Activate the next/previous tab on horizonal scroll

This CL allows us to use mouse with horizontal scroll function,
such as tilting wheel or separate wheel for h-scroll.

Bug: 2384
Change-Id: I770c629bb2391343ce66a398e4d73ad69dde569e
Reviewed-on: https://chromium-review.googlesource.com/c/1414537
Commit-Queue: Sang Woo Ko <sangwoo108@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#628588}

chrome/browser/ui/views/tabs/tab_strip.cc

@@ -1341,7 +1341,7 @@ float TabStrip::GetHoverOpacityForRadialHighlight() const {
 }
 
 ///////////////////////////////////////////////////////////////////////////////
-// TabStrip, views::View overrides:
+// TabStrip, views::AccessiblePaneView overrides:
 
 void TabStrip::Layout() {
   // Only do a layout if our size changed.
@@ -1352,6 +1352,34 @@ void TabStrip::Layout() {
   DoLayout();
 }
 
+bool TabStrip::OnMouseWheel(const ui::MouseWheelEvent& event) {
+  // Change the selected tab on horizontal wheel scrolls.
+  // Honor wheel scrolls over the tabs themselves, but not the NTB/surrounding
+  // space.
+  if ((!event.x_offset() && !event.IsShiftDown()) || tab_count() < 2 ||
+      !FindTabHitByPoint(event.location()))
+    return false;
+
+  accumulated_horizontal_scroll_ +=
+      (event.x_offset() ? event.x_offset() : event.y_offset());
+
+  int horizontal_offset =
+      accumulated_horizontal_scroll_ / ui::MouseWheelEvent::kWheelDelta;
+  if (!horizontal_offset)
+    return true;
+
+  accumulated_horizontal_scroll_ %= ui::MouseWheelEvent::kWheelDelta;
+
+  int new_active_index =
+      (controller_->GetActiveIndex() + horizontal_offset) % tab_count();
+  if (new_active_index < 0)
+    new_active_index += tab_count();
+
+  DCHECK(IsValidModelIndex(new_active_index));
+  controller_->SelectTab(new_active_index);
+  return true;
+}
+
 void TabStrip::PaintChildren(const views::PaintInfo& paint_info) {
   // The view order doesn't match the paint order (tabs_ contains the tab
   // ordering). Additionally we need to paint the tabs that are closing in

chrome/browser/ui/views/tabs/tab_strip.h

@@ -290,8 +290,9 @@ class TabStrip : public views::AccessiblePaneView,
   // MouseWatcherListener:
   void MouseMovedOutOfHost() override;
 
-  // views::View:
+  // views::AccessiblePaneView:
   void Layout() override;
+  bool OnMouseWheel(const ui::MouseWheelEvent& event) override;
   void PaintChildren(const views::PaintInfo& paint_info) override;
   void OnPaint(gfx::Canvas* canvas) override;
   const char* GetClassName() const override;
@@ -711,6 +712,10 @@ class TabStrip : public views::AccessiblePaneView,
   // Number of mouse moves.
   int mouse_move_count_ = 0;
 
+  // Accumulatated offsets from thumb wheel. Used to throttle horizontal
+  // scroll from thumb wheel.
+  int accumulated_horizontal_scroll_ = 0;
+
   // Timer used when a tab is closed and we need to relayout. Only used when a
   // tab close comes from a touch device.
   base::OneShotTimer resize_layout_timer_;

chrome/browser/ui/views/tabs/tab_strip_unittest.cc

@@ -896,4 +896,50 @@ TEST_P(TabStripTest, EventsOnClosingTab) {
   EXPECT_EQ(first_tab, tab_strip_->GetEventHandlerForPoint(tab_center));
 }
 
+// Switch selected tabs on horizontal scroll events.
+TEST_P(TabStripTest, HorizontalScroll) {
+  tab_strip_->SetBounds(0, 0, 200, 20);
+
+  for (int i = 0; i < 3; i++)
+    controller_->AddTab(i, true /* is_active */);
+
+  Tab* tab = tab_strip_->tab_at(0);
+  gfx::Point tab_center = tab->bounds().CenterPoint();
+
+  for (int i = 0; i < tab_strip_->tab_count(); ++i) {
+    ui::MouseWheelEvent wheel_event(
+        gfx::Vector2d(ui::MouseWheelEvent::kWheelDelta, 0), tab_center,
+        tab_center, ui::EventTimeForNow(), 0, 0);
+    tab_strip_->OnMouseWheel(wheel_event);
+    EXPECT_EQ(i, controller_->GetActiveIndex());
+  }
+
+  controller_->SelectTab(0);
+  for (int i = tab_strip_->tab_count() - 1; i >= 0; --i) {
+    ui::MouseWheelEvent wheel_event(
+        gfx::Vector2d(-ui::MouseWheelEvent::kWheelDelta, 0), tab_center,
+        tab_center, ui::EventTimeForNow(), 0, 0);
+    tab_strip_->OnMouseWheel(wheel_event);
+    EXPECT_EQ(i, controller_->GetActiveIndex());
+  }
+
+  // When offset is smaller than kWheelDelta, we don't scroll immediately.
+  // We wait offset until accumulated offset gets bigger than kWheelDelta.
+  const int small_offset = ui::MouseWheelEvent::kWheelDelta / 3;
+  int next_accumulated_offset = small_offset;
+  while (next_accumulated_offset < ui::MouseWheelEvent::kWheelDelta) {
+    ui::MouseWheelEvent wheel_event(gfx::Vector2d(small_offset, 0), tab_center,
+                                    tab_center, ui::EventTimeForNow(), 0, 0);
+    tab_strip_->OnMouseWheel(wheel_event);
+
+    EXPECT_EQ(0, controller_->GetActiveIndex());
+    next_accumulated_offset += small_offset;
+  }
+
+  ui::MouseWheelEvent wheel_event(gfx::Vector2d(small_offset, 0), tab_center,
+                                  tab_center, ui::EventTimeForNow(), 0, 0);
+  tab_strip_->OnMouseWheel(wheel_event);
+  EXPECT_EQ(1, controller_->GetActiveIndex());
+}
+
 INSTANTIATE_TEST_SUITE_P(, TabStripTest, ::testing::Values(false, true));