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<?php
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// This file is part of Moodle - http://moodle.org/
//
// Moodle is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Moodle is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.

/**
 * Library code for manipulating PDFs
 *
 * @package assignfeedback_editpdfplus
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GPL3    
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 * @copyright  2016 Université de Lausanne
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 * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */

namespace assignfeedback_editpdfplus;

defined('MOODLE_INTERNAL') || die();

global $CFG;
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require_once($CFG->libdir . '/pdflib.php');
require_once($CFG->dirroot . '/mod/assign/feedback/editpdf/fpdi/fpdi.php');
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/**
 * Library code for manipulating PDFs
 *
 * @package assignfeedback_editpdfplus
 * @copyright 2012 Davo Smith
 * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */
class pdf extends \FPDI {

    /** @var int the number of the current page in the PDF being processed */
    protected $currentpage = 0;
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    /** @var int the total number of pages in the PDF being processed */
    protected $pagecount = 0;
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    /** @var float used to scale the pixel position of annotations (in the database) to the position in the final PDF */
    protected $scale = 0.0;
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    /** @var string the path in which to store generated page images */
    protected $imagefolder = null;
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    /** @var string the path to the PDF currently being processed */
    protected $filename = null;

    /** No errors */
    const GSPATH_OK = 'ok';
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    /** Not set */
    const GSPATH_EMPTY = 'empty';
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    /** Does not exist */
    const GSPATH_DOESNOTEXIST = 'doesnotexist';
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    /** Is a dir */
    const GSPATH_ISDIR = 'isdir';
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    /** Not executable */
    const GSPATH_NOTEXECUTABLE = 'notexecutable';
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    /** Test file missing */
    const GSPATH_NOTESTFILE = 'notestfile';
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    /** Any other error */
    const GSPATH_ERROR = 'error';
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    /** Min. width an annotation should have */
    const MIN_ANNOTATION_WIDTH = 5;
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    /** Min. height an annotation should have */
    const MIN_ANNOTATION_HEIGHT = 5;

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    /** Blank PDF file used during error. */
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    const BLANK_PDF = '/mod/assign/feedback/editpdfplus/fixtures/blank.pdf';
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    /**
     * Combine the given PDF files into a single PDF. Optionally add a coversheet and coversheet fields.
     * @param string[] $pdflist  the filenames of the files to combine
     * @param string $outfilename the filename to write to
     * @return int the number of pages in the combined PDF
     */
    public function combine_pdfs($pdflist, $outfilename) {

        raise_memory_limit(MEMORY_EXTRA);
        $olddebug = error_reporting(0);

        $this->setPageUnit('pt');
        $this->setPrintHeader(false);
        $this->setPrintFooter(false);
        $this->scale = 72.0 / 100.0;
        $this->SetFont('helvetica', '', 16.0 * $this->scale);
        $this->SetTextColor(0, 0, 0);

        $totalpagecount = 0;

        foreach ($pdflist as $file) {
            $pagecount = $this->setSourceFile($file);
            $totalpagecount += $pagecount;
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            for ($i = 1; $i <= $pagecount; $i++) {
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                $this->create_page_from_source($i);
            }
        }

        $this->save_pdf($outfilename);
        error_reporting($olddebug);

        return $totalpagecount;
    }

    /**
     * The number of the current page in the PDF being processed
     * @return int
     */
    public function current_page() {
        return $this->currentpage;
    }

    /**
     * The total number of pages in the PDF being processed
     * @return int
     */
    public function page_count() {
        return $this->pagecount;
    }

    /**
     * Load the specified PDF and set the initial output configuration
     * Used when processing comments and outputting a new PDF
     * @param string $filename the path to the PDF to load
     * @return int the number of pages in the PDF
     */
    public function load_pdf($filename) {
        raise_memory_limit(MEMORY_EXTRA);
        $olddebug = error_reporting(0);

        $this->setPageUnit('pt');
        $this->scale = 72.0 / 100.0;
        $this->SetFont('helvetica', '', 16.0 * $this->scale);
        $this->SetFillColor(255, 255, 176);
        $this->SetDrawColor(0, 0, 0);
        $this->SetLineWidth(1.0 * $this->scale);
        $this->SetTextColor(0, 0, 0);
        $this->setPrintHeader(false);
        $this->setPrintFooter(false);
        $this->pagecount = $this->setSourceFile($filename);
        $this->filename = $filename;

        error_reporting($olddebug);
        return $this->pagecount;
    }

    /**
     * Sets the name of the PDF to process, but only loads the file if the
     * pagecount is zero (in order to count the number of pages)
     * Used when generating page images (but not a new PDF)
     * @param string $filename the path to the PDF to process
     * @param int $pagecount optional the number of pages in the PDF, if known
     * @return int the number of pages in the PDF
     */
    public function set_pdf($filename, $pagecount = 0) {
        if ($pagecount == 0) {
            return $this->load_pdf($filename);
        } else {
            $this->filename = $filename;
            $this->pagecount = $pagecount;
            return $pagecount;
        }
    }

    /**
     * Copy the next page from the source file and set it as the current page
     * @return bool true if successful
     */
    public function copy_page() {
        if (!$this->filename) {
            return false;
        }
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        if ($this->currentpage >= $this->pagecount) {
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            return false;
        }
        $this->currentpage++;
        $this->create_page_from_source($this->currentpage);
        return true;
    }

    /**
     * Create a page from a source PDF.
     *
     * @param int $pageno
     */
    protected function create_page_from_source($pageno) {
        // Get the size (and deduce the orientation) of the next page.
        $template = $this->importPage($pageno);
        $size = $this->getTemplateSize($template);
        $orientation = 'P';
        if ($size['w'] > $size['h']) {
            $orientation = 'L';
        }
        // Create a page of the required size / orientation.
        $this->AddPage($orientation, array($size['w'], $size['h']));
        // Prevent new page creation when comments are at the bottom of a page.
        $this->setPageOrientation($orientation, false, 0);
        // Fill in the page with the original contents from the student.
        $this->useTemplate($template);
    }

    /**
     * Copy all the remaining pages in the file
     */
    public function copy_remaining_pages() {
        $morepages = true;
        while ($morepages) {
            $morepages = $this->copy_page();
        }
    }

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    /**
     * Get RGB color from label of color or hexa code
     * @param string $colour
     * @return array()
     */
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    private function get_colour_for_pdf($colour) {
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        if (substr($colour, 0, 1) == '#') {
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            $colourarray = $this->hex2RGB($colour, false);
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        } else {
            switch ($colour) {
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                case 'orange':
                    $colourarray = array(255, 207, 53);
                    break;
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                case 'yellow':
                    $colourarray = array(255, 207, 53);
                    break;
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                case 'yellowlemon':
                    $colourarray = array(255, 255, 0);
                    break;
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                case 'green':
                    $colourarray = array(153, 202, 62);
                    break;
                case 'blue':
                    $colourarray = array(125, 159, 211);
                    break;
                case 'white':
                    $colourarray = array(255, 255, 255);
                    break;
                case 'black':
                    $colourarray = array(51, 51, 51);
                    break;
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                default:
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                    $colourarray = array(239, 69, 64);
                    break;
            }
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        }
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        return $colourarray;
    }

    /**
     * Convert a hexa decimal color code to its RGB equivalent
     *
     * @param string $hexStr (hexadecimal color value)
     * @param boolean $returnAsString (if set true, returns the value separated by the separator character. Otherwise returns associative array)
     * @param string $seperator (to separate RGB values. Applicable only if second parameter is true.)
     * @return array or string (depending on second parameter. Returns False if invalid hex color value)
     */
    private function hex2RGB($hexStr, $returnAsString = false, $seperator = ',') {
        $hexStr = preg_replace("/[^0-9A-Fa-f]/", '', $hexStr); // Gets a proper hex string
        $rgbArray = array();
        if (strlen($hexStr) == 6) { //If a proper hex code, convert using bitwise operation. No overhead... faster
            $colorVal = hexdec($hexStr);
            $rgbArray['red'] = 0xFF & ($colorVal >> 0x10);
            $rgbArray['green'] = 0xFF & ($colorVal >> 0x8);
            $rgbArray['blue'] = 0xFF & $colorVal;
        } elseif (strlen($hexStr) == 3) { //if shorthand notation, need some string manipulations
            $rgbArray['red'] = hexdec(str_repeat(substr($hexStr, 0, 1), 2));
            $rgbArray['green'] = hexdec(str_repeat(substr($hexStr, 1, 1), 2));
            $rgbArray['blue'] = hexdec(str_repeat(substr($hexStr, 2, 1), 2));
        } else {
            return false; //Invalid hex color code
        }
        return $returnAsString ? implode($seperator, $rgbArray) : $rgbArray; // returns the rgb string or the associative array
    }

    /**
     * Add an annotation to the current page
     * @param int $sx starting x-coordinate (in pixels)
     * @param int $sy starting y-coordinate (in pixels)
     * @param int $ex ending x-coordinate (in pixels)
     * @param int $ey ending y-coordinate (in pixels)
     * @param string $colour optional the colour of the annotation (red, yellow, green, blue, white, black)
     * @param string $type optional the type of annotation (line, oval, rectangle, highlight, pen, stamp)
     * @param int[]|string $path optional for 'pen' annotations this is an array of x and y coordinates for
     *              the line, for 'stamp' annotations it is the name of the stamp file (without the path)
     * @param string $imagefolder - Folder containing stamp images.
     * @return bool true if successful (always)
     */
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    public function add_annotation(annotation $annotation, $path, $imagefolder, $annotation_index) {
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        global $CFG;
        if (!$this->filename) {
            return false;
        }
        $colour = $annotation->colour;
        $colourarray = $this->get_colour_for_pdf($colour);
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        $this->SetDrawColorArray($colourarray);

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        $sx = $this->scale * $annotation->x;
        $sy = $this->scale * $annotation->y;
        $ex = $this->scale * $annotation->endx;
        $ey = $this->scale * $annotation->endy;
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        $this->SetLineWidth(2.0 * $this->scale);
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        //$type = 'line';
        $toolid = $annotation->toolid;
        $toolObject = page_editor::get_tool($toolid);
        $typetool = page_editor::get_type_tool($toolObject->type);
        $type = $typetool->label;
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        $colourcartridge = $toolObject->cartridge_color;
        if (!$colourcartridge) {
            $colourcartridge = $typetool->cartridge_color;
        }
        $colourcartridgearray = $this->get_colour_for_pdf($colourcartridge);
        $this->SetTextColorArray($colourcartridgearray);
        $this->SetFontSize(10);

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        switch ($type) {
            case 'oval':
                $rx = abs($sx - $ex) / 2;
                $ry = abs($sy - $ey) / 2;
                $sx = min($sx, $ex) + $rx;
                $sy = min($sy, $ey) + $ry;

                // $rx and $ry should be >= min width and height
                if ($rx < self::MIN_ANNOTATION_WIDTH) {
                    $rx = self::MIN_ANNOTATION_WIDTH;
                }
                if ($ry < self::MIN_ANNOTATION_HEIGHT) {
                    $ry = self::MIN_ANNOTATION_HEIGHT;
                }

                $this->Ellipse($sx, $sy, $rx, $ry);
                break;
            case 'rectangle':
                $w = abs($sx - $ex);
                $h = abs($sy - $ey);
                $sx = min($sx, $ex);
                $sy = min($sy, $ey);

                // Width or height should be >= min width and height
                if ($w < self::MIN_ANNOTATION_WIDTH) {
                    $w = self::MIN_ANNOTATION_WIDTH;
                }
                if ($h < self::MIN_ANNOTATION_HEIGHT) {
                    $h = self::MIN_ANNOTATION_HEIGHT;
                }
                $this->Rect($sx, $sy, $w, $h);
                break;
            case 'highlight':
                $w = abs($sx - $ex);
                $h = 8.0 * $this->scale;
                $sx = min($sx, $ex);
                $sy = min($sy, $ey) + ($h * 0.5);
                $this->SetAlpha(0.5, 'Normal', 0.5, 'Normal');
                $this->SetLineWidth(8.0 * $this->scale);

                // width should be >= min width
                if ($w < self::MIN_ANNOTATION_WIDTH) {
                    $w = self::MIN_ANNOTATION_WIDTH;
                }

                $this->Rect($sx, $sy, $w, $h);
                $this->SetAlpha(1.0, 'Normal', 1.0, 'Normal');
                break;
            case 'pen':
                if ($path) {
                    $scalepath = array();
                    $points = preg_split('/[,:]/', $path);
                    foreach ($points as $point) {
                        $scalepath[] = intval($point) * $this->scale;
                    }

                    if (!empty($scalepath)) {
                        $this->PolyLine($scalepath, 'S');
                    }
                }
                break;
            case 'stamp':
                $imgfile = $imagefolder . '/' . clean_filename($path);
                $w = abs($sx - $ex);
                $h = abs($sy - $ey);
                $sx = min($sx, $ex);
                $sy = min($sy, $ey);

                // Stamp is always more than 40px, so no need to check width/height.
                $this->Image($imgfile, $sx, $sy, $w, $h);
                break;
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            case 'highlightplus':
                $w = abs($sx - $ex);
                $h = 8.0 * $this->scale;
                $sx = min($sx, $ex);
                $sy = min($sy, $ey) + ($h * 0.5);
                $this->SetAlpha(0.5, 'Normal', 0.5, 'Normal');
                $this->SetLineWidth(8.0 * $this->scale);

                // width should be >= min width
                if ($w < self::MIN_ANNOTATION_WIDTH) {
                    $w = self::MIN_ANNOTATION_WIDTH;
                }

                $this->Rect($sx, $sy, $w, $h);
                $this->SetAlpha(1.0, 'Normal', 1.0, 'Normal');
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                $scartx = ($annotation->cartridgex + $annotation->x) * $this->scale;
                $scarty = ($annotation->cartridgey + $annotation->y) * $this->scale;
                $this->SetXY($scartx, $scarty);
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                break;
            case 'verticalline':
                $this->Line($sx, $sy, $sx, $ey);
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                $scartx = ($annotation->cartridgex + $annotation->x) * $this->scale;
                $scarty = ($annotation->cartridgey + $annotation->y) * $this->scale;
                $this->SetXY($scartx, $scarty);
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                break;
            case 'frame':
                $w = abs($sx - $ex);
                $h = abs($sy - $ey);
                $sx = min($sx, $ex);
                $sy = min($sy, $ey);

                // Width or height should be >= min width and height
                if ($w < self::MIN_ANNOTATION_WIDTH) {
                    $w = self::MIN_ANNOTATION_WIDTH;
                }
                if ($h < self::MIN_ANNOTATION_HEIGHT) {
                    $h = self::MIN_ANNOTATION_HEIGHT;
                }
                $this->Rect($sx, $sy, $w, $h);
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                if (!$annotation->parent_annot) {
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                    $scartx = max(($annotation->cartridgex) * $this->scale, 0);
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                    $scarty = ($annotation->cartridgey + $annotation->y) * $this->scale;
                    $this->SetXY($scartx, $scarty);
                    $this->SetTextColorArray($colourarray);
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                    //ne pas effacer, pour afficher du dash dans les encadrements
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                    /* $this->writeHTMLCell(20, 20, $scartx, $scarty, "test", array(
                      'LRTB' => array(
                      'width' => 1, // careful, this is not px but the unit you declared
                      'dash' => 1,
                      'color' => array(0, 0, 0)
                      )
                      ), false, false, false, 'L', false); */
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                }
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                break;
            case 'stampcomment':
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                if ($annotation->displayrotation == 1) {
                    $imgfile = $CFG->dirroot . '/mod/assign/feedback/editpdfplus/pix/twoway_v_pdf.png';
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                    $h = 20; //abs($sy - $ey);
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                    $w = $h * 37 / 96;
                    $sx = min($sx, $ex) + 8;
                    $sy = min($sy, $ey) + 2;
                } else {
                    $imgfile = $CFG->dirroot . '/mod/assign/feedback/editpdfplus/pix/twoway_h_pdf.png';
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                    $w = 20; //abs($sx - $ex);
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                    $h = $w * 37 / 96;
                    $sx = min($sx, $ex) + 2;
                    $sy = min($sy, $ey) + 8;
                }
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                // Stamp is always more than 40px, so no need to check width/height.
                $this->Image($imgfile, $sx, $sy, $w, $h);
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                $scartx = ($annotation->cartridgex + $annotation->x) * $this->scale;
                $scarty = ($annotation->cartridgey + $annotation->y) * $this->scale;
                $this->SetXY($scartx, $scarty);
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                break;
            case 'commentplus':
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                $imgfile = $CFG->dirroot . '/mod/assign/feedback/editpdfplus/pix/comment.png';
                $w = 16 * $this->scale;
                $h = 16 * $this->scale;
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                $sx = min($sx, $ex);
                $sy = min($sy, $ey);
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                $this->SetXY($sx + $w + 2, $sy);
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                // Stamp is always more than 40px, so no need to check width/height.
                $this->Image($imgfile, $sx, $sy, $w, $h);
                break;
            case 'stampplus':
                $w = abs($sx - $ex);
                $h = abs($sy - $ey);
                $sx = min($sx, $ex);
                $sy = min($sy, $ey);

                // Width or height should be >= min width and height
                if ($w < self::MIN_ANNOTATION_WIDTH) {
                    $w = self::MIN_ANNOTATION_WIDTH;
                }
                if ($h < self::MIN_ANNOTATION_HEIGHT) {
                    $h = self::MIN_ANNOTATION_HEIGHT;
                }
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                $this->SetXY($sx, $sy);
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                $colourcartridge = $toolObject->colors;
                if (!$colourcartridge) {
                    $colourcartridge = $typetool->color;
                }
                $colourcartridgearray = $this->get_colour_for_pdf($colourcartridge);
                $this->SetTextColorArray($colourcartridgearray);

                $cartouche = $toolObject->label;
                //$this->Cell($w);
                //Texte centré dans une cellule 20*10 mm encadrée et retour à la ligne
                $this->Cell(strlen($cartouche)*6+4, 10, $cartouche, 1, 1, 'C');

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                break;
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            default: // Line.
                $this->Line($sx, $sy, $ex, $ey);
                break;
        }
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        if ($type == 'commentplus' || $type == 'stampcomment' || ($type == 'frame' && !$annotation->parent_annot) || $type == 'verticalline' || $type == 'highlightplus') {
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            $cartouche = $toolObject->cartridge;
            if ($annotation->textannot) {
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                $cartouche .= ' [' . $annotation_index . ']';
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            }
            $this->Write(5, $cartouche);
        }

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        $this->SetDrawColor(0, 0, 0);
        $this->SetLineWidth(1.0 * $this->scale);

        return true;
    }

    /**
     * Save the completed PDF to the given file
     * @param string $filename the filename for the PDF (including the full path)
     */
    public function save_pdf($filename) {
        $olddebug = error_reporting(0);
        $this->Output($filename, 'F');
        error_reporting($olddebug);
    }

    /**
     * Set the path to the folder in which to generate page image files
     * @param string $folder
     */
    public function set_image_folder($folder) {
        $this->imagefolder = $folder;
    }

    /**
     * Generate an image of the specified page in the PDF
     * @param int $pageno the page to generate the image of
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     * @throws \moodle_exception
     * @throws \coding_exception
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     * @return string the filename of the generated image
     */
    public function get_image($pageno) {
        global $CFG;

        if (!$this->filename) {
            throw new \coding_exception('Attempting to generate a page image without first setting the PDF filename');
        }

        if (!$this->imagefolder) {
            throw new \coding_exception('Attempting to generate a page image without first specifying the image output folder');
        }

        if (!is_dir($this->imagefolder)) {
            throw new \coding_exception('The specified image output folder is not a valid folder');
        }

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        $imagefile = $this->imagefolder . '/image_page' . $pageno . '.png';
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        $generate = true;
        if (file_exists($imagefile)) {
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            if (filemtime($imagefile) > filemtime($this->filename)) {
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                // Make sure the image is newer than the PDF file.
                $generate = false;
            }
        }

        if ($generate) {
            // Use ghostscript to generate an image of the specified page.
            $gsexec = \escapeshellarg($CFG->pathtogs);
            $imageres = \escapeshellarg(100);
            $imagefilearg = \escapeshellarg($imagefile);
            $filename = \escapeshellarg($this->filename);
            $pagenoinc = \escapeshellarg($pageno + 1);
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            $command = "$gsexec -q -sDEVICE=png16m -dSAFER -dBATCH -dNOPAUSE -r$imageres -dFirstPage=$pagenoinc -dLastPage=$pagenoinc " .
                    "-dDOINTERPOLATE -dGraphicsAlphaBits=4 -dTextAlphaBits=4 -sOutputFile=$imagefilearg $filename";
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            $output = null;
            $result = exec($command, $output);
            if (!file_exists($imagefile)) {
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                $fullerror = '<pre>' . get_string('command', 'assignfeedback_editpdfplus') . "\n";
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                $fullerror .= $command . "\n\n";
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                $fullerror .= get_string('result', 'assignfeedback_editpdfplus') . "\n";
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                $fullerror .= htmlspecialchars($result) . "\n\n";
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                $fullerror .= get_string('output', 'assignfeedback_editpdfplus') . "\n";
                $fullerror .= htmlspecialchars(implode("\n", $output)) . '</pre>';
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                throw new \moodle_exception('errorgenerateimage', 'assignfeedback_editpdfplus', '', $fullerror);
            }
        }

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        return 'image_page' . $pageno . '.png';
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    }

    /**
     * Check to see if PDF is version 1.4 (or below); if not: use ghostscript to convert it
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     * 
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     * @param stored_file $file
     * @return string path to copy or converted pdf (false == fail)
     */
    public static function ensure_pdf_compatible(\stored_file $file) {
        global $CFG;

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        // Copy the stored_file to local disk for checking.
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        $temparea = make_request_directory();
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        $tempsrc = $temparea . "/source.pdf";
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        $file->copy_content_to($tempsrc);
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        return self::ensure_pdf_file_compatible($tempsrc);
    }

    /**
     * Check to see if PDF is version 1.4 (or below); if not: use ghostscript to convert it
     *
     * @param   string $tempsrc The path to the file on disk.
     * @return  string path to copy or converted pdf (false == fail)
     */
    public static function ensure_pdf_file_compatible($tempsrc) {
        global $CFG;

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        $pdf = new pdf();
        $pagecount = 0;
        try {
            $pagecount = $pdf->load_pdf($tempsrc);
        } catch (\Exception $e) {
            // PDF was not valid - try running it through ghostscript to clean it up.
            $pagecount = 0;
        }
        $pdf->Close(); // PDF loaded and never saved/outputted needs to be closed.

        if ($pagecount > 0) {
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            // PDF is already valid and can be read by tcpdf.
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            return $tempsrc;
        }

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        $temparea = make_request_directory();
        $tempdst = $temparea . "/target.pdf";

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        $gsexec = \escapeshellarg($CFG->pathtogs);
        $tempdstarg = \escapeshellarg($tempdst);
        $tempsrcarg = \escapeshellarg($tempsrc);
        $command = "$gsexec -q -sDEVICE=pdfwrite -dBATCH -dNOPAUSE -sOutputFile=$tempdstarg $tempsrcarg";
        exec($command);
        if (!file_exists($tempdst)) {
            // Something has gone wrong in the conversion.
            return false;
        }

        $pdf = new pdf();
        $pagecount = 0;
        try {
            $pagecount = $pdf->load_pdf($tempdst);
        } catch (\Exception $e) {
            // PDF was not valid - try running it through ghostscript to clean it up.
            $pagecount = 0;
        }
        $pdf->Close(); // PDF loaded and never saved/outputted needs to be closed.

        if ($pagecount <= 0) {
            // Could not parse the converted pdf.
            return false;
        }

        return $tempdst;
    }

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    /**
     * Generate an localised error image for the given pagenumber.
     *
     * @param string $errorimagefolder path of the folder where error image needs to be created.
     * @param int $pageno page number for which error image needs to be created.
     *
     * @return string File name
     * @throws \coding_exception
     */
    public static function get_error_image($errorimagefolder, $pageno) {
        global $CFG;

        $errorfile = $CFG->dirroot . self::BLANK_PDF;
        if (!file_exists($errorfile)) {
            throw new \coding_exception("Blank PDF not found", "File path" . $errorfile);
        }

        $tmperrorimagefolder = make_request_directory();

        $pdf = new pdf();
        $pdf->set_pdf($errorfile);
        $pdf->copy_page();
        $pdf->add_comment(get_string('errorpdfpage', 'assignfeedback_editpdf'), 250, 300, 200, "red");
        $generatedpdf = $tmperrorimagefolder . '/' . 'error.pdf';
        $pdf->save_pdf($generatedpdf);

        $pdf = new pdf();
        $pdf->set_pdf($generatedpdf);
        $pdf->set_image_folder($tmperrorimagefolder);
        $image = $pdf->get_image(0);
        $pdf->Close(); // PDF loaded and never saved/outputted needs to be closed.
        $newimg = 'image_page' . $pageno . '.png';

        copy($tmperrorimagefolder . '/' . $image, $errorimagefolder . '/' . $newimg);
        return $newimg;
    }

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    /**
     * Test that the configured path to ghostscript is correct and working.
     * @param bool $generateimage - If true - a test image will be generated to verify the install.
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     * @return \stdClass
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     */
    public static function test_gs_path($generateimage = true) {
        global $CFG;

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        $ret = (object) array(
                    'status' => self::GSPATH_OK,
                    'message' => null,
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        );
        $gspath = $CFG->pathtogs;
        if (empty($gspath)) {
            $ret->status = self::GSPATH_EMPTY;
            return $ret;
        }
        if (!file_exists($gspath)) {
            $ret->status = self::GSPATH_DOESNOTEXIST;
            return $ret;
        }
        if (is_dir($gspath)) {
            $ret->status = self::GSPATH_ISDIR;
            return $ret;
        }
        if (!is_executable($gspath)) {
            $ret->status = self::GSPATH_NOTEXECUTABLE;
            return $ret;
        }

        if (!$generateimage) {
            return $ret;
        }

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        $testfile = $CFG->dirroot . '/mod/assign/feedback/editpdfplus/tests/fixtures/testgs.pdf';
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        if (!file_exists($testfile)) {
            $ret->status = self::GSPATH_NOTESTFILE;
            return $ret;
        }

        $testimagefolder = \make_temp_directory('assignfeedback_editpdfplus_test');
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        @unlink($testimagefolder . '/image_page0.png'); // Delete any previous test images.
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        $pdf = new pdf();
        $pdf->set_pdf($testfile);
        $pdf->set_image_folder($testimagefolder);
        try {
            $pdf->get_image(0);
        } catch (\moodle_exception $e) {
            $ret->status = self::GSPATH_ERROR;
            $ret->message = $e->getMessage();
        }
        $pdf->Close(); // PDF loaded and never saved/outputted needs to be closed.

        return $ret;
    }

    /**
     * If the test image has been generated correctly - send it direct to the browser.
     */
    public static function send_test_image() {
        global $CFG;
        header('Content-type: image/png');
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        require_once($CFG->libdir . '/filelib.php');
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        $testimagefolder = \make_temp_directory('assignfeedback_editpdfplus_test');
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        $testimage = $testimagefolder . '/image_page0.png';
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        send_file($testimage, basename($testimage), 0);
        die();
    }

}