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LBuffer::CompressRows

Summary

Performs buffer-to-buffer RLE compression of 1-bit image data. Use this function to process multiple lines of image data.

Syntax

#include "ltwrappr.h"

virtual L_INT LBuffer::CompressRows(LBufferSrc, nWidth, nRows)

Parameters

LBuffer& LBufferSrc

The input buffer, which contains the 1-bit image data to be compressed. The size of each row must be rounded up to a multiple of 4 bytes. Use integer math to calculate the required size of this buffer as follows: bytes required = (((nWidth + 31) &~31)/ 8) * nRows.

L_UINT nWidth

The number of pixels in each row.

L_UINT nRows

The number of rows to process.

Returns

Value	Meaning
> 0	The number of pixels processed.
< 1	An error occurred. Refer to Return Codes.

Comments

The output buffer must be larger than the input buffer to accommodate the worst possible case with run-length encoding, where there are alternating black and white pixels. In most cases, however, the actual compressed data will be much smaller than the input data.

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.

The parameter LBufferSrc is passed by reference, and is a required parameter.

Required DLLs and Libraries

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

Platforms

Win32, x64.

Example

L_INT LBuffer__CompressRowsExample(LBitmapBase  * pLeadBitmap) 
{ 
   L_INT nRet; 
   LBuffer LeadBuffer, TmpBuffer ; 
   L_INT nLines = 50 ; 
   L_INT nRow = 0 ; 
   L_CHAR  * pBuffer; 
 
   nRet =pLeadBitmap->Access() ; 
   if(nRet !=SUCCESS) 
      return nRet; 
 
   // Get the top nRow lines  
   nRet =pLeadBitmap->GetRowCompressed( &LeadBuffer, nRow, nLines, NULL) ; 
   if(nRet !=SUCCESS) 
      return nRet; 
    
   // Expand the compressed data  
   nRet =TmpBuffer.ExpandRows(LeadBuffer, pLeadBitmap->GetWidth(), nLines) ; 
   if(nRet < 1) 
      return nRet; 
 
   pBuffer = (L_CHAR  *)TmpBuffer.Lock() ; 
   // Invert the data  
   for(L_INT n=0; n < pLeadBitmap->GetBytesPerLine() * nLines; n++) 
      pBuffer[n] = pBuffer[n] ^ 0xFF; 
 
   TmpBuffer.Unlock() ; 
 
   // Compress the inverted data 
   nRet =LeadBuffer.CompressRows( TmpBuffer, pLeadBitmap->GetWidth(), nLines); 
   if(nRet < 1) 
      return nRet; 
 
   // Put the inverted, compressed data back into the bitmap 
   nRet =pLeadBitmap->PutRowCompressed( LeadBuffer, nRow, nLines); 
   if(nRet < 1) 
      return nRet; 
 
   nRet =pLeadBitmap->Release() ; 
   if(nRet !=SUCCESS) 
      return nRet; 
    
   nRet =TmpBuffer.Free(); 
   if(nRet !=SUCCESS) 
      return nRet; 
   nRet =LeadBuffer.Free() ; 
   if(nRet !=SUCCESS) 
      return nRet; 
 
   return SUCCESS; 
}