masyarakat Belajar Perpustakaan Alatan Masa lapang
cari
Melayu
Rumah > pembangunan bahagian belakang > tutorial php > GIFDecoder的排错以及修改另附完整代码和demo

GIFDecoder的排错以及修改另附完整代码和demo

WBOY
Lepaskan： 2016-08-08 09:23:54
asal
1309 orang telah melayarinya

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>] 8 );
                    }
                }
            } <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>] 8 );
                        <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>
Salin selepas log masuk

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>
Salin selepas log masuk

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_>

 */</diandianxiyu_></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> $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>] 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>] 8 );
                    <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> $GIF_code;
        <span>$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> $len; <span>$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></code>
Salin selepas log masuk

后记

  • 小的知识积累最后会有质变
  • 善于总结永远没有坏处
  • 一个功能写三遍就会变得不一样，如果还一样的话那就是自己的问题了

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。

Label berkaitan：
buffer gif gt this
sumber：php.cn
Artikel sebelumnya：PHP 文件读入到数组 Artikel seterusnya：一键生成各种尺寸Icon的php脚本
Kenyataan Laman Web ini
Kandungan artikel ini disumbangkan secara sukarela oleh netizen, dan hak cipta adalah milik pengarang asal. Laman web ini tidak memikul tanggungjawab undang-undang yang sepadan. Jika anda menemui sebarang kandungan yang disyaki plagiarisme atau pelanggaran, sila hubungi admin@php.cn
Artikel terbaru oleh pengarang
Isu terkini
Tukar React ImageSlider kepada NextJS Saya mempunyai peluncur imej berikut dalam React dan ia berfungsi seperti yang diharapkan:...
daripada 2024-04-05 10:45:23
0
1
2327
Topik-topik yang berkaitan
Lagi>
Cadangan popular
Tutorial Popular
Lagi>
Tutorial berkaitan
Cadangan popular
Kursus terkini
Muat turun terkini
Lagi>
kesan web
Kod sumber laman web
Bahan laman web
Templat hujung hadapan