholder(ByVal e As ImageViewerRenderEventArgs) 
      ' Render the place holder for this page 
      Dim pageNumber As Integer = Me.ImageViewer.Items.IndexOf(e.Item) + 1 
      Dim transform As LeadMatrix = Me.ImageViewer.GetItemImageTransform(e.Item) 
 
      Dim graphics As Graphics = e.PaintEventArgs.Graphics 
 
      ' Render the message at 0,0 in this item transformation 
      Dim pt As LeadPointD = LeadPointD.Create(0, 0) 
      pt = transform.Transform(pt) 
      Dim message As String = String.Format("Loading page {0}...", pageNumber) 
      graphics.DrawString(message, Me.ImageViewer.Font, Brushes.Black, CSng(pt.X), CSng(pt.Y)) 
   End Sub 
End Class 
 
' Form to test the virtualizer 
Private Class MyForm : Inherits Form 
   Public Sub New(ByVal imageFileName As String) 
      _imageFileName = imageFileName 
   End Sub 
 
   Private _imageViewer As ImageViewer 
   Private _imageFileName As String 
 
   Protected Overrides Sub OnLoad(ByVal e As EventArgs) 
      ' Create a new image viewer with vertical layout 
      Dim viewLayout As New ImageViewerVerticalViewLayout 
      viewLayout.Columns = 1 
      Dim _imageViewer As New ImageViewer(viewLayout) 
      _imageViewer.BackColor = Color.Bisque 
      _imageViewer.Dock = DockStyle.Fill 
 
      ' Add pan zoom interactive mode 
      _imageViewer.InteractiveModes.Add(New ImageViewerPanZoomInteractiveMode()) 
 
      Me.Controls.Add(_imageViewer) 
      _imageViewer.BringToFront() 
 
      ' Add empty items, each one with the correct size but with 
      Using codecs As RasterCodecs = New RasterCodecs() 
         Dim pageCount As Integer 
         Dim pageSize As LeadSize 
         Dim pageResolution As LeadSizeD 
 
         Using info As CodecsImageInfo = codecs.GetInformation(_imageFileName, True) 
            pageCount = info.TotalPages 
            pageSize = LeadSize.Create(info.Width, info.Height) 
            pageResolution = LeadSizeD.Create(info.XResolution, info.YResolution) 
         End Using 
 
         _imageViewer.BeginUpdate() 
         Dim page As Integer = 1 
         Do While page <= pageCount 
            ' no image data, the virtualizer will take care of loading the pages and rendering them 
            Dim item As ImageViewerItem = New ImageViewerItem() 
            item.ImageSize = pageSize 
            item.Resolution = pageResolution 
            _imageViewer.Items.Add(item) 
            page += 1 
         Loop 
         _imageViewer.EndUpdate() 
      End Using 
 
      ' 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. 
 
      MyBase.OnLoad(e) 
   End Sub 
End Class 

Requirements

Target Platforms

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Leadtools.Controls Assembly
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