Hacking Filled Polygon Support into FPDF

My preferred way to generate PDFs with PHP is by using the FPDF Library. The library is: free, doesn't require any add ons to run, has a terrific set of tutorials and a clear user manual. It turned out to be a great way to generate official looking PDF documents with a minimum of fuss.

Today, I needed to generate a specific chart type, and ran into a problem using FPDF. Turns out, FPDF doesn't support arbitrarily filled polygon shapes - only rectangles. D'oh.

This, however, turned out to be a great excuse to dig a little deeper into both FPDF and the PDF standard itself. From a review of the FPDF source code, I realized that most of what it was doing was emitting the right PDF operators into a text stream and letting the PDF viewer worry about the details.

I busted out the old PDF Reference Manual and learned that the operators it used were very similar to PostScript. If you've never looked into PostScript, it's a wonderfully fun language to learn.

Using my knowledge of PostScript, and reviewing the source code of FPDF I was able to hack the FPDF source to include:

function Poly($points, $close = false, $style = '') {
 if($style == 'F') {
   $op = 'f';
 } else if($style == 'FD' || $style == 'DF') {
   $op = 'B';
 } else {
   $op = 'S';
 }
 $buffer = sprintf("%.2f %.2f m\n", $points[0][0], $this->h - $points[0][1]);
 for($i = 1; $i <>h - $points[$i][1]);
 }
 if($close) {
   $buffer .= " h\n";
 }
 $buffer .= " $op\n";
 $this->_out($buffer);
}

Here's a sample usage:

require_once('../shared/lib/fpdf/fpdf.php');

$inch = 72;
$fpdf = new FPDF('L','pt','letter');
$fpdf->SetDrawColor(0xA4, 0x17, 0x17);
$fpdf->SetFillColor(0x63, 0x8F, 0xC9);
$fpdf->SetFont('Helvetica', '', 12);
$fpdf->AddPage();

$fpdf->Text($inch, $inch, "Test of the Poly(...) method:");
$fpdf->SetXY($inch, 4 * $inch);

// Build up a set of points
$points = array();
$points[] = array($inch, 4 * $inch);
for($x = 1; $x <>Poly($points, true, 'FD');


$fpdf->Output();

And here's how it looks in the PDF viewer: