php等比例生成缩略图

function reSizeImg($imgSrc, $resize_width, $resize_height, $isCut=false) {
	//图片的类型
	$type = substr ( strrchr ( $imgSrc, "." ), 1 );
	//初始化图象
	if ($type == "jpg") {
		$im = imagecreatefromjpeg ( $imgSrc );
	}
	if ($type == "gif") {
		$im = imagecreatefromgif ( $imgSrc );
	}
	if ($type == "png") {
		$im = imagecreatefrompng ( $imgSrc );
	}
	//目标图象地址
	$full_length = strlen ( $imgSrc );
	$type_length = strlen ( $type );
	$name_length = $full_length - $type_length;
	$name = substr ( $imgSrc, 0, $name_length - 1 );
	$dstimg = $name . "_s." . $type;

	$width = imagesx ( $im );
	$height = imagesy ( $im );

	//生成图象
	//改变后的图象的比例
	$resize_ratio = ($resize_width) / ($resize_height);
	//实际图象的比例
	$ratio = ($width) / ($height);
	if (($isCut) == 1) //裁图
		{
		if ($ratio >= $resize_ratio) //高度优先
		{
			$newimg = imagecreatetruecolor ( $resize_width, $resize_height );
			imagecopyresampled ( $newimg, $im, 0, 0, 0, 0, $resize_width, $resize_height, (($height) * $resize_ratio), $height );
			ImageJpeg ( $newimg, $dstimg );
		}
		if ($ratio < $resize_ratio) //宽度优先
		{
			$newimg = imagecreatetruecolor ( $resize_width, $resize_height );
			imagecopyresampled ( $newimg, $im, 0, 0, 0, 0, $resize_width, $resize_height, $width, (($width) / $resize_ratio) );
			ImageJpeg ( $newimg, $dstimg );
		}
	} else //不裁图
	{
		if ($ratio >= $resize_ratio) {
			$newimg = imagecreatetruecolor ( $resize_width, ($resize_width) / $ratio );
			imagecopyresampled ( $newimg, $im, 0, 0, 0, 0, $resize_width, ($resize_width) / $ratio, $width, $height );
			ImageJpeg ( $newimg, $dstimg );
		}
		if ($ratio < $resize_ratio) {
			$newimg = imagecreatetruecolor ( ($resize_height) * $ratio, $resize_height );
			imagecopyresampled ( $newimg, $im, 0, 0, 0, 0, ($resize_height) * $ratio, $resize_height, $width, $height );
			ImageJpeg ( $newimg, $dstimg );
		}
	}
	ImageDestroy ( $im );
}