php 输出动态处理后的图片

php动态改变图片尺寸后输出，输出图片时使用下面的地址：
image_resize.php?img=image.jpg&w=150&h=150&constrain=1
w和h为要显示的尺寸

 0) {
	// calculate resized height and width if percent is defined
	$percent = $percent * 0.01;
	$w = $sw * $percent;
	$h = $sh * $percent;
} else {
	if (isset ($w) AND !isset ($h)) {
		// autocompute height if only width is set
		$h = (100 / ($sw / $w)) * .01;
		$h = @round ($sh * $h);
	} elseif (isset ($h) AND !isset ($w)) {
		// autocompute width if only height is set
		$w = (100 / ($sh / $h)) * .01;
		$w = @round ($sw * $w);
	} elseif (isset ($h) AND isset ($w) AND isset ($constrain)) {
		// get the smaller resulting image dimension if both height
		// and width are set and $constrain is also set
		$hx = (100 / ($sw / $w)) * .01;
		$hx = @round ($sh * $hx);
 
		$wx = (100 / ($sh / $h)) * .01;
		$wx = @round ($sw * $wx);
 
		if ($hx