Support css clip on fixed-position GeometryMapper

third_party/WebKit/Source/platform/graphics/paint/GeometryMapper.h

 // 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.
 
 #ifndef GeometryMapper_h
 #define GeometryMapper_h
 
 #include "platform/geometry/FloatRect.h"
 #include "platform/graphics/paint/PropertyTreeState.h"
 #include "platform/transforms/TransformationMatrix.h"
@@ skipping 58 matching lines @@
     // then flattening into 2D space, then intersecting by the "clip visual rect" for |localTransformState|'s clips.
     // See above for the definition of "clip visual rect".
     //
     // Note that the clip of |ancestorState| is *not* applied.
     //
     // If any of the paint property tree nodes in |localTransformState| are not equal
     // to or a descendant of that in |ancestorState|, returns the passed-in rect and sets |success| to false. Otherwise,
     // sets |success| to true.
     FloatRect localToVisualRectInAncestorSpace(const FloatRect&,
         const PropertyTreeState& localTransformState,
-        const PropertyTreeState& ancestorState, bool& success);
+        const PropertyTreeState& ancestorState,
+        bool& success);
 
     // Maps from a rect in |localTransformSpace| to its transformed rect in |ancestorSpace|. This is computed
     // by multiplying the rect by the combined transform between |localTransformState| and |ancestorState|,
     // then flattening into 2D space.
     //
     // If any of the paint property tree nodes in |localTransformState| are not equal
     // to or a descendant of that in |ancestorState|, returns the passed-in rec and sets |success| to false. Otherwise,
     // sets |success| to true.
     //
     // If any of the paint property tree nodes in |localTransformState| are not equal
     // to or a descendant of that in |ancestorState|, returns the passed-in rect and sets |success| to false. Otherwise,
     // sets |success| to true.
     FloatRect localToAncestorRect(const FloatRect&,
         const PropertyTreeState& localTransformState,
-        const PropertyTreeState& ancestorState, bool& success);
+        const PropertyTreeState& ancestorState,
+        bool& success);
 
     // Maps from a rect in |ancestorSpace| to its transformed rect in |localTransformSpace|. This is computed
     // by multiplying the rect by the inverse combined transform between |localTransformState| and |ancestorState|,
     // if the transform is invertible.
     //
     // If any of the paint property tree nodes in |localTransformState| are not equal
     // to or a descendant of that in |ancestorState|, returns the passed-in rect and sets |success| to false. Otherwise,
     // sets |success| to true.
     FloatRect ancestorToLocalRect(const FloatRect&,
         const PropertyTreeState& localTransformState,
-        const PropertyTreeState& ancestorState, bool& success);
+        const PropertyTreeState& ancestorState,
+        bool& success);
 
 private:
-    // Used by mapToVisualRectInDestinationSpace() and mapRectToDestinationSpace() after fast mapping
-    // (assuming destination is an ancestor of source) failed.
+    // Used by mapToVisualRectInDestinationSpace() after fast mapping (assuming destination is an ancestor of source) failed.
+    FloatRect slowMapToVisualRectInDestinationSpace(const FloatRect&,

[chrishtr, 2016/08/22 22:27:32]

Please add a direct unittest to GeometryMapperTest to exercise this code, for
completeness.

[Xianzhu, 2016/08/22 23:30:20]

Done.

+        const PropertyTreeState& sourceState,
+        const PropertyTreeState& destinationState,
+        bool& success);
+
+    // Used by mapRectToDestinationSpace() after fast mapping (assuming destination is an ancestor of source) failed.
     FloatRect slowMapRectToDestinationSpace(const FloatRect&,
         const PropertyTreeState& sourceState,
         const PropertyTreeState& destinationState,
         bool& success);
 
     // Returns the matrix used in |LocalToAncestorRect|. Sets |success| to failse iff |localTransformNode| is not
     // equal to or a descendant of |ancestorState.transform|.
     const TransformationMatrix& localToAncestorMatrix(
         const TransformPaintPropertyNode* localTransformNode,
-        const PropertyTreeState& ancestorState, bool& success);
+        const PropertyTreeState& ancestorState,
+        bool& success);
 
     // Returns the "clip visual rect" between |localTransformState| and |ancestorState|. See above for the definition
     // of "clip visual rect".
-    const FloatRect& localToAncestorClipRect(
+    FloatRect localToAncestorClipRect(
         const PropertyTreeState& localTransformState,
-        const PropertyTreeState& ancestorState);
+        const PropertyTreeState& ancestorState,
+        bool& success);
 
     // Returns the precomputed data if already set, or adds and memoizes a new PrecomputedDataForAncestor otherwise.
     PrecomputedDataForAncestor& getPrecomputedDataForAncestor(const PropertyTreeState&);
 
     // Returns the least common ancestor in the transform tree.
     PassRefPtr<TransformPaintPropertyNode> leastCommonAncestor(PassRefPtr<TransformPaintPropertyNode>, PassRefPtr<TransformPaintPropertyNode>);
 
     friend class GeometryMapperTest;
 
     HashMap<const TransformPaintPropertyNode*, std::unique_ptr<PrecomputedDataForAncestor>> m_data;
 
     const TransformationMatrix m_identity;
 
     DISALLOW_COPY_AND_ASSIGN(GeometryMapper);
 };
 
 } // namespace blink
 
 #endif // GeometryMapper_h