Fix an issue where hit detection could fail on rect and ellipse shapes

Source/core/rendering/svg/RenderSVGRect.cpp

 /*
  * Copyright (C) 2011 University of Szeged
  * Copyright (C) 2011 Renata Hodovan <reni@webkit.org>
  * All rights reserved.
  *
  * 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 44 matching lines @@
 
     SVGLengthContext lengthContext(rect);
     FloatSize boundingBoxSize(rect->width()->currentValue()->value(lengthContext), rect->height()->currentValue()->value(lengthContext));
 
     // Spec: "A negative value is an error."
     if (boundingBoxSize.width() < 0 || boundingBoxSize.height() < 0)
         return;
 
     // Spec: "A value of zero disables rendering of the element."
     if (!boundingBoxSize.isEmpty()) {
-        // Fallback to RenderSVGShape if rect has rounded corners or a non-scaling stroke.
-        if (rect->rx()->currentValue()->value(lengthContext) > 0 || rect->ry()->currentValue()->value(lengthContext) > 0 || hasNonScalingStroke()) {
+        // Fallback to RenderSVGShape and path-based hit detection if the rect
+        // has rounded corners or a non-scaling or non-simple stroke.
+        if (rect->rx()->currentValue()->value(lengthContext) > 0
+            || rect->ry()->currentValue()->value(lengthContext) > 0
+            || hasNonScalingStroke()
+            || !definitelyHasSimpleStroke()) {
             RenderSVGShape::updateShapeFromElement();
             m_usePathFallback = true;
             return;
         }
     }
 
     m_fillBoundingBox = FloatRect(FloatPoint(rect->x()->currentValue()->value(lengthContext), rect->y()->currentValue()->value(lengthContext)), boundingBoxSize);
 
     // To decide if the stroke contains a point we create two rects which represent the inner and
     // the outer stroke borders. A stroke contains the point, if the point is between them.
     m_innerStrokeRect = m_fillBoundingBox;
     m_outerStrokeRect = m_fillBoundingBox;
 
     if (style()->svgStyle().hasStroke()) {
         float strokeWidth = this->strokeWidth();
         m_innerStrokeRect.inflate(-strokeWidth / 2);
         m_outerStrokeRect.inflate(strokeWidth / 2);
     }
 
     m_strokeBoundingBox = m_outerStrokeRect;
 }
 
 bool RenderSVGRect::shapeDependentStrokeContains(const FloatPoint& point)
 {
-    // The optimized contains code below does not support non-smooth strokes so we need
+    // The optimized code below does not support non-simple strokes so we need
     // to fall back to RenderSVGShape::shapeDependentStrokeContains in these cases.
-    if (m_usePathFallback || !hasSmoothStroke()) {
+    if (m_usePathFallback || !definitelyHasSimpleStroke()) {
         if (!hasPath())
             RenderSVGShape::updateShapeFromElement();
         return RenderSVGShape::shapeDependentStrokeContains(point);
     }
 
     return m_outerStrokeRect.contains(point, FloatRect::InsideOrOnStroke) && !m_innerStrokeRect.contains(point, FloatRect::InsideButNotOnStroke);
 }
 
 bool RenderSVGRect::shapeDependentFillContains(const FloatPoint& point, const WindRule fillRule) const
 {
     if (m_usePathFallback)
         return RenderSVGShape::shapeDependentFillContains(point, fillRule);
     return m_fillBoundingBox.contains(point.x(), point.y());
 }
 
+// Returns true if the stroke is continuous and definitely uses miter joins.
+bool RenderSVGRect::definitelyHasSimpleStroke() const
+{
+    const SVGRenderStyle& svgStyle = style()->svgStyle();
+
+    // The four angles of a rect are 90 degrees. Using the formula at:
+    // http://www.w3.org/TR/SVG/painting.html#StrokeMiterlimitProperty
+    // when the join style of the rect is "miter", the ratio of the miterLength
+    // to the stroke-width is found to be
+    // miterLength / stroke-width = 1 / sin(45 degrees)
+    //                            = 1 / (1 / sqrt(2))
+    //                            = sqrt(2)
+    //                            = 1.414213562373095...
+    // When sqrt(2) exceeds the miterlimit, then the join style switches to
+    // "bevel". When the miterlimit is greater than or equal to sqrt(2) then
+    // the join style remains "miter".
+    //
+    // An approximation of sqrt(2) is used here because at certain precise
+    // miterlimits, the join style used might not be correct (e.g. a miterlimit
+    // of 1.4142135 should result in bevel joins, but may be drawn using miter
+    // joins).
+    return svgStyle.strokeDashArray()->isEmpty()
+        && svgStyle.joinStyle() == MiterJoin
+        && svgStyle.strokeMiterLimit() >= 1.5;
 }
+
+}