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
functiongifreadextensions() { 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
gifgetframes(); * $i = 0; * $fname = rand(1000, 9999). $fic . _0$i.png; * $hfic = fopen( . $fname, wb); * fwrite($hfic, $frames [$i]); * fclose($hfic); * } * * * * @copyright (c) 2015, calvin lee * @author calvin lee */classgifdecoder {public$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$gif_colorf; functiongifdecoder($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]) { case0x21: gifdecoder::gifreadextensions(); break; case0x2c: gifdecoder::gifreaddescriptor(); break; case0x3b: $cycle = 0; break; } } else { $cycle = 0; } } } functiongifreadextensions() { gifdecoder::gifgetbyte(1); if ($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 = $this->gif_buffer [3]; } } } } } functiongifreaddescriptor() {$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) { $this->gif_screen [4] |= 0x08; } //gif data beginif ($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[] = $this->gif_string; } functiongifgetbyte($len) {$this->gif_buffer = array(); for ($i = 0; $i $len; $i++) { if ($this->gif_bfseek > strlen($this->gif_stream)) { return0; } $this->gif_buffer[] = ord($this->gif_stream { $this->gif_bfseek++}); } return1; } functiongifputbyte($bytes) {foreach ($bytesas$byte) { $this->gif_string .= chr($byte); } } functiongifgetframes() {return ( $this->gif_arrays ); } functiongifgetdelays() {return ( $this->gif_delays ); } functiongifgetloop() {return ( $this->gif_anloop ); } functiongifgetdisposal() {return ( $this->gif_dispos ); } functiongifgettransparentr() {return ( $this->gif_transparentr ); } functiongifgettransparentg() {return ( $this->gif_transparentg ); } functiongifgettransparentb() {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 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。