前言
好久没有写技术类的博客了，今天有些小的收获，记录下来，留作备份
Gif图片的处理
由于业务需求，需要对gif动图的第一帧进行截取，然后我就搜索，发现了GIFDecoder这样的一个类，是做gif图片的处理的，怎奈国内人博客环境还是那么差，各种网站博客到处抄抄抄，没有一个完整的内容，经过多个站的资料整理，终于能用了。
出现了异常
在运行demo的时候，遇到了显示错误的问题
Notice: Undefined offset: 4 in /Applications/XAMPP/xamppfiles/htdocs/giftest/gifdecoder.class.php on line 83
查看源码发现83行是这样的
<code><span><span>function</span><span>GIFReadExtensions</span><span>()</span> {</span>
GIFDecoder::GIFGetByte(<span>1</span>);
<span>if</span> (<span>$this</span>->GIF_buffer [<span>0</span>] == <span>0xff</span>) {
<span>for</span> (;;) {
GIFDecoder::GIFGetByte(<span>1</span>);
<span>if</span> (( <span>$u</span> = <span>$this</span>->GIF_buffer [<span>0</span>] ) == <span>0x00</span>) {
<span>break</span>;
}
GIFDecoder::GIFGetByte(<span>$u</span>);
<span>if</span> (<span>$u</span> == <span>0x03</span>) {
<span>$this</span>->GIF_anloop = ( <span>$this</span>->GIF_buffer [<span>1</span>] | <span>$this</span>->GIF_buffer [<span>2</span>] << <span>8</span> );
}
}
} <span>else</span> {
<span>for</span> (;;) {
GIFDecoder::GIFGetByte(<span>1</span>);
<span>if</span> (( <span>$u</span> = <span>$this</span>->GIF_buffer [<span>0</span>] ) == <span>0x00</span>) {
<span>break</span>;
}
GIFDecoder::GIFGetByte(<span>$u</span>);
<span>if</span> (<span>$u</span> == <span>0x04</span>) {
<span>if</span> (<span>$this</span>->GIF_buffer [<span>4</span>] & <span>0x80</span>) { <span>//这里是第83行</span><span>$this</span>->GIF_dispos [] = ( <span>$this</span>->GIF_buffer [<span>0</span>] >> <span>2</span> ) - <span>1</span>;
} <span>else</span> {
<span>$this</span>->GIF_dispos [] = ( <span>$this</span>->GIF_buffer [<span>0</span>] >> <span>2</span> ) - <span>0</span>;
}
<span>$this</span>->GIF_delays [] = ( <span>$this</span>->GIF_buffer [<span>1</span>] | <span>$this</span>->GIF_buffer [<span>2</span>] << <span>8</span> );
<span>if</span> (<span>$this</span>->GIF_buffer [<span>3</span>]) {
<span>$this</span>->GIF_TransparentI = <span>$this</span>->GIF_buffer [<span>3</span>];
}
}
}
}
}</code>原因
经过搜索引擎的努力，我得到的比较正规的解释是
offset:接下去的数字是出错的数组下标,一般是超出了数组的取值范围,如定义了数组
A[] 有 10个 元 数 ,如 果 出 现 了 A[10]就会出现错误(Notice: Undefined offset: 10 ….),因为数组的下标是从0开始的,所以这个数组的下标就只能是0~9.
所以，原因就是
数组找不到下标为4的元素
解决方案
我们需要判断下标是不是存在
<code><span>if</span> (<span>isset</span>(<span>$this</span>->GIF_buffer [<span>4</span>]) & <span>0x80</span>) { </code>酱紫就搞定啦，啦啦啦~
源码
<code><span><span><span><?php</span>/**
* GIFDecoder <br/>
*
* 日期: 2015年05月21日 <br/>
* 原作者: 不详 <br/>
* 修改: CalvinLee <br/>
*
*
* <code>
* require_once("gifdecoder.class.php");
*
* $FIC = "test.gif";
* //获取gif的第一帧进行保存
* if (file_exists($FIC)) {
* $GIF_frame = fread(fopen($FIC, 'rb'), filesize($FIC));
* $decoder = new GIFDecoder($GIF_frame);
* $frames = $decoder->GIFGetFrames();
* $i = 0;
* $fname = rand(1000, 9999). $FIC . "_0$i.png";
* $hfic = fopen("" . $fname, "wb");
* fwrite($hfic, $frames [$i]);
* fclose($hfic);
* }
* </code>
*
*
*<span> @copyright</span> (c) 2015, Calvin Lee
*<span> @author</span> Calvin Lee <diandianxiyu_@live.cn>
*/</span><span><span>Class</span><span>GIFDecoder</span> {</span><span>public</span><span>$GIF_TransparentR</span> = -<span>1</span>;
<span>public</span><span>$GIF_TransparentG</span> = -<span>1</span>;
<span>public</span><span>$GIF_TransparentB</span> = -<span>1</span>;
<span>public</span><span>$GIF_TransparentI</span> = <span>0</span>;
<span>public</span><span>$GIF_buffer</span> = <span>array</span>();
<span>public</span><span>$GIF_arrays</span> = <span>array</span>();
<span>public</span><span>$GIF_delays</span> = <span>array</span>();
<span>public</span><span>$GIF_dispos</span> = <span>array</span>();
<span>public</span><span>$GIF_stream</span> = <span>""</span>;
<span>public</span><span>$GIF_string</span> = <span>""</span>;
<span>public</span><span>$GIF_bfseek</span> = <span>0</span>;
<span>public</span><span>$GIF_anloop</span> = <span>0</span>;
<span>public</span><span>$GIF_screen</span> = <span>array</span>();
<span>public</span><span>$GIF_global</span> = <span>array</span>();
<span>public</span><span>$GIF_sorted</span>;
<span>public</span><span>$GIF_colorS</span>;
<span>public</span><span>$GIF_colorC</span>;
<span>public</span><span>$GIF_colorF</span>;
<span><span>function</span><span>GIFDecoder</span><span>(<span>$GIF_pointer</span>)</span> {</span><span>$this</span>->GIF_stream = <span>$GIF_pointer</span>;
GIFDecoder::GIFGetByte(<span>6</span>);
GIFDecoder::GIFGetByte(<span>7</span>);
<span>$this</span>->GIF_screen = <span>$this</span>->GIF_buffer;
<span>$this</span>->GIF_colorF = <span>$this</span>->GIF_buffer [<span>4</span>] & <span>0x80</span> ? <span>1</span> : <span>0</span>;
<span>$this</span>->GIF_sorted = <span>$this</span>->GIF_buffer [<span>4</span>] & <span>0x08</span> ? <span>1</span> : <span>0</span>;
<span>$this</span>->GIF_colorC = <span>$this</span>->GIF_buffer [<span>4</span>] & <span>0x07</span>;
<span>$this</span>->GIF_colorS = <span>2</span> << <span>$this</span>->GIF_colorC;
<span>if</span> (<span>$this</span>->GIF_colorF == <span>1</span>) {
GIFDecoder::GIFGetByte(<span>3</span> * <span>$this</span>->GIF_colorS);
<span>$this</span>->GIF_global = <span>$this</span>->GIF_buffer;
}
<span>for</span> (<span>$cycle</span> = <span>1</span>; <span>$cycle</span>;) {
<span>if</span> (GIFDecoder::GIFGetByte(<span>1</span>)) {
<span>switch</span> (<span>$this</span>->GIF_buffer [<span>0</span>]) {
<span>case</span><span>0x21</span>:
GIFDecoder::GIFReadExtensions();
<span>break</span>;
<span>case</span><span>0x2C</span>:
GIFDecoder::GIFReadDescriptor();
<span>break</span>;
<span>case</span><span>0x3B</span>:
<span>$cycle</span> = <span>0</span>;
<span>break</span>;
}
} <span>else</span> {
<span>$cycle</span> = <span>0</span>;
}
}
}
<span><span>function</span><span>GIFReadExtensions</span><span>()</span> {</span>
GIFDecoder::GIFGetByte(<span>1</span>);
<span>if</span> (<span>$this</span>->GIF_buffer [<span>0</span>] == <span>0xff</span>) {
<span>for</span> (;;) {
GIFDecoder::GIFGetByte(<span>1</span>);
<span>if</span> (( <span>$u</span> = <span>$this</span>->GIF_buffer [<span>0</span>] ) == <span>0x00</span>) {
<span>break</span>;
}
GIFDecoder::GIFGetByte(<span>$u</span>);
<span>if</span> (<span>$u</span> == <span>0x03</span>) {
<span>$this</span>->GIF_anloop = ( <span>$this</span>->GIF_buffer [<span>1</span>] | <span>$this</span>->GIF_buffer [<span>2</span>] << <span>8</span> );
}
}
} <span>else</span> {
<span>for</span> (;;) {
GIFDecoder::GIFGetByte(<span>1</span>);
<span>if</span> (( <span>$u</span> = <span>$this</span>->GIF_buffer [<span>0</span>] ) == <span>0x00</span>) {
<span>break</span>;
}
GIFDecoder::GIFGetByte(<span>$u</span>);
<span>if</span> (<span>$u</span> == <span>0x04</span>) {
<span>if</span> (<span>isset</span>(<span>$this</span>->GIF_buffer [<span>4</span>]) & <span>0x80</span>) {
<span>$this</span>->GIF_dispos [] = ( <span>$this</span>->GIF_buffer [<span>0</span>] >> <span>2</span> ) - <span>1</span>;
} <span>else</span> {
<span>$this</span>->GIF_dispos [] = ( <span>$this</span>->GIF_buffer [<span>0</span>] >> <span>2</span> ) - <span>0</span>;
}
<span>$this</span>->GIF_delays [] = ( <span>$this</span>->GIF_buffer [<span>1</span>] | <span>$this</span>->GIF_buffer [<span>2</span>] << <span>8</span> );
<span>if</span> (<span>$this</span>->GIF_buffer [<span>3</span>]) {
<span>$this</span>->GIF_TransparentI = <span>$this</span>->GIF_buffer [<span>3</span>];
}
}
}
}
}
<span><span>function</span><span>GIFReadDescriptor</span><span>()</span> {</span><span>$GIF_screen</span> = <span>Array</span>();
GIFDecoder::GIFGetByte(<span>9</span>);
<span>$GIF_screen</span> = <span>$this</span>->GIF_buffer;
<span>$GIF_colorF</span> = <span>$this</span>->GIF_buffer [<span>8</span>] & <span>0x80</span> ? <span>1</span> : <span>0</span>;
<span>if</span> (<span>$GIF_colorF</span>) {
<span>$GIF_code</span> = <span>$this</span>->GIF_buffer [<span>8</span>] & <span>0x07</span>;
<span>$GIF_sort</span> = <span>$this</span>->GIF_buffer [<span>8</span>] & <span>0x20</span> ? <span>1</span> : <span>0</span>;
} <span>else</span> {
<span>$GIF_code</span> = <span>$this</span>->GIF_colorC;
<span>$GIF_sort</span> = <span>$this</span>->GIF_sorted;
}
<span>$GIF_size</span> = <span>2</span> << <span>$GIF_code</span>;
<span>$this</span>->GIF_screen [<span>4</span>] &= <span>0x70</span>;
<span>$this</span>->GIF_screen [<span>4</span>] |= <span>0x80</span>;
<span>$this</span>->GIF_screen [<span>4</span>] |= <span>$GIF_code</span>;
<span>if</span> (<span>$GIF_sort</span>) {
<span>$this</span>->GIF_screen [<span>4</span>] |= <span>0x08</span>;
}
<span>//GIF Data Begin</span><span>if</span> (<span>$this</span>->GIF_TransparentI) {
<span>$this</span>->GIF_string = <span>"GIF89a"</span>;
} <span>else</span> {
<span>$this</span>->GIF_string = <span>"GIF87a"</span>;
}
GIFDecoder::GIFPutByte(<span>$this</span>->GIF_screen);
<span>if</span> (<span>$GIF_colorF</span> == <span>1</span>) {
GIFDecoder::GIFGetByte(<span>3</span> * <span>$GIF_size</span>);
<span>if</span> (<span>$this</span>->GIF_TransparentI) {
<span>$this</span>->GIF_TransparentR = <span>$this</span>->GIF_buffer [<span>3</span> * <span>$this</span>->GIF_TransparentI + <span>0</span>];
<span>$this</span>->GIF_TransparentG = <span>$this</span>->GIF_buffer [<span>3</span> * <span>$this</span>->GIF_TransparentI + <span>1</span>];
<span>$this</span>->GIF_TransparentB = <span>$this</span>->GIF_buffer [<span>3</span> * <span>$this</span>->GIF_TransparentI + <span>2</span>];
}
GIFDecoder::GIFPutByte(<span>$this</span>->GIF_buffer);
} <span>else</span> {
<span>if</span> (<span>$this</span>->GIF_TransparentI) {
<span>$this</span>->GIF_TransparentR = <span>$this</span>->GIF_global [<span>3</span> * <span>$this</span>->GIF_TransparentI + <span>0</span>];
<span>$this</span>->GIF_TransparentG = <span>$this</span>->GIF_global [<span>3</span> * <span>$this</span>->GIF_TransparentI + <span>1</span>];
<span>$this</span>->GIF_TransparentB = <span>$this</span>->GIF_global [<span>3</span> * <span>$this</span>->GIF_TransparentI + <span>2</span>];
}
GIFDecoder::GIFPutByte(<span>$this</span>->GIF_global);
}
<span>if</span> (<span>$this</span>->GIF_TransparentI) {
<span>$this</span>->GIF_string .= <span>"!\xF9\x04\x1\x0\x0"</span> . chr(<span>$this</span>->GIF_TransparentI) . <span>"\x0"</span>;
}
<span>$this</span>->GIF_string .= chr(<span>0x2C</span>);
<span>$GIF_screen</span> [<span>8</span>] &= <span>0x40</span>;
GIFDecoder::GIFPutByte(<span>$GIF_screen</span>);
GIFDecoder::GIFGetByte(<span>1</span>);
GIFDecoder::GIFPutByte(<span>$this</span>->GIF_buffer);
<span>for</span> (;;) {
GIFDecoder::GIFGetByte(<span>1</span>);
GIFDecoder::GIFPutByte(<span>$this</span>->GIF_buffer);
<span>if</span> (( <span>$u</span> = <span>$this</span>->GIF_buffer [<span>0</span>] ) == <span>0x00</span>) {
<span>break</span>;
}
GIFDecoder::GIFGetByte(<span>$u</span>);
GIFDecoder::GIFPutByte(<span>$this</span>->GIF_buffer);
}
<span>$this</span>->GIF_string .= chr(<span>0x3B</span>);
<span>//GIF Data End</span><span>$gif_array</span> = &<span>$this</span>->GIF_arrays;
<span>$gif_array</span>[] = <span>$this</span>->GIF_string;
}
<span><span>function</span><span>GIFGetByte</span><span>(<span>$len</span>)</span> {</span><span>$this</span>->GIF_buffer = <span>Array</span>();
<span>for</span> (<span>$i</span> = <span>0</span>; <span>$i</span> < <span>$len</span>; <span>$i</span>++) {
<span>if</span> (<span>$this</span>->GIF_bfseek > strlen(<span>$this</span>->GIF_stream)) {
<span>return</span><span>0</span>;
}
<span>$this</span>->GIF_buffer[] = ord(<span>$this</span>->GIF_stream { <span>$this</span>->GIF_bfseek++});
}
<span>return</span><span>1</span>;
}
<span><span>function</span><span>GIFPutByte</span><span>(<span>$bytes</span>)</span> {</span><span>foreach</span> (<span>$bytes</span><span>as</span><span>$byte</span>) {
<span>$this</span>->GIF_string .= chr(<span>$byte</span>);
}
}
<span><span>function</span><span>GIFGetFrames</span><span>()</span> {</span><span>return</span> ( <span>$this</span>->GIF_arrays );
}
<span><span>function</span><span>GIFGetDelays</span><span>()</span> {</span><span>return</span> ( <span>$this</span>->GIF_delays );
}
<span><span>function</span><span>GIFGetLoop</span><span>()</span> {</span><span>return</span> ( <span>$this</span>->GIF_anloop );
}
<span><span>function</span><span>GIFGetDisposal</span><span>()</span> {</span><span>return</span> ( <span>$this</span>->GIF_dispos );
}
<span><span>function</span><span>GIFGetTransparentR</span><span>()</span> {</span><span>return</span> ( <span>$this</span>->GIF_TransparentR );
}
<span><span>function</span><span>GIFGetTransparentG</span><span>()</span> {</span><span>return</span> ( <span>$this</span>->GIF_TransparentG );
}
<span><span>function</span><span>GIFGetTransparentB</span><span>()</span> {</span><span>return</span> ( <span>$this</span>->GIF_TransparentB );
}
}
<span>?></span></span></code>后记
以上就介绍了GIFDecoder的排错以及修改另附完整代码和demo，包括了方面的内容，希望对PHP教程有兴趣的朋友有所帮助。
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