GIFDecoder的排錯以及修改另附完整程式碼和demo
前言
好久沒有寫技術類的博客了,今天有些小的收穫,記錄下來,留作備份
Gif圖片的處理
由於業務需求,需要對gif動圖的第一幀進行截取,然後我就搜索,發現了GIFDecoder這樣的一個類,是做gif圖片的處理的,怎奈國內人博客環境還是那麼差,各種網站博客到處抄抄抄,沒有一個完整的內容,經過多個站的資料整理,終於能用了。
出現了異常
在運行demo的時候,遇到了顯示錯誤的問題
Notice: Undefined offset: 4 in /Applications/XAMPP/xamppfiles/htdocs/phptest/gifdecoderline.class.
查看源碼發現83行是這樣的
<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>$this</span>->GIF_buffer [<span>3</span>]; } } } } }</code>
原因
經過搜尋引擎的努力,我得到的比較正規的解釋是
offset:接下去的數字是出錯的數組下標,一般是超出了一般是超出了陣列的值範圍,如定義了陣列
A[]A[] 出個 元 元 , 現 了 : 錯誤數組的下標是從0開始的,所以這個陣列的下標就只能是0~9. 所以,原因就是數組找不到下標為4的元素解決方案我們需要判斷下標為下標是不是存在醬紫就搞定啦,啦啦啦~源碼<code><span>if</span> (<span>isset</span>(<span>$this</span>->GIF_buffer [<span>4</span>]) & <span>0x80</span>) { </code>登入後複製
<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></span></code>
後記
得不一樣,如果還一樣的話那就是自己的問題了小的知識累積最後會有質變
以上就介紹了GIFDecoder的排錯以及修改另附完整程式碼和demo,包括了方面的內容,希望對PHP教程有興趣的朋友有所幫助。

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