Only update system power indicators on change

ash/system/power/power_status_view.cc

 // 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 "ash/system/power/power_status_view.h"
 
 #include "ash/shell.h"
 #include "ash/shell_delegate.h"
 #include "ash/system/power/tray_power.h"
 #include "ash/system/tray/tray_constants.h"
@@ skipping 21 matching lines @@
 const int kPaddingBetweenBatteryStatusAndIcon = 3;
 }  // namespace
 
 PowerStatusView::PowerStatusView(ViewType view_type,
                                  bool default_view_right_align)
     : default_view_right_align_(default_view_right_align),
       status_label_(NULL),
       time_label_(NULL),
       time_status_label_(NULL),
       icon_(NULL),
+      battery_image_index_(-1),
       view_type_(view_type) {
   if (view_type == VIEW_DEFAULT) {
     time_status_label_ = new views::Label;
     LayoutDefaultView();
   } else {
     status_label_ = new views::Label;
     time_label_ = new views::Label;
     LayoutNotificationView();
   }
   Update();
@@ skipping 58 matching lines @@
     // call in a crOS session. Until this bug is fixed, use
     // supply_status_.battery_seconds_to_empty to render battery time.
     // Change back to use averaged_battery_time_to_empty to display in UI
     // once crosbug.com/31633 is fixed.
     base::TimeDelta time = base::TimeDelta::FromSeconds(
         supply_status_.averaged_battery_time_to_empty);
     hour = time.InHours();
     min = (time - base::TimeDelta::FromHours(hour)).InMinutes();
   }
 
+  // Only update label text if the text changes, to save a GPU repaint
+
+  string16 time_status_text;
   if (supply_status_.line_power_on && supply_status_.battery_is_full) {
-    time_status_label_->SetText(
-        ui::ResourceBundle::GetSharedInstance().GetLocalizedString(
-            IDS_ASH_STATUS_TRAY_BATTERY_FULL));
+    time_status_text = ui::ResourceBundle::GetSharedInstance()
+        .GetLocalizedString(IDS_ASH_STATUS_TRAY_BATTERY_FULL);
   } else {
     string16 battery_percentage = l10n_util::GetStringFUTF16(
         IDS_ASH_STATUS_TRAY_BATTERY_PERCENT_ONLY,
         base::IntToString16(
             static_cast<int>(supply_status_.battery_percentage)));
     string16 battery_time = string16();
     if (supply_status_.is_calculating_battery_time) {
       battery_time =
           ui::ResourceBundle::GetSharedInstance().GetLocalizedString(
               IDS_ASH_STATUS_TRAY_BATTERY_CALCULATING);
     } else if (hour || min){
       string16 minute = min < 10 ?
           ASCIIToUTF16("0") + base::IntToString16(min) :
           base::IntToString16(min);
       battery_time =
           l10n_util::GetStringFUTF16(
               IDS_ASH_STATUS_TRAY_BATTERY_TIME_ONLY,
               base::IntToString16(hour),
               minute);
     }
-    string16 battery_status = battery_time.empty() ?
+    time_status_text = battery_time.empty() ?
         battery_percentage :
         battery_percentage + ASCIIToUTF16(" - ") + battery_time;
-    time_status_label_->SetText(battery_status);
   }
+  if (time_status_text != time_status_label_->text())
+    time_status_label_->SetText(time_status_text);

[Daniel Erat, 2012/09/04 21:51:58]

This seems like a worthwhile optimization to do elsewhere.  Any reason it can't
be placed in Views instead?

 }
 
 void PowerStatusView::UpdateTextForNotificationView() {
   int hour = 0;
   int min = 0;
   if (!supply_status_.is_calculating_battery_time) {
     base::TimeDelta time = base::TimeDelta::FromSeconds(
         supply_status_.line_power_on ?
         supply_status_.averaged_battery_time_to_full :
         supply_status_.averaged_battery_time_to_empty);
     hour = time.InHours();
     min = (time - base::TimeDelta::FromHours(hour)).InMinutes();
   }
 
+  // Only update label text if the text changes, to save a GPU repaint
+
+  string16 status_text;
   if (supply_status_.line_power_on && supply_status_.battery_is_full) {
-    status_label_->SetText(
-        ui::ResourceBundle::GetSharedInstance().GetLocalizedString(
-            IDS_ASH_STATUS_TRAY_BATTERY_FULL));
+    status_text = ui::ResourceBundle::GetSharedInstance().GetLocalizedString(
+        IDS_ASH_STATUS_TRAY_BATTERY_FULL);
   } else {
-    status_label_->SetText(
-        l10n_util::GetStringFUTF16(
-            IDS_ASH_STATUS_TRAY_BATTERY_PERCENT,
-            base::IntToString16(
-                static_cast<int>(supply_status_.battery_percentage))));
+    status_text = l10n_util::GetStringFUTF16(
+        IDS_ASH_STATUS_TRAY_BATTERY_PERCENT,
+        base::IntToString16(
+            static_cast<int>(supply_status_.battery_percentage)));
   }
+  if (status_text != status_label_->text())
+    status_label_->SetText(status_text);
 
+  string16 time_text;
   if (supply_status_.is_calculating_battery_time) {
-    time_label_->SetText(
-        ui::ResourceBundle::GetSharedInstance().GetLocalizedString(
-            IDS_ASH_STATUS_TRAY_BATTERY_CALCULATING));
+    time_text = ui::ResourceBundle::GetSharedInstance().GetLocalizedString(
+        IDS_ASH_STATUS_TRAY_BATTERY_CALCULATING);
   } else if (hour || min) {
     if (supply_status_.line_power_on) {
-      time_label_->SetText(
-        l10n_util::GetStringFUTF16(
-            IDS_ASH_STATUS_TRAY_BATTERY_TIME_UNTIL_FULL,
-            base::IntToString16(hour),
-            base::IntToString16(min)));
+      time_text = l10n_util::GetStringFUTF16(
+          IDS_ASH_STATUS_TRAY_BATTERY_TIME_UNTIL_FULL,
+          base::IntToString16(hour),
+          base::IntToString16(min));
     } else {
       // This is a low battery warning, which prompts user when battery
       // time left is not much (ie in minutes).
       min = hour * 60 + min;
       ShellDelegate* delegate = Shell::GetInstance()->delegate();
       if (delegate) {
-        time_label_->SetText(delegate->GetTimeRemainingString(
-                                 base::TimeDelta::FromMinutes(min)));
-      } else {
-        time_label_->SetText(string16());
+        time_text = delegate->GetTimeRemainingString(
+            base::TimeDelta::FromMinutes(min));
       }
     }
-  } else {
-    time_label_->SetText(string16());
   }
-
+  if (time_text != time_label_->text())
+    time_label_->SetText(time_text);
 }
 
 void PowerStatusView::UpdateIcon() {
   if (icon_) {
-    icon_->SetImage(TrayPower::GetBatteryImage(supply_status_, ICON_DARK));
+    int index = TrayPower::GetBatteryImageIndex(supply_status_);
+    if (battery_image_index_ != index) {
+      battery_image_index_ = index;
+      icon_->SetImage(
+          TrayPower::GetBatteryImage(battery_image_index_, ICON_DARK));
+    }
     icon_->SetVisible(true);
   }
 }
 
 void PowerStatusView::Update() {
   UpdateText();
   UpdateIcon();
 }
 
 void PowerStatusView::ChildPreferredSizeChanged(views::View* child) {
   PreferredSizeChanged();
 }
 
 gfx::Size PowerStatusView::GetPreferredSize() {
   gfx::Size size = views::View::GetPreferredSize();
   return gfx::Size(size.width(), kTrayPopupItemHeight);
 }
 
 }  // namespace internal
 }  // namespace ash