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StartOverlay Method
See Also  Example
Leadtools.Codecs Namespace > RasterCodecs Class : StartOverlay Method



callback
The method which should be called when an overlay is detected. Use a null reference (Nothing in Visual Basic) to indicate that LEADTOOLS should handle overlays automatically.
mode
Indicates when should this method be called. See CodecsOverlayCallbackMode for possible values.
Indicates which method should be called when an overlay is detected inside a file.

Syntax

Visual Basic (Declaration) 
Public Sub StartOverlay( _
   ByVal callback As CodecsOverlayCallback, _
   ByVal mode As CodecsOverlayCallbackMode _
)
Visual Basic (Usage)Copy Code
Dim instance As RasterCodecs
Dim callback As CodecsOverlayCallback
Dim mode As CodecsOverlayCallbackMode
 
instance.StartOverlay(callback, mode)
C# 
public void StartOverlay( 
   CodecsOverlayCallback callback,
   CodecsOverlayCallbackMode mode
)
C++/CLI 
public:
void StartOverlay( 
   CodecsOverlayCallback^ callback,
   CodecsOverlayCallbackMode mode
)

Parameters

callback
The method which should be called when an overlay is detected. Use a null reference (Nothing in Visual Basic) to indicate that LEADTOOLS should handle overlays automatically.
mode
Indicates when should this method be called. See CodecsOverlayCallbackMode for possible values.

Example

This example will read a PTOKA file and overlays a TIF file on it

Visual BasicCopy Code
Private Sub PtokaOverlayExample(ByVal ptokaFileName As String, ByVal ptokaFilesPath As String)
   RasterCodecs.Startup()
   Dim codecs As RasterCodecs = New RasterCodecs()
   Dim destFileName As String = LeadtoolsExamples.Common.ImagesPath.Path + "PtokaOverlay.tif"

   ' Set up the private variables used in the callback
   myCodecs = codecs
   myPtokaFilesPath = ptokaFilesPath

   ' Set the overlay callback
   codecs.StartOverlay(AddressOf MyOverlayCallback, CodecsOverlayCallbackMode.CallLoad)

   ' Load the PTOKA file
   Dim image As RasterImage = codecs.Load(ptokaFileName)

   ' Stop the overlay by resetting the old callback.
   codecs.StopOverlay()

   ' Save the image as TIFF
   codecs.Save(image, destFileName, RasterImageFormat.Tif, 1)
   image.Dispose()

   ' Clean up
   codecs.Dispose()
   RasterCodecs.Shutdown()
End Sub

Private myCodecs As RasterCodecs
Private myPtokaFilesPath As String

Private Sub MyOverlayCallback(ByVal data As CodecsOverlayData)
   ' Show overlay information
   Console.WriteLine("File: {0}", data.FileName)
   Console.WriteLine("Page Number: {0}", data.PageNumber)
   Console.WriteLine("Info: {0}", data.Info)

   ' Construct the overlay file name
   Dim overlayFileName As String = Path.Combine(myPtokaFilesPath, data.FileName)

   If data.Info Then
      ' Info, we only need to fill in the .InfoXXX members of the data
      Dim imageInfo As CodecsImageInfo = myCodecs.GetInformation(overlayFileName, False)
      data.InfoWidth = imageInfo.Width
      data.InfoHeight = imageInfo.Height
      data.InfoXResolution = imageInfo.XResolution
      data.InfoYResolution = imageInfo.YResolution
   Else
      ' We need to load the overlay image into the .Image member
      data.Image = myCodecs.Load(overlayFileName)
   End If
End Sub
C#Copy Code
void PtokaOverlayExample(string ptokaFileName, string ptokaFilesPath) 
{ 
   RasterCodecs.Startup(); 
   RasterCodecs codecs = new RasterCodecs(); 
   string destFileName = LeadtoolsExamples.Common.ImagesPath.Path + "PtokaOverlay.tif"; 
 
   // Set up the private variables used in the callback 
   myCodecs = codecs; 
   myPtokaFilesPath = ptokaFilesPath; 
 
   // Set the overlay callback 
   codecs.StartOverlay(MyOverlayCallback, CodecsOverlayCallbackMode.CallLoad); 
 
   // Load the PTOKA file 
   RasterImage image = codecs.Load(ptokaFileName); 
 
   // Stop the overlay by resetting the old callback. 
   codecs.StopOverlay(); 
 
   // Save the image as TIFF 
   codecs.Save(image, destFileName, RasterImageFormat.Tif, 1); 
   image.Dispose(); 
 
   // Clean up 
   codecs.Dispose(); 
   RasterCodecs.Shutdown(); 
} 
 
RasterCodecs myCodecs; 
string myPtokaFilesPath; 
 
void MyOverlayCallback(CodecsOverlayData data) 
{ 
   // Show overlay information 
   Console.WriteLine("File: {0}", data.FileName); 
   Console.WriteLine("Page Number: {0}", data.PageNumber); 
   Console.WriteLine("Info: {0}", data.Info); 
 
   // Construct the overlay file name 
   string overlayFileName = Path.Combine(myPtokaFilesPath, data.FileName); 
 
   if(data.Info) 
   { 
      // Info, we only need to fill in the .InfoXXX members of the data 
      CodecsImageInfo imageInfo = myCodecs.GetInformation(overlayFileName, false); 
      data.InfoWidth = imageInfo.Width; 
      data.InfoHeight = imageInfo.Height; 
      data.InfoXResolution = imageInfo.XResolution; 
      data.InfoYResolution = imageInfo.YResolution; 
   } 
   else 
   { 
      // We need to load the overlay image into the .Image member 
      data.Image = myCodecs.Load(overlayFileName); 
   } 
}

Remarks

Currently, only PTOCA files are known to use such overlays.

PTOCA files contain file references (ie filenames) to external files that contain overlay bitmaps. (These files are typically in IOCA format)

These external overlay files will be resized and placed on the current page according to the information from the PTOCA files. By default, LEADTOOLS will load these external overlay files from disk. You should override this behaviour if you load files that are not stored locally (eg: on a remote storage or in a database).

To load overlays stored on other storage, you have to pass your overlay callback to this method and load the overlays in your overlay callback.

The overlay callback will be used until StopOverlay is called.

Requirements

Target Platforms: Microsoft .NET Framework 3.0, Windows XP, Windows Server 2003 family, Windows Server 2008 family

See Also