Preload image resources of type png and gif into qx.ui.basic.Image instances and add them to the application root offscreen at position -5000, -5000

MPreloadImageResources.js

/* ************************************************************************

   qooxdoo - the new era of web development

   http://qooxdoo.org

   Copyright:
     2015 Visionet GmbH, http://www.visionet.de

   License:
     LGPL: http://www.gnu.org/licenses/lgpl.html
     EPL: http://www.eclipse.org/org/documents/epl-v10.php
     See the LICENSE file in the project's top-level directory for details.

   Authors:
     * Dietrich Streifert (level420)

************************************************************************ */

/**
 * Add a method to preload images
 *
 */
qx.Mixin.define("visionet.application.MPreloadImageResources",
{
  /*
  *****************************************************************************
     MEMBERS
  *****************************************************************************
  */

  members :
  {
    /**
     * Preload image resources of type png and gif into qx.ui.basic.Image instances
     * and add them to the application root offscreen at position -5000, -5000
     * 
     * @param pathfragment {String|null} only preload if pathfragment is contained (via indexOf) in the resource name
     */
    preloadImageResources : function(pathfragment) {
      var resources = qx.$$resources;
      if(!resources || typeof resources !== "object") {
        this.warn("unable to preload images: resource hash qx.$$resources not initialized or not an object");
        return;
      }
      
      var root = qx.core.Init.getApplication().getRoot();
      if(!root) {
        this.error("unable to preload images: qx.core.Init.getApplication().getRoot() not yet available!");
        return;
      }
      
      var loadedCombined = {};
      
      for (var resname in resources) {
        if (resources.hasOwnProperty(resname)) {
          
          if(pathfragment && resname.indexOf(pathfragment) == -1) {
            continue;
          }
          
          var res = resources[resname];
          if(qx.lang.Type.isArray(res) && (res[2] == "png" || res[2] == "gif")) {
            // simple images
            if(res.length == 4) {
              if (qx.core.Environment.get("qx.debug")) {
                this.debug("preloading image: " + resname);
              }
            }
            // combined images
            else if(res.length == 7) {
              var combinedresname = res[4];
              
              if(!combinedresname || loadedCombined[combinedresname]) {
                // combined base image already loaded 
                continue;
              }
              loadedCombined[combinedresname] = true;
              resname = combinedresname;
              if (qx.core.Environment.get("qx.debug")) {
                this.debug("preloading combined image: " + resname);
              }
            }
            
            var image = new qx.ui.basic.Image(resname);
            root.add(image, {top:-5000, left:-5000});
          }
        }
      }
    }
  }
});

I have another version of this mixin which uses the not yes implemented getIds method of qx.util.ResourceManager which hopefully gets soon merged from pull request qooxdoo/qooxdoo#163

Then we don't need the internal qx.$$resources anymore