Draw Lines in PDF document using FPDF

Line(x1,y1,x2,y2);

<?Php
require('fpdf.php');
$pdf = new FPDF(); 
$pdf->AddPage();
$pdf -> Line(20, 20, 150, 200);

$pdf->Output();
?>

Draw a cross X using full length of page

<?Php
require('fpdf.php');
$pdf = new FPDF(); 
$pdf->AddPage();

$width=$pdf->GetPageWidth(); // Width of Current Page
$height=$pdf->GetPageHeight(); // Height of Current Page

$pdf->Line(0, 0,$width,$height); // Line one Cross
$pdf->Line($width, 0,0,$height); // Line two Cross

$pdf->Output();
?>

Draw border at a gap of 2 across the page

<?Php
require('fpdf.php');
$pdf = new FPDF(); 
$pdf->AddPage();

$width=$pdf->GetPageWidth(); // Width of Current Page
$height=$pdf->GetPageHeight(); // Height of Current Page
$gap=2; // Gap between line and border , change this value

$pdf->Line($gap, $gap,$width-$gap,$gap); // Horizontal line at top
$pdf->Line($gap, $height-$gap,$width-$gap,$height-$gap); // Horizontal line at bottom
$pdf->Line($gap, $gap,$gap,$height-$gap); // Vetical line at left 
$pdf->Line($width-$gap, $gap,$width-$gap,$height-$gap); // Vetical line at Right
$pdf->Output();
?>

Draw horizontal lines at a gap of 10 throughout the page

<?Php
require('fpdf.php');
$pdf = new FPDF(); 
$pdf->AddPage();
$width=$pdf->GetPageWidth(); // Width of Current Page
$height=$pdf->GetPageHeight(); // Height of Current Page
$i=0;
for($i=0;$i<=$height;$i +=10){
$pdf -> Line(0, $i, $pdf -> w, $i);
}
$pdf->Output();
?>

Draw patterns of square boxes with reducing dimension across the page

<?Php
require('fpdf.php');
$pdf = new FPDF(); 
$pdf->AddPage();

$width=$pdf->GetPageWidth(); // Width of Current Page
$height=$pdf->GetPageHeight(); // Height of Current Page
$gap=2; // Gap between line and border 

for($gap=2;$gap<=$width/2; $gap+=2){
$pdf->Line($gap, $gap,$width-$gap,$gap); // Horizontal line at top
$pdf->Line($gap, $height-$gap,$width-$gap,$height-$gap); // Horizontal line at bottom
$pdf->Line($gap, $gap,$gap,$height-$gap); // Vetical line at left 
$pdf->Line($width-$gap, $gap,$width-$gap,$height-$gap); // Vetical line at Right
}
$pdf->Output();
?>

SetLineWidth(float width)

$pdf->SetLineWidth(0.8);

SetDrawColor(R,G,B) to change line color

$pdf->SetDrawColor(10,10,10);

<?Php
require('fpdf.php');
$pdf = new FPDF(); 
$pdf->AddPage();

$width=$pdf->GetPageWidth(); // Width of Current Page
$height=$pdf->GetPageHeight(); // Height of Current Page
$gap=2; // Gap between line and border 
$pdf->SetLineWidth(0.8);
$pdf->SetDrawColor(10,10,10);

for($gap=2;$gap<=$width/2; $gap+=5){
$pdf->SetDrawColor(10+(3*$gap),10+$gap,10+$gap);
$pdf->Line($gap, $gap,$width-$gap,$gap); // Horizontal line at top
$pdf->Line($gap, $height-$gap,$width-$gap,$height-$gap); // Horizontal line at bottom
$pdf->Line($gap, $gap,$gap,$height-$gap); // Vetical line at left 
$pdf->Line($width-$gap, $gap,$width-$gap,$height-$gap); // Vetical line at Right
}
$pdf->Output();
?>