Delay wallpaper load by 2 * average wallpaper load time.

chrome/browser/resources/chromeos/login/user_pod_row.js

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+<include src="wallpaper_loader.js"></include>
+
 /**
  * @fileoverview User pod row implementation.
  */
 
 cr.define('login', function() {
   /**
    * Number of displayed columns depending on user pod count.
    * @type {Array.<number>}
    * @const
    */
   var COLUMNS = [0, 1, 2, 3, 4, 5, 4, 4, 4, 5, 5, 6, 6, 5, 5, 6, 6, 6, 6];
 
   /**
    * Whether to preselect the first pod automatically on login screen.
    * @type {boolean}
    * @const
    */
   var PRESELECT_FIRST_POD = true;
 
   /**
-   * Wallpaper load delay in milliseconds.
-   * @type {number}
-   * @const
-   */
-  var WALLPAPER_LOAD_DELAY_MS = 500;
-
-  /**
-   * Wallpaper load delay in milliseconds. TODO(nkostylev): Tune this constant.
-   * @type {number}
-   * @const
-   */
-  var WALLPAPER_BOOT_LOAD_DELAY_MS = 100;
-
-  /**
    * Maximum time for which the pod row remains hidden until all user images
    * have been loaded.
    * @type {number}
    * @const
    */
   var POD_ROW_IMAGES_LOAD_TIMEOUT_MS = 3000;
 
   /**
    * Public session help topic identifier.
    * @type {number}
@@ skipping 903 matching lines @@
    * @extends {HTMLDivElement}
    */
   var PodRow = cr.ui.define('podrow');
 
   PodRow.prototype = {
     __proto__: HTMLDivElement.prototype,
 
     // Whether this user pod row is shown for the first time.
     firstShown_: true,
 
-    // Whether the initial wallpaper load after boot has been requested. Used
-    // only if |Oobe.getInstance().shouldLoadWallpaperOnBoot()| is true.
-    bootWallpaperLoaded_: false,
-
     // True if inside focusPod().
     insideFocusPod_: false,
 
-    // True if user pod has been activated with keyboard.
-    // In case of activation with keyboard we delay wallpaper change.
-    keyboardActivated_: false,
-
     // Focused pod.
     focusedPod_: undefined,
 
     // Activated pod, i.e. the pod of current login attempt.
     activatedPod_: undefined,
 
     // Pod that was most recently focused, if any.
     lastFocusedPod_: undefined,
 
-    // When moving through users quickly at login screen, set a timeout to
-    // prevent loading intermediate wallpapers.
-    loadWallpaperTimeout_: null,
+    // Note: created only in decorate() !
+    wallpaperLoader_: undefined,
 
     // Pods whose initial images haven't been loaded yet.
     podsWithPendingImages_: [],
 
     /** @override */
     decorate: function() {
       this.style.left = 0;
 
       // Event listeners that are installed for the time period during which
       // the element is visible.
       this.listeners_ = {
         focus: [this.handleFocus_.bind(this), true /* useCapture */],
         click: [this.handleClick_.bind(this), true],
         mousemove: [this.handleMouseMove_.bind(this), false],
         keydown: [this.handleKeyDown.bind(this), false]
       };
+      this.wallpaperLoader_ = new login.WallpaperLoader();
     },
 
     /**
      * Returns all the pods in this pod row.
      * @type {NodeList}
      */
     get pods() {
       return this.children;
     },
 
@@ skipping 224 matching lines @@
         return;
       }
 
       // Make sure there's only one focusPod operation happening at a time.
       if (this.insideFocusPod_) {
         this.keyboardActivated_ = false;
         return;
       }
       this.insideFocusPod_ = true;
 
-      clearTimeout(this.loadWallpaperTimeout_);
+      this.wallpaperLoader_.reset();
       for (var i = 0, pod; pod = this.pods[i]; ++i) {
         if (!this.isSinglePod) {
           pod.isActionBoxMenuActive = false;
         }
         if (pod != podToFocus) {
           pod.isActionBoxMenuHovered = false;
           pod.classList.remove('focused');
           pod.classList.remove('faded');
           pod.reset(false);
         }
       }
 
       // Clear any error messages for previous pod.
       if (!this.isFocused(podToFocus))
         Oobe.clearErrors();
 
       var hadFocus = !!this.focusedPod_;
       this.focusedPod_ = podToFocus;
       if (podToFocus) {
         podToFocus.classList.remove('faded');
         podToFocus.classList.add('focused');
         podToFocus.reset(true);  // Reset and give focus.
-        chrome.send('focusPod', [podToFocus.user.emailAddress]);
-        if (hadFocus && this.keyboardActivated_) {
-          // Delay wallpaper loading to let user tab through pods without lag.
-          this.loadWallpaperTimeout_ = window.setTimeout(
-              this.loadWallpaper_.bind(this), WALLPAPER_LOAD_DELAY_MS);
-        } else if (!this.firstShown_) {
-          // Load wallpaper immediately if there no pod was focused
-          // previously, and it is not a boot into user pod list case.
-          this.loadWallpaper_();
-        }
+        chrome.send('focusPod', [podToFocus.user.username]);
+
+        this.wallpaperLoader_.scheduleLoad(podToFocus.user.username);
         this.firstShown_ = false;
         this.lastFocusedPod_ = podToFocus;
       }
       this.insideFocusPod_ = false;
       this.keyboardActivated_ = false;
     },
 
     /**
-     * Loads wallpaper for the active user pod, if any.
-     * @private
-     */
-    loadWallpaper_: function() {
-      if (this.focusedPod_)
-        chrome.send('loadWallpaper', [this.focusedPod_.user.username]);
-    },
-
-    /**
      * Focuses a given user pod by index or clear focus when given null.
      * @param {int=} podToFocus index of User pod to focus.
      * @param {boolean=} opt_force If true, forces focus update even when
      *                             podToFocus is already focused.
      */
     focusPodByIndex: function(podToFocus, opt_force) {
       if (podToFocus < this.pods.length)
         this.focusPod(this.pods[podToFocus], opt_force);
     },
 
     /**
      * Resets wallpaper to the last active user's wallpaper, if any.
      */
     loadLastWallpaper: function() {
       if (this.lastFocusedPod_)
-        chrome.send('loadWallpaper', [this.lastFocusedPod_.user.username]);
+        this.wallpaperLoader_.scheduleLoad(this.lastFocusedPod_.user.username);
     },
 
     /**
+     * Handles 'onWallpaperLoaded' event. Recalculates statistics and
+     * [re]schedules next wallpaper load.
+     */
+    onWallpaperLoaded: function(username) {
+      this.wallpaperLoader_.onWallpaperLoaded(username);
+    },
+
+    /**
      * Returns the currently activated pod.
      * @type {UserPod}
      */
     get activatedPod() {
       return this.activatedPod_;
     },
     set activatedPod(pod) {
       if (pod && pod.activate())
         this.activatedPod_ = pod;
     },
@@ skipping 240 matching lines @@
       if (this.focusedPod_) {
         var focusedPod = this.focusedPod_;
         var screen = this.parentNode;
         var self = this;
         focusedPod.addEventListener('webkitTransitionEnd', function f(e) {
           if (e.target == focusedPod) {
             focusedPod.removeEventListener('webkitTransitionEnd', f);
             focusedPod.reset(true);
             // Notify screen that it is ready.
             screen.onShow();
-            // Boot transition: load wallpaper.
-            if (!self.bootWallpaperLoaded_ &&
-                Oobe.getInstance().shouldLoadWallpaperOnBoot()) {
-              self.loadWallpaperTimeout_ = window.setTimeout(
-                  self.loadWallpaper_.bind(self), WALLPAPER_BOOT_LOAD_DELAY_MS);
-              self.bootWallpaperLoaded_ = true;
-            }
+            self.wallpaperLoader_.scheduleLoad(focusedPod.user.username);
           }
         });
         // Guard timer for 1 second -- it would conver all possible animations.
         ensureTransitionEndEvent(focusedPod, 1000);
       }
     },
 
     /**
      * Called right before the pod row is shown.
      */
@@ skipping 29 matching lines @@
       if (this.podsWithPendingImages_.length == 0) {
         this.classList.remove('images-loading');
       }
     }
   };
 
   return {
     PodRow: PodRow
   };
 });