exo: Replace fling cancel with generic zero distance scroll

This change will suppress all fling cancel events unless the last event
was a fling event. Also it generates a proper sequence of a scroll
event with zero distance.

BUG=590754
TEST=Fling and touch the touchpad after fling. Should stop scrolling
motion in android apps.

Review-Url: https://codereview.chromium.org/2840113002
Cr-Commit-Position: refs/heads/master@{#469403}

components/exo/pointer.cc

@@ -207,13 +207,26 @@ void Pointer::OnMouseEvent(ui::MouseEvent* event) {
       break;
     }
     case ui::ET_SCROLL_FLING_START: {
+      // Fling start in chrome signals the lifting of fingers after scrolling.
+      // In wayland terms this signals the end of a scroll sequence.
       delegate_->OnPointerScrollStop(event->time_stamp());
       delegate_->OnPointerFrame();
       break;
     }
     case ui::ET_SCROLL_FLING_CANCEL: {
-      delegate_->OnPointerScrollCancel(event->time_stamp());
-      delegate_->OnPointerFrame();
+      // Fling cancel is generated very generously at every touch of the
+      // touchpad. Since it's not directly supported by the delegate, we do not
+      // want limit this event to only right after a fling start has been
+      // generated to prevent erronous behavior.
+      if (last_event_type_ == ui::ET_SCROLL_FLING_START) {
+        // We emulate fling cancel by starting a new scroll sequence that
+        // scrolls by 0 pixels, effectively stopping any kinetic scroll motion.
+        delegate_->OnPointerScroll(event->time_stamp(), gfx::Vector2dF(),
+                                   false);
+        delegate_->OnPointerFrame();
+        delegate_->OnPointerScrollStop(event->time_stamp());
+        delegate_->OnPointerFrame();
+      }
       break;
     }
     case ui::ET_MOUSE_MOVED:
@@ -227,6 +240,7 @@ void Pointer::OnMouseEvent(ui::MouseEvent* event) {
       break;
   }
 
+  last_event_type_ = event->type();
   UpdateCursorScale();
 }
 

components/exo/pointer.h

@@ -14,6 +14,7 @@
 #include "components/exo/surface_observer.h"
 #include "components/exo/wm_helper.h"
 #include "ui/base/cursor/cursor.h"
+#include "ui/events/event_constants.h"
 #include "ui/events/event_handler.h"
 #include "ui/gfx/geometry/point.h"
 #include "ui/gfx/geometry/point_f.h"
@@ -107,6 +108,9 @@ class Pointer : public ui::EventHandler,
   // Source used for cursor capture copy output requests.
   const base::UnguessableToken cursor_capture_source_id_;
 
+  // Last received event type.
+  ui::EventType last_event_type_ = ui::ET_UNKNOWN;
+
   // Weak pointer factory used for cursor capture callbacks.
   base::WeakPtrFactory<Pointer> cursor_capture_weak_ptr_factory_;
 

components/exo/pointer_delegate.h

@@ -56,9 +56,6 @@ class PointerDelegate {
                                const gfx::Vector2dF& offset,
                                bool discrete) = 0;
 
-  // Called when a current kinetic scroll should be canceled.
-  virtual void OnPointerScrollCancel(base::TimeTicks time_stamp) = 0;
-
   // Called when pointer scroll has stopped and a fling is happening (e.g.
   // lifting the fingers from the touchpad after scrolling quickly)
   virtual void OnPointerScrollStop(base::TimeTicks time_stamp) = 0;

components/exo/pointer_unittest.cc

@@ -37,7 +37,6 @@ class MockPointerDelegate : public PointerDelegate {
   MOCK_METHOD3(OnPointerButton, void(base::TimeTicks, int, bool));
   MOCK_METHOD3(OnPointerScroll,
                void(base::TimeTicks, const gfx::Vector2dF&, bool));
-  MOCK_METHOD1(OnPointerScrollCancel, void(base::TimeTicks));
   MOCK_METHOD1(OnPointerScrollStop, void(base::TimeTicks));
   MOCK_METHOD0(OnPointerFrame, void());
 };
@@ -245,7 +244,7 @@ TEST_F(PointerTest, OnPointerScroll) {
 
   EXPECT_CALL(delegate, CanAcceptPointerEventsForSurface(surface.get()))
       .WillRepeatedly(testing::Return(true));
-  EXPECT_CALL(delegate, OnPointerFrame()).Times(4);
+  EXPECT_CALL(delegate, OnPointerFrame()).Times(3);
 
   EXPECT_CALL(delegate, OnPointerEnter(surface.get(), gfx::PointF(), 0));
   generator.MoveMouseTo(location);
@@ -254,7 +253,6 @@ TEST_F(PointerTest, OnPointerScroll) {
     // Expect fling stop followed by scroll and scroll stop.
     testing::InSequence sequence;
 
-    EXPECT_CALL(delegate, OnPointerScrollCancel(testing::_));
     EXPECT_CALL(delegate,
                 OnPointerScroll(testing::_, gfx::Vector2dF(1.2, 1.2), false));
     EXPECT_CALL(delegate, OnPointerScrollStop(testing::_));
@@ -352,7 +350,6 @@ TEST_F(PointerTest, IgnorePointerEventDuringModal) {
 
   {
     testing::InSequence sequence;
-    EXPECT_CALL(delegate, OnPointerScrollCancel(testing::_));
     EXPECT_CALL(delegate,
                 OnPointerScroll(testing::_, gfx::Vector2dF(1.2, 1.2), false));
     EXPECT_CALL(delegate, OnPointerScrollStop(testing::_));
@@ -393,7 +390,6 @@ TEST_F(PointerTest, IgnorePointerEventDuringModal) {
 
   {
     testing::InSequence sequence;
-    EXPECT_CALL(delegate, OnPointerScrollCancel(testing::_)).Times(0);
     EXPECT_CALL(delegate,
                 OnPointerScroll(testing::_, gfx::Vector2dF(1.2, 1.2), false))
         .Times(0);
@@ -435,7 +431,6 @@ TEST_F(PointerTest, IgnorePointerEventDuringModal) {
 
   {
     testing::InSequence sequence;
-    EXPECT_CALL(delegate, OnPointerScrollCancel(testing::_));
     EXPECT_CALL(delegate,
                 OnPointerScroll(testing::_, gfx::Vector2dF(1.2, 1.2), false));
     EXPECT_CALL(delegate, OnPointerScrollStop(testing::_));

components/exo/wayland/server.cc

@@ -2661,12 +2661,6 @@ class WaylandPointerDelegate : public PointerDelegate {
                          WL_POINTER_AXIS_VERTICAL_SCROLL,
                          wl_fixed_from_double(-y_value));
   }
-  void OnPointerScrollCancel(base::TimeTicks time_stamp) override {
-    // Wayland doesn't know the concept of a canceling kinetic scrolling.
-    // But we can send a 0 distance scroll to emulate this behavior.
-    OnPointerScroll(time_stamp, gfx::Vector2dF(0, 0), false);
-    OnPointerScrollStop(time_stamp);
-  }
   void OnPointerScrollStop(base::TimeTicks time_stamp) override {
     if (wl_resource_get_version(pointer_resource_) >=
         WL_POINTER_AXIS_STOP_SINCE_VERSION) {