Delay wallpaper load by 2 * average wallpaper load time.

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

Index: chrome/browser/resources/chromeos/login/user_pod_row.js
diff --git a/chrome/browser/resources/chromeos/login/user_pod_row.js b/chrome/browser/resources/chromeos/login/user_pod_row.js
index c1b03eed5bfd9d8bbddcc70519420d319b05f086..cf42e9fddd02a6e0d4eea1e0db0a0a8e76769a4d 100644
--- a/chrome/browser/resources/chromeos/login/user_pod_row.js
+++ b/chrome/browser/resources/chromeos/login/user_pod_row.js
@@ -22,18 +22,34 @@ cr.define('login', function() {
   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
@@ -924,17 +940,9 @@ cr.define('login', function() {
     // 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,
 
@@ -948,6 +956,28 @@ cr.define('login', function() {
     // 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_: [],
 
@@ -1189,6 +1219,39 @@ cr.define('login', function() {
     },
 
     /**
+     * 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
@@ -1231,15 +1294,8 @@ cr.define('login', function() {
         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;
       }
@@ -1248,12 +1304,20 @@ cr.define('login', function() {
     },
 
     /**
-     * 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]);
+      }
     },
 
     /**
@@ -1261,7 +1325,58 @@ cr.define('login', function() {
      */
     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);
+        }
+      }
     },
 
     /**
@@ -1525,13 +1640,7 @@ cr.define('login', function() {
             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);
           }
         });
       }