Consolidate WebInputEvent coalescing logic

content/common/input/web_input_event_traits.cc

Index: content/common/input/web_input_event_traits.cc
diff --git a/content/common/input/web_input_event_traits.cc b/content/common/input/web_input_event_traits.cc
index 15c334bc01da7497e640a03c3f7427a7ec86169c..e7406c8cb86c085bf233bb39da4340b1d4025c85 100644
--- a/content/common/input/web_input_event_traits.cc
+++ b/content/common/input/web_input_event_traits.cc
@@ -16,50 +16,182 @@ using WebKit::WebTouchEvent;
 namespace content {
 namespace {
 
+bool CanCoalesce(const WebKeyboardEvent& event_to_coalesce,
+                 const WebKeyboardEvent& event) {
+  return false;
+}
+
+void Coalesce(const WebKeyboardEvent& event_to_coalesce,
+              WebKeyboardEvent* event) {
+  NOTREACHED() << "Keyboard coalescing not possible.";
+}
+
+bool CanCoalesce(const WebMouseEvent& event_to_coalesce,
+                 const WebMouseEvent& event) {
+  return event.type == event_to_coalesce.type &&
+         event.type == WebInputEvent::MouseMove;
+}
+
+void Coalesce(const WebMouseEvent& event_to_coalesce, WebMouseEvent* event) {
+  // Accumulate movement deltas.
+  int x = event->movementX;

[aelias_OOO_until_Jul13, 2013/10/14 19:05:58]

Please add DCHECK(CanCoalesce(event_to_coalsece, *event)); here and in the
others.

[jdduke (slow), 2013/10/14 19:10:12]

OK.  I had the DCHECK in WebInputEventTraits::Coalesce, but maybe having it
closer to the end usage is better.

+  int y = event->movementY;
+  *event = event_to_coalesce;
+  event->movementX += x;
+  event->movementY += y;
+}
+
+bool CanCoalesce(const WebMouseWheelEvent& event_to_coalesce,
+                 const WebMouseWheelEvent& event) {
+  return event.modifiers == event_to_coalesce.modifiers &&
+         event.scrollByPage == event_to_coalesce.scrollByPage &&
+         event.phase == event_to_coalesce.phase &&
+         event.momentumPhase == event_to_coalesce.momentumPhase &&
+         event.hasPreciseScrollingDeltas ==
+             event_to_coalesce.hasPreciseScrollingDeltas;
+}
+
+float GetUnacceleratedDelta(float accelerated_delta, float acceleration_ratio) {
+  return accelerated_delta * acceleration_ratio;
+}
+
+float GetAccelerationRatio(float accelerated_delta, float unaccelerated_delta) {
+  if (unaccelerated_delta == 0.f || accelerated_delta == 0.f)
+    return 1.f;
+  return unaccelerated_delta / accelerated_delta;
+}
+
+void Coalesce(const WebMouseWheelEvent& event_to_coalesce,
+              WebMouseWheelEvent* event) {
+  float unaccelerated_x =
+      GetUnacceleratedDelta(event->deltaX,
+                            event->accelerationRatioX) +
+      GetUnacceleratedDelta(event_to_coalesce.deltaX,
+                            event_to_coalesce.accelerationRatioX);
+  float unaccelerated_y =
+      GetUnacceleratedDelta(event->deltaY,
+                            event->accelerationRatioY) +
+      GetUnacceleratedDelta(event_to_coalesce.deltaY,
+                            event_to_coalesce.accelerationRatioY);
+  event->deltaX += event_to_coalesce.deltaX;
+  event->deltaY += event_to_coalesce.deltaY;
+  event->wheelTicksX += event_to_coalesce.wheelTicksX;
+  event->wheelTicksY += event_to_coalesce.wheelTicksY;
+  event->accelerationRatioX =
+      GetAccelerationRatio(event->deltaX, unaccelerated_x);
+  event->accelerationRatioY =
+      GetAccelerationRatio(event->deltaY, unaccelerated_y);
+  DCHECK_GE(event_to_coalesce.timeStampSeconds, event->timeStampSeconds);
+  event->timeStampSeconds = event_to_coalesce.timeStampSeconds;
+}
+
+bool CanCoalesce(const WebTouchEvent& event_to_coalesce,
+                 const WebTouchEvent& event) {
+  return event.type == event_to_coalesce.type &&
+         event.type == WebInputEvent::TouchMove &&
+         event.modifiers == event_to_coalesce.modifiers &&
+         event.touchesLength == event_to_coalesce.touchesLength;
+}
+
+void Coalesce(const WebTouchEvent& event_to_coalesce, WebTouchEvent* event) {
+  // The WebTouchPoints include absolute position information. So it is
+  // sufficient to simply replace the previous event with the new event->
+  // However, it is necessary to make sure that all the points have the
+  // correct state, i.e. the touch-points that moved in the last event, but
+  // didn't change in the current event, will have Stationary state. It is
+  // necessary to change them back to Moved state.
+  WebTouchEvent old_event = *event;
+  *event = event_to_coalesce;
+  for (unsigned i = 0; i < event->touchesLength; ++i) {
+    if (old_event.touches[i].state == WebKit::WebTouchPoint::StateMoved)
+      event->touches[i].state = WebKit::WebTouchPoint::StateMoved;
+  }
+}
+
+bool CanCoalesce(const WebGestureEvent& event_to_coalesce,
+                 const WebGestureEvent& event) {
+  return event.type == event_to_coalesce.type &&
+         event.type == WebInputEvent::GestureScrollUpdate &&
+         event.modifiers == event_to_coalesce.modifiers;
+}
+
+void Coalesce(const WebGestureEvent& event_to_coalesce,
+              WebGestureEvent* event) {
+  event->data.scrollUpdate.deltaX += event_to_coalesce.data.scrollUpdate.deltaX;
+  event->data.scrollUpdate.deltaY += event_to_coalesce.data.scrollUpdate.deltaY;
+}
+
 struct WebInputEventSize {
   template <class EventType>
-  void Execute(WebInputEvent::Type /* type */, size_t* type_size) const {
+  bool Execute(WebInputEvent::Type /* type */, size_t* type_size) const {
     *type_size = sizeof(EventType);
+    return true;
   }
 };
 
 struct WebInputEventClone {
   template <class EventType>
-  void Execute(const WebInputEvent& event,
+  bool Execute(const WebInputEvent& event,
                ScopedWebInputEvent* scoped_event) const {
     DCHECK_EQ(sizeof(EventType), event.size);
     *scoped_event = ScopedWebInputEvent(
         new EventType(static_cast<const EventType&>(event)));
+    return true;
   }
 };
 
 struct WebInputEventDelete {
   template <class EventType>
-  void Execute(WebInputEvent* event, bool* /* dummy_var */) const {
+  bool Execute(WebInputEvent* event, bool* /* dummy_var */) const {
     if (!event)
-      return;
+      return false;
     DCHECK_EQ(sizeof(EventType), event->size);
     delete static_cast<EventType*>(event);
+    return true;
+  }
+};
+
+struct WebInputEventCanCoalesce {
+  template <class EventType>
+  bool Execute(const WebInputEvent& event_to_coalesce,
+               const WebInputEvent* event) const {
+    if (event_to_coalesce.type != event->type)
+      return false;
+    DCHECK_EQ(sizeof(EventType), event->size);
+    DCHECK_EQ(sizeof(EventType), event_to_coalesce.size);
+    return CanCoalesce(static_cast<const EventType&>(event_to_coalesce),
+                       *static_cast<const EventType*>(event));
+  }
+};
+
+struct WebInputEventCoalesce {
+  template <class EventType>
+  bool Execute(const WebInputEvent& event_to_coalesce,
+               WebInputEvent* event) const {
+    Coalesce(static_cast<const EventType&>(event_to_coalesce),
+             static_cast<EventType*>(event));
+    return true;
   }
 };
 
 template <typename Operator, typename ArgIn, typename ArgOut>
-void Apply(Operator op,
+bool Apply(Operator op,
            WebInputEvent::Type type,
            const ArgIn& arg_in,
            ArgOut* arg_out) {
   if (WebInputEvent::isMouseEventType(type))
-    op.template Execute<WebMouseEvent>(arg_in, arg_out);
+    return op.template Execute<WebMouseEvent>(arg_in, arg_out);
   else if (type == WebInputEvent::MouseWheel)
-    op.template Execute<WebMouseWheelEvent>(arg_in, arg_out);
+    return op.template Execute<WebMouseWheelEvent>(arg_in, arg_out);
   else if (WebInputEvent::isKeyboardEventType(type))
-    op.template Execute<WebKeyboardEvent>(arg_in, arg_out);
+    return op.template Execute<WebKeyboardEvent>(arg_in, arg_out);
   else if (WebInputEvent::isTouchEventType(type))
-    op.template Execute<WebTouchEvent>(arg_in, arg_out);
+    return op.template Execute<WebTouchEvent>(arg_in, arg_out);
   else if (WebInputEvent::isGestureEventType(type))
-    op.template Execute<WebGestureEvent>(arg_in, arg_out);
-  else
-    NOTREACHED() << "Unknown webkit event type " << type;
+    return op.template Execute<WebGestureEvent>(arg_in, arg_out);
+
+  NOTREACHED() << "Unknown webkit event type " << type;
+  return false;
 }
 
 }  // namespace
@@ -83,4 +215,22 @@ void WebInputEventTraits::Delete(WebInputEvent* event) {
   Apply(WebInputEventDelete(), event->type, event, &dummy_var);
 }
 
+bool WebInputEventTraits::CanCoalesce(const WebInputEvent& event_to_coalesce,
+                                      const WebInputEvent& event) {
+  // Early out before casting.
+  if (event_to_coalesce.type != event.type)
+    return false;
+  return Apply(WebInputEventCanCoalesce(),
+               event.type,
+               event_to_coalesce,
+               &event);
+}
+
+void WebInputEventTraits::Coalesce(const WebInputEvent& event_to_coalesce,
+                                   WebInputEvent* event) {
+  DCHECK(event);
+  DCHECK(CanCoalesce(event_to_coalesce, *event));
+  Apply(WebInputEventCoalesce(), event->type, event_to_coalesce, event);
+}
+
 }  // namespace content