Handles the output image data that the calling function has written to a buffer.


#include "ltwrappr.h"

virtual L_INT LFile::CreateThumbnailCallBack (pFileInfo, pLBitmap, pLBuffer, uFlags, nRow, nLines)



The pointer to the FILEINFO structure that contains image information.

LBitmapBase * pLBitmap

The pointer to the bitmap handle referencing the bitmap that contains the image information.

LBuffer * pLBuffer

A pointer to a buffer containing one or more lines of output image data that the calling function has already processed (read or decompressed).

L_UINT uFlags

Flags that describe whether this is the first or last call of the callback, and whether the buffer contains first or last row of image data. Possible values are:

Value Meaning
FILEREAD_FIRSTPASS [0x0001] This is the first pass through a progressive JPEG or CMP file.
FILEREAD_LASTPASS [0x0002] This is the last pass through a progressive JPEG or CMP file.
FILEREAD_FIRSTROW [0x0004] The first row of the buffer is the first row of the bitmap.
FILEREAD_LASTROW [0x0008] The last row of the buffer is the last row of the bitmap.
FILEREAD_COMPRESSED [0x0010] The data in the buffer is 1-bit compressed data, which you can handle as explained in Speeding Up 1-Bit Documents.
FILEREAD_CLIPVERT [0x0020] Internal flag.
FILEREAD_CLIPHORZ [0x0040] Internal flag.
FILEREAD_UPDATELUT [0x0080] Internal flag.

L_INT nRow

The current bitmap row number of the first line in the buffer.

L_INT nLines

The number of lines in the pLBuffer buffer.


Value Meaning
SUCCESS The function was successful.
< 1 An error occurred. Refer to Return Codes.


Several LEADTOOLS functions use this type of callback function. In some cases, The pLBuffer buffer contains data that your callback function must output in order for the calling function to accomplish anything. In other cases, where the callback is optional, the callback gets a copy of the data, and the callback's output is in addition to the calling function's output. Refer to the description of the calling function to see how it uses the callback.

The FILEINFO structure that gets passed to the LFile::CreateThumbnailCallBack function does not contain the total number of pages. To get the total number of pages, you should call LFile::GetInfo and set the FILEINFO_TOTALPAGES flag.

Required DLLs and Libraries


Win32, x64.

See Also




For an example, refer to LFile::CreateThumbnail.

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