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ImageViewerVirtualizer Class




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Leadtools.Controls Assembly > Leadtools.Controls Namespace : ImageViewerVirtualizer Class
Support for loading large amount of items in an ImageViewer
Object Model
Syntax
public abstract class ImageViewerVirtualizer 
'Declaration
 

Public MustInherit Class ImageViewerVirtualizer
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
Copy Code   
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
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);
   }
}
Requirements

Target Platforms

See Also

Reference

ImageViewerVirtualizer Members
Leadtools.Controls Namespace

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