【GIFDecoder】GIFDecoder的排错以及修改另附完整代码和demo

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

            function GIFReadExtensions() {
            GIFDecoder::GIFGetByte(1);
            if ($this->GIF_buffer [0] == 0xff) {
                for (;;) {
                    GIFDecoder::GIFGetByte(1);
                    if (( $u = $this->GIF_buffer [0] ) == 0x00) {
                        break;
                    }
                    GIFDecoder::GIFGetByte($u);
                    if ($u == 0x03) {
                        $this->GIF_anloop = ( $this->GIF_buffer [1] | $this->GIF_buffer [2] << 8 );
                    }
                }
            } else {
                for (;;) {
                    GIFDecoder::GIFGetByte(1);
                    if (( $u = $this->GIF_buffer [0] ) == 0x00) {
                        break;
                    }
                    GIFDecoder::GIFGetByte($u);
                    if ($u == 0x04) {
                        if ($this->GIF_buffer [4] & 0x80) {   //这里是第83行
                            $this->GIF_dispos [] = ( $this->GIF_buffer [0] >> 2 ) - 1;
                        } else {
                            $this->GIF_dispos [] = ( $this->GIF_buffer [0] >> 2 ) - 0;
                        }
                        $this->GIF_delays [] = ( $this->GIF_buffer [1] | $this->GIF_buffer [2] << 8 );
                        if ($this->GIF_buffer [3]) {
                            $this->GIF_TransparentI = $this->GIF_buffer [3];
                        }
                    }
                }
            }
        }

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

 if (isset($this->GIF_buffer [4]) & 0x80) { 

酱紫就搞定啦，啦啦啦~

源码

<?php /** * 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> * * * @copyright (c) 2015, Calvin Lee * @author Calvin Lee <[email protected]> */ Class GIFDecoder { public $GIF_TransparentR = -1; public $GIF_TransparentG = -1; public $GIF_TransparentB = -1; public $GIF_TransparentI = 0; public $GIF_buffer = array(); public $GIF_arrays = array(); public $GIF_delays = array(); public $GIF_dispos = array(); public $GIF_stream = ""; public $GIF_string = ""; public $GIF_bfseek = 0; public $GIF_anloop = 0; public $GIF_screen = array(); public $GIF_global = array(); public $GIF_sorted; public $GIF_colorS; public $GIF_colorC; public $GIF_colorF; function GIFDecoder($GIF_pointer) { $this->GIF_stream = $GIF_pointer; GIFDecoder::GIFGetByte(6); GIFDecoder::GIFGetByte(7); $this->GIF_screen = $this->GIF_buffer; $this->GIF_colorF = $this->GIF_buffer [4] & 0x80 ? 1 : 0; $this->GIF_sorted = $this->GIF_buffer [4] & 0x08 ? 1 : 0; $this->GIF_colorC = $this->GIF_buffer [4] & 0x07; $this->GIF_colorS = 2 << $this->GIF_colorC; if ($this->GIF_colorF == 1) { GIFDecoder::GIFGetByte(3 * $this->GIF_colorS); $this->GIF_global = $this->GIF_buffer; } for ($cycle = 1; $cycle;) { if (GIFDecoder::GIFGetByte(1)) { switch ($this->GIF_buffer [0]) { case 0x21: GIFDecoder::GIFReadExtensions(); break; case 0x2C: GIFDecoder::GIFReadDescriptor(); break; case 0x3B: $cycle = 0; break; } } else { $cycle = 0; } } } function GIFReadExtensions() { GIFDecoder::GIFGetByte(1); if ($this->GIF_buffer [0] == 0xff) { for (;;) { GIFDecoder::GIFGetByte(1); if (( $u = $this->GIF_buffer [0] ) == 0x00) { break; } GIFDecoder::GIFGetByte($u); if ($u == 0x03) { $this->GIF_anloop = ( $this->GIF_buffer [1] | $this->GIF_buffer [2] << 8 ); } } } else { for (;;) { GIFDecoder::GIFGetByte(1); if (( $u = $this->GIF_buffer [0] ) == 0x00) { break; } GIFDecoder::GIFGetByte($u); if ($u == 0x04) { if (isset($this->GIF_buffer [4]) & 0x80) { $this->GIF_dispos [] = ( $this->GIF_buffer [0] >> 2 ) - 1; } else { $this->GIF_dispos [] = ( $this->GIF_buffer [0] >> 2 ) - 0; } $this->GIF_delays [] = ( $this->GIF_buffer [1] | $this->GIF_buffer [2] << 8 ); if ($this->GIF_buffer [3]) { $this->GIF_TransparentI = $this->GIF_buffer [3]; } } } } } function GIFReadDescriptor() { $GIF_screen = Array(); GIFDecoder::GIFGetByte(9); $GIF_screen = $this->GIF_buffer; $GIF_colorF = $this->GIF_buffer [8] & 0x80 ? 1 : 0; if ($GIF_colorF) { $GIF_code = $this->GIF_buffer [8] & 0x07; $GIF_sort = $this->GIF_buffer [8] & 0x20 ? 1 : 0; } else { $GIF_code = $this->GIF_colorC; $GIF_sort = $this->GIF_sorted; } $GIF_size = 2 << $GIF_code; $this->GIF_screen [4] &= 0x70; $this->GIF_screen [4] |= 0x80; $this->GIF_screen [4] |= $GIF_code; if ($GIF_sort) { $this->GIF_screen [4] |= 0x08; } //GIF Data Begin if ($this->GIF_TransparentI) { $this->GIF_string = "GIF89a"; } else { $this->GIF_string = "GIF87a"; } GIFDecoder::GIFPutByte($this->GIF_screen); if ($GIF_colorF == 1) { GIFDecoder::GIFGetByte(3 * $GIF_size); if ($this->GIF_TransparentI) { $this->GIF_TransparentR = $this->GIF_buffer [3 * $this->GIF_TransparentI + 0]; $this->GIF_TransparentG = $this->GIF_buffer [3 * $this->GIF_TransparentI + 1]; $this->GIF_TransparentB = $this->GIF_buffer [3 * $this->GIF_TransparentI + 2]; } GIFDecoder::GIFPutByte($this->GIF_buffer); } else { if ($this->GIF_TransparentI) { $this->GIF_TransparentR = $this->GIF_global [3 * $this->GIF_TransparentI + 0]; $this->GIF_TransparentG = $this->GIF_global [3 * $this->GIF_TransparentI + 1]; $this->GIF_TransparentB = $this->GIF_global [3 * $this->GIF_TransparentI + 2]; } GIFDecoder::GIFPutByte($this->GIF_global); } if ($this->GIF_TransparentI) { $this->GIF_string .= "!\xF9\x04\x1\x0\x0" . chr($this->GIF_TransparentI) . "\x0"; } $this->GIF_string .= chr(0x2C); $GIF_screen [8] &= 0x40; GIFDecoder::GIFPutByte($GIF_screen); GIFDecoder::GIFGetByte(1); GIFDecoder::GIFPutByte($this->GIF_buffer); for (;;) { GIFDecoder::GIFGetByte(1); GIFDecoder::GIFPutByte($this->GIF_buffer); if (( $u = $this->GIF_buffer [0] ) == 0x00) { break; } GIFDecoder::GIFGetByte($u); GIFDecoder::GIFPutByte($this->GIF_buffer); } $this->GIF_string .= chr(0x3B); //GIF Data End $gif_array = &$this->GIF_arrays; $gif_array[] = $this->GIF_string; } function GIFGetByte($len) { $this->GIF_buffer = Array(); for ($i = 0; $i < $len; $i++) { if ($this->GIF_bfseek > strlen($this->GIF_stream)) { return 0; } $this->GIF_buffer[] = ord($this->GIF_stream { $this->GIF_bfseek++}); } return 1; } function GIFPutByte($bytes) { foreach ($bytes as $byte) { $this->GIF_string .= chr($byte); } } function GIFGetFrames() { return ( $this->GIF_arrays ); } function GIFGetDelays() { return ( $this->GIF_delays ); } function GIFGetLoop() { return ( $this->GIF_anloop ); } function GIFGetDisposal() { return ( $this->GIF_dispos ); } function GIFGetTransparentR() { return ( $this->GIF_TransparentR ); } function GIFGetTransparentG() { return ( $this->GIF_TransparentG ); } function GIFGetTransparentB() { return ( $this->GIF_TransparentB ); } } ?>

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

后后记

后来发现这个类在Yii2中还是不能使用，识别不出gif里面的图片，所以，我又去github上找到了这个类的2.0版

https://github.com/xurei/GIFDecoder_optimized

下面是用的源码，已经加上了namespace和注释

<?php
namespace common\components\helper;
/* ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: :: :: GIFDecoder Version 2.0 by László Zsidi :: Optimized version by xurei :: :: Created at 2007. 02. 01. '07.47.AM' :: :: Updated at 2009. 06. 23. '06.00.AM' :: ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: * * * * <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> * * * * */
use SplFixedArray;  
class GIFDecoder {
    var $GIF_TransparentR =  -1;
    var $GIF_TransparentG =  -1;
    var $GIF_TransparentB =  -1;
    var $GIF_TransparentI =   0;

    var $GIF_buffer = null;
    var $GIF_arrays = Array ( );
    var $GIF_delays = Array ( );
    var $GIF_dispos = Array ( );
    var $GIF_stream = "";
    var $GIF_string = "";
    var $GIF_bfseek =  0;
    var $GIF_anloop =  0;

    //xurei - frames metadata
    var $GIF_frames_meta =  Array();

    var $GIF_screen = Array ( );
    var $GIF_global = Array ( ); //global color map
    var $GIF_sorted;
    var $GIF_colorS; //
    var $GIF_colorC; //Size of global color table
    var $GIF_colorF; //if 1, global color table follows image descriptor
    /* ::::::::::::::::::::::::::::::::::::::::::::::::::: :: :: GIFDecoder ( $GIF_pointer ) :: */
    function __construct ( $GIF_pointer ) {
        $this->GIF_stream = $GIF_pointer;

        GIFDecoder::GIFGetByte ( 6 );
        GIFDecoder::GIFGetByte ( 7 );

        $this->GIF_screen = $this->GIF_buffer;
        $this->GIF_colorF = $this->GIF_buffer [ 4 ] & 0x80 ? 1 : 0;
        $this->GIF_sorted = $this->GIF_buffer [ 4 ] & 0x08 ? 1 : 0;
        $this->GIF_colorC = $this->GIF_buffer [ 4 ] & 0x07;
        $this->GIF_colorS = 2 << $this->GIF_colorC;

        if ( $this->GIF_colorF == 1 ) {
            GIFDecoder::GIFGetByte ( 3 * $this->GIF_colorS );
            $this->GIF_global = $this->GIF_buffer;
        }
        for ( $cycle = 1; $cycle; ) {
            if ( GIFDecoder::GIFGetByte ( 1 ) ) {
                switch ( $this->GIF_buffer [ 0 ] ) {
                    case 0x21:
                        GIFDecoder::GIFReadExtensions ( );
                        break;
                    case 0x2C:
                        GIFDecoder::GIFReadDescriptor ( );
                        break;
                    case 0x3B:
                        $cycle = 0;
                        break;
                }
            }
            else {
                $cycle = 0;
            }
        }
    }
    /* ::::::::::::::::::::::::::::::::::::::::::::::::::: :: :: GIFReadExtension ( ) :: */
    function GIFReadExtensions ( ) {
        GIFDecoder::GIFGetByte ( 1 );
        if ( $this->GIF_buffer [ 0 ] == 0xff ) {
            for ( ; ; ) {
                GIFDecoder::GIFGetByte ( 1 );
                if ( ( $u = $this->GIF_buffer [ 0 ] ) == 0x00 ) {
                    break;
                }
                GIFDecoder::GIFGetByte ( $u );
                if ( $u == 0x03 ) {
                    $this->GIF_anloop = ( $this->GIF_buffer [ 1 ] | $this->GIF_buffer [ 2 ] << 8 );
                }
            }
        }
        else {
            for ( ; ; ) {
                GIFDecoder::GIFGetByte ( 1 );
                if ( ( $u = $this->GIF_buffer [ 0 ] ) == 0x00 ) {
                    break;
                }
                GIFDecoder::GIFGetByte ( $u );
                if ( $u == 0x04 ) {
                    $buf4 = count($this->GIF_buffer) >= 5 ? $this->GIF_buffer [ 4 ] : 0;
                    if ( $buf4 & 0x80 ) {
                        $this->GIF_dispos [ ] = ( $this->GIF_buffer [ 0 ] >> 2 ) - 1;
                    }
                    else {
                        $this->GIF_dispos [ ] = ( $this->GIF_buffer [ 0 ] >> 2 ) - 0;
                    }
                    $this->GIF_delays [ ] = ( $this->GIF_buffer [ 1 ] | $this->GIF_buffer [ 2 ] << 8 );
                    if ( $this->GIF_buffer [ 3 ] ) {
                        $this->GIF_TransparentI = $this->GIF_buffer [ 3 ];
                    }
                }
            }
        }
    }
    /* ::::::::::::::::::::::::::::::::::::::::::::::::::: :: :: GIFReadDescriptor ( ) :: */
    function GIFReadDescriptor ( ) {
        $GIF_screen    = Array ( );

        GIFDecoder::GIFGetByte ( 9 );

        //xurei - metadata saving
        $this->GIF_frames_meta[] = array(
            'left'=>$this->GIF_buffer[0] + ($this->GIF_buffer[1] << 8),
            'top'=>$this->GIF_buffer[2] + ($this->GIF_buffer[3] << 8),
            'width'=>$this->GIF_buffer[4] + ($this->GIF_buffer[5] << 8),
            'height'=>$this->GIF_buffer[6] + ($this->GIF_buffer[7] << 8),
        ); 

        $GIF_screen = $this->GIF_buffer;
        $GIF_colorF = $this->GIF_buffer [ 8 ] & 0x80 ? 1 : 0;
        if ( $GIF_colorF ) {
            $GIF_code = $this->GIF_buffer [ 8 ] & 0x07;
            $GIF_sort = $this->GIF_buffer [ 8 ] & 0x20 ? 1 : 0;
        }
        else {
            $GIF_code = $this->GIF_colorC;
            $GIF_sort = $this->GIF_sorted;
        }
        $GIF_size = 2 << $GIF_code;
        $this->GIF_screen [ 4 ] &= 0x70;
        $this->GIF_screen [ 4 ] |= 0x80;
        $this->GIF_screen [ 4 ] |= $GIF_code;
        if ( $GIF_sort ) {
            $this->GIF_screen [ 4 ] |= 0x08;
        }

        /* * * GIF Data Begin * */
        if ( $this->GIF_TransparentI ) {
            $this->GIF_string = "GIF89a";
        }
        else {
            $this->GIF_string = "GIF87a";
        }
        GIFDecoder::GIFPutByte ( $this->GIF_screen );
        if ( $GIF_colorF == 1 ) {
            GIFDecoder::GIFGetByte ( 3 * $GIF_size );
            if ( $this->GIF_TransparentI ) {
                $this->GIF_TransparentR = $this->GIF_buffer [ 3 * $this->GIF_TransparentI + 0 ];
                $this->GIF_TransparentG = $this->GIF_buffer [ 3 * $this->GIF_TransparentI + 1 ];
                $this->GIF_TransparentB = $this->GIF_buffer [ 3 * $this->GIF_TransparentI + 2 ];
            }
            GIFDecoder::GIFPutByte ( $this->GIF_buffer );
        }
        else {
            if ( $this->GIF_TransparentI ) {
                $this->GIF_TransparentR = $this->GIF_global [ 3 * $this->GIF_TransparentI + 0 ];
                $this->GIF_TransparentG = $this->GIF_global [ 3 * $this->GIF_TransparentI + 1 ];
                $this->GIF_TransparentB = $this->GIF_global [ 3 * $this->GIF_TransparentI + 2 ];
            }
            GIFDecoder::GIFPutByte ( $this->GIF_global );
        }
        if ( $this->GIF_TransparentI ) {
            $this->GIF_string .= "!\xF9\x04\x1\x0\x0". chr ( $this->GIF_TransparentI ) . "\x0";
        }
        $this->GIF_string .= chr ( 0x2C );
        $GIF_screen [ 8 ] &= 0x40;
        GIFDecoder::GIFPutByte ( $GIF_screen );
        GIFDecoder::GIFGetByte ( 1 );
        GIFDecoder::GIFPutByte ( $this->GIF_buffer );
        for ( ; ; ) {
            GIFDecoder::GIFGetByte ( 1 );
            GIFDecoder::GIFPutByte ( $this->GIF_buffer );
            if ( ( $u = $this->GIF_buffer [ 0 ] ) == 0x00 ) {
                break;
            }

            /*for ($i=0; $i!=$u; ++$i) { $this->GIF_string .= $this->GIF_stream { $this->GIF_bfseek++ }; }*/
            $this->GIF_string .= substr($this->GIF_stream, $this->GIF_bfseek, $u);
            $this->GIF_bfseek += $u;

            //GIFDecoder::GIFGetByte ( $u );
            //GIFDecoder::GIFPutByte ( $this->GIF_buffer );
        }
        $this->GIF_string .= chr ( 0x3B );
        /* * * GIF Data End * */
        $this->GIF_arrays [ ] = $this->GIF_string;
    }
    /* ::::::::::::::::::::::::::::::::::::::::::::::::::: :: :: GIFGetByte ( $len ) :: */
    function GIFGetByte ( $len ) {
        $this->GIF_buffer = new SplFixedArray($len);

        $l = strlen ( $this->GIF_stream );
        for ( $i = 0; $i < $len; $i++ ) {
            if ( $this->GIF_bfseek > $l ) {
                $this->GIF_buffer->setSize($i);
                return 0;
            }
            $this->GIF_buffer [$i] = ord ( $this->GIF_stream { $this->GIF_bfseek++ } );
        }
        return 1;
    }
    /* ::::::::::::::::::::::::::::::::::::::::::::::::::: :: :: GIFPutByte ( $bytes ) :: */
    function GIFPutByte ( $bytes ) {
        $out = '';
        foreach ( $bytes as $byte ) {
            $out .= chr($byte);
        }
        $this->GIF_string .= $out;
    }
    /* ::::::::::::::::::::::::::::::::::::::::::::::::::: :: :: PUBLIC FUNCTIONS :: :: :: GIFGetFrames ( ) :: */
    function GIFGetFrames ( ) {
        return ( $this->GIF_arrays );
    }
    /* ::::::::::::::::::::::::::::::::::::::::::::::::::: :: :: GIFGetFramesMeta ( ) :: :: xurei - returns metadata as an array of arrays */
    function GIFGetFramesMeta ( ) {
        return ( $this->GIF_frames_meta );
    }
    /* ::::::::::::::::::::::::::::::::::::::::::::::::::: :: :: GIFGetDelays ( ) :: */
    function GIFGetDelays ( ) {
        return ( $this->GIF_delays );
    }
    /* ::::::::::::::::::::::::::::::::::::::::::::::::::: :: :: GIFGetLoop ( ) :: */
    function GIFGetLoop ( ) {
        return ( $this->GIF_anloop );
    }
    /* ::::::::::::::::::::::::::::::::::::::::::::::::::: :: :: GIFGetDisposal ( ) :: */
    function GIFGetDisposal ( ) {
        return ( $this->GIF_dispos );
    }
    /* ::::::::::::::::::::::::::::::::::::::::::::::::::: :: :: GIFGetTransparentR ( ) :: */
    function GIFGetTransparentR ( ) {
        return ( $this->GIF_TransparentR );
    }
    /* ::::::::::::::::::::::::::::::::::::::::::::::::::: :: :: GIFGetTransparentG ( ) :: */
    function GIFGetTransparentG ( ) {
        return ( $this->GIF_TransparentG );
    }
    /* ::::::::::::::::::::::::::::::::::::::::::::::::::: :: :: GIFGetTransparentB ( ) :: */
    function GIFGetTransparentB ( ) {
        return ( $this->GIF_TransparentB );
    }
}