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.cpp

@@ -50,24 +50,119 @@
 
 namespace blink {
 
+static void adjustClipRectsForChildren(const LayoutObject& layoutObject, ClipRects& clipRects)
+{
+    EPosition position = layoutObject.style()->position();
+    // A fixed object is essentially the root of its containing block hierarchy, so when
+    // we encounter such an object, we reset our clip rects to the fixedClipRect.
+    if (position == FixedPosition) {
+        clipRects.setPosClipRect(clipRects.fixedClipRect());
+        clipRects.setOverflowClipRect(clipRects.fixedClipRect());
+        clipRects.setFixed(true);
+    } else if (position == RelativePosition) {
+        clipRects.setPosClipRect(clipRects.overflowClipRect());
+    } else if (position == AbsolutePosition) {
+        clipRects.setOverflowClipRect(clipRects.posClipRect());
+    }
+}
+static void applyClipRects(const ClipRectsContext& context, LayoutObject& layoutObject, LayoutPoint offset, ClipRects& clipRects)
+{
+    ASSERT(layoutObject.hasOverflowClip() || layoutObject.hasClip());
+    LayoutView* view = layoutObject.view();
+    ASSERT(view);
+    if (clipRects.fixed() && context.rootLayer->layoutObject() == view)
+        offset -= toIntSize(view->frameView()->scrollPosition());
+    if (layoutObject.hasOverflowClip()) {
+        ClipRect newOverflowClip = toLayoutBox(layoutObject).overflowClipRect(offset, context.scrollbarRelevancy);
+        newOverflowClip.setHasRadius(layoutObject.style()->hasBorderRadius());
+        clipRects.setOverflowClipRect(intersection(newOverflowClip, clipRects.overflowClipRect()));
+        if (layoutObject.isPositioned())
+            clipRects.setPosClipRect(intersection(newOverflowClip, clipRects.posClipRect()));
+        if (layoutObject.isLayoutView())
+            clipRects.setFixedClipRect(intersection(newOverflowClip, clipRects.fixedClipRect()));
+    }
+    if (layoutObject.hasClip()) {
+        LayoutRect newClip = toLayoutBox(layoutObject).clipRect(offset);
+        clipRects.setPosClipRect(intersection(newClip, clipRects.posClipRect()));
+        clipRects.setOverflowClipRect(intersection(newClip, clipRects.overflowClipRect()));
+        clipRects.setFixedClipRect(intersection(newClip, clipRects.fixedClipRect()));
+    }
+}
+
 DeprecatedPaintLayerClipper::DeprecatedPaintLayerClipper(LayoutBoxModelObject& layoutObject)
     : m_layoutObject(layoutObject)
 {
 }
 
+ClipRects* DeprecatedPaintLayerClipper::clipRectsIfCached(const ClipRectsContext& context) const
+{
+    ASSERT(context.usesCache());
+    if (!m_cache)
+        return 0;
+    ClipRectsCache::Entry& entry = m_cache->get(context.cacheSlot());
+    // FIXME: We used to ASSERT that we always got a consistent root layer.
+    // We should add a test that has an inconsistent root. See
+    // http://crbug.com/366118 for an example.
+    if (context.rootLayer != entry.root)
+        return 0;
+    ASSERT(entry.scrollbarRelevancy == context.scrollbarRelevancy);
+#ifdef CHECK_CACHED_CLIP_RECTS
+    // This code is useful to check cached clip rects, but is too expensive to leave enabled in debug builds by default.
+    ClipRectsContext tempContext(context);
+    tempContext.cacheSlot = UncachedClipRects;
+    RefPtr<ClipRects> clipRects = ClipRects::create();
+    calculateClipRects(tempContext, *clipRects);
+    ASSERT(clipRects == *entry.clipRects);
+#endif
+    return entry.clipRects.get();
+}
+ClipRects* DeprecatedPaintLayerClipper::storeClipRectsInCache(const ClipRectsContext& context, ClipRects* parentClipRects, const ClipRects& clipRects) const
+{
+    ClipRectsCache::Entry& entry = cache().get(context.cacheSlot());
+    entry.root = context.rootLayer;
+#if ENABLE(ASSERT)
+    entry.scrollbarRelevancy = context.scrollbarRelevancy;
+#endif
+    if (parentClipRects) {
+        // If our clip rects match the clip rects of our parent, we share storage.
+        if (clipRects == *parentClipRects) {
+            entry.clipRects = parentClipRects;
+            return parentClipRects;
+        }
+    }
+    entry.clipRects = ClipRects::create(clipRects);
+    return entry.clipRects.get();
+}
+ClipRects* DeprecatedPaintLayerClipper::getClipRects(const ClipRectsContext& context) const
+{
+    if (ClipRects* result = clipRectsIfCached(context))
+        return result;
+    // Note that it's important that we call getClipRects on our parent
+    // before we call calculateClipRects so that calculateClipRects will hit
+    // the cache.
+    ClipRects* parentClipRects = 0;
+    if (context.rootLayer != m_layoutObject.layer() && m_layoutObject.layer()->parent())
+        parentClipRects = m_layoutObject.layer()->parent()->clipper().getClipRects(context);
+    RefPtr<ClipRects> clipRects = ClipRects::create();
+    calculateClipRects(context, *clipRects);
+    return storeClipRectsInCache(context, parentClipRects, *clipRects);
+}
+
 void DeprecatedPaintLayerClipper::clearClipRectsIncludingDescendants()
 {
+    m_cache = nullptr;
+
     for (DeprecatedPaintLayer* layer = m_layoutObject.layer()->firstChild(); layer; layer = layer->nextSibling()) {
-        for (int i = 0; i < NumberOfClipRectsCacheSlots; i++)
-            layer->clipper().m_clips[i] = nullptr;
         layer->clipper().clearClipRectsIncludingDescendants();
     }
 }
 
 void DeprecatedPaintLayerClipper::clearClipRectsIncludingDescendants(ClipRectsCacheSlot cacheSlot)
 {
+    if (m_cache)
+        m_cache->clear(cacheSlot);
+
     for (DeprecatedPaintLayer* layer = m_layoutObject.layer()->firstChild(); layer; layer = layer->nextSibling()) {
-        layer->clipper().m_clips[cacheSlot] = nullptr;
         layer->clipper().clearClipRectsIncludingDescendants(cacheSlot);
     }
 }
@@ -170,260 +265,81 @@ void DeprecatedPaintLayerClipper::calculateRects(const ClipRectsContext& context
     }
 }
 
-void precalculate(const ClipRectsContext& context)
+void DeprecatedPaintLayerClipper::calculateClipRects(const ClipRectsContext& context, ClipRects& clipRects) const
 {
-    bool isComputingPaintingRect = context.isComputingPaintingRect();
-    ClipRectComputationState rects;
-    const DeprecatedPaintLayer* rootLayer = context.rootLayer;
-    if (isComputingPaintingRect) {
-        // Starting arbitrarily in the tree when calculating painting clipRects will
-        // not allow you to fill in all layers cache because some intermediate layer
-        // may need clips with respect to an ancestor further up. For efficiency we
-        // start at the top in order to fill in the cache for all layers.
-        rootLayer = context.rootLayer->layoutObject()->view()->layer();
-        rects.stackingContextClipRects.setRootLayer(rootLayer);
-    }
-    rects.currentClipRects.setRootLayer(rootLayer);
-
-    rootLayer->clipper().calculateClipRects(context, rects);
-}
-
-void DeprecatedPaintLayerClipper::precalculateAbsoluteClipRects()
-{
-    ASSERT(m_layoutObject.layer()->isRootLayer());
-    // The absolute rectangles rely on layout sizes and position only.
-    ASSERT(m_layoutObject.document().lifecycle().state() >= DocumentLifecycle::LayoutClean);
-    precalculate(ClipRectsContext(m_layoutObject.layer(), AbsoluteClipRects));
-}
-
-// Calculates clipRect for each element in the section of the tree starting with context.rootLayer
-// For painting, context.rootLayer is ignored and the entire tree is calculated.
-// TODO(chadarmstrong): When using the cache context shouldn't be able to specify the rootLayer. This affects
-// what is stored in the 5 caches, and should therefore be enforced internally. Currently
-// different callers have different ideas of what the rootLayer should be for a particular
-// cacheSlot, which can fill the cache with bad data. If this can be made consistent it should
-// be possible to eliminate rootLayer.
-ClipRect DeprecatedPaintLayerClipper::backgroundClipRect(const ClipRectsContext& context) const
-{
-    ASSERT(m_layoutObject.layer()->parent());
-    ASSERT(m_layoutObject.view());
-
-    // Ideally backgroundClipRect would not be called with itself as the rootLayer.
-    // This behavior can be seen in the following test
-    // LayoutTests/compositing/squashing/abspos-under-abspos-overflow-scroll.html
-    if (m_layoutObject.layer() == context.rootLayer)
-        return LayoutRect(LayoutRect::infiniteIntRect());
-
-    // TODO(chadarmstrong): If possible, all queries should use one of the clipRectsCacheSlots.
-    // Without caching this operation involves walking all the way to rootLayer.
-    if (!context.usesCache())
-        return uncachedBackgroundClipRect(context);
-
-    // TODO(chadarmstrong): precalculation for painting should be moved to updateLifecyclePhasesInternal
-    // and precalculation could be done for all hit testing. This would let us avoid clearing the cache
-    if (!m_clips[context.cacheSlot()]) {
-        // AbsoluteClipRects should have been updated during compositing updates so we shouldn't miss here.
-        ASSERT(context.cacheSlot() != AbsoluteClipRects);
-        precalculate(context);
+    bool rootLayerScrolls = m_layoutObject.document().settings() && m_layoutObject.document().settings()->rootLayerScrolls();
+    if (!m_layoutObject.layer()->parent() && !rootLayerScrolls) {
+        // The root layer's clip rect is always infinite.
+        clipRects.reset(LayoutRect(LayoutRect::infiniteIntRect()));
+        return;
     }
 
-    // TODO(chadarmstrong): eliminate this if possible.
-    // It is necessary only because of a seemingly atypical use of rootLayer that
-    // can be seen in LayoutTests/fullscreen/full-screen-line-boxes-crash.html and
-    // fast/block/multicol-paint-invalidation-assert.html.
-    if (!m_clips[context.cacheSlot()])
-        return uncachedBackgroundClipRect(context);
-    // As soon as crbug.com/517173 is resolved this assert should be enabled in place of the check
-    // ASSERT(m_clips[context.cacheSlot()]->rootLayer() == context.rootLayer);
-    if (m_clips[context.cacheSlot()]->rootLayer() != context.rootLayer)
-        return uncachedBackgroundClipRect(context);
-
-
-    return *m_clips[context.cacheSlot()];
-}
-
-static bool shouldStopClipRectCalculation(LayoutBoxModelObject& layoutObject, const ClipRectsContext& context)
-{
-    // The entire tree is calculated for both painting and absolutClipRects
-    if (context.cacheSlot() == PaintingClipRectsIgnoringOverflowClip || context.cacheSlot() == PaintingClipRects || context.cacheSlot() == AbsoluteClipRects)
-        return false;
-    DeprecatedPaintLayer* layer = layoutObject.layer();
-    return layer->transform() || layer == layer->enclosingPaginationLayer();
-}
+    bool isClippingRoot = m_layoutObject.layer() == context.rootLayer;
 
-// Updates clipRects so that descendants can calculate
-// clipping relative to different root layers.
-static void resetPaintRects(LayoutBoxModelObject& layoutObject, ClipRectComputationState& rects, ClipRectsCacheSlot slot)
-{
-    const DeprecatedPaintLayer* layer = layoutObject.layer();
-    if (layer->isPaintInvalidationContainer() || layer->transform()) {
-        // If this element is hardware accelerated, we let the compositor handle the
-        // clipping (in case we want to paint bigger than a scrollable area for smooth
-        // scrolling) so we reset the clip rects.
-        // If the element has a transform, the clip rect could become a quad so we
-        // reset the layer and let the paint code apply the CTM during paint to
-        // transform the clip during paint.
-        rects.currentClipRects.reset(LayoutRect(LayoutRect::infiniteIntRect()));
-        rects.currentClipRects.setRootLayer(layoutObject.layer());
-        rects.currentClipRects.setFixed(false);
+    // For transformed layers, the root layer was shifted to be us, so there is no need to
+    // examine the parent. We want to cache clip rects with us as the root.
+    DeprecatedPaintLayer* parentLayer = !isClippingRoot ? m_layoutObject.layer()->parent() : 0;
+    // Ensure that our parent's clip has been calculated so that we can examine the values.
+    if (parentLayer) {
+        // FIXME: Why don't we just call getClipRects here?
+        if (context.usesCache() && parentLayer->clipper().cachedClipRects(context)) {
+            clipRects = *parentLayer->clipper().cachedClipRects(context);
+        } else {
+            parentLayer->clipper().calculateClipRects(context, clipRects);
         }
-    if (layer->stackingNode()->isStackingContext()) {
-        rects.stackingContextClipRects = rects.currentClipRects;
+    } else {
+        clipRects.reset(LayoutRect(LayoutRect::infiniteIntRect()));
     }
-}
 
-void DeprecatedPaintLayerClipper::addClipsFromThisObject(const ClipRectsContext& context, ClipRects& clipRects) const
-{
-    LayoutView* view = m_layoutObject.view();
-    ASSERT(view);
+    adjustClipRectsForChildren(m_layoutObject, clipRects);
+
+    if ((m_layoutObject.hasOverflowClip() && shouldRespectOverflowClip(context)) || m_layoutObject.hasClip()) {
         // This offset cannot use convertToLayerCoords, because sometimes our rootLayer may be across
         // some transformed layer boundary, for example, in the DeprecatedPaintLayerCompositor overlapMap, where
         // clipRects are needed in view space.
-    LayoutPoint offset = roundedLayoutPoint(m_layoutObject.localToContainerPoint(FloatPoint(), context.rootLayer->layoutObject()));
-    if (clipRects.fixed() && context.rootLayer->layoutObject() == view)
-        offset -= toIntSize(view->frameView()->scrollPosition());
-
-    // The condition for hasClip here seems wrong. See https://crbug.com/504577
-    // (overflowClips can be applied even when shouldRespectOverflowClip returns false)
-    if (m_layoutObject.hasOverflowClip() && (shouldRespectOverflowClip(context) || m_layoutObject.hasClip())) {
-        ClipRect newOverflowClip = toLayoutBox(m_layoutObject).overflowClipRect(offset, context.scrollbarRelevancy);
-        newOverflowClip.setHasRadius(m_layoutObject.style()->hasBorderRadius());
-        clipRects.setOverflowClipRect(intersection(newOverflowClip, clipRects.overflowClipRect()));
-        if (m_layoutObject.isPositioned())
-            clipRects.setPosClipRect(intersection(newOverflowClip, clipRects.posClipRect()));
-        if (m_layoutObject.isLayoutView())
-            clipRects.setFixedClipRect(intersection(newOverflowClip, clipRects.fixedClipRect()));
+        applyClipRects(context, m_layoutObject, roundedLayoutPoint(m_layoutObject.localToContainerPoint(FloatPoint(), context.rootLayer->layoutObject())), clipRects);
     }
-
-    if (m_layoutObject.hasClip())
-        clipRects.setFixedClipRect(intersection(toLayoutBox(m_layoutObject).clipRect(offset), clipRects.fixedClipRect()));
 }
 
-void DeprecatedPaintLayerClipper::calculateClipRects(const ClipRectsContext& context, ClipRectComputationState& rects) const
+static ClipRect backgroundClipRectForPosition(const ClipRects& parentRects, EPosition position)
 {
-    bool isComputingPaintingRect = context.isComputingPaintingRect();
-
-    // backgroundClipRect does not include clips from yourself
-    ClipRectsContext current = context;
-    current.rootLayer = rects.currentClipRects.rootLayer();
-    addClipsFromThisObject(current, rects.currentClipRects);
-    if (isComputingPaintingRect) {
-        current.rootLayer = rects.stackingContextClipRects.rootLayer();
-        addClipsFromThisObject(current, rects.stackingContextClipRects);
-    }
+    if (position == FixedPosition)
+        return parentRects.fixedClipRect();
 
-    for (DeprecatedPaintLayer* child = m_layoutObject.layer()->firstChild(); child; child = child->nextSibling()) {
-        child->clipper().setClipRect(context, rects);
-    }
-}
+    if (position == AbsolutePosition)
+        return parentRects.posClipRect();
 
-// This function propagate the appropriate clip down to descendants. It is required
-// as CSS overflow clips are inherited based on the containing blocks chain:
-// ['overflow'] "affects the clipping of all of the element's content
-// except any descendant elements (and their respective content and descendants)
-// whose containing block is the viewport or an ancestor of the element."
-void DeprecatedPaintLayerClipper::updateClipRectBasedOnPosition(ClipRects* clipRects) const
-{
-    switch (m_layoutObject.style()->position()) {
-    case FixedPosition:
-        // Clip is applied to all descendants but overflow does not propogate to fixed
-        // position elements.
-        clipRects->setPosClipRect(ClipRect(LayoutRect(LayoutRect::infiniteIntRect())));
-        clipRects->setOverflowClipRect(ClipRect(LayoutRect(LayoutRect::infiniteIntRect())));
-        clipRects->setFixed(true);
-        break;
-    case AbsolutePosition:
-        // Overflow clips from staticly positioned elements can be escaped by absolute and fixed
-        // position elements.
-        clipRects->setOverflowClipRect(clipRects->posClipRect());
-        break;
-    case RelativePosition:
-        // Overflow clips that apply to a relative position element are not escaped by absolute
-        // position elements further down the tree.  (Because the relative position element is a
-        // containing block.
-        clipRects->setPosClipRect(clipRects->overflowClipRect());
-        break;
-    case StaticPosition:
-    case StickyPosition:
-        // TODO(flakr): Position sticky should inherit the clip like relative position does (crbug.com/231752).
-        break;
-    }
+    return parentRects.overflowClipRect();
 }
 
-void DeprecatedPaintLayerClipper::setClipRect(const ClipRectsContext& context, const ClipRectComputationState& parentRects) const
+ClipRect DeprecatedPaintLayerClipper::backgroundClipRect(const ClipRectsContext& context) const
 {
-    bool isComputingPaintingRect = context.isComputingPaintingRect();
-    ClipRectComputationState rects;
-    rects.currentClipRects = parentRects.currentClipRects;
-    if (isComputingPaintingRect)
-        rects.stackingContextClipRects = parentRects.stackingContextClipRects;
-    updateClipRectBasedOnPosition(&rects.currentClipRects);
-    if (isComputingPaintingRect)
-        updateClipRectBasedOnPosition(&rects.stackingContextClipRects);
-    ClipRects* clipRects;
-    if (isComputingPaintingRect && (m_layoutObject.isPositioned() || m_layoutObject.layer()->transform()))
-        clipRects = &rects.stackingContextClipRects;
-    else
-        clipRects = &rects.currentClipRects;
-
-    m_clips[context.cacheSlot()] = ClipRect::create(intersection(clipRects->overflowClipRect(), clipRects->fixedClipRect()));
-    m_clips[context.cacheSlot()]->setRootLayer(clipRects->rootLayer());
-    // Note: infinite clipRects should not be scrolled here, otherwise they will accidentally no longer be considered infinite.
-    if (clipRects->fixed() && clipRects->rootLayer()->layoutObject() == m_layoutObject.view() && *m_clips[context.cacheSlot()] != LayoutRect(LayoutRect::infiniteIntRect()))
-        m_clips[context.cacheSlot()]->move(toIntSize(m_layoutObject.view()->frameView()->scrollPosition()));
-
-    if (shouldStopClipRectCalculation(m_layoutObject, context))
-        return;
-    if (isComputingPaintingRect)
-        resetPaintRects(m_layoutObject, rects, context.cacheSlot());
-
-    calculateClipRects(context, rects);
-}
+    ASSERT(m_layoutObject.layer()->parent());
+    ASSERT(m_layoutObject.view());
 
-ClipRect DeprecatedPaintLayerClipper::uncachedBackgroundClipRect(const ClipRectsContext& context) const
-{
-    ClipRects clipRects;
-    m_layoutObject.layer()->parent()->clipper().uncachedCalculateClipRects(context, clipRects);
+    RefPtr<ClipRects> parentClipRects = ClipRects::create();
+    if (m_layoutObject.layer() == context.rootLayer)
+        parentClipRects->reset(LayoutRect(LayoutRect::infiniteIntRect()));
+    else
+        m_layoutObject.layer()->parent()->clipper().getOrCalculateClipRects(context, *parentClipRects);
 
-    updateClipRectBasedOnPosition(&clipRects);
-    ClipRect result(intersection(clipRects.overflowClipRect(), clipRects.fixedClipRect()));
+    ClipRect result = backgroundClipRectForPosition(*parentClipRects, m_layoutObject.style()->position());
 
     // Note: infinite clipRects should not be scrolled here, otherwise they will accidentally no longer be considered infinite.
-    if (clipRects.fixed() && context.rootLayer->layoutObject() == m_layoutObject.view() && result != LayoutRect(LayoutRect::infiniteIntRect()))
+    if (parentClipRects->fixed() && context.rootLayer->layoutObject() == m_layoutObject.view() && result != LayoutRect(LayoutRect::infiniteIntRect()))
         result.move(toIntSize(m_layoutObject.view()->frameView()->scrollPosition()));
 
     return result;
 }
 
-void DeprecatedPaintLayerClipper::uncachedCalculateClipRects(const ClipRectsContext& context, ClipRects& clipRects) const
+void DeprecatedPaintLayerClipper::getOrCalculateClipRects(const ClipRectsContext& context, ClipRects& clipRects) const
 {
-    bool rootLayerScrolls = m_layoutObject.document().settings() && m_layoutObject.document().settings()->rootLayerScrolls();
-    if (!m_layoutObject.layer()->parent() && !rootLayerScrolls) {
-        // The root layer's clip rect is always infinite.
-        clipRects.reset(LayoutRect(LayoutRect::infiniteIntRect()));
-        return;
-    }
-
-    bool isClippingRoot = m_layoutObject.layer() == context.rootLayer;
-
-    // For transformed layers, the root layer was shifted to be us, so there is no need to
-    // examine the parent. We want to cache clip rects with us as the root.
-    DeprecatedPaintLayer* parentLayer = !isClippingRoot ? m_layoutObject.layer()->parent() : 0;
-
-    // Ensure that our parent's clip has been calculated so that we can examine the values.
-    if (parentLayer) {
-        parentLayer->clipper().uncachedCalculateClipRects(context, clipRects);
-    } else {
-        clipRects.reset(LayoutRect(LayoutRect::infiniteIntRect()));
-    }
-
-    updateClipRectBasedOnPosition(&clipRects);
-    addClipsFromThisObject(context, clipRects);
+    if (context.usesCache())
+        clipRects = *getClipRects(context);
+    else
+        calculateClipRects(context, clipRects);
 }
 
-// TODO(chadarmstrong): Clipping roots should be consistent for a given clipRectsCacheSlot
-// As things are, different callers clash over the same slot because they use
-// different root layers.
 DeprecatedPaintLayer* DeprecatedPaintLayerClipper::clippingRootForPainting() const
 {
     const DeprecatedPaintLayer* current = m_layoutObject.layer();

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