TRANSFORMFILECALLBACK Function

#include "l_bitmap.h"

L_INT pEXT_CALLBACK YourFunction (uMarker, uMarkerSize, pMarkerData, pUserData, uTransform, pfnLEADCallback, pLEADUserData)

L_UINT uMarker;	/* ID of the JPEG marker */
L_UINT uMarkerSize;	/* size of the JPEG marker */
L_UCHAR* pMarkerData;	/* marker data */
L_VOID* pUserData;	/* pointer to additional parameters */
L_UINT uTransform;	/* transform to be performed */
LEADMARKERCALLBACK pfnLEADCallback;	/* pointer to a LEAD callback function */
L_VOID* pLEADUserData;	/* pointer to additional parameters for pfnLEADCallback */

Handles the processing of every JPEG marker present in the file transformed by L_TransformFile.

Parameter	Description
uMarker	ID of the JPEG marker. The JPEG markers are uniquely identified by a byte value. Possible values are 1 to 254. (0 and 255 are not allowed.)
uMarkerSize	Size of the JPEG marker. The size will be less than 65535. If this value is 0, then the marker does not have any extra data.
pMarkerData	Pointer to a buffer containing the marker data. This parameter is valid only if the uMarkerSize is > 0.
pUserData	A void pointer that you can use to access a variable or structure containing data that your callback function needs. This gives you a way to receive data indirectly from the function that uses this callback function. (This is the same pointer that you pass in the pUserData parameter of the calling function.)
	Keep in mind that this is a void pointer, which must be cast to the appropriate data type within your callback function.
uTransform	Binary flags that indicate the transform to be performed. These are the same flags passed to the L_TransformFile function. Possible values are:
	Value	Meaning
	FILE_TRANSFORM_FLIP	[0x0001] Flip the image.
	FILE_TRANSFORM_REVERSE	[0x0002] Reverse the image.
	FILE_TRANSFORM_ROTATE90	[0x0004] Rotate the image clockwise by 90 degrees.
	FILE_TRANSFORM_ROTATE180	[0x0008] Rotate the image clockwise by 180 degrees.
	FILE_TRANSFORM_ROTATE270	[0x000C] Rotate the image clockwise by 270 degrees.
pfnLEADCallback	Pointer to a callback function, provided by LEADTOOLS, for writing transformed markers.
	The callback function adheres to the function prototype described in LEADMARKERCALLBACK Function.
pLEADUserData	Void pointer that you can use to pass one or more additional parameters that the LEADMARKERCALLBACK function needs.

	To use this feature, assign a value to a variable or create a structure that contains as many fields as you need. Then, in this parameter, pass the address of the variable or structure, casting it to L_VOID . The callback function, which receives the address in its own pLEADUserData* parameter, can cast it to a pointer of the appropriate data type to access your variable or structure.
	If the additional parameters are not needed, you can pass NULL in this parameter.

Returns

SUCCESS	The function was successful. The default processing for this marker can be performed.
SUCCESS_IGNOREMARKER	The function was successful. Do not process this marker and do not write it to the file.
< 1	An error occurred. Refer to Return Codes.

Comments

This callback function is called by the L_TransformFile function.

This callback can also be used to enumerate the markers in a JPEG file. The last marker enumerated by this function is always the SOS (0xDA) marker.

If the marker data is transformed, make sure the size of the marker data is less than 0xFFFE.

Note that uMarkerSize is the size of the data contained in the pMarkerData buffer. It does not include the size of the marker size (like the size stored in the file). If you are not familiar with JPEG markers and the previous didnt make sense to you, then you can safely ignore this paragraph.

If the marker data is transformed, it should be written by calling the pfnLEADCallback function. Then, SUCCESS_IGNOREMARKER should be returned by the TRANSFORMFILECALLBACK function. If SUCCESS is returned by the TRANSFORMFILECALLBACK function instead of SUCCESS_IGNOREMARKER, LEADTOOLS will perform the default transformation and will also write this marker information to the file. Therefore, there will be two copies of the marker in the file.

As an example, if a user-defined marker that contains a stamp of the image is stored in a file and that file is transformed, the stamp should be transformed in the same way and resaved.

If this function returns an error code, the transformation is aborted and L_TransformFile will return the error code returned by this callback function.

Required DLLs and Libraries

LTFIL

For a listing of the exact DLLs and Libraries needed, based on the toolkit version, refer to Files To Be Included With Your Application

See Also

Functions:	L_TransformFile, LEADMARKERCALLBACK
Topics:	Raster Image Functions: Processing an Image

Example

For a short example, refer to L_StartCompressBuffer. For complete sample code, refer to the COMPCB example.

#define APP0 0xE0

L_INT EXT_CALLBACK MyRotateMarker(
   L_UINT uMarker,
   L_UINT uMarkerSize,
   L_UCHAR* pMarkerData,
   L_VOID* pUserData,
   L_UINT uTransform,
   LEADMARKERCALLBACK pfnLEADCallback,
   L_VOID* pLEADUserData)
{
   UNREFERENCED_PARAMETER(uTransform);
   UNREFERENCED_PARAMETER(pUserData);
   
    L_INT nRet;
    /* I will transform only the APP0 marker  */
    if (uMarker != APP0)
       return SUCCESS;
    /* Transform the marker data. Do your transformation here... */
    /* write the transformed data */
    nRet  = pfnLEADCallback(uMarker, uMarkerSize, pMarkerData, pLEADUserData);
    if (nRet != SUCCESS)
       return nRet;
    /* since I wrote the marker, tell LEADTOOLS not to transform it */
    return SUCCESS_IGNOREMARKER;
}

 L_INT TransformfileCallbackExample()
{
   L_INT nRet;
    /* This example rotates the file by 90 degrees */
    nRet = L_TransformFile (TEXT("C:\\Program Files\\LEAD Technologies\\LEADTOOLS 15\\Images\\IMAGE1.JPG"), NULL, FILE_TRANSFORM_ROTATE90, MyRotateMarker, NULL, NULL);

    return nRet;
}