Tiimer based phase info generated for mouse wheel events.

content/browser/renderer_host/render_widget_host_view_event_handler.cc

Index: content/browser/renderer_host/render_widget_host_view_event_handler.cc
diff --git a/content/browser/renderer_host/render_widget_host_view_event_handler.cc b/content/browser/renderer_host/render_widget_host_view_event_handler.cc
index 980a6780b411c34b8988b6bb93bf7d1c3dd833a0..dbbcd0a090c8fcaa5fcc5e144f46e7faf22b3b40 100644
--- a/content/browser/renderer_host/render_widget_host_view_event_handler.cc
+++ b/content/browser/renderer_host/render_widget_host_view_event_handler.cc
@@ -336,8 +336,12 @@ void RenderWidgetHostViewEventHandler::OnMouseEvent(ui::MouseEvent* event) {
     blink::WebMouseWheelEvent mouse_wheel_event =
         ui::MakeWebMouseWheelEvent(static_cast<ui::MouseWheelEvent&>(*event),
                                    base::Bind(&GetScreenLocationFromEvent));
+    bool should_route_event = ShouldRouteEvent(event);

[bokan, 2017/05/18 16:47:00]

Nit: move this inside the `if` block.

[sahel, 2017/05/18 18:15:14]

Done.

+
     if (mouse_wheel_event.delta_x != 0 || mouse_wheel_event.delta_y != 0) {
-      if (ShouldRouteEvent(event)) {
+      if (host_view_->wheel_scroll_latching_enabled())
+        AddSyntheticPhase(mouse_wheel_event, should_route_event);
+      if (should_route_event) {
         host_->delegate()->GetInputEventRouter()->RouteMouseWheelEvent(
             host_view_, &mouse_wheel_event, *event->latency());
       } else {
@@ -404,7 +408,11 @@ void RenderWidgetHostViewEventHandler::OnScrollEvent(ui::ScrollEvent* event) {
     gesture_event.y = event->y();
     blink::WebMouseWheelEvent mouse_wheel_event = ui::MakeWebMouseWheelEvent(
         *event, base::Bind(&GetScreenLocationFromEvent));
-    if (ShouldRouteEvent(event)) {
+
+    bool should_route_event = ShouldRouteEvent(event);
+    if (host_view_->wheel_scroll_latching_enabled())
+      AddSyntheticPhase(mouse_wheel_event, should_route_event);
+    if (should_route_event) {
       host_->delegate()->GetInputEventRouter()->RouteGestureEvent(
           host_view_, &gesture_event,
           ui::LatencyInfo(ui::SourceEventType::WHEEL));
@@ -419,15 +427,23 @@ void RenderWidgetHostViewEventHandler::OnScrollEvent(ui::ScrollEvent* event) {
              event->type() == ui::ET_SCROLL_FLING_CANCEL) {
     blink::WebGestureEvent gesture_event = ui::MakeWebGestureEvent(
         *event, base::Bind(&GetScreenLocationFromEvent));
-    if (ShouldRouteEvent(event)) {
+    bool should_route_event = ShouldRouteEvent(event);

[bokan, 2017/05/18 16:47:00]

Define this variable outside only once and use in both blocks.

[sahel, 2017/05/18 18:15:14]

Done.

+    if (should_route_event) {
       host_->delegate()->GetInputEventRouter()->RouteGestureEvent(
           host_view_, &gesture_event,
           ui::LatencyInfo(ui::SourceEventType::WHEEL));
     } else {
       host_->ForwardGestureEvent(gesture_event);
     }
-    if (event->type() == ui::ET_SCROLL_FLING_START)
+    if (event->type() == ui::ET_SCROLL_FLING_START) {
       RecordAction(base::UserMetricsAction("TrackpadScrollFling"));
+
+      if (mouse_wheel_phase_timer_.IsRunning()) {
+        // Stop the timer to avoid sending a synthetic wheel event with
+        // kPhaseEnded.
+        mouse_wheel_phase_timer_.Stop();

[bokan, 2017/05/18 16:47:00]

Is there any harm in calling Stop on a timer that isn't running? If not, remove
the `if`.

[sahel, 2017/05/18 18:15:15]

Done.

+      }
+    }
   }
 
   event->SetHandled();
@@ -519,18 +535,34 @@ void RenderWidgetHostViewEventHandler::OnGestureEvent(ui::GestureEvent* event) {
   }
 
   if (gesture.GetType() != blink::WebInputEvent::kUndefined) {
+    if (event->type() == ui::ET_GESTURE_SCROLL_BEGIN) {
+      RecordAction(base::UserMetricsAction("TouchscreenScroll"));
+
+      if (mouse_wheel_phase_timer_.IsRunning()) {
+        // If there is a current scroll going on and a new scroll that isn't
+        // wheel based send a synthetic wheel event with kPhaseEnded to cancel
+        // the current scroll.
+        base::Closure task = mouse_wheel_phase_timer_.user_task();
+        mouse_wheel_phase_timer_.Stop();
+        task.Run();
+      }
+    } else if (event->type() == ui::ET_GESTURE_SCROLL_END) {
+      // Make sure that the next wheel event will have phase = |kPhaseBegan|.
+      // This is for maintaining the correct phase info when some of the wheel
+      // events get ignored while a touchscreen scroll is going on.
+      if (mouse_wheel_phase_timer_.IsRunning()) {

[bokan, 2017/05/18 16:47:00]

If the wheel events are ignored while a touchscreen scroll is in progress, and
we stopped the timer when the touchscreen scroll started, how can this happen?

[sahel, 2017/05/18 18:15:15]

They will be still generated (with phase info) and sent to
mouse_wheel_event_queue, but there they will be ignored. It can happen when in
the middle of touch screen scrolling sequence we start wheel scrolling and then
we stop touch screen scrolling.

[bokan, 2017/05/19 15:52:59]

Acknowledged.

+        mouse_wheel_phase_timer_.Stop();
+      }
+    } else if (event->type() == ui::ET_SCROLL_FLING_START) {
+      RecordAction(base::UserMetricsAction("TouchscreenScrollFling"));
+    }
+
     if (ShouldRouteEvent(event)) {
       host_->delegate()->GetInputEventRouter()->RouteGestureEvent(
           host_view_, &gesture, *event->latency());
     } else {
       host_->ForwardGestureEventWithLatencyInfo(gesture, *event->latency());
     }
-
-    if (event->type() == ui::ET_GESTURE_SCROLL_BEGIN) {
-      RecordAction(base::UserMetricsAction("TouchscreenScroll"));
-    } else if (event->type() == ui::ET_SCROLL_FLING_START) {
-      RecordAction(base::UserMetricsAction("TouchscreenScrollFling"));
-    }
   }
 
   // If a gesture is not processed by the webpage, then WebKit processes it
@@ -887,4 +919,50 @@ void RenderWidgetHostViewEventHandler::ProcessTouchEvent(
   host_->ForwardTouchEventWithLatencyInfo(event, latency);
 }
 
+void RenderWidgetHostViewEventHandler::SendSyntheticWheelEventWithPhaseEnded(

[bokan, 2017/05/18 16:47:00]

Please add a DCHECK that touchpad latching is enabled here and in
AddSyntheticPhase.

[sahel, 2017/05/18 18:15:15]

Done.

+    blink::WebMouseWheelEvent last_mouse_wheel_event,
+    bool should_route_event) {
+  blink::WebMouseWheelEvent mouse_wheel_event = last_mouse_wheel_event;
+  mouse_wheel_event.delta_x = 0;
+  mouse_wheel_event.delta_y = 0;
+  mouse_wheel_event.phase = blink::WebMouseWheelEvent::kPhaseEnded;
+  mouse_wheel_event.dispatch_type =
+      blink::WebInputEvent::DispatchType::kEventNonBlocking;
+  if (should_route_event) {
+    host_->delegate()->GetInputEventRouter()->RouteMouseWheelEvent(
+        host_view_, &mouse_wheel_event,
+        ui::LatencyInfo(ui::SourceEventType::WHEEL));
+  } else {
+    ProcessMouseWheelEvent(mouse_wheel_event,
+                           ui::LatencyInfo(ui::SourceEventType::WHEEL));
+  }
+}
+
+void RenderWidgetHostViewEventHandler::AddSyntheticPhase(

[tdresser, 2017/05/18 13:49:05]

The name of this function doesn't make it clear that it might start a timer
which dispatches an event.

I haven't come up with a name I really like though.
Any ideas?

[bokan, 2017/05/18 16:47:00]

IMO, it doesn't matter that the phase is "synthetic" (it's synthetic by virtue
of us adding it here), I'd call this AddPhaseAndScheduleEndEvent. I'd also
rename the method to just "AddPhase".

[sahel, 2017/05/18 18:15:15]

Done.

[sahel, 2017/05/18 18:15:15]

I changed the name, it might be too long but is descriptive. 

[bokan, 2017/05/19 15:52:59]

We have (much) longer :)

+    blink::WebMouseWheelEvent& mouse_wheel_event,
+    bool should_route_event) {
+  DCHECK(mouse_wheel_event.phase == blink::WebMouseWheelEvent::kPhaseNone &&

[bokan, 2017/05/18 16:47:00]

Where do the Mac events that do have this go?

[sahel, 2017/05/18 18:15:15]

This event handler is aura only, mac events are handled in
render_widget_host_view_mac.mm

[bokan, 2017/05/19 15:52:59]

Acknowledged.

+         mouse_wheel_event.momentum_phase ==
+             blink::WebMouseWheelEvent::kPhaseNone);
+
+  if (!mouse_wheel_phase_timer_.IsRunning()) {
+    mouse_wheel_event.phase = blink::WebMouseWheelEvent::kPhaseBegan;
+    mouse_wheel_phase_timer_.Start(
+        FROM_HERE,
+        base::TimeDelta::FromMilliseconds(
+            kDefaultMouseWheelLatchingTransactionMs),
+        base::Bind(&RenderWidgetHostViewEventHandler::
+                       SendSyntheticWheelEventWithPhaseEnded,
+                   base::Unretained(this), mouse_wheel_event,
+                   should_route_event));
+  } else {
+    bool non_zero_delta =
+        mouse_wheel_event.delta_x || mouse_wheel_event.delta_y;
+    mouse_wheel_event.phase = non_zero_delta
+                                  ? blink::WebMouseWheelEvent::kPhaseChanged
+                                  : blink::WebMouseWheelEvent::kPhaseStationary;
+    mouse_wheel_phase_timer_.Reset();
+  }
+}
+
 }  // namespace content