overview gesture: Fade in overview when drag starts or during dragging.

When the window drag starts or slows down, fade in overview windows.

Bug: 997885
Change-Id: Ica9e256df32babeb6dab3d7d027447217a577c65
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1900127
Commit-Queue: Xiaoqian Dai <xdai@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#712785}

ash/home_screen/drag_window_from_shelf_controller.cc

@@ -149,6 +149,10 @@ void DragWindowFromShelfController::Drag(const gfx::Point& location_in_screen,
     overview_session->OnWindowDragStarted(window_, /*animate=*/false);
     if (ShouldAllowSplitView())
       overview_session->SetSplitViewDragIndicatorsDraggedWindow(window_);
+    // Hide overview windows first and fade in the windows after delaying
+    // kShowOverviewTimeWhenDragSuspend.
+    overview_session->SetVisibleDuringWindowDragging(/*visible=*/false,
+                                                     /*animate=*/false);
   }
 
   // If overview is active, update its splitview indicator during dragging if
@@ -178,7 +182,8 @@ void DragWindowFromShelfController::Drag(const gfx::Point& location_in_screen,
                std::abs(scroll_y) > kShowOverviewThreshold) {
       // If the dragging velocity is large enough, hide overview windows.
       show_overview_timer_.Stop();
-      overview_session->SetVisibleDuringWindowDragging(/*visible=*/false);
+      overview_session->SetVisibleDuringWindowDragging(/*visible=*/false,
+                                                       /*animate=*/false);
     } else {
       // Otherwise start the |show_overview_timer_| to show and update overview
       // when the dragging slows down or stops.
@@ -488,7 +493,7 @@ void DragWindowFromShelfController::ShowOverviewDuringOrAfterDrag() {
     return;
 
   overview_controller->overview_session()->SetVisibleDuringWindowDragging(
-      /*visible=*/true);
+      /*visible=*/true, /*animate=*/true);
 }
 
 void DragWindowFromShelfController::ScaleDownWindowAfterDrag() {

ash/wm/overview/overview_animation_type.h

@@ -47,6 +47,8 @@ enum OverviewAnimationType {
   OVERVIEW_ANIMATION_SELECTION_WINDOW,
   // Used to animate the clipping of the windows frame header.
   OVERVIEW_ANIMATION_FRAME_HEADER_CLIP,
+  // Used to fade in all windows when window drag starts or during window drag.
+  OVERVIEW_ANIMATION_OPACITY_ON_WINDOW_DRAG,
 };
 
 }  // namespace ash

ash/wm/overview/overview_grid.cc

@@ -893,13 +893,26 @@ void OverviewGrid::OnWindowDragEnded(aura::Window* dragged_window,
                               /*animate=*/true);
 }
 
-void OverviewGrid::SetVisibleDuringWindowDragging(bool visible) {
+void OverviewGrid::SetVisibleDuringWindowDragging(bool visible, bool animate) {
   for (const auto& window_item : window_list_)
-    window_item->SetVisibleDuringWindowDragging(visible);
+    window_item->SetVisibleDuringWindowDragging(visible, animate);
 
   // Update |desks_widget_|.
-  if (desks_widget_)
-    desks_widget_->GetNativeWindow()->layer()->SetOpacity(visible ? 1.f : 0.f);
+  if (desks_widget_) {
+    ui::Layer* layer = desks_widget_->GetNativeWindow()->layer();
+    float new_opacity = visible ? 1.f : 0.f;
+    if (layer->GetTargetOpacity() == new_opacity)
+      return;
+
+    if (animate) {
+      ScopedOverviewAnimationSettings settings(
+          OVERVIEW_ANIMATION_OPACITY_ON_WINDOW_DRAG,
+          desks_widget_->GetNativeWindow());
+      layer->SetOpacity(new_opacity);
+    } else {
+      layer->SetOpacity(new_opacity);
+    }
+  }
 }
 
 bool OverviewGrid::IsDropTargetWindow(aura::Window* window) const {

ash/wm/overview/overview_grid.h

@@ -177,7 +177,7 @@ class ASH_EXPORT OverviewGrid : public SplitViewObserver,
                          bool snap);
   // Shows/Hides windows during window dragging. Used when swiping up a window
   // from shelf.
-  void SetVisibleDuringWindowDragging(bool visible);
+  void SetVisibleDuringWindowDragging(bool visible, bool animate);
 
   // Returns true if |window| is the placeholder window from the drop target.
   bool IsDropTargetWindow(aura::Window* window) const;

ash/wm/overview/overview_item.cc

@@ -563,11 +563,21 @@ void OverviewItem::OnSelectorItemDragEnded(bool snap) {
   is_being_dragged_ = false;
 }
 
-void OverviewItem::SetVisibleDuringWindowDragging(bool visible) {
+void OverviewItem::SetVisibleDuringWindowDragging(bool visible, bool animate) {
   aura::Window::Windows windows = GetWindowsForHomeGesture();
+  float new_opacity = visible ? 1.f : 0.f;
   for (auto* window : windows) {
     ui::Layer* layer = window->layer();
-    layer->SetOpacity(visible ? 1.f : 0.f);
+    if (layer->GetTargetOpacity() == new_opacity)
+      continue;
+
+    if (animate) {
+      ScopedOverviewAnimationSettings settings(
+          OVERVIEW_ANIMATION_OPACITY_ON_WINDOW_DRAG, window);
+      layer->SetOpacity(new_opacity);
+    } else {
+      layer->SetOpacity(new_opacity);
+    }
   }
 }
 

ash/wm/overview/overview_item.h

@@ -120,7 +120,7 @@ class ASH_EXPORT OverviewItem : public views::ButtonListener,
 
   // Shows/Hides window item during window dragging. Used when swiping up a
   // window from shelf.
-  void SetVisibleDuringWindowDragging(bool visible);
+  void SetVisibleDuringWindowDragging(bool visible, bool animate);
 
   ScopedOverviewTransformWindow::GridWindowFillMode GetWindowDimensionsType()
       const;

ash/wm/overview/overview_item_view.cc

@@ -7,6 +7,7 @@
 #include "ash/resources/vector_icons/vector_icons.h"
 #include "ash/strings/grit/ash_strings.h"
 #include "ash/wm/overview/overview_constants.h"
+#include "ash/wm/overview/overview_grid.h"
 #include "ash/wm/overview/overview_item.h"
 #include "ash/wm/overview/rounded_rect_view.h"
 #include "ash/wm/window_preview_view.h"
@@ -161,7 +162,9 @@ OverviewItemView::OverviewItemView(OverviewItem* overview_item,
   // Call this last as it calls |Layout()| which relies on the some of the other
   // elements existing.
   SetShowPreview(show_preview);
-  if (show_preview) {
+  // Do not show header if the current overview item is the drop target widget.
+  if (show_preview || overview_item_->overview_grid()->IsDropTargetWindow(
+                          overview_item_->GetWindow())) {
     header_view()->layer()->SetOpacity(0.f);
     current_header_visibility_ = HeaderVisibility::kInvisible;
   }

ash/wm/overview/overview_session.cc

@@ -502,9 +502,10 @@ void OverviewSession::OnWindowDragEnded(aura::Window* dragged_window,
                                  should_drop_window_into_overview, snap);
 }
 
-void OverviewSession::SetVisibleDuringWindowDragging(bool visible) {
+void OverviewSession::SetVisibleDuringWindowDragging(bool visible,
+                                                     bool animate) {
   for (auto& grid : grid_list_)
-    grid->SetVisibleDuringWindowDragging(visible);
+    grid->SetVisibleDuringWindowDragging(visible, animate);
 }
 
 void OverviewSession::PositionWindows(

ash/wm/overview/overview_session.h

@@ -196,7 +196,7 @@ class ASH_EXPORT OverviewSession : public display::DisplayObserver,
   // overview. It's used when dragging a window from bottom, when the user slows
   // down or stops dragging the window, shows overview windows and when the user
   // resumes dragging, hides overview windows.
-  void SetVisibleDuringWindowDragging(bool visible);
+  void SetVisibleDuringWindowDragging(bool visible, bool animate);
 
   // Positions all overview items except those in |ignored_items|.
   void PositionWindows(bool animate,

ash/wm/overview/scoped_overview_animation_settings.cc

@@ -50,6 +50,11 @@ constexpr base::TimeDelta kOverviewHighlightTransition =
 constexpr base::TimeDelta kDropTargetFade =
     base::TimeDelta::FromMilliseconds(250);
 
+// Time duration to fade in overview windows when a window drag slows down or
+// stops.
+constexpr base::TimeDelta kFadeInOnWindowDrag =
+    base::TimeDelta::FromMilliseconds(350);
+
 base::TimeDelta GetAnimationDuration(OverviewAnimationType animation_type) {
   switch (animation_type) {
     case OVERVIEW_ANIMATION_NONE:
@@ -80,6 +85,8 @@ base::TimeDelta GetAnimationDuration(OverviewAnimationType animation_type) {
     case OVERVIEW_ANIMATION_SELECTION_WINDOW:
     case OVERVIEW_ANIMATION_FRAME_HEADER_CLIP:
       return kOverviewHighlightTransition;
+    case OVERVIEW_ANIMATION_OPACITY_ON_WINDOW_DRAG:
+      return kFadeInOnWindowDrag;
   }
   NOTREACHED();
   return base::TimeDelta();
@@ -192,6 +199,11 @@ ScopedOverviewAnimationSettings::ScopedOverviewAnimationSettings(
       animation_settings_->SetPreemptionStrategy(
           ui::LayerAnimator::IMMEDIATELY_ANIMATE_TO_NEW_TARGET);
       break;
+    case OVERVIEW_ANIMATION_OPACITY_ON_WINDOW_DRAG:
+      animation_settings_->SetTweenType(gfx::Tween::FAST_OUT_SLOW_IN);
+      animation_settings_->SetPreemptionStrategy(
+          ui::LayerAnimator::IMMEDIATELY_ANIMATE_TO_NEW_TARGET);
+      break;
   }
   animation_settings_->SetTransitionDuration(
       GetAnimationDuration(animation_type));