TCPDF - 设置头部Logo不显示问题

在生成的pdf文件的页眉设置logo有以下解决方案

1. 重新定义TCPDF中的K_PATH_IMAGES常量(define('K_PATH_IMAGES', xxxx) , 需要定义在加载tcpdf.php 之前)

## 示例
$logo = "xxxx"; //相对地址
$pdf->SetHeaderData(PDF_HEADER_LOGO, PDF_HEADER_LOGO_WIDTH, "标题", "标语", array(0,64,255), array(0,64,128));
$pdf->setFooterData(array(0,64,0), array(0,64,128));

2. 若不定义常量，可以将logo图片移动到vendor/tecnickcom/examples/images下

## 示例
$logo = "xxxx"; //相对地址
$pdf->SetHeaderData(PDF_HEADER_LOGO, PDF_HEADER_LOGO_WIDTH, "标题", "标语", array(0,64,255), array(0,64,128));
$pdf->setFooterData(array(0,64,0), array(0,64,128));

3. 重写 public function Header() {} 方法

    public function Header() {
        $logo = xxxx;//绝对地址
        $this->Image($logo, 5, 2, 15, '', 'PNG', '', 'T', false, 300, '', false, false, 0, false, false, false);
        $this->SetFont('stsongstdlight', '', 10);
        $this->MultiCell(0, 15, $this->title, 0, "R", false, 1, 0, 5);
    }

设置头部Logo源码分析

$this->Image(K_PATH_IMAGES.$headerdata['logo'], '', '', $headerdata['logo_width']);

根据源码分析，发现此处 会在配置的 $headerdata['logo'] 数据前面，自动加上 常量 K_PATH_IMAGES，所以才有了解决方案1，方案2

## 源码
public function Header() {
        if ($this->header_xobjid === false) {
            // start a new XObject Template
            $this->header_xobjid = $this->startTemplate($this->w, $this->tMargin);
            $headerfont = $this->getHeaderFont();
            $headerdata = $this->getHeaderData();
            $this->y = $this->header_margin;
            if ($this->rtl) {
                $this->x = $this->w - $this->original_rMargin;
            } else {
                $this->x = $this->original_lMargin;
            }
            if (($headerdata['logo']) AND ($headerdata['logo'] != K_BLANK_IMAGE)) {
                $imgtype = TCPDF_IMAGES::getImageFileType(K_PATH_IMAGES.$headerdata['logo']);
                if (($imgtype == 'eps') OR ($imgtype == 'ai')) {
                    $this->ImageEps(K_PATH_IMAGES.$headerdata['logo'], '', '', $headerdata['logo_width']);
                } elseif ($imgtype == 'svg') {
                    $this->ImageSVG(K_PATH_IMAGES.$headerdata['logo'], '', '', $headerdata['logo_width']);
                } else {
                    $this->Image(K_PATH_IMAGES.$headerdata['logo'], '', '', $headerdata['logo_width']);
                }
                $imgy = $this->getImageRBY();
            } else {
                $imgy = $this->y;
            }
            $cell_height = $this->getCellHeight($headerfont[2] / $this->k);
            // set starting margin for text data cell
            if ($this->getRTL()) {
                $header_x = $this->original_rMargin + ($headerdata['logo_width'] * 1.1);
            } else {
                $header_x = $this->original_lMargin + ($headerdata['logo_width'] * 1.1);
            }
            $cw = $this->w - $this->original_lMargin - $this->original_rMargin - ($headerdata['logo_width'] * 1.1);
            $this->SetTextColorArray($this->header_text_color);
            // header title
            $this->SetFont($headerfont[0], 'B', $headerfont[2] + 1);
            $this->SetX($header_x);
            $this->Cell($cw, $cell_height, $headerdata['title'], 0, 1, '', 0, '', 0);
            // header string
            $this->SetFont($headerfont[0], $headerfont[1], $headerfont[2]);
            $this->SetX($header_x);
            $this->MultiCell($cw, $cell_height, $headerdata['string'], 0, '', 0, 1, '', '', true, 0, false, true, 0, 'T', false);
            // print an ending header line
            $this->SetLineStyle(array('width' => 0.85 / $this->k, 'cap' => 'butt', 'join' => 'miter', 'dash' => 0, 'color' => $headerdata['line_color']));
            $this->SetY((2.835 / $this->k) + max($imgy, $this->y));
            if ($this->rtl) {
                $this->SetX($this->original_rMargin);
            } else {
                $this->SetX($this->original_lMargin);
            }
            $this->Cell(($this->w - $this->original_lMargin - $this->original_rMargin), 0, '', 'T', 0, 'C');
            $this->endTemplate();
        }
        // print header template
        $x = 0;
        $dx = 0;
        if (!$this->header_xobj_autoreset AND $this->booklet AND (($this->page % 2) == 0)) {
            // adjust margins for booklet mode
            $dx = ($this->original_lMargin - $this->original_rMargin);
        }
        if ($this->rtl) {
            $x = $this->w + $dx;
        } else {
            $x = 0 + $dx;
        }
        $this->printTemplate($this->header_xobjid, $x, 0, 0, 0, '', '', false);
        if ($this->header_xobj_autoreset) {
            // reset header xobject template at each page
            $this->header_xobjid = false;
        }
    }