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

Source/core/paint/DeprecatedPaintLayerClipper.cpp

Index: Source/core/paint/DeprecatedPaintLayerClipper.cpp
diff --git a/Source/core/paint/DeprecatedPaintLayerClipper.cpp b/Source/core/paint/DeprecatedPaintLayerClipper.cpp
index 3b2be6a93e110d5f8d69da2d76b899776b772312..441854efe3e3d20e384bd5b4fa181f3f8ad8644d 100644
--- a/Source/core/paint/DeprecatedPaintLayerClipper.cpp
+++ b/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);
+    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;
     }
-    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());
+    bool isClippingRoot = m_layoutObject.layer() == context.rootLayer;
 
-    // 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);
+    // 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);
+        }
+    } else {
+        clipRects.reset(LayoutRect(LayoutRect::infiniteIntRect()));
     }
 
-    // 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);
-
+    adjustClipRectsForChildren(m_layoutObject, clipRects);
 
-    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();
-}
-
-// 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);
-    }
-    if (layer->stackingNode()->isStackingContext()) {
-        rects.stackingContextClipRects = rects.currentClipRects;
+    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.
+        applyClipRects(context, m_layoutObject, roundedLayoutPoint(m_layoutObject.localToContainerPoint(FloatPoint(), context.rootLayer->layoutObject())), clipRects);
     }
 }
 
-void DeprecatedPaintLayerClipper::addClipsFromThisObject(const ClipRectsContext& context, ClipRects& clipRects) const
+static ClipRect backgroundClipRectForPosition(const ClipRects& parentRects, EPosition position)
 {
-    LayoutView* view = m_layoutObject.view();
-    ASSERT(view);
-    // 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());
+    if (position == FixedPosition)
+        return parentRects.fixedClipRect();
 
-    // 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()));
-    }
+    if (position == AbsolutePosition)
+        return parentRects.posClipRect();
 
-    if (m_layoutObject.hasClip())
-        clipRects.setFixedClipRect(intersection(toLayoutBox(m_layoutObject).clipRect(offset), clipRects.fixedClipRect()));
+    return parentRects.overflowClipRect();
 }
 
-void DeprecatedPaintLayerClipper::calculateClipRects(const ClipRectsContext& context, ClipRectComputationState& rects) const
-{
-    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);
-    }
-
-    for (DeprecatedPaintLayer* child = m_layoutObject.layer()->firstChild(); child; child = child->nextSibling()) {
-        child->clipper().setClipRect(context, rects);
-    }
-}
-
-// 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
+ClipRect DeprecatedPaintLayerClipper::backgroundClipRect(const ClipRectsContext& context) 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;
-    }
-}
+    ASSERT(m_layoutObject.layer()->parent());
+    ASSERT(m_layoutObject.view());
 
-void DeprecatedPaintLayerClipper::setClipRect(const ClipRectsContext& context, const ClipRectComputationState& parentRects) 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;
+    RefPtr<ClipRects> parentClipRects = ClipRects::create();
+    if (m_layoutObject.layer() == context.rootLayer)
+        parentClipRects->reset(LayoutRect(LayoutRect::infiniteIntRect()));
     else
-        clipRects = &rects.currentClipRects;
+        m_layoutObject.layer()->parent()->clipper().getOrCalculateClipRects(context, *parentClipRects);
 
-    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);
-}
-
-ClipRect DeprecatedPaintLayerClipper::uncachedBackgroundClipRect(const ClipRectsContext& context) const
-{
-    ClipRects clipRects;
-    m_layoutObject.layer()->parent()->clipper().uncachedCalculateClipRects(context, clipRects);
-
-    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();