Memory optimisation

Informations

Author: Philip Clarke
License: FPDF

Description

Normally FPDF compresses the entire PDF at the very end of PDF generation, this can lead to a large uncompressed PDF being stored in memory. This modification compresses each page as soon as it is finished, reducing the overall memory usage when generating large PDFs.

To test with minimal external influences, use a file such as the provided test.php. In one terminal window as root run top like so:

~> top -q | grep php

then run the script from the command line, using:

~> php -f test.php > with_opt.pdf

The "top" terminal window will scroll detailing memory usage of php (press q to exit). Then altering test.php to use the base class and running:

~> php -f test.php > no_opt.pdf

will show the original behaviour giving identical sized PDF files (no_opt.pdf and with_opt.pdf). On a 600 MHz dual processor typical results were that the optimised php code uses a maximum of 7.3 Megabytes wheareas the original uses 15 M. Both tests typically take 2 minutes 15 secs. Over very large reports (2000 pages +) the optimised version is very slightly slower by a few seconds.

Remark: there is also another script for memory optimisation.

Source

<?php
require('fpdf.php');

class PDF_Opt extends FPDF
{

function _putpages()
{
    $nb = $this->page;
    if(!empty($this->AliasNbPages))
    {
        // Replace number of pages
        for($n=1;$n<=$nb;$n++)
        {
            if($this->compress)
                $this->pages[$n] = gzcompress(str_replace($this->AliasNbPages,$nb,gzuncompress($this->pages[$n])));
            else
                $this->pages[$n] = str_replace($this->AliasNbPages,$nb,$this->pages[$n]);
        }
    }
    if($this->DefOrientation=='P')
    {
        $wPt = $this->DefPageSize[0]*$this->k;
        $hPt = $this->DefPageSize[1]*$this->k;
    }
    else
    {
        $wPt = $this->DefPageSize[1]*$this->k;
        $hPt = $this->DefPageSize[0]*$this->k;
    }
    $filter = ($this->compress) ? '/Filter /FlateDecode ' : '';
    for($n=1;$n<=$nb;$n++)
    {
        // Page
        $this->_newobj();
        $this->_out('<</Type /Page');
        $this->_out('/Parent 1 0 R');
        if(isset($this->PageSizes[$n]))
            $this->_out(sprintf('/MediaBox [0 0 %.2F %.2F]',$this->PageSizes[$n][0],$this->PageSizes[$n][1]));
        $this->_out('/Resources 2 0 R');
        if(isset($this->PageLinks[$n]))
        {
            // Links
            $annots = '/Annots [';
            foreach($this->PageLinks[$n] as $pl)
            {
                $rect = sprintf('%.2F %.2F %.2F %.2F',$pl[0],$pl[1],$pl[0]+$pl[2],$pl[1]-$pl[3]);
                $annots .= '<</Type /Annot /Subtype /Link /Rect ['.$rect.'] /Border [0 0 0] ';
                if(is_string($pl[4]))
                    $annots .= '/A <</S /URI /URI '.$this->_textstring($pl[4]).'>>>>';
                else
                {
                    $l = $this->links[$pl[4]];
                    $h = isset($this->PageSizes[$l[0]]) ? $this->PageSizes[$l[0]][1] : $hPt;
                    $annots .= sprintf('/Dest [%d 0 R /XYZ 0 %.2F null]>>',1+2*$l[0],$h-$l[1]*$this->k);
                }
            }
            $this->_out($annots.']');
        }
        if($this->PDFVersion>'1.3')
            $this->_out('/Group <</Type /Group /S /Transparency /CS /DeviceRGB>>');
        $this->_out('/Contents '.($this->n+1).' 0 R>>');
        $this->_out('endobj');
        // Page content
        $p = $this->pages[$n];
        $this->_newobj();
        $this->_out('<<'.$filter.'/Length '.strlen($p).'>>');
        $this->_putstream($p);
        $this->_out('endobj');
    }
    // Pages root
    $this->offsets[1] = strlen($this->buffer);
    $this->_out('1 0 obj');
    $this->_out('<</Type /Pages');
    $kids = '/Kids [';
    for($i=0;$i<$nb;$i++)
        $kids .= (3+2*$i).' 0 R ';
    $this->_out($kids.']');
    $this->_out('/Count '.$nb);
    $this->_out(sprintf('/MediaBox [0 0 %.2F %.2F]',$wPt,$hPt));
    $this->_out('>>');
    $this->_out('endobj');
}

function _endpage()
{
    parent::_endpage();
    if($this->compress)
        $this->pages[$this->page] = gzcompress($this->pages[$this->page]);
}

}
?>

Example

Here is an example of test script: 
<?php
require('memory_opt.php');

$pdf = new PDF_Opt();
$pdf->AddPage();
$pdf->SetFont('Arial','',9);
$txt = str_repeat('ashfsd kjsahkasjh akjhdsfjkh djshf sjkh ',200);
for($i=0;$i<1000;$i++)
    $pdf->Write(9,$txt);
$pdf->Output();
?>

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