PHP创建缩略图

以下代码摘自《PHP深度分析：101个核心技巧、窍门和问题解决方法》 第八章

Thumbnail.class.php

<?php

	class ThumbnailException extends Exception
	{
		public function __construct($message = null, $code = 0)
		{
			parent::__construct($message, $code);
			error_log('Error in '. $this->getFile(). 
				' Line: '.$this->getLine().
				' Error: '.$this->getMessage());
		}
	}

	class ThumbnailFileException extends ThumbnailException {}
	class ThumbnailNotSupportedException extends ThumbnailException {}

	class Thumbnail
	{
		private $maxWidth;
		private $maxHeight;
		private $scale;
		private $inflate;
		private $types;
		private $imgLoaders;
		private $imgCreators;
		private $source;
		private $sourceWidth;
		private $sourceHeight;
		private $sourceMime;
		private $thumb;
		private $thumbWidth;
		private $thumbHeight;

		public function __construct($maxWidth, $maxHeight, $scale = true, $inflate = true)
		{
			$this->maxWidth = $maxWidth;
			$this->maxHeight = $maxHeight;
			$this->scale = $scale;
			$this->inflate = $inflate;


			$this->types = array('image/jpeg', 'image/png', 'image/gif');
			$this->imgLoaders = array(
				'image/jpeg' => 'imagecreatefromjpeg',
				'image/png' => 'imagecreatefrompng',
				'image/gif' => 'imagecreatefromgif'
				);
			$this->imgCreators = array(
				'image/jpeg' => 'imagejpeg',
				'image/png' => 'imagepng',
				'image/gif' => 'imagegif'
				);
		}

		// load a image from path
		public function loadFile($image)
		{
			if (!$dims = @getimagesize($image)) {
				throw new ThumbnailFileException("Could not find image: ".$image);
			}

			if (in_array($dims['mime'], $this->types)) {
				$loader = $this->imgLoaders[$dims['mime']];
				$this->source = $loader($image);
				$this->sourceWidth =$dims[0];
				$this->sourceHeight = $dims[1];
				$this->sourceMime = $dims['mime'];
				$this->initThumb();
				return true;
			}
			else {
				throw new ThumbnailNotSupportedException(
					'Image MIME type ').$dims['mime'].' not supported';
			}
		}

		// Load a image from binary string
		public function loadData($image, $mime)
		{
			if( in_array($mime, $this->types)) {
				if($this->source = @imagecreatefromstring($image)) {
					$this->sourceWidth = imagesx($this->source);
					$this->sourceHeight = imagesy($this->source);
					$this->sourceMime = $mime;
					$this->initThumb();
					return true;
				}else {
					throw new ThumbnailFileException('Could not load image from string');
				}
			} else {
				throw new ThumbnailNotSupportedException(
					'Image MIME type '.$mime.' not supported');
			}
		}

		// Create the thumb and save to the file or return 
		public function buildThumb($file = null)
		{
			$creator = $this->imgCreators[$this->sourceMime];
			if (isset($file)) {
				return $creator($this->thumb, $file);
			} else {
				return $creator($this->thumb);
			}
		}

		public function getMime() 
		{
			return $this->sourceMime;
		}

		public function getThumbWidth()
		{
			return $this->thumbWidth;
		}
		public function getThumbHeight()
		{
			return $this->thumbHeight;
		}


		private function initThumb()
		{
			if ($this->scale)//等比例缩放图片
			{
				if ($this->sourceWidth > $this->sourceHeight)
				{
					$this->thumbWidth = $this->maxWidth;
					$this->thumbHeight = floor($this->sourceHeight * ($this->maxWidth / $this->sourceWidth));
				}
				else if ($this->sourceWidth < $this->sourceHeight) {
					$this->thumbHeight = $this->maxHeight;
					$this->thumbWidth = floor($this->sourceWidth * ($this->maxHeight / $this->sourceHeight));
				} else {
					$this->thumbWidth = $this->maxWidth;
					$this->thumbHeight = $this->maxHeight;
				}

				$this->thumb = imagecreatetruecolor($this->thumbWidth, $this->thumbHeight);
			}

			if($this->sourceWidth <= $this->maxWidth && $this->sourceHeight <= $this->maxHeight 
				&& $this->inflate == false) //是否按需放大图片
			{
				$this->thumb = $this->source;
			}else {
				imagecopyresampled($this->thumb, $this->source, 0, 0, 0, 0, 
					$this->thumbWidth, $this->thumbHeight, $this->sourceWidth, $this->sourceHeight);

			}
		}
	}
?>

说明：

从构造函数__construct($maxWidth, $maxHeight, $scale = true, $inflate = true)得知，至少需要传入两个参数$maxWidth 和 $maxHeight， 分别代表缩略图的宽高，

$scale代表是否按照原图片等比例缩放，默认为true, 实际生成的缩略图的宽高不一定全部等于$maxWidth和$maxHeight，可能只有一个达到，而另一个小于。

$inflate代表当原图过小而要生成的缩略图大的时候是否要进行填充放大，默认为true。 当为false的时候，意味着缩略图和原图一样大小。

使用如下：

1. 获取本地或远程图片路径，创建200x200像素的图片，并输出到网页上：

<?php

require_once('Thumbnail.class.php');

$tn = new Thumbnail(200, 200);

// $tn ->loadFile('test.jpg');//本地图片
$tn ->loadFile('http://7.su.bdimg.com/skin/65.jpg');//网络图片
header('Content-Type: '.$tn->getMime());//输出图片到页面
$tn->buildThumb();


?>

2.获取图片内容（本地、网络、或者数据库），创建缩略图并保存到本地图片，然后在页面上以<img>标签来引用显示：

<?php

require_once('Thumbnail.class.php');

$tn = new Thumbnail(200, 200);


$image = file_get_contents('test.jpg');
$tn->loadData($image, 'image/jpeg');
$tn->buildThumb('test_200.jpg');
echo "<img src='test_200.jpg' width='".
<span style="white-space:pre">	</span>$tn->getThumbWidth()."' height='".$tn->getThumbHeight()."' alt='resized image' />";

?>