Extract colors from wallpaper and dynamically update login screen overlay

chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager.cc

 // Copyright 2014 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 "chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager.h"
 
 #include <utility>
 
 #include "ash/ash_constants.h"
 #include "ash/public/cpp/shelf_types.h"
@@ skipping 186 matching lines @@
 void SetKnownUserWallpaperFilesId(
     const AccountId& account_id,
     const wallpaper::WallpaperFilesId& wallpaper_files_id) {
   user_manager::known_user::SetStringPref(account_id, kWallpaperFilesId,
                                           wallpaper_files_id.id());
 }
 
 // A helper to set the wallpaper image for Classic Ash and Mash.
 void SetWallpaper(const gfx::ImageSkia& image,
                   wallpaper::WallpaperLayout layout) {
+  WallpaperManager::Get()->CalculateProminentColor(image);
   if (ash_util::IsRunningInMash()) {
     // In mash, connect to the WallpaperController interface via mojo.
     service_manager::Connector* connector =
         content::ServiceManagerConnection::GetForProcess()->GetConnector();
     if (!connector)
       return;
 
     ash::mojom::WallpaperControllerPtr wallpaper_controller;
     connector->BindInterface(ash::mojom::kServiceName, &wallpaper_controller);
     // TODO(crbug.com/655875): Optimize ash wallpaper transport; avoid sending
@@ skipping 203 matching lines @@
 
 bool WallpaperManager::IsPendingWallpaper(uint32_t image_id) {
   for (size_t i = 0; i < loading_.size(); ++i) {
     if (loading_[i]->GetImageId() == image_id) {
       return true;
     }
   }
   return false;
 }
 
+void WallpaperManager::CalculateProminentColor(const gfx::ImageSkia& image) {
+  if (color_calculator_) {
+    color_calculator_->RemoveObserver(this);

[jdufault, 2017/06/12 21:37:28]

Add a comment along the lines of 

  // Cancel any in-flight color calculations

[Wenzhao (Colin) Zang, 2017/06/12 23:40:34]

Done.

+    color_calculator_.reset();
+  }
+
+  color_utils::LumaRange luma = color_utils::LumaRange::DARK;

[jdufault, 2017/06/12 21:37:28]

Eliminate the |luma| and |saturation| temporaries. They don't provide additional
semantic value and the typing reduction is minimal.

[Wenzhao (Colin) Zang, 2017/06/12 23:40:34]

Done.

+  color_utils::SaturationRange saturation = color_utils::SaturationRange::MUTED;
+
+  color_calculator_ = base::MakeUnique<wallpaper::WallpaperColorCalculator>(
+      image, luma, saturation, task_runner_);
+  color_calculator_->AddObserver(this);
+  if (!color_calculator_->StartCalculation())
+    SetProminentColor(SK_ColorTRANSPARENT);
+}
+
 WallpaperManager::WallpaperResolution
 WallpaperManager::GetAppropriateResolution() {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
   gfx::Size size = ash::WallpaperController::GetMaxDisplaySizeInNative();
   return (size.width() > wallpaper::kSmallWallpaperMaxWidth ||
           size.height() > wallpaper::kSmallWallpaperMaxHeight)
              ? WALLPAPER_RESOLUTION_LARGE
              : WALLPAPER_RESOLUTION_SMALL;
 }
 
@@ skipping 464 matching lines @@
     window_observer_.Add(gained_active);
   }
 }
 
 void WallpaperManager::OnWindowDestroying(aura::Window* window) {
   window_observer_.Remove(window);
   chromeos::WallpaperWindowStateManager::RestoreWindows(
       user_manager::UserManager::Get()->GetActiveUser()->username_hash());
 }
 
+void WallpaperManager::OnColorCalculationComplete() {
+  const SkColor color = color_calculator_->prominent_color();
+  color_calculator_.reset();

[jdufault, 2017/06/12 21:37:28]

Add a comment explaining why you cache color instead of just using
color_calculator_->prominent_color() directly, ie,

  SetProminentColor(color_calculator_->prominent_color());
  color_calculator_.reset().

[Wenzhao (Colin) Zang, 2017/06/12 23:40:34]

Changed to using the color directly.

+  SetProminentColor(color);
+}
+
 // WallpaperManager, private: --------------------------------------------------
 
 WallpaperManager::WallpaperManager()
     : binding_(this),
       pending_inactive_(nullptr),
       activation_client_observer_(this),
       window_observer_(this),
       weak_factory_(this) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
   wallpaper::WallpaperManagerBase::SetPathIds(
@@ skipping 174 matching lines @@
   WallpaperInfo wallpaper_info = {GetDeviceWallpaperFilePath().value(),
                                   wallpaper::WALLPAPER_LAYOUT_CENTER_CROPPED,
                                   user_manager::User::DEVICE,
                                   base::Time::Now().LocalMidnight()};
   DCHECK(!user_manager::UserManager::Get()->IsUserLoggedIn());
   // In the login screen set the device wallpaper as the wallpaper.
   GetPendingWallpaper(user_manager::SignInAccountId(), false)
       ->ResetSetWallpaperImage(user_image->image(), wallpaper_info);
 }
 
+void WallpaperManager::SetProminentColor(SkColor color) {
+  if (prominent_color_ == color)
+    return;
+
+  prominent_color_ = color;
+  for (auto& observer : observers_)
+    observer.OnColorCalculationComplete();
+}
+
 void WallpaperManager::InitializeRegisteredDeviceWallpaper() {
   if (user_manager::UserManager::Get()->IsUserLoggedIn())
     return;
 
   bool disable_boot_animation =
       GetCommandLine()->HasSwitch(switches::kDisableBootAnimation);
   bool show_users = true;
   bool result = CrosSettings::Get()->GetBoolean(
       kAccountsPrefShowUserNamesOnSignIn, &show_users);
   DCHECK(result) << "Unable to fetch setting "
@@ skipping 327 matching lines @@
 
   UMA_HISTOGRAM_ENUMERATION(
       "Ash.Wallpaper.Apps",
       wallpaper_manager_util::ShouldUseAndroidWallpapersApp(profile)
           ? WALLPAPERS_APP_ANDROID
           : WALLPAPERS_PICKER_APP_CHROMEOS,
       WALLPAPERS_APPS_NUM);
 }
 
 }  // namespace chromeos