Fix draggable elements are painted at incorrect position

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 669 matching lines @@
         return false;
     // FIXME: Broken for OOPI.
     return toLocalFrame(parentFrame)->eventHandler().bubblingScroll(direction, granularity, m_frame->deprecatedLocalOwner());
 }
 
 IntPoint EventHandler::lastKnownMousePosition() const
 {
     return m_lastKnownMousePosition;
 }
 
+IntPoint EventHandler::dragDataTransferLocation()
+{
+    IntPoint loc;
+    if (dragState().m_dragDataTransfer) {

[fs, 2016/02/23 17:27:45]

if (...)
    return ...;
return IntPoint();

[hyunjunekim2, 2016/02/24 13:06:36]

Done.

+        loc = dragState().m_dragDataTransfer->dragLocation();
+    }
+    return loc;
+}
+
 static LocalFrame* subframeForTargetNode(Node* node)
 {
     if (!node)
         return nullptr;
 
     LayoutObject* layoutObject = node->layoutObject();
     if (!layoutObject || !layoutObject->isLayoutPart())
         return nullptr;
 
     Widget* widget = toLayoutPart(layoutObject)->widget();
@@ skipping 2612 matching lines @@
 bool EventHandler::tryStartDrag(const MouseEventWithHitTestResults& event)
 {
     // The DataTransfer would only be non-empty if we missed a dragEnd.
     // Clear it anyway, just to make sure it gets numbified.
     clearDragDataTransfer();
 
     dragState().m_dragDataTransfer = createDraggingDataTransfer();
 
     // Check to see if this a DOM based drag, if it is get the DOM specified drag
     // image and offset
     if (dragState().m_dragType == DragSourceActionDHTML) {

[fs, 2016/02/23 17:27:45]

(I wonder why this code isn't in DragController::populateDragDataTransfer like
the code for all the other types...)

[hyunjunekim2, 2016/02/24 12:00:07]

This is the report that is flow to draw dragged image simply.

1) There is |m_dragLoc| on DataTransfer. When call setDragImageElement function,
set |m_dragLoc| that is offset on the image.
2) Call |dataTransfer->createDragImage| on |DragController::startDrag| to get
dragOffset that is
|m_dragLoc| also to create image. And calcultate |dragLocation| with dragOffset.
3) Next call DragController::doSystemDrag with dragLocation and image created.
4) Call DragClientImpl::startDrag with dragLocation and image created.
5) finally call WebViewImpl::startDragging with dragLocation and image created.
I guess because of 1), 2) processes.

[hyunjunekim2, 2016/02/24 12:04:41]

Did you say that this codes need to transfer on
|DragController::populateDragDataTransfer|?

[fs, 2016/02/24 12:47:48]

No need to take any action on this - I was mostly thinking out aloud. (If
something were to be done about it, a separate CL would be the way to go
regardless.)

         if (LayoutObject* layoutObject = dragState().m_dragSrc->layoutObject()) {
-            FloatPoint absPos = layoutObject->localToAbsolute(FloatPoint(), UseTransforms);
+            IntRect boundingIncludingDescendants = layoutObject->absoluteBoundingBoxRectIncludingDescendants();

[fs, 2016/02/23 17:27:45]

I guess this makes sense since it's what LocalFrame::nodeImage uses.

+            FloatPoint absPos(boundingIncludingDescendants.x(), boundingIncludingDescendants.y());

[fs, 2016/02/23 17:27:45]

No need to do int -> float and then round to int again, so maybe just:

IntSize delta = m_mouseDownPos - boundingIncludingDescendants.location();

?

[hyunjunekim2, 2016/02/24 13:06:36]

Done.

             IntSize delta = m_mouseDownPos - roundedIntPoint(absPos);
             dragState().m_dragDataTransfer->setDragImageElement(dragState().m_dragSrc.get(), IntPoint(delta));
         } else {
             // The layoutObject has disappeared, this can happen if the onStartDrag handler has hidden
             // the element in some way. In this case we just kill the drag.
             return false;
         }
     }
 
     DragController& dragController = m_frame->page()->dragController();
@@ skipping 639 matching lines @@
 PlatformEvent::Modifiers EventHandler::accessKeyModifiers()
 {
 #if OS(MACOSX)
     return static_cast<PlatformEvent::Modifiers>(PlatformEvent::CtrlKey | PlatformEvent::AltKey);
 #else
     return PlatformEvent::AltKey;
 #endif
 }
 
 } // namespace blink