Fix invalid selection produced when dragging mouse outside the SVG text element

third_party/WebKit/Source/core/layout/svg/SVGLayoutSupport.cpp

 /*
  * Copyright (C) 2007, 2008 Rob Buis <buis@kde.org>
  * Copyright (C) 2007 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2007 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2009 Google, Inc.  All rights reserved.
  * Copyright (C) 2009 Dirk Schulze <krit@webkit.org>
  * Copyright (C) Research In Motion Limited 2009-2010. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 458 matching lines @@
     ASSERT(layoutObject);
 
     // FIXME: trying to compute a device space transform at record time is wrong. All clients
     // should be updated to avoid relying on this information, and the method should be removed.
     AffineTransform ctm = deprecatedCalculateTransformToLayer(layoutObject) * SubtreeContentTransformScope::currentContentTransformation();
     ctm.scale(layoutObject->document().frameHost()->deviceScaleFactor());
 
     return narrowPrecisionToFloat(sqrt((pow(ctm.xScale(), 2) + pow(ctm.yScale(), 2)) / 2));
 }
 
+LayoutObject* SVGLayoutSupport::findSelectedLayoutSVGText(LayoutObject* layoutObject, const FloatPoint point)

[fs, 2016/01/18 12:44:11]

"Selected" doesn't seem like the correct term here. Maybe "nearest" or "closest"
would be better.

+{
+    LayoutObject* closestLayoutObject = nullptr;
+    float closestDistance = std::numeric_limits<float>::max();
+    Vector<LayoutObject*> overlappedObjects;
+    for (LayoutObject* child = layoutObject->slowLastChild(); child; child = child->previousSibling()) {
+        if (!child->isSVGContainer() && !child->isSVGText())
+            continue;
+        if (child->isSVGContainer() && child->isSVGHiddenContainer())

[fs, 2016/01/18 12:44:11]

No need to check isSVGContainer() again. It would really be preferable to have
this in the same check as the above. If you find this tricky to get right/rad,
just add a helper function.

+            continue;
+
+        FloatRect bound = child->objectBoundingBox();

[fs, 2016/01/18 12:44:11]

Move down to just before you need it and rename to "boundingBox" or something a
little more verbose.

+
+        if (!child->localToParentTransform().isInvertible())
+            continue;
+
+        FloatPoint childLocalPoint = child->localToParentTransform().inverse().mapPoint(point);
+        float distance = bound.squaredDistanceTo(childLocalPoint);
+
+        if (distance < closestDistance) {
+            // If child is overlapped by closesLayoutObject, It's candiate to search sub-tree.

[fs, 2016/01/18 12:44:11]

Lot's of typos that needs fixing here ("closesLayoutObject"; "It's"; "candiate",
etc)

I also think that it might be better to have a comment like this either at the
top of the function - describing the what it's intended to do - maybe at a
higher level - and then shorter ones describing each step. 

+            // When closestLayoutObject' sub-tree hasn't LayoutSVGText object, try to search
+            // on the sub-tree which store on vector called `overlappedObjects`.
+            if (closestLayoutObject && bound.contains(closestLayoutObject->objectBoundingBox())) {

[fs, 2016/01/18 12:44:11]

I don't quite see why the "overlapped" property matters - the distance is what
will matter for the "nearest" property. Unless you have a different strategy (in
which case you should document the "why".) Also consider a case where a <text>
is found in this stage and a container is considered to be "closer" by the
metric. Maybe it would be reasonable to visit "distance == 0" LayoutObjects
directly and only "queue" LayoutObjects with "distance > 0" of something?

+                overlappedObjects.append(child);
+                continue;
+            }
+
+            overlappedObjects.clear();
+
+            closestLayoutObject = child;
+            closestDistance = distance;
+        }
+    }
+
+    if (!closestLayoutObject || closestLayoutObject->isSVGText())
+        return closestLayoutObject;
+
+    FloatPoint absolutePoint = closestLayoutObject->localToParentTransform().inverse().mapPoint(point);
+    LayoutObject* result  = findSelectedLayoutSVGText(closestLayoutObject, absolutePoint);

[fs, 2016/01/18 12:44:11]

if (LayoutObject* result = ...)
    return result;

and then you can de-indent the following for-loop. It might also make sense to
just let |closestLayoutObject| be the first in the vector and handle it in the
loop with all the other candidates.

+
+    // No found LayoutSVGText on closest subtree, after all try to search on the sub-tree which store
+    // on vector called `overlappedObjects`.
+    if (!result) {
+        for (LayoutObject* overlappedObject : overlappedObjects) {
+            absolutePoint = overlappedObject->localToParentTransform().inverse().mapPoint(point);
+            result = findSelectedLayoutSVGText(overlappedObject, absolutePoint);
+            if (result)
+                break;
+        }
+    }
+
+    return result;
 }
+
+}