interletter.php

example.php

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

$pdf=new PDF();
$pdf->AddPage();
$pdf->SetFont('Arial','',9);
$pdf->Cell(85,4,"EXAMPLE OF FUNCTION USAGE",1,1,'C');
$pdf->Write(4,"\nSource: http://www.swg-fr.com\n\n");
$text=file_get_contents('ex.txt');
$pdf->Interletter(0.5, 'custom interlettering', 100, 100, 1, 1, 'C');
$pdf->Output();

interletter.php

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

class PDF extends FPDF
{

function Interletter($interletter, $textLine, $w, $h, $x, $y, $align)
    {
        $ecart = $interletter;
        $lineWidth = 0.0;
        foreach (str_split($textLine) as $letter) {
            $lineWidth += $this->GetStringWidth($letter);
        }
        $lineWidth += (strlen($textLine) - 1) * $ecart;
        $computexX = $x;//default is L
        if ($align == 'R') {
            $computexX = $x + ($w - $lineWidth);
        } else if ($align == 'C') {
            $computexX = $x + (($w / 2) - ($lineWidth / 2));
        }
        $this->SetXY($computexX, $y);
        $this->_out(sprintf('%.3F Tc', $ecart * $this->k));
        $this->Cell($w, $h, $textLine, 0, 0, 'L');
        $this->_out('BT 0 Tc ET');
    }
}