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Click two points to draw a line.

Info  |  Source
Info
A demonstration of using PHP to generate a graphic based upon a user's mouse clicks.

How it works: Notes
PHP Source
Below is the PHP source to generate the gif line. View the HTML source for the javascript code.
<?
# this code is in here since I got 17,000 hits yesterday from someone
# using this script
if (eregi("Simulator",$HTTP_REFERER))
    {
    # please run this script locally, otherwise I will just take it offline
    header("Location: http://i.cnn.net/cnn/images/main/cnn_logo_260.gif");
    exit;
    }
    
# draws a line based upon cordinates ($x1,$x2,$y1,$y2)
# syntax:
# image.php?$x1=&$x2=&$y1=&$y2=

$x1 = $_REQUEST["x1"];
$x2 = $_REQUEST["x2"];
$y1 = $_REQUEST["y1"];
$y2 = $_REQUEST["y2"];

$width = abs($x1-$x2);
$height = abs($y1-$y2);


$imgOut = ImageCreate($width,$height);
$white = ImageColorAllocate($imgOut, 255, 255, 255);
$black = ImageColorAllocate($imgOut, 0, 0, 0);
$gray = ImageColorAllocate($imgOut, 255, 255, 255);

# fill background color
imageFill($imgOut, $width, $height, $white);

# get slope
if ($width != 0 && $height != 0)
    $m = ($x1-$x2)/($y1-$y2);
    
else $m = 0;

# draw line based on slope
if ($m >= 0) 
    {
    imageline($imgOut, 1, 1, $width+1, $height+1, $black);
    #draw shadow
    #imageline($imgOut, 0, 0, $width, $height, $black);
    }
else  
    {
    imageline($imgOut, $width+1, 1, 1,$height+1, $black);
    #draw shadow
    #imageline($imgOut, $width, 0, 0,$height, $black);
    }

imagecolortransparent ($imgOut, $white);

    Header("Content-type: image/png");
    ImagePNG($imgOut);
    ImageDestroy($imgOut);
?>