Zend Framework view helper to render a sheet of address labels as a PDF

Labels.php

<?php
/**
 * A view helper to render a sheet of address labels as a PDF. 
 */
class My_View_Helper_Labels extends Zend_View_Helper_Abstract {
    
    /**
     * @var int A page size constant from Zend_Pdf_Page
     */
    private $_pageSize;
    
    /**
     * @var Array Associative array containing the height, width and
     * padding values for each label
     */
    private $_labelSize;
    
    /**
     * @var Array Associative array containing the top, bottom, left
     * and right margins for the page
     */
    private $_margins;
    
    /**
     * @var int The number of columns on each page
     */
    private $_columns;
    
    /**
     * @var int The number of rows on each page
     */
    private $_rows;
    
    /**
     * @var Array Associative array containing the horizontal and vertical
     * spacing for each label
     */
    private $_padding;
    
    /**
     * @var int The size of font to use
     */
    private $_fontSize;
    
    /**
     * @var Array Two dimensional array containing starting x/y coordinates 
     * for each label on the page
     */
    private $_cursors;
    
    /**
     * @var Zend_Pdf_Page The page we are working on
     */
    private $_page;
    
    /**
     * @var Zend_Pdf The document we are working on
     */
    private $_pdf;
    
    /**
     * Let's render some labels
     *
     * @param $spec array Associative array specifying the layout we want to use.
     * Something like this (values in mm, font size in pts) 
     *     array(
     *           'pageSize' => 'A4',
     *           'columns' => 3,
     *           'rows' => 6,
     *           'fontSize' => 12,
     *           'margins' => array('top' => 5, 'bottom' => 5, 'left' => 5, 'right' => 5),
     *           'padding' => array('horizontal' => 5, 'vertical' => 5),
     *           'labels' => array('height' => 25, 'width' => 45)
     *        )
     *         
     * @param $data array|string Array of things to print on each label, or one
     * thing to print on all labels
     */
    public function labels($spec, $data) {
        
        $this->_parseSpec($spec);
        
        $this->_pdf = new Zend_Pdf();
        
        $labelsPerPage = $this->_rows * $this->_columns;
        
        if(is_array($data)) {
            $paginatedData = array_chunk($data, $labelsPerPage);
            foreach($paginatedData as $pageData) {
                $this->_renderPage($pageData);
            }
        }
        else {
            $this->_renderPage($data);
        }
                
        return $this->_pdf->render();
        
    }
    
    /**
     * Render a single page of labels
     *
     * @param $data array|string Array of things to print on each label, or one
     * thing to print on all labels
     */
    protected function _renderPage($data) {
        $this->_page = new Zend_Pdf_Page($this->_pageSize);
        
        $this->_page->setFont(Zend_Pdf_Font::fontWithName(Zend_Pdf_Font::FONT_HELVETICA),
                $this->_fontSize);
        
        $this->_setCursorPositions();
        
        $this->_pdf->pages[] = $this->_page;
        
        $this->_renderLabels($data);
               
    }
    
    /**
     * Render the labels for a single page, having populated $this->_cursors
     *
     * @param $data array|string Array of things to print on each label, or one
     * thing to print on all labels
     */
    protected function _renderLabels($data) {
        
        if(is_array($data)) {
            
            foreach($data as $i => $datum) {
                
                $this->_writeLines($datum, $this->_cursors[$i]['x'], $this->_cursors[$i]['y']);
            }
            
        }
        else {
            foreach($this->_cursors as $cursor) {

                $this->_writeLines($data, $cursor['x'], $cursor['y']);

            }
        }
    }
    
    /**
     * Write some lines of text on the PDF
     *
     * @param $text string
     * @param $x float The x coodinate to start at in points
     * @param $y float The y coodinate to start at in points
     */
    protected function _writeLines($text, $x, $y) {
        
        $lines = explode("\n", $text);
        
        foreach($lines as $i => $line) {
            $this->_page->drawText($line, $x, $y - ($i *
                    $this->_getFontHeight($this->_page->getFont(), $this->_page->getFontSize())));
        }
        
    }
    
    /**
     * Sets up the view helper with info from the spec or suitable defaults.
     * 
     * @param array $spec 
     */
    private function _parseSpec($spec) {
        
        if(isset($spec['pageSize']) && $spec['pageSize'] == 'A4') {
           $this->_pageSize = Zend_Pdf_Page::SIZE_A4;
        }
        else {
            throw new Zend_View_Exception('No valid page size specified');
        }
        
        if(isset($spec['columns'])) {
           $this->_columns = $spec['columns'];
        }
        else {
            throw new Zend_View_Exception('No valid column count specified');
        }
        
        if(isset($spec['rows'])) {
           $this->_rows = $spec['rows'];
        }
        else {
            throw new Zend_View_Exception('No valid row count specified');
        }
        
        if(isset($spec['fontSize'])) {
           $this->_fontSize = $spec['fontSize'];
        }
        else {
            throw new Zend_View_Exception('No valid font size specified');
        }
        
        if(isset($spec['margins'])) {
            
            $this->_margins = array('top' => 0, 'bottom' => 0, 'left' => 0, 'right' => 0);
            
            foreach($spec['margins'] as $k => $v) {
                
                if($k == 'top' || $k == 'bottom' || $k == 'left' || $k == 'right') {
                    $this->_margins[$k] = $this->_mmToPts($v);
                }
            }
        }
        else {
            throw new Zend_View_Exception('No margins specified');
        }
        
        if(isset($spec['padding'])) {
            
            $this->_padding = array('horizontal' => 0, 'vertical' => 0);
            
            foreach($spec['padding'] as $k => $v) {
                if($k == 'horizontal' || $k == 'vertical') {
                    $this->_padding[$k] = $this->_mmToPts($v);
                }
            }
        }
        else {
            throw new Zend_View_Exception('No padding specified');
        }
        
        if(isset($spec['labels'])) {
            
            $this->_labelSize = array('height' => 0, 'width' => 0, 'padding' => 0);
            
            foreach($spec['labels'] as $k => $v) {
                
                if($k == 'height' || $k == 'width') {
                    $this->_labelSize[$k] = $this->_mmToPts($v);
                }
            }
        }
        else {
            throw new Zend_View_Exception('No label size specified');
        }
        
    }
    
    /**
     * Populates the _cursors variable with starting x/y coordinates for each label on the page.
     */
    private function _setCursorPositions() {
        
        $this->_cursors = array();
        
        $startingY = $this->_page->getHeight();
        
        $fontHeight = $this->_getFontHeight($this->_page->getFont(), $this->_page->getFontSize());
        
        for($j = 0; $j < $this->_rows; $j++) { // rows...
            
            $y = $startingY;
            
            // we always need to add some top margin...
            $y -= $this->_margins['top'];

            if($j > 0) {
                // if this isn't the first then we also need to add 
                // the vertical padding (i.e. the gap between rows) plus the height of the
                // number of labels down we have got...
                $y -= $this->_padding['vertical'] * ($j);

                $y -= ($this->_labelSize['height'] + $this->_labelSize['padding']) * $j;
                
            }
            
            // shunt downwards by the height of the font - coordinates for fonts 
            // are set by their baseline.
            $y -= $fontHeight;
            
            for($i = 0; $i < $this->_columns; $i++) { // columns...

                $x = 0;

                // we always need to add some left margin...
                $x += $this->_margins['left'];

                if($i > 0) {
                    // if this isn't the first label in the row then we also need to add 
                    // the horizontal padding (i.e. the gap between columns) plus the width of the
                    // number of labels across we have got...
                    $x += $this->_padding['horizontal'] * ($i);

                    $x += ($this->_labelSize['width'] + $this->_labelSize['padding']) * $i;

                }

                $this->_cursors[] = array(
                    'x' => $x,
                    'y' => $y
                );
            }
        }
        
    }
    
    /**
     * Find the height of a line of the font in points.
     * 
     * @param Zend_Pdf_Resource_Font $font
     * @param float $fontSize
     * @return float 
     */
    private function _getFontHeight($font, $fontSize) {
        
        return ($font->getLineHeight() / $font->getUnitsPerEm() * $fontSize);
    }
    
    /**
     * Convert millimeters to points.
     * 
     * @param float $mm
     * @return float
     */
    private function _mmToPts($mm) {
        return $mm * 2.834645669;
    }
}