Revert "Reworks the clipping logic" and follow-up.

This change reverts commit
f5bd7257166f313f8bed1ceffa2802e6540b53da and
25907d23a2b4a963c879fb44c18ed05ad388f00e.

The change has been the cause of numerous regressions
(painting and hit-testing clip rects wrongly computed)
and several performance regressions.

Reverting the change so that I can investigate offline
and reland in a smaller bits.

BUG=518215,521452,522829,518219

Review URL: https://codereview.chromium.org/1307203004

git-svn-id: svn://svn.chromium.org/blink/trunk@201739 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/frame/FrameView.cpp

@@ -2480,14 +2480,6 @@ void FrameView::updateLifecyclePhasesInternal(LifeCycleUpdateOption phases)
                 || (RuntimeEnabledFeatures::slimmingPaintV2Enabled() && lifecycle().state() == DocumentLifecycle::CompositingForSlimmingPaintV2Clean));
         }
     }
-
-#ifndef NDEBUG
-    // TODO(jchaffraix): We will want to clear the clip rects in release too
-    // to reduce our long-term memory consumption. However this requires us
-    // to migrate all of the clip rects to the state machine and evaluate
-    // the performance impacts of this.
-    layoutView()->layer()->clipper().clearClipRectsIncludingDescendants(AbsoluteClipRects);
-#endif
 }
 
 void FrameView::paintForSlimmingPaintV2()

third_party/WebKit/Source/core/layout/ClipRect.h

@@ -28,21 +28,14 @@
 
 #include "platform/geometry/LayoutRect.h"
 #include "wtf/FastAllocBase.h"
-#include "wtf/PassOwnPtr.h"
 
 namespace blink {
 
-class DeprecatedPaintLayer;
 class HitTestLocation;
 
 class ClipRect {
     WTF_MAKE_FAST_ALLOCATED(ClipRect);
 public:
-    static PassOwnPtr<ClipRect> create(const ClipRect& other)
-    {
-        return adoptPtr(new ClipRect(other));
-    }
-
     ClipRect()
         : m_hasRadius(false)
     { }
@@ -75,18 +68,7 @@ public:
     bool isEmpty() const { return m_rect.isEmpty(); }
     bool intersects(const HitTestLocation&) const;
 
-    const DeprecatedPaintLayer* rootLayer() const
-    {
-        return m_rootLayer;
-    }
-
-    void setRootLayer(const DeprecatedPaintLayer* rootLayer)
-    {
-        m_rootLayer = rootLayer;
-    }
-
 private:
-    const DeprecatedPaintLayer* m_rootLayer;
     LayoutRect m_rect;
     bool m_hasRadius;
 };

third_party/WebKit/Source/core/layout/ClipRects.h

@@ -31,15 +31,20 @@
 
 namespace blink {
 
-class DeprecatedPaintLayer;
-
-class ClipRects {
+class ClipRects : public RefCounted<ClipRects> {
     WTF_MAKE_FAST_ALLOCATED(ClipRects);
 public:
+    static PassRefPtr<ClipRects> create()
+    {
+        return adoptRef(new ClipRects);
+    }
+    static PassRefPtr<ClipRects> create(const ClipRects& other)
+    {
+        return adoptRef(new ClipRects(other));
+    }
 
     ClipRects()
-        : m_rootLayer(nullptr)
-        , m_fixed(0)
+        : m_fixed(0)
     {
     }
 
@@ -77,24 +82,12 @@ public:
         m_fixedClipRect = other.fixedClipRect();
         m_posClipRect = other.posClipRect();
         m_fixed = other.fixed();
-        m_rootLayer = other.m_rootLayer;
         return *this;
     }
 
-    void setRootLayer(const DeprecatedPaintLayer* layer)
-    {
-        m_rootLayer = layer;
-    }
-
-    const DeprecatedPaintLayer* rootLayer()
-    {
-        return m_rootLayer;
-    }
-
 private:
     ClipRects(const LayoutRect& r)
-        : m_rootLayer(nullptr)
-        , m_overflowClipRect(r)
+        : m_overflowClipRect(r)
         , m_fixedClipRect(r)
         , m_posClipRect(r)
         , m_fixed(0)
@@ -102,18 +95,13 @@ private:
     }
 
     ClipRects(const ClipRects& other)
-        : m_rootLayer(other.m_rootLayer)
-        , m_overflowClipRect(other.overflowClipRect())
+        : m_overflowClipRect(other.overflowClipRect())
         , m_fixedClipRect(other.fixedClipRect())
         , m_posClipRect(other.posClipRect())
         , m_fixed(other.fixed())
     {
     }
 
-    // ClipRects are accumulated relative to this layer. Its clips and the clips
-    // of its descendents are intersected down to the layer being calculated. It
-    // also determines the coordinate space of the clips.
-    const DeprecatedPaintLayer* m_rootLayer;
     ClipRect m_overflowClipRect;
     ClipRect m_fixedClipRect;
     ClipRect m_posClipRect;

third_party/WebKit/Source/core/layout/ClipRectsCache.h

@@ -15,14 +15,12 @@ namespace blink {
 
 class DeprecatedPaintLayer;
 
-// TODO: Because this is mostly empty, this should be moved to a better place
 enum ClipRectsCacheSlot {
     // Relative to the ancestor treated as the root (e.g. transformed layer). Used for hit testing.
     RootRelativeClipRects,
     RootRelativeClipRectsIgnoringViewportClip,
 
     // Relative to the LayoutView's layer. Used for compositing overlap testing.
-    // Computed during the compositing update step (see CompositingInputsUpdater::update).
     AbsoluteClipRects,
 
     // Relative to painting ancestor. Used for painting.
@@ -33,6 +31,37 @@ enum ClipRectsCacheSlot {
     UncachedClipRects,
 };
 
+class ClipRectsCache {
+    WTF_MAKE_FAST_ALLOCATED(ClipRectsCache);
+public:
+    struct Entry {
+        Entry()
+            : root(nullptr)
+#if ENABLE(ASSERT)
+            , scrollbarRelevancy(IgnoreOverlayScrollbarSize)
+#endif
+        {
+        }
+        const DeprecatedPaintLayer* root;
+        RefPtr<ClipRects> clipRects;
+#if ENABLE(ASSERT)
+        OverlayScrollbarSizeRelevancy scrollbarRelevancy;
+#endif
+    };
+    Entry& get(ClipRectsCacheSlot slot)
+    {
+        ASSERT(slot < NumberOfClipRectsCacheSlots);
+        return m_entries[slot];
+    }
+    void clear(ClipRectsCacheSlot slot)
+    {
+        ASSERT(slot < NumberOfClipRectsCacheSlots);
+        m_entries[slot] = Entry();
+    }
+private:
+    Entry m_entries[NumberOfClipRectsCacheSlots];
+};
+
 } // namespace blink
 
 #endif // ClipRectsCache_h

third_party/WebKit/Source/core/layout/compositing/CompositingInputsUpdater.cpp

@@ -26,7 +26,6 @@ CompositingInputsUpdater::~CompositingInputsUpdater()
 void CompositingInputsUpdater::update()
 {
     TRACE_EVENT0("blink", "CompositingInputsUpdater::update");
-    m_rootLayer->clipper().precalculateAbsoluteClipRects();
     updateRecursive(m_rootLayer, DoNotForceUpdate, AncestorInfo());
 }
 

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

@@ -376,6 +376,8 @@ void DeprecatedPaintLayer::updateTransform(const ComputedStyle* oldStyle, const
 
         // DeprecatedPaintLayers with transforms act as clip rects roots, so clear the cached clip rects here.
         m_clipper.clearClipRectsIncludingDescendants();
+    } else if (hasTransform) {
+        m_clipper.clearClipRectsIncludingDescendants(AbsoluteClipRects);
     }
 
     updateTransformationMatrix();
@@ -1400,10 +1402,7 @@ void DeprecatedPaintLayer::collectFragments(DeprecatedPaintLayerFragments& fragm
 
     // Calculate clip rects relative to the enclosingPaginationLayer. The purpose of this call is to determine our bounds clipped to intermediate
     // layers between us and the pagination context. It's important to minimize the number of fragments we need to create and this helps with that.
-    // This code uses a non-standard root layer, which can populate our cache with unexpected values.
-    // Thus we bypass the clip rect cache by ignoring |clipRectsCacheSlot| and passing UncachedClipRects.
-    // TODO(chadarmstrong): If possible, this code should use the cache (one way would be by computing the root layer relative to |clipRectsCacheSlot|).
-    ClipRectsContext paginationClipRectsContext(enclosingPaginationLayer(), UncachedClipRects, inOverlayScrollbarSizeRelevancy);
+    ClipRectsContext paginationClipRectsContext(enclosingPaginationLayer(), clipRectsCacheSlot, inOverlayScrollbarSizeRelevancy);
     if (respectOverflowClip == IgnoreOverflowClip)
         paginationClipRectsContext.setIgnoreOverflowClip();
     LayoutRect layerBoundsInFlowThread;
@@ -1442,10 +1441,7 @@ void DeprecatedPaintLayer::collectFragments(DeprecatedPaintLayerFragments& fragm
     ClipRect ancestorClipRect = dirtyRect;
     if (const DeprecatedPaintLayer* paginationParentLayer = enclosingPaginationLayer()->parent()) {
         const DeprecatedPaintLayer* ancestorLayer = rootLayerIsInsidePaginationLayer ? paginationParentLayer : rootLayer;
-        // This code uses a non-standard root layer, which can populate our cache with unexpected values.
-        // Thus we bypass the clip rect cache by ignoring |clipRectsCacheSlot| and passing UncachedClipRects.
-        // TODO(chadarmstrong): If possible, this code should use the cache (one way would be by computing the root layer relative to |clipRectsCacheSlot|).
-        ClipRectsContext clipRectsContext(ancestorLayer, UncachedClipRects, inOverlayScrollbarSizeRelevancy);
+        ClipRectsContext clipRectsContext(ancestorLayer, clipRectsCacheSlot, inOverlayScrollbarSizeRelevancy);
         if (respectOverflowClip == IgnoreOverflowClip)
             clipRectsContext.setIgnoreOverflowClip();
         ancestorClipRect = enclosingPaginationLayer()->clipper().backgroundClipRect(clipRectsContext);

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

@@ -45,7 +45,6 @@
 #ifndef DeprecatedPaintLayerClipper_h
 #define DeprecatedPaintLayerClipper_h
 
-#include "core/layout/ClipRects.h"
 #include "core/layout/ClipRectsCache.h"
 #include "core/layout/LayoutBox.h"
 #include "wtf/Allocator.h"
@@ -54,25 +53,6 @@ namespace blink {
 
 class DeprecatedPaintLayer;
 
-// This is the state information passed down
-// on the stack for calculating clip rects.
-struct ClipRectComputationState {
-    STACK_ALLOCATED();
-    ClipRectComputationState()
-    {
-        currentClipRects.reset(LayoutRect(LayoutRect::infiniteIntRect()));
-        stackingContextClipRects.reset(LayoutRect(LayoutRect::infiniteIntRect()));
-    }
-    // Depending on the value of context.isComputingPaintingRect() can have different meanings
-    // In painting, this ClipRects is used for statically positioned elements,
-    // outside painting, it is the only ClipRects, and is used for all elements.
-    ClipRects currentClipRects;
-    // During painting this ClipRects is used for positioned elements. It can have
-    // a rootLayer further up the tree than currentClipRects because its root must be
-    // beyond the enclosing stacking context. See resetPaintRects.
-    ClipRects stackingContextClipRects;
-};
-
 enum ShouldRespectOverflowClip {
     IgnoreOverflowClip,
     RespectOverflowClip
@@ -149,25 +129,33 @@ public:
     // Pass offsetFromRoot if known.
     void calculateRects(const ClipRectsContext&, const LayoutRect& paintDirtyRect, LayoutRect& layerBounds,
         ClipRect& backgroundRect, ClipRect& foregroundRect, ClipRect& outlineRect, const LayoutPoint* offsetFromRoot = 0) const;
-    void calculateClipRects(const ClipRectsContext&, ClipRectComputationState&) const;
-
-    DeprecatedPaintLayer* clippingRootForPainting() const;
+private:
+    void calculateClipRects(const ClipRectsContext&, ClipRects&) const;
+    ClipRects* clipRectsIfCached(const ClipRectsContext&) const;
+    ClipRects* storeClipRectsInCache(const ClipRectsContext&, ClipRects* parentClipRects, const ClipRects&) const;
 
-    void precalculateAbsoluteClipRects();
+    // cachedClipRects looks buggy: It doesn't check whether context.rootLayer and entry.root match.
+    // FIXME: Move callers to clipRectsIfCached, which does the proper checks.
+    ClipRects* cachedClipRects(const ClipRectsContext& context) const
+    {
+        return m_cache ? m_cache->get(context.cacheSlot()).clipRects.get() : 0;
+    }
+    void getOrCalculateClipRects(const ClipRectsContext&, ClipRects&) const;
 
-private:
-    void setClipRect(const ClipRectsContext&, const ClipRectComputationState&) const;
-    void addClipsFromThisObject(const ClipRectsContext&, ClipRects&) const;
-    void updateClipRectBasedOnPosition(ClipRects*) const;
+    DeprecatedPaintLayer* clippingRootForPainting() const;
 
-    ClipRect uncachedBackgroundClipRect(const ClipRectsContext&) const;
-    void uncachedCalculateClipRects(const ClipRectsContext&, ClipRects&) const;
+    ClipRectsCache& cache() const
+    {
+        if (!m_cache)
+            m_cache = adoptPtr(new ClipRectsCache);
+        return *m_cache;
+    }
 
     bool shouldRespectOverflowClip(const ClipRectsContext&) const;
 
     // FIXME: Could this be a LayoutBox?
     LayoutBoxModelObject& m_layoutObject;
-    mutable OwnPtr<ClipRect> m_clips[NumberOfClipRectsCacheSlots];
+    mutable OwnPtr<ClipRectsCache> m_cache;
 };
 
 } // namespace blink