Reset drag state variables on mouse up

third_party/WebKit/Source/core/input/EventHandler.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2012 Digia Plc. and/or its subsidiary(-ies)
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 414 matching lines @@
 {
     selectionController().updateSelectionForMouseDrag(m_mousePressNode.get(), m_dragStartPos, m_lastKnownMousePosition);
 }
 
 WebInputEventResult EventHandler::handleMouseReleaseEvent(const MouseEventWithHitTestResults& event)
 {
     AutoscrollController* controller = m_scrollManager.autoscrollController();
     if (controller && controller->autoscrollInProgress())
         m_scrollManager.stopAutoscroll();
 
-    // Used to prevent mouseMoveEvent from initiating a drag before
-    // the mouse is pressed again.
-    m_mousePressed = false;
-    m_capturesDragging = false;
-    m_mouseDownMayStartDrag = false;
-    m_mouseDownMayStartAutoscroll = false;
+    clearMouseDragState();
 
     return selectionController().handleMouseReleaseEvent(event, m_dragStartPos) ? WebInputEventResult::HandledSystem : WebInputEventResult::NotHandled;
 }
 
 #if OS(WIN)
 
 void EventHandler::startPanScrolling(LayoutObject* layoutObject)
 {
     if (!layoutObject->isBox())
         return;
@@ skipping 748 matching lines @@
                 event->stopPropagation();
 
             clickEventResult = toWebInputEventResult(clickTargetNode->dispatchEvent(event));
         }
     }
 
     m_scrollManager.clearResizeScrollableArea(false);
 
     if (eventResult == WebInputEventResult::NotHandled)
         eventResult = handleMouseReleaseEvent(mev);
+    else
+        clearMouseDragState();

[dtapuska, 2016/06/09 21:18:58]

what about the code path for gesture tap that has a similar flow?

Also there are a few places that assign m_mousePressed = false; do we need to
every clear the drag state in those?

I'm wondering if we took the code path out of handleMouseReleaseEvent and always
did the clearMouseDragState whether that would be more logical?

Or should we put an AutoReset like object on the stack of the
handleMouseReleaseEvent(...) so clearMouseDragState is always cleared at the end
of its return?

[mustaq, 2016/06/10 15:44:04]

handleMousePressEvent(MouseEventWithHitTestResults) is called from this method
and handleGestureTap. Clearing the state unconditionally at both these callers
should work (so we won't need it in
handleMousePressEvent(MouseEventWithHitTestResults).

[Navid Zolghadr, 2016/06/10 19:19:55]

I added the call as suggested to the tap flow as well.

To be honest with you I don't know about all those state variable. I need to
look deeper which was in my plan when I start refactoring the mouse code out of
EventHandler. So I don't have a good answer right now what each of these
variables mean.

Is calling the clean right from the function okay or do you like those object
cleanup methods?

[mustaq, 2016/06/10 19:30:16]

I am indifferent about AutoReset here, mainly for slightly better readability
w/o it. Dave's call.

 
     invalidateClick();
 
     return mergeEventResult(clickEventResult, eventResult);
 }
 
 WebInputEventResult EventHandler::dispatchDragEvent(const AtomicString& eventType, Node* dragTarget, const PlatformMouseEvent& event, DataTransfer* dataTransfer)
 {
     FrameView* view = m_frame->view();
 
@@ skipping 157 matching lines @@
     if (targetIsFrame(m_dragTarget.get(), targetFrame)) {
         if (targetFrame)
             result = targetFrame->eventHandler().performDragAndDrop(event, dataTransfer);
     } else if (m_dragTarget.get()) {
         result = dispatchDragEvent(EventTypeNames::drop, m_dragTarget.get(), event, dataTransfer);
     }
     clearDragState();
     return result;
 }
 
+void EventHandler::clearMouseDragState()
+{
+    // Used to prevent mouseMoveEvent from initiating a drag before
+    // the mouse is pressed again.
+    m_mousePressed = false;
+    m_capturesDragging = false;
+    m_mouseDownMayStartDrag = false;
+    m_mouseDownMayStartAutoscroll = false;
+}
+
 void EventHandler::clearDragState()
 {
     m_scrollManager.stopAutoscroll();
     m_dragTarget = nullptr;
     m_capturingMouseEventsNode = nullptr;
     m_shouldOnlyFireDragOverEvent = false;
 }
 
 void EventHandler::setCapturingMouseEventsNode(Node* n)
 {
@@ skipping 1427 matching lines @@
 
 FrameHost* EventHandler::frameHost() const
 {
     if (!m_frame->page())
         return nullptr;
 
     return &m_frame->page()->frameHost();
 }
 
 } // namespace blink