Implement basic parts of hit regions on canvas2d.

Source/platform/graphics/GraphicsContext.cpp

 /*
  * Copyright (C) 2003, 2004, 2005, 2006, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Google Inc. 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.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 31 matching lines @@
 #include "third_party/skia/include/core/SkDevice.h"
 #include "third_party/skia/include/core/SkPicture.h"
 #include "third_party/skia/include/core/SkRRect.h"
 #include "third_party/skia/include/core/SkRefCnt.h"
 #include "third_party/skia/include/core/SkSurface.h"
 #include "third_party/skia/include/effects/SkBlurMaskFilter.h"
 #include "third_party/skia/include/effects/SkCornerPathEffect.h"
 #include "third_party/skia/include/effects/SkLumaColorFilter.h"
 #include "third_party/skia/include/gpu/GrRenderTarget.h"
 #include "third_party/skia/include/gpu/GrTexture.h"
+#include "third_party/skia/include/pathops/SkPathOps.h"
 #include "wtf/Assertions.h"
 #include "wtf/MathExtras.h"
 
 #if OS(MACOSX)
 #include <ApplicationServices/ApplicationServices.h>
 #endif
 
 using namespace std;
 using blink::WebBlendMode;
 
@@ skipping 1308 matching lines @@
     SkPath& path = const_cast<SkPath&>(pathToClip.skPath());
     SkPath::FillType previousFillType = path.getFillType();
 
     SkPath::FillType temporaryFillType = clipRule == RULE_EVENODD ? SkPath::kEvenOdd_FillType : SkPath::kWinding_FillType;
     path.setFillType(temporaryFillType);
     clipPath(path, AntiAliased);
 
     path.setFillType(previousFillType);
 }
 
+Path GraphicsContext::getCurrentClipPath(const Path& path)
+{
+    if (contextDisabled())
+        return Path();
+
+    const SkClipStack* clipStack = m_canvas->getClipStack();
+    SkClipStack::Iter iter(*clipStack, SkClipStack::Iter::kBottom_IterStart);
+    const SkClipStack::Element* element;
+
+    SkPath totalClipPath(path.skPath());

[fs, 2014/06/09 11:06:27]

This doesn't appear to work in the general case - i.e. consider for instance a
sequence of an empty element followed by a non-empty replace-op element (or
really just a replace-op element). That may or may not be problematic in 
practice, but it'd probably make sense to at least document (and possibly
assert) what isn't expected to work.

[zino, 2014/06/10 10:09:34]

Done.

+
+    while ((element = iter.next())) {
+
+        SkClipStack::Element::Type type = element->getType();
+        SkPath clipPath;
+        if (type != SkClipStack::Element::kEmpty_Type)
+            element->asPath(&clipPath);
+
+        SkRegion::Op elementOp = element->getOp();
+        if (elementOp == SkRegion::kReplace_Op)
+            totalClipPath = clipPath;

[fs, 2014/06/09 11:06:27]

Since the result of this method should be the intersection between |path| and
the clip-stack, this won't do the right thing. Maybe it'd be better to simply
compute the actual clip-path, and then perform the intersection against |path|?

[zino, 2014/06/10 10:09:34]

Done.

+        else
+            Op(totalClipPath, clipPath, (SkPathOp)element->getOp(), &totalClipPath);
+    }
+
+    return Path(totalClipPath);
+}
+
 void GraphicsContext::clipConvexPolygon(size_t numPoints, const FloatPoint* points, bool antialiased)
 {
     if (contextDisabled())
         return;
 
     if (numPoints <= 1)
         return;
 
     SkPath path;
     setPathFromConvexPoints(&path, numPoints, points);
@@ skipping 436 matching lines @@
 
 void GraphicsContext::didDrawTextInRect(const SkRect& textRect)
 {
     if (m_trackTextRegion) {
         TRACE_EVENT0("skia", "PlatformContextSkia::trackTextRegion");
         m_textRegion.join(textRect);
     }
 }
 
 }