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 26 matching lines @@
 #include "core/layout/svg/LayoutSVGViewportContainer.h"
 #include "core/layout/svg/SVGResources.h"
 #include "core/layout/svg/SVGResourcesCache.h"
 #include "core/paint/PaintLayer.h"
 #include "core/svg/SVGElement.h"
 #include "platform/geometry/TransformState.h"
 #include "platform/graphics/StrokeData.h"
 
 namespace blink {
 
+struct SearchCandidate {
+public:
+    SearchCandidate() {}
+    SearchCandidate(LayoutObject* layoutObject, float dist)
+        : candidateLayoutObject(layoutObject)
+        , distance(dist)
+    {
+    }
+    LayoutObject* candidateLayoutObject;
+    float distance;
+};
+
 static inline LayoutRect adjustedEnclosingIntRect(const FloatRect& rect,
     const AffineTransform& rootTransform, float strokeWidthForHairlinePadding)
 {
     FloatRect adjustedRect = rect;
 
     if (strokeWidthForHairlinePadding) {
         // For hairline strokes (stroke-width < 1 in device space), Skia rasterizes up to 0.4(9) off
         // the stroke center. That means enclosingIntRect is not enough - we must also pad to 0.5.
         // This is still fragile as it misses out on CC/DSF CTM components.
         const FloatSize strokeSize = rootTransform.mapSize(
@@ skipping 412 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));
 }
 
+static inline bool compareCandidateDistance(const SearchCandidate& r1, const SearchCandidate& r2)
+{
+    return r1.distance < r2.distance;
 }
+
+LayoutObject* SVGLayoutSupport::findClosestLayoutSVGText(LayoutObject* layoutObject, const FloatPoint& point)
+{
+    // Try to search closest LayoutSVGText on sub-tree of |layoutObject|.

[fs, 2016/01/21 15:32:02]

Comments could use some touch-up. (I'd prefer not to "micro-manage" them.)

+    // On this level of tree, try to find the closest LayoutSVGText. If not find this level, try to search
+    // next level which is candidates.
+    LayoutObject* closestLayoutObject = nullptr;
+    float closestDistance = std::numeric_limits<float>::max();
+    Vector<SearchCandidate> candidates;
+    for (LayoutObject* child = layoutObject->slowLastChild(); child; child = child->previousSibling()) {
+        if (child->isSVGHiddenContainer())
+            continue;
+        if (!child->localToParentTransform().isInvertible())

[fs, 2016/01/21 15:32:02]

This still makes us do work for example for shapes (which we don't care about
here.) If it helps you could put the distance calculation in a helper function.

+            continue;
+
+        FloatRect boundingBox = child->objectBoundingBox();
+        FloatPoint childLocalPoint = child->localToParentTransform().inverse().mapPoint(point);
+        float distance = boundingBox.squaredDistanceTo(childLocalPoint);
+
+        if (child->isSVGText()) {
+            if (distance >= closestDistance)
+                continue;
+            candidates.clear();
+            closestLayoutObject = child;
+            closestDistance = distance;
+            continue;
+        }
+
+        if (child->isSVGContainer()) {
+            if (distance > closestDistance)
+                continue;
+            candidates.append(SearchCandidate(child, distance));
+        }
+    }
+
+    // If find LayoutSVGText this level of tree, return it.
+    if (closestLayoutObject && closestLayoutObject->isSVGText())
+        return closestLayoutObject;
+
+    // Sort using the distance between the mouse point and a candidate.
+    // Because if the distance is close, It is high priority to search LayoutSVGText.
+    std::stable_sort(candidates.begin(), candidates.end(), compareCandidateDistance);
+
+    // If not find LayoutSVGText on this level of tree, try to search it on sub-tree of |condidate|.
+    // This vector called |candidates| is the sort in order of distance from the mouse point.
+    // If can not find the LayoutSVGText on |candidates|, after all return nullptr.
+    for (SearchCandidate& searchCandidate : candidates) {
+        LayoutObject* candidateLayoutObject = searchCandidate.candidateLayoutObject;
+        FloatPoint candidateLocalPoint = candidateLayoutObject->localToParentTransform().inverse().mapPoint(point);
+        if (LayoutObject* result = findClosestLayoutSVGText(candidateLayoutObject, candidateLocalPoint))

[fs, 2016/01/21 15:32:02]

Should this be considering all candidates with equal distance regardless of if
one LayoutSVGText was found already (with the same original distance)?

+            return result;
+    }
+
+    return nullptr;
+}
+
+}