Graph using php and gd. How do I display an image created from a function? - Webmaster Forums - Webmaster forum for HTML, PHP, ASP, CSS and more

bumling · 03-13-2006, 10:37 PM

I want to have a graph on a web page, a simple x-y graph from two arrays, $x and $y.

I have written a php page that can be used as an image, you know <img src="plot.php"> on my main page, but I can only plot hard coded data. I cannot figure out how to send my $x and $y from the main page to "plot.php". I don't want to send data in the url since I don't want to limit the size of $x and $y. And I don't know how to post form data to the page when I include it in an <img> tag.

I had an idea to create a graph object or a function that would return an image that I would somehow display. Something on the form:

include("plot.php");
$p = new plot($x, $y);
echo '<img src='.$p->render()...

I hope you understand what I mean, because I'm confused myself. Any suggestions are welcome. Here is plot.php:

Code:

<?php
    header("Content-type: image/png");

    $x = array(0,1,2,3,4);
    $y = array(-1,0,2,2,1);
    $image;
    $width = 800;
    $height = 250;
    $marginleft = 25;
    $marginright = 25;
    $margintop = 20;
    $marginbottom = 20;

    function xpix($p) {
        global $x, $width, $marginleft, $marginright;
        return ( ($p-min($x)) * ($width-$marginleft-$marginright) / (max($x)-min($x)) ) + $marginleft;
    }

    function ypix($p) {
        global $y, $height, $margintop, $marginbottom;
        return ( (max($y)-$p) * ($height-$margintop-$marginbottom) / (max($y)-min($y)) ) + $margintop;
    }

    # Make sure x and y are of equal size.
    $x = array_slice($x, 0, min(count($x),count($y)));
    $y = array_slice($y, 0, min(count($x),count($y)));
    $image = imagecreate($width,$height);
    $background = imagecolorallocate($image, 127, 127, 127);
    $black = imagecolorallocate($image, 0, 0, 0);

    for ($i = 0; $i < count($x)-1; $i++) {
        imageline($image, xpix($x[$i]), ypix($y[$i]), xpix($x[$i+1]), ypix($y[$i+1]), $black);
        imagestring($image, 5, xpix($x[$i+1])-25, ypix($y[$i+1]), "(".$x[$i+1].",".$y[$i+1].")", $black);
    }
    imagestring($image, 5, xpix($x[0])-25, ypix($y[0]), "(".$x[0].",".$y[0].")", $black);
    imageline($image, xpix(min($x)), ypix(0), xpix(max($x)), ypix(0), $black);

    imagepng($image);
    imageDestroy($image);
?>

edit: ok, problem solved using a session. Not much life on these forums by the way?