Implementation method of generating GIF animation in PHP_PHP tutorial

class GifMerge {
    var $ver            = '1.1';
    var $dly            = 50;
    var $mod            = 'C_FILE';
    var $first            = true;
    var $use_loop            = false;
    var $transparent        = false;
    var $use_global_in        = false;
    where $x                = 0;
    where $y                = 0;
    where $ch                = 0;
    var $fin            = 0;
    var $fout            = '';
    var $loop            = 0;
    var $delay            = 0;
    var $width            = 0;
    var $height            = 0;
    var $trans1             = 255;
    var $trans2             = 255;
    var $trans3             = 255;
    var $disposal            = 2;
    var $out_color_table_size    = 0;
    var $local_color_table_flag    = 0;
    var $global_color_table_size    = 0;
    var $out_color_table_sizecode    = 0;
    var $global_color_table_sizecode= 0;
    var $gif            = array(0x47, 0x49, 0x46);
    var $buffer            = array();
    var $local_in            = array();
    var $global_in            = array();
    var $global_out            = array();
    var $logical_screen_descriptor    = array();
    function GifMerge($images, $t1, $t2, $t3, $loop, $dl, $xpos, $ypos, $model) {
        if($model) {
            $this-> ;mode = $model;
        }
        if($loop > -1) {
            $this->loop = floor($loop - 1);
            $this->use_loop = true;
        }
        if($t1 > -1 && $t2 > -1 && $t3 > -1) {
            $this->trans1 = $t1;
            $this->trans2 = $t2;
            $this->trans3 = $t3;
            $this->transparent = true;
        }
        for($i = 0; $i < count($images); $i++) {
            $dl[$i]    ? $this->delay = $dl[$i] : $this->delay = $this->dly;
            $xpos[$i] ? $this->x = $xpos[$i] : $this->x = 0;
            $ypos[$i] ? $this->y = $ypos[$i] : $this->y = 0;
            $this->start_gifmerge_process($images[$i]);
        }
        $this->fout .= "/x3b";
    }
    function start_gifmerge_process($fp) {
        if($this->mod == 'C_FILE') {
            if(!$this->fin = fopen($fp, 'rb')) {
                return;
            }
        } elseif($this->mod == 'C_MEMORY') {
            $this->ch = 0;
            $this->fin = $fp;
        }
        $this->getbytes(6);
        if(!$this->arrcmp($this->buffer, $this->gif, 3)) {
            return;
        }
        $this->getbytes(7);
        if($this->first) $this->logical_screen_descriptor = $this->buffer;
        $this->global_color_table_sizecode = $this->buffer[4] & 0x07;
        $this->global_color_table_size = 2 << $this->global_color_table_sizecode;
        if($this->buffer[4] & 0x80) {
            $this->getbytes((3 * $this->global_color_table_size));
            for($i = 0; $i < ((3 * $this->global_color_table_size)); $i++) {
                $this->global_in[$i] = $this->buffer[$i];
            }
            if($this->out_color_table_size == 0) {
                $this->out_color_table_size = $this->global_color_table_size;
                $out_color_table_sizecode = $this->global_color_table_sizecode;
                $this->global_out = $this->global_in;
            }
            if($this->global_color_table_size != $this->out_color_table_size || $this->arrcmp($this->global_out, $this->global_in, (3 * $this->global_color_table_size))) {
                $this->use_global_in = true;
            }
        }
        for($loop = true; $loop;) {
            $this->getbytes(1);
            switch($this->buffer[0]) {
                case 0x21:
                    $this->read_extension();
                    break;
                case 0x2c:
                    $this->read_image_descriptor();
                    break;
                case 0x3b:
                    $loop = false;
                break;
                default:
                    $loop = false;
            }
        }
        if($this->mod == 'C_FILE') {
            fclose($this->fin);
        }
    }
    function read_image_descriptor() {
        $this->getbytes(9);
        $head = $this->buffer;
            $this->local_color_table_flag = ($this->buffer[8] & 0x80) ? true : false;
            if($this->local_color_table_flag) {
            $sizecode = $this->buffer[8] & 0x07;
            $size = 2 << $sizecode;
            $this->getbytes(3 * $size);
            for($i = 0; $i < (3 * $size); $i++) {
                    $this->local_in[$i] = $this->buffer[$i];
                }
                if($this->out_color_table_size == 0) {
                    $this->out_color_table_size = $size;
                    $out_color_table_sizecode = $sizecode;
                for($i = 0; $i < (3 * $size); $i++)
                {
                    $this->global_out[$i] = $this->local_in[$i];
                }
                }
            }
            if($this->first) {
            $this->first = false;
            $this->fout .= "/x47/x49/x46/x38/x39/x61";
            if($this->width && $this->height) {
                $this->logical_screen_descriptor[0] = $this->width & 0xFF;
                $this->logical_screen_descriptor[1] = ($this->width & 0xFF00) >> 8;
                $this->logical_screen_descriptor[2] = $this->height & 0xFF;
                $this->logical_screen_descriptor[3] = ($this->height & 0xFF00) >> 8;
            }
            $this->logical_screen_descriptor[4] |= 0x80;
            $this->logical_screen_descriptor[5] &= 0xF0;
            $this->logical_screen_descriptor[6] |= $this->out_color_table_sizecode;
            $this->putbytes($this->logical_screen_descriptor, 7);
                $this->putbytes($this->global_out, ($this->out_color_table_size * 3));
            if($this->use_loop) {
                $ns[0] = 0x21;
                $ns[1] = 0xFF;
                $ns[2] = 0x0B;
                $ns[3] = 0x4e;
                $ns[4] = 0x45;
                $ns[5] = 0x54;
                $ns[6] = 0x53;
                $ns[7] = 0x43;
                $ns[8] = 0x41;
                $ns[9] = 0x50;
                $ns[10] = 0x45;
                $ns[11] = 0x32;
                $ns[12] = 0x2e;
                $ns[13] = 0x30;
                $ns[14] = 0x03;
                $ns[15] = 0x01;
                $ns[16] = $this->loop & 255;
                    $ns[17] = $this->loop >> 8;
                $ns[18] = 0x00;
                $this->putbytes($ns, 19);
            }
            }
          if($this->use_global_in) {
            $outtable = $this->global_in;
            $outsize = $this->global_color_table_size;
            $outsizecode = $this->global_color_table_sizecode;
        } else {
            $outtable = $this->global_out;
            $outsize = $this->out_color_table_size;
        }
        if($this->local_color_table_flag) {
            if($size == $this->out_color_table_size && !$this->arrcmp($this->local_in, $this->global_out, $size)) {
                $outtable = $global_out;
                $outsize = $this->out_color_table_size;
            } else {
                $outtable = $this->local_in;
                $outsize = $size;
                $outsizecode = $sizecode;
            }
        }
        $use_trans = false;
        if($this->transparent) {
            for($i = 0; $i < $outsize; $i++) {
                if($outtable[3 * $i] == $this->trans1 && $outtable [3 * $i + 1] == $this->trans2 && $outtable [3 * $i + 2] == $this->trans3) {
                    break;
                }
            }
            if($i < $outsize) {
                $transindex = $i;
                $use_trans = true;
            }
        }
        if($this->delay || $use_trans) {
            $this->buffer[0] = 0x21;
            $this->buffer[1] = 0xf9;
            $this->buffer[2] = 0x04;
            $this->buffer[3] = ($this->disposal << 2) + ($use_trans ? 1 : 0);
            $this->buffer[4] = $this->delay & 0xff;
            $this->buffer[5] = ($this->delay & 0xff00) >> 8;
            $this->buffer[6] = $use_trans ? $transindex : 0;
            $this->buffer[7] = 0x00;
            $this->putbytes($this->buffer,8);
        }
        $this->buffer[0] = 0x2c;
        $this->putbytes($this->buffer,1);
        $head[0] = $this->x & 0xff;
        $head[1] = ($this->x & 0xff00) >> 8;
        $head[2] = $this->y & 0xff;
        $head[3] = ($this->y & 0xff00) >> 8;
        $head[8] &= 0x40;
        if($outtable != $this->global_out) {
            $head[8] |= 0x80;
            $head[8] |= $outsizecode;
        }
        $this->putbytes($head,9);
        if($outtable != $this->global_out) {
            $this->putbytes($outtable, (3 * $outsize));
        }
        $this->getbytes(1);
        $this->putbytes($this->buffer,1);
        for(;;) {
            $this->getbytes(1);
            $this->putbytes($this->buffer,1);
            if(($u = $this->buffer[0]) == 0) {
                break;
            }
            $this->getbytes($u);
            $this->putbytes($this->buffer, $u);
            }
    }
    function read_extension() {
        $this->getbytes(1);
        switch($this->buffer[0]) {
            case 0xf9:
                    $this->getbytes(6);
                   break;
            case 0xfe:
                    for(;;) {
                    $this->getbytes(1);
                            if(($u = $this->buffer[0]) == 0) {
                            break;
                        }
                    $this->getbytes($u);
                    }
                break;
            case 0x01:
                    $this->getbytes(13);
                    for(;;) {
                    $this->getbytes(0);
                            if(($u = $this->buffer[0]) == 0) {
                            break;
                        }
                    $this->getbytes($u);
                    }
                break;
                   case 0xff:
                    $this->getbytes(9);
                    $this->getbytes(3);
                    for(;;) {
                    $this->getbytes(1);
                            if(!$this->buffer[0]) {
                                break;
                            }
                            $this->getbytes($this->buffer[0]);
                        }
                break;
            default:
                    for(;;) {
                    $this->getbytes(1);
                        if(!$this->buffer[0]) {
                            break;
                        }
                    $this->getbytes($this->buffer[0]);
                }
            }
    }
    function arrcmp($b, $s, $l) {
        for($i = 0; $i < $l; $i++) {
            if($s{$i} != $b{$i}) {
                return false;
            }
        }
        return true;
    }
    function getbytes($l) {
        for($i = 0; $i < $l; $i++) {
            if($this->mod == 'C_FILE') {
                    $bin = unpack('C*', fread($this->fin, 1));
                    $this->buffer[$i] = $bin[1];
                } elseif($this->mod == 'C_MEMORY') {
                        $bin = unpack('C*', substr($this->fin, $this->ch, 1));
                        $this->buffer[$i] = $bin[1];
                        $this->ch++;
                }
        }
        return $this->buffer;
    }
    function putbytes($s, $l) {
        for($i = 0; $i < $l; $i++) {
            $this->fout .= pack('C*', $s[$i]);
        }
    }
    function getAnimation() {
        return $this->fout;
    }
}
?>