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StartOverlay Method

Summary

Indicates which method should be called when an overlay is detected inside a file.

Syntax
C#
VB
Java
Objective-C
C++
Public Sub StartOverlay( _ 
   ByVal callback As CodecsOverlayCallback, _ 
   ByVal mode As CodecsOverlayCallbackMode _ 
)  
- (BOOL)startOverlay:(nullable LTCodecsOverlayCallback)callback  
                mode:(LTCodecsOverlayCallbackMode)mode  
               error:(NSError **)error 
public void startOverlay(CodecsOverlayListener listener, CodecsOverlayCallbackMode mode) 

Parameters

callback
The method which should be called when an overlay is detected. Use a null reference to indicate that LEADTOOLS should handle overlays automatically.

mode
Indicates when this method should be called. See CodecsOverlayCallbackMode for possible values.

Remarks

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

PTOCA files contain file references (i.e. 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 behavior if you load files that are not stored locally (for example, 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.

Example

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

C#
VB
using Leadtools; 
using Leadtools.Codecs; 
using Leadtools.ImageProcessing; 
using Leadtools.ImageProcessing.Color; 
using Leadtools.Svg; 
using LeadtoolsExamples.Common; 
 
void PtokaOverlayExample(string ptokaFileName, string ptokaFilesPath) 
{ 
   RasterCodecs codecs = new RasterCodecs(); 
 
   string destFileName = Path.Combine(LEAD_VARS.ImagesDir, "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 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); 
   } 
} 
 
static class LEAD_VARS 
{ 
   public const string ImagesDir = @"C:\Users\Public\Documents\LEADTOOLS Images"; 
} 
Imports Leadtools 
Imports Leadtools.Codecs 
Imports Leadtools.ImageProcessing 
Imports Leadtools.ImageProcessing.Color 
Imports Leadtools.Drawing 
Imports Leadtools.Svg 
 
Private Sub PtokaOverlayExample(ByVal ptokaFileName As String, ByVal ptokaFilesPath As String) 
   Dim codecs As RasterCodecs = New RasterCodecs() 
 
   Dim destFileName As String = Path.Combine(LEAD_VARS.ImagesDir, "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() 
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 
 
Public NotInheritable Class LEAD_VARS 
   Public Const ImagesDir As String = "C:\Users\Public\Documents\LEADTOOLS Images" 
End Class 

Requirements

Target Platforms

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Leadtools.Codecs Assembly