pdf-rendering.js
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	/**
	* Copyright (C) 2018-2019 The Software Heritage developers
	* See the AUTHORS file at the top-level directory of this distribution
	* License: GNU Affero General Public License version 3, or any later version
	* See top-level LICENSE file for more information
	*/

	// adapted from pdf.js examples located at http://mozilla.github.io/pdf.js/examples/

	import {staticAsset} from 'utils/functions';

	export async function renderPdf(pdfUrl) {

	let pdfDoc = null;
	let pageNum = 1;
	let pageRendering = false;
	let pageNumPending = null;
	let defaultScale = 1.5;
	let canvas = $('#pdf-canvas')[0];
	let ctx = canvas.getContext('2d');

	// Get page info from document, resize canvas accordingly, and render page.
	function renderPage(num) {
	pageRendering = true;
	// Using promise to fetch the page
	pdfDoc.getPage(num).then(page => {
	let divWidth = $('.swh-content').width();
	let scale = Math.min(defaultScale, divWidth / page.getViewport({scale: 1.0}).width);

	let viewport = page.getViewport({scale: scale});
	canvas.width = viewport.width;
	canvas.height = viewport.height;

	// Render PDF page into canvas context
	let renderContext = {
	canvasContext: ctx,
	viewport: viewport
	};
	let renderTask = page.render(renderContext);

	// Wait for rendering to finish
	renderTask.promise.then(() => {
	pageRendering = false;
	if (pageNumPending !== null) {
	// New page rendering is pending
	renderPage(pageNumPending);
	pageNumPending = null;
	}
	});
	});

	// Update page counters
	$('#pdf-page-num').text(num);
	}

	// If another page rendering in progress, waits until the rendering is
	// finished. Otherwise, executes rendering immediately.
	function queueRenderPage(num) {
	if (pageRendering) {
	pageNumPending = num;
	} else {
	renderPage(num);
	}
	}

	// Displays previous page.
	function onPrevPage() {
	if (pageNum <= 1) {
	return;
	}
	pageNum--;
	queueRenderPage(pageNum);
	}

	// Displays next page.
	function onNextPage() {
	if (pageNum >= pdfDoc.numPages) {
	return;
	}
	pageNum++;
	queueRenderPage(pageNum);
	}

	let pdfjs = await import(/* webpackChunkName: "pdfjs" */ 'pdfjs-dist');

	pdfjs.GlobalWorkerOptions.workerSrc = staticAsset('js/pdf.worker.min.js');

	$(document).ready(() => {
	$('#pdf-prev').click(onPrevPage);
	$('#pdf-next').click(onNextPage);
	let loadingTask = pdfjs.getDocument(pdfUrl);
	loadingTask.promise.then(pdf => {
	pdfDoc = pdf;
	$('#pdf-page-count').text(pdfDoc.numPages);
	// Initial/first page rendering
	renderPage(pageNum);
	}, function(reason) {
	// PDF loading error
	console.error(reason);
	});

	// Render PDF on resize
	$(window).on('resize', function() {
	queueRenderPage(pageNum);
	});
	});

	}

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