#include "l_bitmap.h"

L_LTKRN_API L_INT L_GetBitmapRowCompressed(pBitmap, pWorkBuffer, pRunBuffer, nRow, nLines)

Retrieves one or more rows of 1-bit compressed data from a bitmap that has been loaded in its compressed format.



Pointer to the bitmap handle referencing the bitmap to get the data from.

L_UCHAR* pWorkBuffer

NULL or a pointer to an optional work buffer. Allocating the work buffer speeds processing if you call this function more than once, because if you do not allocate a work buffer, the function allocates and frees a temporary buffer each time it is called. The size of this buffer should be the same as the bitmap handle's BytesPerLine field.

L_UINT16* pRunBuffer

Pointer to the output buffer, which will be filled with 1-bit compressed image data. Calculate the required size of this buffer as follows: bytes required = nLines * ((bitmap width + 3) * 2).


Number of the first row to retrieve.

L_UINT nLines

Number of rows to retrieve.


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


This function is useful for working with 1-bit images that are loaded in their compressed formats for faster loading and display. For more information, refer to Speeding Up 1-Bit Documents.

Required DLLs and Libraries


Win32, x64, Linux.

See Also




The following example is designed to work with bitmaps that have a bottom-left
or top-left view perspective:
This example demonstrates the low-level functions for accessing
1-bit compressed bitmap data. It demonstrates the ability to get and put
rows, and the ability to process rows in buffer-to-buffer processing.
The result of the function is an the first 50 lines are inverted.

L_INT GetBitmapRowCompressedExample(L_TCHAR*  pszFilename,HWND  hWnd) 
   BITMAPHANDLE   LeadBitmap;  /* Bitmap handle for the image */ 
   L_UCHAR*       pBuffer;     /* Buffer to hold the expanded row */ 
   L_UINT16*      pRunBuffer;  /* Buffer to hold the compressed row */ 
   HGLOBAL        hBuffer;     /* Handle to the pBuffer */ 
   HGLOBAL        hRunBuffer;  /* Handle to the pRunBuffer */ 
   L_INT          n;           /* Counters */ 
   L_INT          nRow = 0;    /* first row to get */ 
   L_INT          nYSize = 50; /* # of rows to get */ 
   L_INT          nRet; 
   /* Load the bitmap, as compressed */ 
   nRet = L_LoadFile(pszFilename,&LeadBitmap, sizeof(BITMAPHANDLE),1,0, 
               NULL, NULL, NULL, NULL); 
   if(nRet != SUCCESS) 
      return nRet; 
   /* if the ViewPerspective is not TOP_LEFT or BOTTOM_LEFT, make it TOP_LEFT */ 
   /* Get/PutRow functions only work with TOP_LEFT or BOTTOM_LEFT */ 
   if ( (LeadBitmap.ViewPerspective != TOP_LEFT) 
      || (LeadBitmap.ViewPerspective != BOTTOM_LEFT) ) 
      L_ChangeBitmapViewPerspective ( NULL, &LeadBitmap, sizeof(BITMAPHANDLE), TOP_LEFT ); 
   if (LeadBitmap.ViewPerspective == BOTTOM_LEFT) 
      nRow = LeadBitmap.Height - nRow - nYSize; 
   /* Allocate the buffers */ 
   hBuffer = GlobalAlloc(GMEM_MOVEABLE, (((LeadBitmap.Width + 31) &~31)/ 8) * nYSize); 
   pBuffer = (L_UCHAR*)GlobalLock( hBuffer ); 
   hRunBuffer = GlobalAlloc (GMEM_MOVEABLE, (L_UINT32)((LeadBitmap.Width + 3) * 2) * nYSize); 
   pRunBuffer = (L_UINT16*)GlobalLock (hRunBuffer); 
   /* Access the bitmap */ 
   /* Get the top nRow lines */ 
   nRet = L_GetBitmapRowCompressed ( &LeadBitmap, NULL, pRunBuffer, nRow, nYSize ); 
   if(nRet != SUCCESS) 
      return nRet; 
   /* Expand the compressed data */ 
   nRet = L_ExpandRows( pRunBuffer, pBuffer, LeadBitmap.Width, nYSize); 
   if(nRet != SUCCESS) 
      return nRet; 
   /* Invert the data */ 
   for(n=0; n < (L_INT)LeadBitmap.BytesPerLine * nYSize; n++) 
      pBuffer[n] = pBuffer[n] ^ 0xFF; 
   /* Compress the inverted data */ 
   nRet = L_CompressRows( pRunBuffer, pBuffer, LeadBitmap.Width, nYSize); 
   if(nRet != SUCCESS) 
      return nRet; 
   /* Put the inverted, compressed data back into the bitmap */ 
   nRet = L_PutBitmapRowCompressed ( &LeadBitmap, NULL, pRunBuffer, nRow, nYSize );  
   if(nRet != SUCCESS) 
      return nRet; 
   /* Free memory that we no longer need */ 
   return SUCCESS; 

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