
<?php





function sendGetPage () {

  //too many ' and " in heredoc?

  $serverNamePhpSelf = $_SERVER['SERVER_NAME'].$_SERVER['PHP_SELF'];

  $width = $_POST['width'];

  $height = $_POST['height'];

  $x1 = $_POST['x1'];

  $y1 = $_POST['y1'];

  $x2 = $_POST['x2'];

  $y2 = $_POST['y2'];

  $x3 = $_POST['x3'];

  $y3 = $_POST['y3'];

  $xcur = $_POST['xcur'];

  $ycur = $_POST['ycur'];

  $points = $_POST['points'];



 echo <<< endOfGetPage

<html>

<head>

<title>PHP Sierpinski triangle</title>

</head>

<body>

<form name="drawingForm" 

action="http://$serverNamePhpSelf";

method="post">

Image size: Width

<input type="text" size="3" maxlength="4"  name="width" value="$width" $sizeReadonly>

Height

<input type="text" size="3" maxlength="4"  name="height" value="$height" $sizeReadonly>

<br>

Vertices of triangle: 

X1

<input type="text" size="3" maxlength="4"  name="x1" value="$x1">

Y1

<input type="text" size="3" maxlength="4"  name="y1" value="$y1">

X2

<input type="text" size="3" maxlength="4"  name="x2" value="$x2">

Y2

<input type="text" size="3" maxlength="4"  name="y2" value="$y2">

X3

<input type="text" size="3" maxlength="4"  name="x3" value="$x3">

Y3

<input type="text" size="3" maxlength="4"  name="y3" value="$y3">

<br>

  Starting point:

XStart

<input type="text" size="3" maxlength="4"  name="xcur" value="$xcur">

YStart

<input type="text" size="3" maxlength="4"  name="ycur" value="$ycur">

<br>

  Number of points:

<input type="text" size="5" maxlength="7"  name="points" value="$points">

<br>

<input value="Draw it" type="submit">

</form>

endOfGetPage;

}



//initial page load.  display form

if ($_SERVER['REQUEST_METHOD'] == 'GET') {

  unlink("sierpinski.png");

  bail("");   

}







$width = $_POST['width'];

$height = $_POST['height'];

$x = array();

$y = array();



$x[] = $_POST['x1'];

$y[] = $_POST['y1'];

$x[] = $_POST['x2'];

$y[] = $_POST['y2'];

$x[] = $_POST['x3'];

$y[] = $_POST['y3'];

$xcur = $_POST['xcur'];

$ycur = $_POST['ycur'];

$points = $_POST['points'];



//type check and range check here...

//form input is always string!!!  must use is-numeric, not is-int

if (!is_numeric($width) || !is_numeric($height) || !is_numeric($x[0]) || !is_numeric($y[0]) || 

    !is_numeric($x[2]) || !is_numeric($y[2]) ||

    !is_numeric($x[1]) || !is_numeric($y[1]) ||

    !is_numeric($xcur) || !is_numeric($ycur) ||

    !is_numeric($points) || $points<0 || $points>1000000 ||

    $width<1 || $width>1000 || $height<1 || $height>1000) {

  bail( "BAD INPUT. width: $width h: $height  or somewhere...\n"); 

}  

//larger than 1000 crashes???





$im = ImageCreateTrueColor($width, $height);



ImageAlphaBlending($im, false);

ImageFilledRectangle($im, 0, 0, $width, $height, ImageColorAllocate($im, 255, 255, 255));







$black = ImageColorAllocate($im, 0, 0, 0);



$color = $black;  





for ($i=1; $i<=$points; $i++) {

  $r = rand(0,2);

  $xcur = ($x[$r] + $xcur) / 2;

  $ycur = ($y[$r] + $ycur) / 2;

  ImageSetPixel($im, $xcur, $ycur, $color);

}









//my directory needs to be 777 for apache to write to it:

if (($fp = fopen("sierpinski.png","w")) == false) {

  bail( "<p>file open failed!</p>");

}

ImagePNG($im,"sierpinski.png");



sendGetPage();

echo "<hr>\n<img src=\"sierpinski.png\">\n";

echo "</body>\n</html>";











function bail ($reason) {

  echo $reason;

  sendGetPage();

  echo "</body>\n</html>";

  exit();

}



?>