Refactor ClipPathHelper in PaintLayerPainter.cpp for reuse

third_party/WebKit/Source/core/paint/ClipPathClipper.cpp

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "core/paint/ClipPathClipper.h"
+
+#include "core/layout/svg/LayoutSVGResourceClipper.h"
+#include "core/style/ClipPathOperation.h"
+#include "platform/graphics/paint/ClipPathRecorder.h"
+
+namespace blink {
+
+ClipPathClipper::ClipPathClipper(
+    GraphicsContext& context,
+    const LayoutObject& layoutObject,
+    const FloatRect& referenceBox,
+    const FloatRect& visualOverflowRect,
+    const FloatPoint& origin)
+    : m_resourceClipper(nullptr)
+    , m_clipperState(SVGClipPainter::ClipperNotApplied)
+    , m_layoutObject(layoutObject)
+    , m_context(context)
+{
+    DCHECK(layoutObject.styleRef().clipPath());
+    ClipPathOperation* clipPathOperation = layoutObject.styleRef().clipPath();
+    if (clipPathOperation->type() == ClipPathOperation::SHAPE) {
+        ShapeClipPathOperation* shape = toShapeClipPathOperation(clipPathOperation);
+        if (shape->isValid())
+            m_clipPathRecorder.emplace(context, layoutObject, shape->path(referenceBox));
+    } else {
+        DCHECK_EQ(clipPathOperation->type(), ClipPathOperation::REFERENCE);
+        ReferenceClipPathOperation* referenceClipPathOperation = toReferenceClipPathOperation(clipPathOperation);
+        Document& document = layoutObject.document();
+        // TODO(fs): It doesn't work with forward or external SVG references (https://bugs.webkit.org/show_bug.cgi?id=90405)
+        Element* element = document.getElementById(referenceClipPathOperation->fragment());
+        if (isSVGClipPathElement(element) && element->layoutObject()) {
+            m_resourceClipper = toLayoutSVGResourceClipper(toLayoutSVGResourceContainer(element->layoutObject()));
+            // When SVG applies the clip, and the coordinate system is "userspace on use", we must explicitly pass in
+            // the offset to have the clip paint in the correct location. When the coordinate system is
+            // "object bounding box" the offset should already be accounted for in the visualOverflowRect.
+            FloatPoint originTranslation = m_resourceClipper->clipPathUnits() == SVGUnitTypes::kSvgUnitTypeUserspaceonuse ?
+                origin : FloatPoint();
+            if (!SVGClipPainter(*m_resourceClipper).prepareEffect(layoutObject, referenceBox,
+                visualOverflowRect, originTranslation, context, m_clipperState)) {
+                // No need to "finish" the clipper if this failed.
+                m_resourceClipper = nullptr;
+            }
+        }
+    }
+}
+
+ClipPathClipper::~ClipPathClipper()
+{
+    if (m_resourceClipper)
+        SVGClipPainter(*m_resourceClipper).finishEffect(m_layoutObject, m_context, m_clipperState);
+}
+
+} // namespace blink