InPrePaint document state and PrePaintTreeWalk class

third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.h

 // Copyright 2015 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 PaintPropertyTreeBuilder_h
 #define PaintPropertyTreeBuilder_h
 
+#include "platform/geometry/LayoutPoint.h"
+#include "platform/graphics/paint/ClipPaintPropertyNode.h"
+#include "platform/graphics/paint/EffectPaintPropertyNode.h"
+#include "platform/graphics/paint/TransformPaintPropertyNode.h"
+#include "wtf/RefPtr.h"
+
 namespace blink {
 
 class FrameView;
 class LayoutObject;
-struct PaintPropertyTreeBuilderContext;
 
-// This class walks the whole layout tree, beginning from the root FrameView, across
-// frame boundaries. The walk will collect special things in the layout tree and create
-// paint property nodes for them. Special things include but not limit to: overflow clip,
-// transform, fixed-pos, animation, mask, filter, ... etc.
-// It expects to be invoked after layout clean, i.e. during InPaintPropertyUpdate phase.
+// The context for PaintPropertyTreeBuilder.
+// It's responsible for bookkeeping tree state in other order, for example, the most recent
+// position container seen.
+struct PaintPropertyTreeBuilderContext {
+    PaintPropertyTreeBuilderContext()
+        : currentTransform(nullptr)
+        , currentClip(nullptr)
+        , transformForAbsolutePosition(nullptr)
+        , containerForAbsolutePosition(nullptr)
+        , clipForAbsolutePosition(nullptr)
+        , transformForFixedPosition(nullptr)
+        , clipForFixedPosition(nullptr)
+        , currentEffect(nullptr) { }
+
+    // The combination of a transform and paint offset describes a linear space.
+    // When a layout object recur to its children, the main context is expected to refer
+    // the object's border box, then the callee will derive its own border box by translating
+    // the space with its own layout location.
+    TransformPaintPropertyNode* currentTransform;
+    LayoutPoint paintOffset;
+    // The clip node describes the accumulated raster clip for the current subtree.
+    // Note that the computed raster region in canvas space for a clip node is independent from
+    // the transform and paint offset above. Also the actual raster region may be affected
+    // by layerization and occlusion tracking.
+    ClipPaintPropertyNode* currentClip;
+
+    // Separate context for out-of-flow positioned and fixed positioned elements are needed
+    // because they don't use DOM parent as their containing block.
+    // These additional contexts normally pass through untouched, and are only copied from
+    // the main context when the current element serves as the containing block of corresponding
+    // positioned descendants.
+    // Overflow clips are also inherited by containing block tree instead of DOM tree, thus they
+    // are included in the additional context too.
+    TransformPaintPropertyNode* transformForAbsolutePosition;
+    LayoutPoint paintOffsetForAbsolutePosition;
+    const LayoutObject* containerForAbsolutePosition;
+    ClipPaintPropertyNode* clipForAbsolutePosition;
+
+    TransformPaintPropertyNode* transformForFixedPosition;
+    LayoutPoint paintOffsetForFixedPosition;
+    ClipPaintPropertyNode* clipForFixedPosition;
+
+    // The effect hierarchy is applied by the stacking context tree. It is guaranteed that every
+    // DOM descendant is also a stacking context descendant. Therefore, we don't need extra
+    // bookkeeping for effect nodes and can generate the effect tree from a DOM-order traversal.
+    EffectPaintPropertyNode* currentEffect;
+};
+
+// Holds references to root property nodes to keep them alive during tree walk.
+struct PaintPropertyTreeBuilderRootContext : public PaintPropertyTreeBuilderContext {
+    RefPtr<TransformPaintPropertyNode> transformRoot;
+    RefPtr<ClipPaintPropertyNode> clipRoot;
+    RefPtr<EffectPaintPropertyNode> effectRoot;
+};
+
+// Creates paint property tree nodes for special things in the layout tree.
+// Special things include but not limit to: overflow clip, transform, fixed-pos, animation,
+// mask, filter, ... etc.
+// It expects to be invoked for each layout tree node in DOM order during InPrePaint phase.
 class PaintPropertyTreeBuilder {
 public:
-    void buildPropertyTrees(FrameView& rootFrame);
+    void buildTreeRootNodes(FrameView&, PaintPropertyTreeBuilderRootContext&);
+    void buildTreeNodes(FrameView&, PaintPropertyTreeBuilderContext&);
+    void buildTreeNodes(const LayoutObject&, PaintPropertyTreeBuilderContext&);
 
 private:
-    void walk(FrameView&, const PaintPropertyTreeBuilderContext&);
-
-    static void updatePaintOffsetTranslation(LayoutObject&, PaintPropertyTreeBuilderContext&);
-    static void updateTransform(LayoutObject&, PaintPropertyTreeBuilderContext&);
-    static void updateEffect(LayoutObject&, PaintPropertyTreeBuilderContext&);
-    static void updateCssClip(LayoutObject&, PaintPropertyTreeBuilderContext&);
-    static void updateLocalBorderBoxContext(LayoutObject&, const PaintPropertyTreeBuilderContext&);
-    static void updateScrollbarPaintOffset(LayoutObject&, const PaintPropertyTreeBuilderContext&);
-    static void updateOverflowClip(LayoutObject&, PaintPropertyTreeBuilderContext&);
-    static void updatePerspective(LayoutObject&, PaintPropertyTreeBuilderContext&);
-    static void updateSvgLocalTransform(LayoutObject&, PaintPropertyTreeBuilderContext&);
-    static void updateScrollTranslation(LayoutObject&, PaintPropertyTreeBuilderContext&);
-    static void updateOutOfFlowContext(LayoutObject&, PaintPropertyTreeBuilderContext&);
-
-    void walk(LayoutObject&, const PaintPropertyTreeBuilderContext&);
+    static void updatePaintOffsetTranslation(const LayoutObject&, PaintPropertyTreeBuilderContext&);
+    static void updateTransform(const LayoutObject&, PaintPropertyTreeBuilderContext&);
+    static void updateEffect(const LayoutObject&, PaintPropertyTreeBuilderContext&);
+    static void updateCssClip(const LayoutObject&, PaintPropertyTreeBuilderContext&);
+    static void updateLocalBorderBoxContext(const LayoutObject&, const PaintPropertyTreeBuilderContext&);
+    static void updateScrollbarPaintOffset(const LayoutObject&, const PaintPropertyTreeBuilderContext&);
+    static void updateOverflowClip(const LayoutObject&, PaintPropertyTreeBuilderContext&);
+    static void updatePerspective(const LayoutObject&, PaintPropertyTreeBuilderContext&);
+    static void updateSvgLocalTransform(const LayoutObject&, PaintPropertyTreeBuilderContext&);
+    static void updateScrollTranslation(const LayoutObject&, PaintPropertyTreeBuilderContext&);
+    static void updateOutOfFlowContext(const LayoutObject&, PaintPropertyTreeBuilderContext&);
 };
 
 } // namespace blink
 
 #endif // PaintPropertyTreeBuilder_h