Function msSHXLoadPage

mapshape.c:1076–1122

** msSHXLoadPage() ** ** The SHX tells us what the byte offsets of the shapes in the SHP file are. ** We read the SHX file in ~8K pages and store those pages in memory for ** successive accesses during the reading cycle (first bounds are read, ** then entire shapes). Each time we read a page, we mark it as read. */

** then entire shapes). Each time we read a page, we mark it as read.
*/
int msSHXLoadPage( SHPHandle psSHP, int shxBufferPage )
{
  int i;

  /* Each SHX record is 8 bytes long (two ints), hence our buffer size. */
  char buffer[SHX_BUFFER_PAGE * 8];

  /*  Validate the page number. */
  if( shxBufferPage < 0  )
    return(MS_FAILURE);

  /* The SHX file starts with 100 bytes of header, skip that. */
  fseek( psSHP->fpSHX, 100 + shxBufferPage * SHX_BUFFER_PAGE * 8, 0 );
  fread( buffer, 8, SHX_BUFFER_PAGE, psSHP->fpSHX );

  /* Copy the buffer contents out into the working arrays. */
  for( i = 0; i < SHX_BUFFER_PAGE; i++ ) {
    int tmpOffset, tmpSize;
    
    /* Don't write information past the end of the arrays, please. */
    if(psSHP->nRecords <= (shxBufferPage * SHX_BUFFER_PAGE + i) )
      break;
    
    memcpy( &tmpOffset, (buffer + (8*i)), 4);
    memcpy( &tmpSize, (buffer + (8*i) + 4), 4);
  
    /* SHX uses big endian numbers for the offsets, so we have to flip them */
    /* if we are a little endian machine. */
    if( !bBigEndian ) {
      tmpOffset = SWAP_FOUR_BYTES(tmpOffset);
      tmpSize = SWAP_FOUR_BYTES(tmpSize);
    }
    
    /* SHX stores the offsets in 2 byte units, so we double them to get */
    /* an offset in bytes. */
    tmpOffset = tmpOffset * 2;
    tmpSize = tmpSize * 2;

    /* Write the answer into the working arrays on the SHPHandle */
    psSHP->panRecOffset[shxBufferPage * SHX_BUFFER_PAGE + i] = tmpOffset;
    psSHP->panRecSize[shxBufferPage * SHX_BUFFER_PAGE + i] = tmpSize;
  }
    
  msSetBit(psSHP->panRecLoaded, shxBufferPage, 1);
  
  return(MS_SUCCESS);
}

int msSHXLoadAll( SHPHandle psSHP ) {