Fix draggable elements are painted at incorrect position

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

Index: third_party/WebKit/Source/core/input/EventHandler.cpp
diff --git a/third_party/WebKit/Source/core/input/EventHandler.cpp b/third_party/WebKit/Source/core/input/EventHandler.cpp
index 188d4c4fab19cba46bedd6102aa61ee868924cc9..473a8be7f44e7aa28979d11104a0266b6bedd417 100644
--- a/third_party/WebKit/Source/core/input/EventHandler.cpp
+++ b/third_party/WebKit/Source/core/input/EventHandler.cpp
@@ -687,6 +687,15 @@ 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)
@@ -3321,7 +3330,8 @@ bool EventHandler::tryStartDrag(const MouseEventWithHitTestResults& event)
     // 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 {