<pre class="brush:php;">    set_time_limit(0);							// 关闭代码执行时间限制

$s = 100;								// 图片大小		
$step = 500;								// step
$area = 2;												
 
$image = imagecreate($s, $s);
imagecolorallocate($image,255,255,255);
$color = imagecolorallocate($image,0,0,0);
$s2 = $s/2;

$grid[$s2][$s2] = 1;
imagesetpixel($image,$s2,$s2,$color);
 
while($i＜$step){
	//calculate releasing area
	$n = max($max_x - $min_x, $max_y - $min_y) + $area;
	$s2mn = $s2-$n;
	$s2an = $s2+$n;
	//release a molecule
	do{
		$x = rand($s2mn,$s2an);
		$y = rand($s2mn,$s2an);
	}while($grid[$x][$y]);
	//move the molecule randomly
while(!($grid[$x-1][$y-1]+$grid[$x-1][$y]+$grid[$x-1][$y+1] + 
		$grid[$x][$y-1]+$grid[$x][$y+1]+$grid[$x+1][$y-1] +
		$grid[$x+1][$y]+$grid[$x+1][$y+1])){
		$x += rand(-1,1);
		$y += rand(-1,1);
		if($x＜$s2mn||$x＞$s2an||$y＜$s2mn||$y＞$s2an){
			continue 2;
		}
	}
	$grid[$x][$y] = 1;
	if($max_x＜$x){
		$max_x = $x;
	}elseif($min_x＞$x){
		$min_x = $x;
	}
	if($max_y＜$y){
		$max_y = $y;
	}elseif($min_y＞$y){
		$min_y = $y;
	}
	imagesetpixel($image,$x,$y,$color);
 
	++$i;
}
 
header("Content-type: image/png");
imagepng($image);
```
<p>
	参考地址：</p>