@cquiroz/aladin-lite/lib/js/Downloader.js

AladinLite module

// Copyright 2013 - UDS/CNRS
// The Aladin Lite program is distributed under the terms
// of the GNU General Public License version 3.
//
// This file is part of Aladin Lite.
//
//    Aladin Lite 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, version 3 of the License.
//
//    Aladin Lite 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.
//
//    The GNU General Public License is available in COPYING file
//    along with Aladin Lite.
//

/******************************************************************************
 * Aladin Lite project
 *
 * File Downloader
 * Queue downloading for image elements
 *
 * Author: Thomas Boch[CDS]
 *
 *****************************************************************************/
var Downloader = function () {
  var NB_MAX_SIMULTANEOUS_DL = 4; // TODO : le fading ne marche pas bien actuellement

  var FADING_ENABLED = false;
  var FADING_DURATION = 700; // in milliseconds

  var Downloader = function Downloader(view) {
    this.view = view; // reference to the view to be able to request redraw

    this.nbDownloads = 0; // number of current downloads

    this.dlQueue = []; // queue of items being downloaded

    this.urlsInQueue = {};
  };

  Downloader.prototype.emptyQueue = function () {
    this.dlQueue = [];
    this.urlsInQueue = {};
  };

  Downloader.prototype.requestDownload = function (img, url, cors) {
    // first check if url already in queue
    if (url in this.urlsInQueue) {
      return;
    } // put in queue


    this.dlQueue.push({
      img: img,
      url: url,
      cors: cors
    });
    this.urlsInQueue[url] = 1;
    this.tryDownload();
  }; // try to download next items in queue if possible


  Downloader.prototype.tryDownload = function () {
    //if (this.dlQueue.length>0 && this.nbDownloads<NB_MAX_SIMULTANEOUS_DL) {
    while (this.dlQueue.length > 0 && this.nbDownloads < NB_MAX_SIMULTANEOUS_DL) {
      this.startDownloadNext();
    }
  };

  Downloader.prototype.startDownloadNext = function () {
    // get next in queue
    var next = this.dlQueue.shift();

    if (!next) {
      return;
    }

    this.nbDownloads++;
    var downloaderRef = this;

    next.img.onload = function () {
      downloaderRef.completeDownload(this, true); // in this context, 'this' is the Image
    };

    next.img.onerror = function () {
      downloaderRef.completeDownload(this, false); // in this context, 'this' is the Image
    };

    if (next.cors) {
      next.img.crossOrigin = 'anonymous';
    } else {
      if (next.img.crossOrigin !== undefined) {
        delete next.img.crossOrigin;
      }
    }

    next.img.src = next.url;
  };

  Downloader.prototype.completeDownload = function (img, success) {
    delete this.urlsInQueue[img.src];
    img.onerror = null;
    img.onload = null;
    this.nbDownloads--;

    if (success) {
      if (FADING_ENABLED) {
        var now = new Date().getTime();
        img.fadingStart = now;
        img.fadingEnd = now + FADING_DURATION;
      }

      this.view.requestRedraw();
    } else {
      img.dlError = true;
    }

    this.tryDownload();
  };

  return Downloader;
}();

export default Downloader;