php动态处理图片后输出显示

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