tablet: Take a screenshot and place under top window when enter tablet.

This will make sure everything underneath is completely occluded, so
nothing gets drawn.

Test: manual
Bug: 961549
Change-Id: I5124f8ffcee607964b8460f7214d962092a2e697
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1642370Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#668467}

ash/shell_test_api.cc

@@ -182,6 +182,7 @@ bool ShellTestApi::IsSystemModalWindowOpen() {
 
 void ShellTestApi::EnableTabletModeWindowManager(bool enable) {
   AccelerometerReader::GetInstance()->DisableForTest();
+  TabletModeController::SetForceNoScreenshotForTest();
   shell_->tablet_mode_controller()->EnableTabletModeWindowManager(enable);
 }
 

ash/test/ash_test_helper.cc

@@ -30,6 +30,7 @@
 #include "ash/test_shell_delegate.h"
 #include "ash/wallpaper/wallpaper_controller_impl.h"
 #include "ash/wm/overview/overview_controller.h"
+#include "ash/wm/tablet_mode/tablet_mode_controller.h"
 #include "base/bind.h"
 #include "base/run_loop.h"
 #include "base/strings/string_split.h"
@@ -186,6 +187,8 @@ void AshTestHelper::SetUp(bool start_session, bool provide_local_state) {
 
   // Ensure tests have a wallpaper as placeholder.
   shell->wallpaper_controller()->CreateEmptyWallpaperForTesting();
+
+  TabletModeController::SetForceNoScreenshotForTest();
 }
 
 void AshTestHelper::TearDown() {

ash/wm/tablet_mode/tablet_mode_controller.h

@@ -50,6 +50,10 @@ namespace views {
 class Widget;
 }
 
+namespace viz {
+class CopyOutputResult;
+}
+
 namespace ash {
 
 class InternalInputDevicesEventBlocker;
@@ -87,6 +91,10 @@ class ASH_EXPORT TabletModeController
   TabletModeController();
   ~TabletModeController() override;
 
+  // Disables taking screenshots for testing as it makes the initialization flow
+  // async.
+  static void SetForceNoScreenshotForTest();
+
   // TODO(jonross): Merge this with AttemptEnterTabletMode. Currently these are
   // separate for several reasons: there is no internal display when running
   // unittests; the event blocker prevents keyboard input when running ChromeOS
@@ -121,15 +129,15 @@ class ASH_EXPORT TabletModeController
   // Starts observing |window| for animation changes.
   void MaybeObserveBoundsAnimation(aura::Window* window);
 
+  // Stops observing the window which is being animated from tablet <->
+  // clamshell.
+  void StopObservingAnimation(bool record_stats, bool delete_screenshot);
+
   // TabletMode:
   void SetTabletModeToggleObserver(TabletModeToggleObserver* observer) override;
   bool IsEnabled() const override;
   void SetEnabledForTest(bool enabled) override;
 
-  // Stops observing the window which is being animated from tablet <->
-  // clamshell.
-  void StopObservingAnimation(bool record_stats);
-
   // ShellObserver:
   void OnShellInitialized() override;
 
@@ -271,6 +279,24 @@ class ASH_EXPORT TabletModeController
   // Resets |occlusion_tracker_pauser_|.
   void ResetPauser();
 
+  // Deletes the enter tablet mode screenshot and associated callbacks.
+  void DeleteScreenshot();
+
+  // Finishes initializing for tablet mode. May be called async if a screenshot
+  // was requested while starting initializing.
+  void FinishInitTabletMode();
+
+  // Takes a screenshot of everything in the rotation container, except for
+  // |top_window|.
+  void TakeScreenshot(aura::Window* top_window,
+                      base::OnceClosure on_screenshot_taken);
+
+  // Called when a screenshot is taken. Creates |screenshot_widget_| which holds
+  // the screenshot results and stacks it under |top_window|.
+  void OnScreenshotTaken(aura::Window* top_window,
+                         base::OnceClosure on_screenshot_taken,
+                         std::unique_ptr<viz::CopyOutputResult> copy_result);
+
   // The maximized window manager (if enabled).
   std::unique_ptr<TabletModeWindowManager> tablet_mode_window_manager_;
 
@@ -373,6 +399,17 @@ class ASH_EXPORT TabletModeController
 
   std::unique_ptr<TabletModeTransitionFpsCounter> fps_counter_;
 
+  base::CancelableOnceCallback<void(std::unique_ptr<viz::CopyOutputResult>)>
+      screenshot_taken_callback_;
+  base::CancelableOnceClosure screenshot_set_callback_;
+
+  // A layer that is created before an enter tablet mode animations is started,
+  // and destroyed when the animation is ended. It contains a screenshot of
+  // everything in the screen rotation container except the top window. It helps
+  // with animation performance because it fully occludes all windows except the
+  // animating window for the duration of the animation.
+  std::unique_ptr<ui::Layer> screenshot_layer_;
+
   base::ObserverList<TabletModeObserver>::Unchecked tablet_mode_observers_;
 
   base::WeakPtrFactory<TabletModeController> weak_factory_{this};

ash/wm/tablet_mode/tablet_mode_window_manager.cc

@@ -106,7 +106,7 @@ class ScopedObserveWindowAnimation {
       return;
 
     Shell::Get()->tablet_mode_controller()->StopObservingAnimation(
-        /*record_stats=*/false);
+        /*record_stats=*/false, /*delete_screenshot=*/true);
   }
 
  private:
@@ -117,6 +117,14 @@ class ScopedObserveWindowAnimation {
 
 TabletModeWindowManager::~TabletModeWindowManager() = default;
 
+// static
+aura::Window* TabletModeWindowManager::GetTopWindow() {
+  MruWindowTracker::WindowList windows =
+      Shell::Get()->mru_window_tracker()->BuildWindowForCycleList(kActiveDesk);
+
+  return windows.empty() ? nullptr : windows[0];
+}
+
 void TabletModeWindowManager::Init() {
   // The overview mode needs to be ended before the tablet mode is started. To
   // guarantee the proper order, it will be turned off from here.
@@ -187,13 +195,6 @@ void TabletModeWindowManager::WindowStateDestroyed(aura::Window* window) {
     window_state_map_.erase(it);
 }
 
-aura::Window* TabletModeWindowManager::GetTopWindow() {
-  MruWindowTracker::WindowList windows =
-      Shell::Get()->mru_window_tracker()->BuildWindowForCycleList(kActiveDesk);
-
-  return windows.empty() ? nullptr : windows[0];
-}
-
 void TabletModeWindowManager::OnOverviewModeEndingAnimationComplete(
     bool canceled) {
   if (canceled)

ash/wm/tablet_mode/tablet_mode_window_manager.h

@@ -50,6 +50,8 @@ class ASH_EXPORT TabletModeWindowManager : public aura::WindowObserver,
   // This should only be deleted by the creator (TabletModeController).
   ~TabletModeWindowManager() override;
 
+  static aura::Window* GetTopWindow();
+
   void Init();
 
   // Stops tracking windows and returns them to their clamshell mode state. Work
@@ -72,8 +74,6 @@ class ASH_EXPORT TabletModeWindowManager : public aura::WindowObserver,
   // Called from a window state object when it gets destroyed.
   void WindowStateDestroyed(aura::Window* window);
 
-  aura::Window* GetTopWindow();
-
   // OverviewObserver:
   void OnOverviewModeEndingAnimationComplete(bool canceled) override;
 

ash/wm/tablet_mode/tablet_mode_window_state.cc

@@ -153,6 +153,12 @@ bool IsTabDraggingSourceWindow(aura::Window* window) {
          window;
 }
 
+// True if |window| is the top window in BuildWindowForCycleList.
+bool IsTopWindow(aura::Window* window) {
+  DCHECK(window);
+  return window == TabletModeWindowManager::GetTopWindow();
+}
+
 }  // namespace
 
 // static
@@ -479,9 +485,4 @@ void TabletModeWindowState::UpdateBounds(wm::WindowState* window_state,
   }
 }
 
-bool TabletModeWindowState::IsTopWindow(aura::Window* window) {
-  DCHECK(window);
-  return window == creator_->GetTopWindow();
-}
-
 }  // namespace ash

ash/wm/tablet_mode/tablet_mode_window_state.h

@@ -79,9 +79,6 @@ class TabletModeWindowState : public wm::WindowState::State {
   // window state. If |animated| is set we animate the change.
   void UpdateBounds(wm::WindowState* window_state, bool animated);
 
-  // True if |window| is the top window in BuildWindowForCycleList.
-  bool IsTopWindow(aura::Window* window);
-
   // The original state object of the window.
   std::unique_ptr<wm::WindowState::State> old_state_;