splitview: Fix animation parameters for fading out the preview area.

According to the specification, when you drag a window to snap it, the
preview area (referred to as "Indicator") should fade out over 67 ms,
fast out, linear in:
https://mccanny.users.x20web.corp.google.com/www/splitscreen-motion/index.html#window-drop

Currently, it fades out over 250 ms, fast out, slow in.

BEFORE:
https://photos.app.goo.gl/MQa3rZ4jKX4hZLba7

AFTER:
https://photos.app.goo.gl/iLFHyvqxFZsfreEC6

Test: manual
Bug: 934977
Change-Id: I27d3e4d758097f2a87207880b2bc5ca9622dad7e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1504037
Commit-Queue: Avery Musbach <amusbach@chromium.org>
Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638300}

ash/wm/splitview/split_view_drag_indicators.cc

@@ -298,8 +298,10 @@ class SplitViewDragIndicators::SplitViewDragIndicatorsView
                                                previous_indicator_state_);
     right_rotated_view_->OnIndicatorTypeChanged(indicator_state,
                                                 previous_indicator_state_);
-    left_highlight_view_->OnIndicatorTypeChanged(indicator_state);
-    right_highlight_view_->OnIndicatorTypeChanged(indicator_state);
+    left_highlight_view_->OnIndicatorTypeChanged(indicator_state,
+                                                 previous_indicator_state_);
+    right_highlight_view_->OnIndicatorTypeChanged(indicator_state,
+                                                  previous_indicator_state_);
 
     if (indicator_state != IndicatorState::kNone)
       Layout(previous_indicator_state_ != IndicatorState::kNone);

ash/wm/splitview/split_view_highlight_view.cc

@@ -171,22 +171,46 @@ void SplitViewHighlightView::SetColor(SkColor color) {
 }
 
 void SplitViewHighlightView::OnIndicatorTypeChanged(
-    IndicatorState indicator_state) {
+    IndicatorState indicator_state,
+    IndicatorState previous_indicator_state) {
   if (indicator_state == IndicatorState::kNone) {
-    DoSplitviewOpacityAnimation(layer(),
-                                SPLITVIEW_ANIMATION_HIGHLIGHT_FADE_OUT);
+    if (!SplitViewDragIndicators::IsPreviewAreaState(
+            previous_indicator_state)) {
+      DoSplitviewOpacityAnimation(layer(),
+                                  SPLITVIEW_ANIMATION_HIGHLIGHT_FADE_OUT);
+      return;
+    }
+
+    // There are two SplitViewHighlightView objects,
+    // |SplitViewDragIndicatorsView::left_highlight_view_| and
+    // |SplitViewDragIndicatorsView::right_highlight_view_|.
+    // |was_this_the_preview| indicates that this (in the sense of the keyword
+    // this) is the one that represented the preview area.
+    const bool was_this_the_preview =
+        is_right_or_bottom_ !=
+        SplitViewDragIndicators::IsPreviewAreaOnLeftTopOfScreen(
+            previous_indicator_state);
+    if (was_this_the_preview) {
+      DoSplitviewOpacityAnimation(layer(),
+                                  SPLITVIEW_ANIMATION_PREVIEW_AREA_FADE_OUT);
+    }
     return;
   }
 
   if (SplitViewDragIndicators::IsPreviewAreaState(indicator_state)) {
-    const bool is_preview_on_left_or_top =
+    // There are two SplitViewHighlightView objects,
+    // |SplitViewDragIndicatorsView::left_highlight_view_| and
+    // |SplitViewDragIndicatorsView::right_highlight_view_|.
+    // |is_this_the_preview| indicates that this (in the sense of the keyword
+    // this) is the one that represents the preview area.
+    const bool is_this_the_preview =
+        is_right_or_bottom_ !=
         SplitViewDragIndicators::IsPreviewAreaOnLeftTopOfScreen(
             indicator_state);
-    const bool should_fade_in = is_right_or_bottom_ ? !is_preview_on_left_or_top
-                                                    : is_preview_on_left_or_top;
     DoSplitviewOpacityAnimation(
-        layer(), should_fade_in ? SPLITVIEW_ANIMATION_PREVIEW_AREA_FADE_IN
-                                : SPLITVIEW_ANIMATION_OTHER_HIGHLIGHT_FADE_OUT);
+        layer(), is_this_the_preview
+                     ? SPLITVIEW_ANIMATION_PREVIEW_AREA_FADE_IN
+                     : SPLITVIEW_ANIMATION_OTHER_HIGHLIGHT_FADE_OUT);
     return;
   }
 

ash/wm/splitview/split_view_highlight_view.h

@@ -31,8 +31,10 @@ class ASH_EXPORT SplitViewHighlightView : public views::View {
 
   void SetColor(SkColor color);
 
-  // Called to update the opacity of the highlights view on |indicator_state|.
-  void OnIndicatorTypeChanged(IndicatorState indicator_state);
+  // Called to update the opacity of the highlights view on transition from
+  // |previous_indicator_state| to |indicator_state|.
+  void OnIndicatorTypeChanged(IndicatorState indicator_state,
+                              IndicatorState previous_indicator_state);
 
  private:
   friend class SplitViewHighlightViewTestApi;

ash/wm/splitview/split_view_utils.cc

@@ -42,6 +42,8 @@ constexpr base::TimeDelta kLabelAnimationDelayMs =
 // The time duration for the window transformation animations.
 constexpr base::TimeDelta kWindowTransformMs =
     base::TimeDelta::FromMilliseconds(250);
+constexpr base::TimeDelta kPreviewAreaFadeOutMs =
+    base::TimeDelta::FromMilliseconds(67);
 
 constexpr float kHighlightOpacity = 0.3f;
 constexpr float kPreviewAreaHighlightOpacity = 0.18f;
@@ -91,6 +93,10 @@ void GetAnimationValuesForType(
       *out_preemption_strategy =
           ui::LayerAnimator::IMMEDIATELY_ANIMATE_TO_NEW_TARGET;
       return;
+    case SPLITVIEW_ANIMATION_PREVIEW_AREA_FADE_OUT:
+      *out_duration = kPreviewAreaFadeOutMs;
+      *out_tween_type = gfx::Tween::FAST_OUT_LINEAR_IN;
+      return;
   }
 
   NOTREACHED();
@@ -125,6 +131,7 @@ void DoSplitviewOpacityAnimation(ui::Layer* layer,
   switch (type) {
     case SPLITVIEW_ANIMATION_HIGHLIGHT_FADE_OUT:
     case SPLITVIEW_ANIMATION_OTHER_HIGHLIGHT_FADE_OUT:
+    case SPLITVIEW_ANIMATION_PREVIEW_AREA_FADE_OUT:
     case SPLITVIEW_ANIMATION_OVERVIEW_ITEM_FADE_OUT:
     case SPLITVIEW_ANIMATION_TEXT_FADE_OUT:
     case SPLITVIEW_ANIMATION_TEXT_FADE_OUT_WITH_HIGHLIGHT:

ash/wm/splitview/split_view_utils.h

@@ -32,9 +32,10 @@ enum SplitviewAnimationType {
   // highlight is the preview highlight, and the other highlight is the other
   // highlight.
   SPLITVIEW_ANIMATION_OTHER_HIGHLIGHT_FADE_OUT,
-  // Used to fade in the preview area highlight which indicates the bounds of
-  // the window that is about to get snapped.
+  // Used to fade in and out the preview area highlight which indicates the
+  // bounds of the window that is about to get snapped.
   SPLITVIEW_ANIMATION_PREVIEW_AREA_FADE_IN,
+  SPLITVIEW_ANIMATION_PREVIEW_AREA_FADE_OUT,
   // Used to fade in and out the label on the overview item which warns users
   // the item cannot be snapped. The label appears on the overview item after
   // another window has been snapped.