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

class PDF_Grid extends FPDF {
    var $grid = false;

    function DrawGrid()
    {
        if($this->grid===true){
            $spacing = 5;
        } else {
            $spacing = $this->grid;
        }
        $this->SetDrawColor(204, 255, 255);
        $this->SetLineWidth(0.35);
        for($i=0;$i<$this->w;$i+=$spacing){
            $this->Line($i, 0, $i, $this->h);
        }
        for($i=0;$i<$this->h;$i+=$spacing){
            $this->Line(0, $i, $this->w, $i);
        }
        $this->SetDrawColor(0, 0, 0);

        $x = $this->GetX();
        $y = $this->GetY();
        $this->SetFont('Arial', 'I', 8);
        $this->SetTextColor(204, 204, 204);
        for($i=20;$i<$this->h;$i+=20){
            $this->SetXY(1, $i-3);
            $this->Write(4, $i);
        }
        for($i=20;$i<(($this->w)-($this->rMargin)-10);$i+=20){
            $this->SetXY($i-1, 1);
            $this->Write(4, $i);
        }
        $this->SetXY($x, $y);
    }

    function Header()
    {
        if($this->grid)
            $this->DrawGrid();
    }
}
?>

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

$pdf = new PDF_Grid();

// Add page with a grid and default spacing (5mm)
$pdf->grid = true;
$pdf->AddPage();

// Add page with a grid (10mm spacing)
$pdf->grid = 10;
$pdf->AddPage();

// Disable grid
$pdf->grid = false;
$pdf->AddPage();

$pdf->Output();
?>