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Piece Of Pie - PHP

One of the nice things about PHP has to be its support for awide variety of different technologies. And one of the most overlookedextensions in PHP 4 is the PDFLib extension, which allows you todynamically construct PDF documents through your PHP scripts. Find outmore, inside.

  1. PDF Generation With PHP
  2. Getting Started
  3. Anatomy Lesson
  4. Pretty As A Picture
  5. The Shortest Distance Between Two Points
  6. Square Peg, Round Hole
  7. Heaven Is A Place On Earth
  8. Piece Of Pie
By: icarus, (c) Melonfire
Rating: starstarstarstarstar / 113
August 14, 2002

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Now that you've got a good understanding of just how to go about creating PDF files, it's time to see a real-life application. The following example demonstrates how PHP can accept numeric data and turn it into a graph - specifically, a multi-coloured pie chart.

The form below asks for a series of data "slices", in the form of numeric data, separated by commas. Once you've entered a few numbers, the "pie.php" script converts them from absolute numbers into data chunks of different relative sizes, and uses these chunks to create a PDF document containing a pie chart, marking out the different pie slices and filling them with different colours.

<basefont face=arial>
<h3>Pie Chart Generator</h3>
<table cellspacing="5" cellpadding="5">
<form action="pie.php" method=POST>
<td>Enter numeric values (pie segments), separated by commas</td> </tr>
<tr> <td><input type=text name=data></td> </tr> <tr> <td><input
name="submit" type=submit value="Generate PDF Pie Chart"></td> </tr>
</form> </table>
Here's the script that does all the work:
// raw data
$data = $_POST['data'];
$slices = explode(",", $data);
// initialize some variables
$sum = 0;
$degrees = Array();
$diameter = 200;
$radius = $diameter/2;
// set up colours array for pie slices (rgb, as percentages of
intensity) // add more to these if you like $colours = array(
// calculate sum of slices
$sum = array_sum($slices);
// convert each slice into corresponding percentage of 360-degree circle
for ($y=0; $y<sizeof($slices); $y++) {
$degrees[$y] = ($slices[$y]/$sum) * 360;
// start building the PDF document
// create handle for new PDF document
$pdf = pdf_new();
// open a file
pdf_open_file($pdf, "chart.pdf");
// start a new page (A4)
pdf_begin_page($pdf, 500, 500);
// set a stroke colour
pdf_setcolor($pdf, "stroke", "rgb", 1, 1, 0);
// draw baseline
pdf_moveto($pdf, 250, 250);
pdf_lineto($pdf, 350, 250);
for ($z=0; $z<sizeof($slices); $z++)
// set a fill colour
pdf_setcolor($pdf, "fill", "rgb", $colours[$z][0],
$colours[$z][1], $colours[$z][2]);
// calculate coordinate of end-point of each arc by obtaining 
// length of segment and adding radius
// remember that cos() and sin() return value in radians 
// and have to be converted back to degrees!
$end_x = round(250 + ($radius * cos($last_angle*pi()/180))); 
$end_y = round(250 + ($radius * sin($last_angle*pi()/180)));
// demarcate slice with line
pdf_moveto($pdf, 250, 250);
pdf_lineto($pdf, $end_x, $end_y);
// calculate and draw arc corresponding to each slice
pdf_arc($pdf, 250, 250, $radius, $last_angle,
// store last angle
$last_angle = $last_angle+$degrees[$z];
// fill slice with colour
// redraw the circle outline
pdf_circle($pdf, 250, 250, 100);
// end page
// close and save file
The data entered into the form is passed to the "pie.php" script via a variable named $data; this data is then split into its individual components with the explode() function, and each individual value is placed in the $slices array. A loop then converts these numbers into degrees of a circle, and draws arcs for each slice. In each iteration of the loop, the coordinate of the end point of the arc is also calculated and a line segment in drawn to demarcate the arc from the rest of the circle. Once the pie segment has been drawn, the pdf_fill_stroke() function is used to fill it with colour; this colour is obtained from the $colours array.

I'm not going to go into the details of how the script calculates the length of each arc and line segment - the script includes commented code fragments, which should explain most of the details.

If you enter five data slices of equal value, your pie chart will look like this,

Whereas if you enter two slices of equal value, it will look like this:

Go on - play with it and see how the various slices change in shape to reflect the relative sizes of your data chunks. And while you're enjoying yourself, I'll bid you adieu...till next time!

Note: All examples in this article have been tested on Linux/i586 with Apache 1.3.12 and PHP 4.2.0. Examples are illustrative only, and are not meant for a production environment. Melonfire provides no warranties or support for the source code described in this article. YMMV!

>>> More PHP Articles          >>> More By icarus, (c) Melonfire

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