overview: Add scrolling for new overview layout format in tablet mode.

In the new overview layout, scrolling is needed to be able to see each
available window past the sixth window.

R=sammiequon@chromium.org, xdai@chromium.org

Bug: 981174
Change-Id: Idc207bf155e8458231114344650837a5783c8854
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1709876Reviewed-by: Sammie Quon <sammiequon@chromium.org>
Commit-Queue: Danton Vu <dantonvu@google.com>
Cr-Commit-Position: refs/heads/master@{#684035}

ash/wm/overview/overview_grid.cc

@@ -67,6 +67,10 @@ constexpr float kOverviewInsetRatio = 0.05f;
 // Additional vertical inset reserved for windows in overview mode.
 constexpr float kOverviewVerticalInset = 0.1f;
 
+// Number of columns and rows for windows in tablet overview mode.
+constexpr int kTabletLayoutCol = 3;
+constexpr int kTabletLayoutRow = 2;
+
 // Histogram names for overview enter/exit smoothness in clamshell,
 // tablet mode and splitview.
 constexpr char kOverviewEnterClamshellHistogram[] =
@@ -1257,6 +1261,30 @@ bool OverviewGrid::MaybeDropItemOnDeskMiniView(
   return false;
 }
 
+void OverviewGrid::PrepareScrollLimitMin() {
+  // Users are not allowed to scroll past the leftmost or rightmost bounds of
+  // the items on screen in the grid. |scroll_offset_min_| is the amount needed
+  // to fit the rightmost window into |total_bounds|. The max is zero which is
+  // default because windows are aligned to the left from the beginning.
+  gfx::Rect total_bounds = GetGridEffectiveBounds();
+  total_bounds.Inset(GetGridInsets(total_bounds));
+  float rightmost_window_right = 0;
+  for (const auto& window : window_list_) {
+    if (rightmost_window_right < window->target_bounds().right())
+      rightmost_window_right = window->target_bounds().right();
+  }
+  // |rightmost_window_right| may have been modified by an earlier scroll.
+  // |scroll_offset_| is added to adjust for that.
+  rightmost_window_right += scroll_offset_;
+  scroll_offset_min_ = total_bounds.right() - rightmost_window_right;
+}
+
+void OverviewGrid::UpdateScrollOffset(float delta) {
+  scroll_offset_ += delta;
+  scroll_offset_ = base::ClampToRange(scroll_offset_, scroll_offset_min_, 0.0f);
+  PositionWindows(false);
+}
+
 void OverviewGrid::MaybeInitDesksWidget() {
   if (!desks_util::ShouldDesksBarBeCreated() || desks_widget_)
     return;
@@ -1404,8 +1432,8 @@ std::vector<gfx::RectF> OverviewGrid::GetWindowRectsForTabletModeLayout(
   // animation.
   // Since the number of rows is limited, windows are laid out column-wise so
   // that the most recently used windows are displayed first.
-  const int width = total_bounds.width() / 3;
-  const int height = total_bounds.height() / 2;
+  const int width = total_bounds.width() / kTabletLayoutCol;
+  const int height = total_bounds.height() / kTabletLayoutRow;
   size_t window_position = 0u;
   std::vector<gfx::RectF> rects;
 
@@ -1414,12 +1442,14 @@ std::vector<gfx::RectF> OverviewGrid::GetWindowRectsForTabletModeLayout(
       rects.push_back(gfx::RectF());
       continue;
     }
-    const int x = width * (window_position / 2) + total_bounds.x();
+    const int x =
+        width * (window_position / 2) + total_bounds.x() + scroll_offset_;
     const int y = height * (window_position % 2) + total_bounds.y();
     const gfx::RectF bounds(x, y, width, height);
     rects.push_back(bounds);
     ++window_position;
   }
+
   return rects;
 }
 

ash/wm/overview/overview_grid.h

@@ -265,6 +265,14 @@ class ASH_EXPORT OverviewGrid : public aura::WindowObserver,
   bool MaybeDropItemOnDeskMiniView(const gfx::Point& screen_location,
                                    OverviewItem* drag_item);
 
+  // Prepares the |scroll_offset_min_| as a limit for |scroll_offset| from
+  // scrolling or positioning windows too far offscreen.
+  void PrepareScrollLimitMin();
+
+  // |delta| is used for updating |scroll_offset_| with new scroll values so
+  // that windows in tablet overview mode get positioned accordingly.
+  void UpdateScrollOffset(float delta);
+
   // Returns true if the grid has no more windows.
   bool empty() const { return window_list_.empty(); }
 
@@ -415,6 +423,14 @@ class ASH_EXPORT OverviewGrid : public aura::WindowObserver,
   // when reposition windows in tablet overview mode.
   bool suspend_reposition_ = false;
 
+  // Used by |GetWindowRectsForTabletModeLayout| to shift the x position of the
+  // overview items.
+  float scroll_offset_ = 0;
+
+  // Value to clamp |scroll_offset| so scrolling stays limited to windows that
+  // are visible in tablet overview mode.
+  float scroll_offset_min_ = 0;
+
   DISALLOW_COPY_AND_ASSIGN(OverviewGrid);
 };
 

ash/wm/overview/overview_grid_pre_event_handler.cc

@@ -3,10 +3,11 @@
 // found in the LICENSE file.
 
 #include "ash/wm/overview/overview_grid_pre_event_handler.h"
-
 #include "ash/shell.h"
 #include "ash/wm/overview/overview_controller.h"
+#include "ash/wm/overview/overview_grid.h"
 #include "ash/wm/overview/overview_utils.h"
+#include "ash/wm/window_util.h"
 #include "ui/events/event.h"
 
 namespace ash {
@@ -21,13 +22,38 @@ void OverviewGridPreEventHandler::OnMouseEvent(ui::MouseEvent* event) {
 }
 
 void OverviewGridPreEventHandler::OnGestureEvent(ui::GestureEvent* event) {
-  if (event->type() == ui::ET_GESTURE_TAP)
-    HandleClickOrTap(event);
+  // TODO(sammiequon): Investigate why scrolling on the bottom of the grid exits
+  // overview.
+  switch (event->type()) {
+    case ui::ET_GESTURE_TAP:
+      HandleClickOrTap(event);
+      break;
+    case ui::ET_GESTURE_SCROLL_BEGIN: {
+      if (!ShouldUseTabletModeGridLayout())
+        return;
+      StartDrag(event->location());
+      event->SetHandled();
+      break;
+    }
+    case ui::ET_GESTURE_SCROLL_UPDATE: {
+      if (!ShouldUseTabletModeGridLayout())
+        return;
+      UpdateDrag(event->details().scroll_x());
+      event->SetHandled();
+      break;
+    }
+    case ui::ET_GESTURE_SCROLL_END: {
+      event->SetHandled();
+      break;
+    }
+    default:
+      break;
+  }
 }
 
 void OverviewGridPreEventHandler::HandleClickOrTap(ui::Event* event) {
   CHECK_EQ(ui::EP_PRETARGET, event->phase());
-  OverviewController* controller = Shell::Get()->overview_controller();
+  auto* controller = Shell::Get()->overview_controller();
   if (!controller->InOverviewSession())
     return;
   // Events that happen while app list is sliding out during overview should
@@ -37,4 +63,20 @@ void OverviewGridPreEventHandler::HandleClickOrTap(ui::Event* event) {
   event->StopPropagation();
 }
 
+void OverviewGridPreEventHandler::StartDrag(const gfx::Point& location) {
+  // TODO(sammiequon): Investigate if this can be passed in the constructor.
+  auto* controller = Shell::Get()->overview_controller();
+  if (!controller->InOverviewSession())
+    return;
+  grid_ = controller->overview_session()->GetGridWithRootWindow(
+      window_util::GetRootWindowAt(location));
+  grid_->PrepareScrollLimitMin();
+}
+
+void OverviewGridPreEventHandler::UpdateDrag(float scroll) {
+  // Pass new scroll values to update the offset which will also update overview
+  // mode to position windows according to the scroll values.
+  grid_->UpdateScrollOffset(scroll);
+}
+
 }  // namespace ash

ash/wm/overview/overview_grid_pre_event_handler.h

@@ -7,6 +7,7 @@
 
 #include "base/macros.h"
 #include "ui/events/event_handler.h"
+#include "ui/gfx/geometry/point.h"
 
 namespace ui {
 class Event;
@@ -15,11 +16,13 @@ class MouseEvent;
 }  // namespace ui
 
 namespace ash {
+class OverviewGrid;
 
 // This event handler receives events in the pre-target phase and takes care of
 // the following:
 //   - Disabling overview mode on touch release.
 //   - Disabling overview mode on mouse release.
+//   - Scrolling through tablet overview mode on scrolling.
 class OverviewGridPreEventHandler : public ui::EventHandler {
  public:
   OverviewGridPreEventHandler();
@@ -32,6 +35,13 @@ class OverviewGridPreEventHandler : public ui::EventHandler {
 
   void HandleClickOrTap(ui::Event* event);
 
+  void StartDrag(const gfx::Point& location);
+  void UpdateDrag(float scroll);
+
+  // Cached value of the OverviewGrid that handles a series of gesture scroll
+  // events.
+  OverviewGrid* grid_ = nullptr;
+
   DISALLOW_COPY_AND_ASSIGN(OverviewGridPreEventHandler);
 };