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.
 
 /**
  * @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.
+   * Minimum wallpaper load delay in milliseconds.
    * @type {number}
    * @const
    */
-  var WALLPAPER_LOAD_DELAY_MS = 500;
+  var WALLPAPER_LOAD_MIN_DELAY_MS = 100;
 
   /**
-   * Wallpaper load delay in milliseconds. TODO(nkostylev): Tune this constant.
+   * If last walpaper load time cannot be calculated, assume this value.
    * @type {number}
    * @const
    */
-  var WALLPAPER_BOOT_LOAD_DELAY_MS = 100;
+  var WALLPAPER_DEFAULT_LOAD_TIME_MS = 200;
+
+  /**
+   * Min and Max average wallpaper load time.
+   * Delay to next wallpaper load is 2 * <average load time>.
+   * @type {number}
+   * @const
+   */
+  var WALLPAPER_MIN_LOAD_TIME_MS = 50;
+  var WALLPAPER_MAX_LOAD_TIME_MS = 2000;
+
+  /**
+   * Number last wallpaper load times to remember.
+   * @type {number}
+   * @const
+   */
+  var WALLPAPER_LOAD_STATS_MAX_LENGTH = 4;
 
   /**
    * 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;
 
   /**
@@ skipping 870 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,
 
+    // When waiting for wallpaper load, remember load start time.
+    // This is actually associative array with key = username and value =
+    // start time.
+    wallpaperLoadInProgress_: {},
+
+    // Wait a delay and then load this wallpaper. Value = username.
+    wallpaperLoadPending: undefined,
+
+    // Wait untill this Date before loading next wallpaper.
+    wallpaperLoadTryNextAfter: undefined,
+
+    // Username, owner of current wallpaper.
+    wallpaperCurrent: '',
+
+    wallpaperLoadStats: {
+       // Array of times (in milliseconds) of last wallpaper load attempts.
+       // Length is limited by WALLPAPER_LOAD_STATS_MAX_LENGTH.
+       history: [],
+       // sum(history)
+       totalTimeMs: 0
+    },
+
     // 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_ = {
@@ skipping 221 matching lines @@
     /**
      * Whether the pod is currently focused.
      * @param {UserPod} pod Pod to check for focus.
      * @return {boolean} Pod focus status.
      */
     isFocused: function(pod) {
       return this.focusedPod_ == pod;
     },
 
     /**
+     * Schedules wallpaper load.
+     */
+    scheduleLoadWallpaper: function(email) {
+        if (this.wallpaperLoadPending && this.wallpaperLoadPending == email)
+          return;
+        this.wallpaperLoadPending = email;
+        if (this.wallpaperLoadInProgress_.hasOwnProperty(email)) {
+          clearTimeout(this.loadWallpaperTimeout_);
+          delete this.wallpaperLoadPending;
+          return;
+        }
+        if ((Object.getOwnPropertyNames(this.wallpaperLoadInProgress_).length ==
+            0) && (this.wallpaperCurrent == email)) {
+          delete this.wallpaperLoadPending;
+          return;
+        }
+        if (this.loadWallpaperTimeout_) {
+          clearTimeout(this.loadWallpaperTimeout_);
+        }
+        var now = new Date();
+        var timeout = WALLPAPER_LOAD_MIN_DELAY_MS;
+        if (this.wallpaperLoadTryNextAfter &&
+            (now < this.wallpaperLoadTryNextAfter) &&
+            (this.wallpaperLoadTryNextAfter.getTime() -
+              now.getTime() > WALLPAPER_LOAD_MIN_DELAY_MS))
+          timeout = this.wallpaperLoadTryNextAfter.getTime() -
+              now.getTime();
+
+        this.loadWallpaperTimeout_ = window.setTimeout(
+          this.loadWallpaper_.bind(this), timeout);
+     },
+
+    /**
      * Focuses a given user pod or clear focus when given null.
      * @param {UserPod=} podToFocus User pod to focus (undefined clears focus).
      * @param {boolean=} opt_force If true, forces focus update even when
      *                             podToFocus is already focused.
      */
     focusPod: function(podToFocus, opt_force) {
       if (this.isFocused(podToFocus) && !opt_force) {
         this.keyboardActivated_ = false;
         return;
       }
@@ skipping 22 matching lines @@
       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_();
-        }
+
+        this.scheduleLoadWallpaper(podToFocus.user.emailAddress);
         this.firstShown_ = false;
         this.lastFocusedPod_ = podToFocus;
       }
       this.insideFocusPod_ = false;
       this.keyboardActivated_ = false;
     },
 
     /**
-     * Loads wallpaper for the active user pod, if any.
+     * Loads pending wallpaper, if any.
      * @private
      */
     loadWallpaper_: function() {
-      if (this.focusedPod_)
-        chrome.send('loadWallpaper', [this.focusedPod_.user.username]);
+      if (this.wallpaperLoadPending) {
+        var email = this.wallpaperLoadPending;
+        delete this.wallpaperLoadPending;
+        if (email == this.wallpaperCurrent)
+          return;
+        if (this.wallpaperLoadInProgress_[email])
+          return;
+        this.wallpaperLoadInProgress_[email] = new Date();
+        chrome.send('loadWallpaper', [email]);
+      }
     },
 
     /**
      * Resets wallpaper to the last active user's wallpaper, if any.
      */
     loadLastWallpaper: function() {
       if (this.lastFocusedPod_)
-        chrome.send('loadWallpaper', [this.lastFocusedPod_.user.username]);
+        this.scheduleLoadWallpaper(this.lastFocusedPod_.user.username);
     },
 
     /**
+     * Calculates average wallpaper load time.
+     */
+    getWallpaperLoadAvg_: function() {
+      var avg = WALLPAPER_DEFAULT_LOAD_TIME_MS;
+      if (this.wallpaperLoadStats.history.length) {
+        avg = this.wallpaperLoadStats.totalTimeMs /
+            this.wallpaperLoadStats.history.length;
+        if (avg < WALLPAPER_MIN_LOAD_TIME_MS) {
+          avg = WALLPAPER_MIN_LOAD_TIME_MS;
+        }
+        if (avg > WALLPAPER_MAX_LOAD_TIME_MS) {
+          avg = WALLPAPER_MAX_LOAD_TIME_MS;
+        }
+      }
+      return avg;
+    },
+
+    /**
+     * Handles 'onWallpaperLoaded' event. Recalculates statistics and
+     * [re]schedules next wallpaper load.
+     */
+    onWallpaperLoaded: function(email) {
+      this.wallpaperCurrent = email;
+      var started = this.wallpaperLoadInProgress_[email];
+      delete this.wallpaperLoadInProgress_[email];
+      var finished = new Date();
+      var elapsed = started ? finished.getTime() - started.getTime() :
+          WALLPAPER_DEFAULT_LOAD_TIME_MS;
+      this.wallpaperLoadStats.history.push(elapsed);
+      this.wallpaperLoadStats.totalTimeMs += elapsed;
+      if (this.wallpaperLoadStats.history.length >
+          WALLPAPER_LOAD_STATS_MAX_LENGTH) {
+        var tt = this.wallpaperLoadStats.history.shift();
+        this.wallpaperLoadStats.totalTimeMs -= tt;
+      }
+      var nextAfter = new Date();
+      nextAfter.setTime(nextAfter.getTime() +
+          2 * this.getWallpaperLoadAvg_());
+      this.wallpaperLoadTryNextAfter = nextAfter;
+      if (this.wallpaperLoadPending) {
+        var newWallpaperEmail = this.wallpaperLoadPending;
+        delete this.wallpaperLoadPending;
+        if (newWallpaperEmail == email) {
+          clearTimeout(this.loadWallpaperTimeout_);
+        } else {
+          this.scheduleLoadWallpaper(newWallpaperEmail);
+        }
+      }
+    },
+
+    /**
      * 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.scheduleLoadWallpaper(focusedPod.user.username);
           }
         });
       }
     },
 
     /**
      * Called right before the pod row is shown.
      */
     handleBeforeShow: function() {
       for (var event in this.listeners_) {
@@ skipping 27 matching lines @@
       if (this.podsWithPendingImages_.length == 0) {
         this.classList.remove('images-loading');
       }
     }
   };
 
   return {
     PodRow: PodRow
   };
 });