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..c4e908fc6bc0e3c656f8fd0640ffa90209072e31 100644
--- a/content/common/input/web_input_event_traits.cc
+++ b/content/common/input/web_input_event_traits.cc
@@ -16,50 +16,185 @@ using WebKit::WebTouchEvent;
 namespace content {
 namespace {
 
+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)

[aelias_OOO_until_Jul13, 2013/10/14 03:38:57]

I know you're just moving this, but this kind of divide-by-zero avoidance is
usually an error.  It would be better to DCHECK it's nonzero.

[jdduke (slow), 2013/10/14 17:03:18]

Hmm, normally I'd agree, but it looks like they're using the wheel deltaX/Y as
arguments here, which may very well be zero.   In that case, the formula really
doesn't make sense, but... I could add guards before the function? Or maybe I'll
just move the function closer to where it's used.

+    return 1.f;
+  return unaccelerated_delta / accelerated_delta;
+}
+
+bool TryCoalesce(const WebKeyboardEvent& event_to_coalesce,
+                 WebKeyboardEvent* event) {
+  return false;
+}
+
+bool TryCoalesce(const WebMouseEvent& event_to_coalesce, WebMouseEvent* event) {
+  if (event->type != event_to_coalesce.type)
+    return false;
+
+  if (event->type != WebInputEvent::MouseMove)
+    return false;
+
+  // Accumulate movement deltas.
+  int x = event->movementX;
+  int y = event->movementY;
+  *event = event_to_coalesce;
+  event->movementX += x;
+  event->movementY += y;
+  return true;
+}
+
+bool TryCoalesce(const WebMouseWheelEvent& event_to_coalesce,
+                 WebMouseWheelEvent* event) {
+  if (event->modifiers != event_to_coalesce.modifiers)
+    return false;
+
+  if (event->scrollByPage != event_to_coalesce.scrollByPage)
+    return false;
+
+  if (event->hasPreciseScrollingDeltas !=
+      event_to_coalesce.hasPreciseScrollingDeltas)
+    return false;
+
+  if (event->phase != event_to_coalesce.phase)
+    return false;
+
+  if (event->momentumPhase != event_to_coalesce.momentumPhase)
+    return false;
+
+  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;
+  return true;
+}
+
+bool TryCoalesce(const WebTouchEvent& event_to_coalesce, WebTouchEvent* event) {
+  if (event->type != event_to_coalesce.type)
+    return false;
+
+  if (event->type != WebInputEvent::TouchMove)
+    return false;
+
+  if (event->modifiers != event_to_coalesce.modifiers)
+    return false;
+
+  if (event->touchesLength != event_to_coalesce.touchesLength)
+    return false;
+
+  // 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;
+  }
+  return true;
+}
+
+bool TryCoalesce(const WebGestureEvent& event_to_coalesce,
+                 WebGestureEvent* event) {
+  if (event->type != event_to_coalesce.type)
+    return false;
+
+  if (event->type == WebInputEvent::GestureScrollUpdate) {
+    if (event->modifiers != event_to_coalesce.modifiers)
+      return false;
+    event->data.scrollUpdate.deltaX +=
+        event_to_coalesce.data.scrollUpdate.deltaX;
+    event->data.scrollUpdate.deltaY +=
+        event_to_coalesce.data.scrollUpdate.deltaY;
+    return true;
+  }
+
+  // TODO(jdduke): Add support for pinch gesture coalescing.
+  return false;
+}
+
 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 WebInputEventCoalesce {
+  tempalte <class EventType>
+  bool Execute(const WebInputEvent& event_to_coalesce,
+               WebInputEvent* event) const {
+    DCHECK_EQ(event_to_coalesce.type, event->type)
+    DCHECK_EQ(sizeof(EventType), event->size);
+    DCHECK_EQ(sizeof(EventType), event_to_coalesce.size);
+    return TryCoalesce(static_cast<const EventType&>(event_to_coalesce),
+                       static_cast<EventType*>(event));
   }
 };
 
 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 +218,11 @@ void WebInputEventTraits::Delete(WebInputEvent* event) {
   Apply(WebInputEventDelete(), event->type, event, &dummy_var);
 }
 
+bool WebInputEventTraits::TryCoalesce(const WebInputEvent& event_to_coalesce,
+                                      WebInputEvent* event) {
+  if (!event || event_to_coalesce.type != event->type)
+    return false;
+  return Apply(WebInputEventCoalesce(), event->type, event_to_coalesce, event);
+}
+
 }  // namespace content