Articulate the cancel behavior in the WebTouchEvent.

content/common/input/web_input_event_traits.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/common/input/web_input_event_traits.h"
 
 #include <bitset>
 #include <limits>
 
 #include "base/logging.h"
@@ skipping 93 matching lines @@
   point.radiusX,
   point.radiusY,
   point.rotationAngle,
   point.force,
   point.tiltX,
   point.tiltY);
 }
 
 void ApppendEventDetails(const WebTouchEvent& event, std::string* result) {
   StringAppendF(result,
-                "{\n Touches: %u, Cancelable: %d, CausesScrolling: %d,"
+                "{\n Touches: %u, DispatchType: %d, CausesScrolling: %d,"
                 " uniqueTouchEventId: %u\n[\n",
-                event.touchesLength, event.cancelable,
+                event.touchesLength, event.dispatchType,
                 event.movedBeyondSlopRegion, event.uniqueTouchEventId);
   for (unsigned i = 0; i < event.touchesLength; ++i)
     ApppendTouchPointDetails(event.touches[i], result);
   result->append(" ]\n}");
 }
 
 bool CanCoalesce(const WebKeyboardEvent& event_to_coalesce,
                  const WebKeyboardEvent& event) {
   return false;
 }
@@ skipping 65 matching lines @@
 
 // Returns |kInvalidTouchIndex| iff |event| lacks a touch with an ID of |id|.
 int GetIndexOfTouchID(const WebTouchEvent& event, int id) {
   for (unsigned i = 0; i < event.touchesLength; ++i) {
     if (event.touches[i].id == id)
       return i;
   }
   return kInvalidTouchIndex;
 }
 
+WebInputEvent::DispatchType MergeDispatchTypes(
+    WebInputEvent::DispatchType type_1,
+    WebInputEvent::DispatchType type_2) {
+  static_assert(WebInputEvent::DispatchType::Blocking <
+                    WebInputEvent::DispatchType::EventNonBlocking,
+                "Enum not ordered correctly");
+  static_assert(WebInputEvent::DispatchType::EventNonBlocking <
+                    WebInputEvent::DispatchType::ListenersNonBlockingPassive,
+                "Enum not ordered correctly");
+  static_assert(
+      WebInputEvent::DispatchType::ListenersNonBlockingPassive <
+          WebInputEvent::DispatchType::ListenersForcedNonBlockingPassive,
+      "Enum not ordered correctly");
+  return static_cast<WebInputEvent::DispatchType>(
+      std::min(static_cast<int>(type_1), static_cast<int>(type_2)));
+}
+
 bool CanCoalesce(const WebTouchEvent& event_to_coalesce,
                  const WebTouchEvent& event) {
   if (event.type != event_to_coalesce.type ||
       event.type != WebInputEvent::TouchMove ||
       event.modifiers != event_to_coalesce.modifiers ||
       event.touchesLength != event_to_coalesce.touchesLength ||
       event.touchesLength > WebTouchEvent::touchesLengthCap)
     return false;
 
   static_assert(WebTouchEvent::touchesLengthCap <= sizeof(int32_t) * 8U,
@@ skipping 22 matching lines @@
   // 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) {
     int i_old = GetIndexOfTouchID(old_event, event->touches[i].id);
     if (old_event.touches[i_old].state == blink::WebTouchPoint::StateMoved)
       event->touches[i].state = blink::WebTouchPoint::StateMoved;
   }
   event->movedBeyondSlopRegion |= old_event.movedBeyondSlopRegion;
+  event->dispatchType = MergeDispatchTypes(old_event.dispatchType,
+                                           event_to_coalesce.dispatchType);
 }
 
 bool CanCoalesce(const WebGestureEvent& event_to_coalesce,
                  const WebGestureEvent& event) {
   if (event.type != event_to_coalesce.type ||
       event.sourceDevice != event_to_coalesce.sourceDevice ||
       event.modifiers != event_to_coalesce.modifiers)
     return false;
 
   if (event.type == WebInputEvent::GestureScrollUpdate)
@@ skipping 221 matching lines @@
     case WebInputEvent::MouseLeave:
     case WebInputEvent::ContextMenu:
     case WebInputEvent::GestureScrollBegin:
     case WebInputEvent::GestureScrollEnd:
     case WebInputEvent::GestureShowPress:
     case WebInputEvent::GestureTapUnconfirmed:
     case WebInputEvent::GestureTapDown:
     case WebInputEvent::GestureTapCancel:
     case WebInputEvent::GesturePinchBegin:
     case WebInputEvent::GesturePinchEnd:
+      return false;
+
+    // TouchCancel and TouchScrollStarted should always be non-blocking.
     case WebInputEvent::TouchCancel:
     case WebInputEvent::TouchScrollStarted:
+      DCHECK_NE(WebInputEvent::Blocking,
+                static_cast<const WebTouchEvent&>(event).dispatchType);
       return false;
+
+    // Touch start and touch end indicate whether they are non-blocking
+    // (aka uncancelable) on the event.
     case WebInputEvent::TouchStart:
     case WebInputEvent::TouchEnd:
-      return static_cast<const WebTouchEvent&>(event).cancelable;
+      return static_cast<const WebTouchEvent&>(event).dispatchType ==
+             WebInputEvent::Blocking;
+
+    // Touch move events may be non-blocking but are always explicitly
+    // acknowledge by the renderer so they block the event stream.
+    case WebInputEvent::TouchMove:
     default:
       return true;
   }
 }
 
 uint32_t WebInputEventTraits::GetUniqueTouchEventId(
     const WebInputEvent& event) {
   if (WebInputEvent::isTouchEventType(event.type)) {
     return static_cast<const WebTouchEvent&>(event).uniqueTouchEventId;
   }
   return 0U;
 }
 
 }  // namespace content