FILEREADCALLBACK - Raster Imaging C API Help

FILEREADCALLBACK

#include "l_bitmap.h"

L_INT pEXT_CALLBACK YourFunction (pFileInfo, pBitmap, pBuffer, uFlags, nRow, nLines, pUserData)

pFILEINFO pFileInfo;

pointer to the file information handle

pBITMAPHANDLE pBitmap;

pointer to the bitmap handle

L_UCHAR* pBuffer;

pointer to a buffer of the caller's output data

L_UINT uFlags;

flags for first and last row, and first and last pass

L_INT nRow;

current row number of the first line in the buffer

L_INT nLines;

number of lines in the buffer

L_VOID* pUserData;

pointer to additional parameters

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

Parameter Description
pFileInfo The pointer to the FILEINFO structure that contains image information.
pBitmap The pointer to the bitmap handle referencing the bitmap that contains the image information.
pBuffer A pointer to a buffer containing one or more lines of output image data that the calling function has already processed (read or decompressed).
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. The following are possible flags:
  Constant 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.
nRow The current bitmap row number of the first line in the buffer.
nLines The number of lines in the pBuffer buffer.
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.

Returns

Returns SUCCESS to indicate the function was successful.

Returns any other value to terminate the calling function. The calling function will pass this value along to its caller. For a list of error values you may want to use, refer to the Return Codes.

Comments

Several LEADTOOLS functions use this type of callback function. In some cases, The pBuffer 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 FILEREADCALLBACK function does not contain the total number of pages. To get the total number of pages, you should call L_FileInfo and set the FILEINFO_TOTALPAGES flag.

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_LoadFile, L_LoadFileOffset, L_LoadMemory, L_StartFeedLoad

Example

This FILEREADCALLBACK function paints the image as it loads

/**************** Global declarations **************************************/ 
 
/* Structure used for the callback function's user data */ 
typedef struct tagIMAGECBPARM 
{ 
   HWND hwnd;        /* Current window */ 
   HDC hdc;          /* Device context for the current window */ 
   L_INT nRow;       /* First row in the input buffer */ 
   HPALETTE hpalPaint;  /* Paint palette handle */ 
   HINSTANCE hInst;     /* Current instance of the application, set by the InitInstance function */ 
   RECT rLeadDest;      /* Destination rectangle for painting */      
   RECT rLeadSource;    /* Source rectangle for painting */ 
} IMAGECBPARMEX; 
 
/*******************************************************************************/ 
 
L_INT EXT_CALLBACK LoadImageCB(pFILEINFO pFileInfo, 
                               pBITMAPHANDLE pBitmap, L_UCHAR  *pBuffer, 
                               L_UINT uFlags, L_INT nRow, L_INT nLines, IMAGECBPARMEX * pUserData ) 
{ 
   /* If this is the first call (row 0), select and realize the palette */ 
   if((uFlags & FILEREAD_FIRSTPASS) && (uFlags & FILEREAD_FIRSTROW) ) 
   { 
         /* Set the source rectangle to use the whole bitmap */ 
         SetRect(&pUserData->rLeadSource, 0, 0, pFileInfo->Width, pFileInfo->Height); 
         SendMessage (pUserData->hwnd, WM_QUERYNEWPALETTE, 0, 0L); 
         SelectPalette( pUserData->hdc, pUserData->hpalPaint, TRUE ); 
         RealizePalette(pUserData->hdc); 
   } 
 
   /* Paint the buffer to the specified device context */ 
 
   L_PaintDCBuffer( pUserData->hdc, /* Device context - from function parameter */ 
                    pBitmap, /* Bitmap handle - from function parameter */ 
                    &pUserData->rLeadSource, /* Source rect - set globally in WM_CREATE */ 
                    &pUserData->rLeadSource, /* Source clip rect - same as source rect */ 
                    &pUserData->rLeadDest, /* Destination rect - set globally in WM_CREATE */ 
                    &pUserData->rLeadDest, /* Destination clip rect - same as destination rect */ 
                    SRCCOPY, /* ROP code for normal painting */  
                    pBuffer, /* Input buffer - from function parameter */  
                    nRow, /* First row in the buffer - from function parameter */  
                   (uFlags & FILEREAD_COMPRESSED) ? -nLines : nLines ); 
   return( SUCCESS ); 
} 

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LEADTOOLS Raster Imaging C API Help