Only update system power indicators on change

ash/system/power/power_status_view.cc

Index: ash/system/power/power_status_view.cc
diff --git a/ash/system/power/power_status_view.cc b/ash/system/power/power_status_view.cc
index 6f205ade5d352447a3f126f662c79931da7e9b8c..e32c5aa15f52122f7e2f0cb743b92aa6e4dd4b5d 100644
--- a/ash/system/power/power_status_view.cc
+++ b/ash/system/power/power_status_view.cc
@@ -39,6 +39,7 @@ PowerStatusView::PowerStatusView(ViewType view_type,
       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;
@@ -117,10 +118,12 @@ void PowerStatusView::UpdateTextForDefaultView() {
     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,
@@ -141,11 +144,12 @@ void PowerStatusView::UpdateTextForDefaultView() {
               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() {
@@ -160,50 +164,54 @@ void PowerStatusView::UpdateTextForNotificationView() {
     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);
   }
 }