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

/*
 * Copyright (C) 2009, 2010 Apple Inc. All rights reserved.
 * Copyright (C) 2014 Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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#include "core/layout/compositing/CompositingLayerAssigner.h"

#include "core/inspector/InspectorTraceEvents.h"
#include "core/layout/LayoutView.h"
#include "core/layout/compositing/CompositedLayerMapping.h"
#include "core/page/Page.h"
#include "core/page/scrolling/ScrollingCoordinator.h"
#include "platform/TraceEvent.h"

namespace blink {

// We will only allow squashing if the bbox-area:squashed-area doesn't exceed
// the ratio |gSquashingSparsityTolerance|:1.
static uint64_t gSquashingSparsityTolerance = 6;

CompositingLayerAssigner::CompositingLayerAssigner(
    PaintLayerCompositor* compositor)
    : m_compositor(compositor), m_layersChanged(false) {}

CompositingLayerAssigner::~CompositingLayerAssigner() {}

void CompositingLayerAssigner::assign(
    PaintLayer* updateRoot,
    Vector<PaintLayer*>& layersNeedingPaintInvalidation) {
  TRACE_EVENT0("blink", "CompositingLayerAssigner::assign");

  SquashingState squashingState;
  assignLayersToBackingsInternal(updateRoot, squashingState,
                                 layersNeedingPaintInvalidation);
  if (squashingState.hasMostRecentMapping)
    squashingState.mostRecentMapping->finishAccumulatingSquashingLayers(
        squashingState.nextSquashedLayerIndex, layersNeedingPaintInvalidation);
}

void CompositingLayerAssigner::SquashingState::
    updateSquashingStateForNewMapping(
        CompositedLayerMapping* newCompositedLayerMapping,
        bool hasNewCompositedLayerMapping,
        Vector<PaintLayer*>& layersNeedingPaintInvalidation) {
  // The most recent backing is done accumulating any more squashing layers.
  if (hasMostRecentMapping)
    mostRecentMapping->finishAccumulatingSquashingLayers(
        nextSquashedLayerIndex, layersNeedingPaintInvalidation);

  nextSquashedLayerIndex = 0;
  boundingRect = IntRect();
  mostRecentMapping = newCompositedLayerMapping;
  hasMostRecentMapping = hasNewCompositedLayerMapping;
  haveAssignedBackingsToEntireSquashingLayerSubtree = false;
}

bool CompositingLayerAssigner::squashingWouldExceedSparsityTolerance(
    const PaintLayer* candidate,
    const CompositingLayerAssigner::SquashingState& squashingState) {
  IntRect bounds = candidate->clippedAbsoluteBoundingBox();
  IntRect newBoundingRect = squashingState.boundingRect;
  newBoundingRect.unite(bounds);
  const uint64_t newBoundingRectArea = newBoundingRect.size().area();
  const uint64_t newSquashedArea =
      squashingState.totalAreaOfSquashedRects + bounds.size().area();
  return newBoundingRectArea > gSquashingSparsityTolerance * newSquashedArea;
}

bool CompositingLayerAssigner::needsOwnBacking(const PaintLayer* layer) const {
  if (!m_compositor->canBeComposited(layer))
    return false;

  return requiresCompositing(layer->getCompositingReasons()) ||
         (m_compositor->staleInCompositingMode() && layer->isRootLayer());
}

CompositingStateTransitionType
CompositingLayerAssigner::computeCompositedLayerUpdate(PaintLayer* layer) {
  CompositingStateTransitionType update = NoCompositingStateChange;
  if (needsOwnBacking(layer)) {
    if (!layer->hasCompositedLayerMapping()) {
      update = AllocateOwnCompositedLayerMapping;
    }
  } else {
    if (layer->hasCompositedLayerMapping())
      update = RemoveOwnCompositedLayerMapping;

    if (!layer->subtreeIsInvisible() && m_compositor->canBeComposited(layer) &&
        requiresSquashing(layer->getCompositingReasons())) {
      // We can't compute at this time whether the squashing layer update is a
      // no-op, since that requires walking the paint layer tree.
      update = PutInSquashingLayer;
    } else if (layer->groupedMapping() || layer->lostGroupedMapping()) {
      update = RemoveFromSquashingLayer;
    }
  }
  return update;
}

SquashingDisallowedReasons
CompositingLayerAssigner::getReasonsPreventingSquashing(
    const PaintLayer* layer,
    const CompositingLayerAssigner::SquashingState& squashingState) {
  if (!squashingState.haveAssignedBackingsToEntireSquashingLayerSubtree)
    return SquashingDisallowedReasonWouldBreakPaintOrder;

  ASSERT(squashingState.hasMostRecentMapping);
  const PaintLayer& squashingLayer =
      squashingState.mostRecentMapping->owningLayer();

  // FIXME: this special case for video exists only to deal with corner cases
  // where a LayoutVideo does not report that it needs to be directly
  // composited.  Video does not currently support sharing a backing, but this
  // could be generalized in the future. The following layout tests fail if we
  // permit the video to share a backing with other layers.
  //
  // compositing/video/video-controls-layer-creation.html
  if (layer->layoutObject()->isVideo() ||
      squashingLayer.layoutObject()->isVideo())
    return SquashingDisallowedReasonSquashingVideoIsDisallowed;

  // Don't squash iframes, frames or plugins.
  // FIXME: this is only necessary because there is frame code that assumes that
  // composited frames are not squashed.
  if (layer->layoutObject()->isLayoutPart() ||
      squashingLayer.layoutObject()->isLayoutPart())
    return SquashingDisallowedReasonSquashingLayoutPartIsDisallowed;

  if (squashingWouldExceedSparsityTolerance(layer, squashingState))
    return SquashingDisallowedReasonSquashingSparsityExceeded;

  if (layer->layoutObject()->style()->hasBlendMode() ||
      squashingLayer.layoutObject()->style()->hasBlendMode())
    return SquashingDisallowedReasonSquashingBlendingIsDisallowed;

  // FIXME: this is not efficient, since it walks up the tree. We should store
  // these values on the CompositingInputsCache.
  if (layer->clippingContainer() != squashingLayer.clippingContainer() &&
      !squashingLayer.compositedLayerMapping()->containingSquashedLayer(
          layer->clippingContainer(), squashingState.nextSquashedLayerIndex))
    return SquashingDisallowedReasonClippingContainerMismatch;

  // Composited descendants need to be clipped by a child containment graphics
  // layer, which would not be available if the layer is squashed (and therefore
  // has no CLM nor a child containment graphics layer).
  if (m_compositor->clipsCompositingDescendants(layer))
    return SquashingDisallowedReasonSquashedLayerClipsCompositingDescendants;

  if (layer->scrollsWithRespectTo(&squashingLayer))
    return SquashingDisallowedReasonScrollsWithRespectToSquashingLayer;

  if (layer->scrollParent() && layer->hasCompositingDescendant())
    return SquashingDisallowedReasonScrollChildWithCompositedDescendants;

  if (layer->opacityAncestor() != squashingLayer.opacityAncestor())
    return SquashingDisallowedReasonOpacityAncestorMismatch;

  if (layer->transformAncestor() != squashingLayer.transformAncestor())
    return SquashingDisallowedReasonTransformAncestorMismatch;

  if (layer->transform() && !layer->transform()->isIdentityOrTranslation())
    return SquashingDisallowedReasonNonTranslationTransform;

  if (layer->renderingContextRoot() != squashingLayer.renderingContextRoot())
    return SquashingDisallowedReasonRenderingContextMismatch;

  if (layer->hasFilterInducingProperty() ||
      layer->filterAncestor() != squashingLayer.filterAncestor())
    return SquashingDisallowedReasonFilterMismatch;

  if (layer->nearestFixedPositionLayer() !=
      squashingLayer.nearestFixedPositionLayer())
    return SquashingDisallowedReasonNearestFixedPositionMismatch;
  ASSERT(layer->layoutObject()->style()->position() != FixedPosition);

  if ((squashingLayer.layoutObject()->style()->subtreeWillChangeContents() &&
       squashingLayer.layoutObject()
           ->style()
           ->isRunningAnimationOnCompositor()) ||
      squashingLayer.layoutObject()
          ->style()
          ->shouldCompositeForCurrentAnimations())
    return SquashingDisallowedReasonSquashingLayerIsAnimating;

  if (layer->enclosingPaginationLayer())
    return SquashingDisallowedReasonFragmentedContent;

  return SquashingDisallowedReasonsNone;
}

void CompositingLayerAssigner::updateSquashingAssignment(
    PaintLayer* layer,
    SquashingState& squashingState,
    const CompositingStateTransitionType compositedLayerUpdate,
    Vector<PaintLayer*>& layersNeedingPaintInvalidation) {
  // NOTE: In the future as we generalize this, the background of this layer may
  // need to be assigned to a different backing than the squashed PaintLayer's
  // own primary contents. This would happen when we have a composited negative
  // z-index element that needs to paint on top of the background, but below the
  // layer's main contents. For now, because we always composite layers when
  // they have a composited negative z-index child, such layers will never need
  // squashing so it is not yet an issue.
  if (compositedLayerUpdate == PutInSquashingLayer) {
    // A layer that is squashed with other layers cannot have its own
    // CompositedLayerMapping.
    ASSERT(!layer->hasCompositedLayerMapping());
    ASSERT(squashingState.hasMostRecentMapping);

    bool changedSquashingLayer =
        squashingState.mostRecentMapping->updateSquashingLayerAssignment(
            layer, squashingState.nextSquashedLayerIndex);
    if (!changedSquashingLayer)
      return;

    // If we've modified the collection of squashed layers, we must update
    // the graphics layer geometry.
    squashingState.mostRecentMapping->setNeedsGraphicsLayerUpdate(
        GraphicsLayerUpdateSubtree);

    layer->clipper().clearClipRectsIncludingDescendants();

    // Issue a paint invalidation, since |layer| may have been added to an
    // already-existing squashing layer.
    TRACE_LAYER_INVALIDATION(
        layer, InspectorLayerInvalidationTrackingEvent::AddedToSquashingLayer);
    layersNeedingPaintInvalidation.append(layer);
    m_layersChanged = true;
  } else if (compositedLayerUpdate == RemoveFromSquashingLayer) {
    if (layer->groupedMapping()) {
      // Before removing |layer| from an already-existing squashing layer that
      // may have other content, issue a paint invalidation.
      m_compositor->paintInvalidationOnCompositingChange(layer);
      layer->groupedMapping()->setNeedsGraphicsLayerUpdate(
          GraphicsLayerUpdateSubtree);
      layer->setGroupedMapping(nullptr,
                               PaintLayer::InvalidateLayerAndRemoveFromMapping);
    }

    // If we need to issue paint invalidations, do so now that we've removed it
    // from a squashed layer.
    TRACE_LAYER_INVALIDATION(
        layer,
        InspectorLayerInvalidationTrackingEvent::RemovedFromSquashingLayer);
    layersNeedingPaintInvalidation.append(layer);
    m_layersChanged = true;

    layer->setLostGroupedMapping(false);
  }
}

static ScrollingCoordinator* scrollingCoordinatorFromLayer(PaintLayer& layer) {
  Page* page = layer.layoutObject()->frame()->page();
  return (!page) ? nullptr : page->scrollingCoordinator();
}

void CompositingLayerAssigner::assignLayersToBackingsInternal(
    PaintLayer* layer,
    SquashingState& squashingState,
    Vector<PaintLayer*>& layersNeedingPaintInvalidation) {
  if (requiresSquashing(layer->getCompositingReasons())) {
    SquashingDisallowedReasons reasonsPreventingSquashing =
        getReasonsPreventingSquashing(layer, squashingState);
    if (reasonsPreventingSquashing) {
      layer->setCompositingReasons(layer->getCompositingReasons() |
                                   CompositingReasonSquashingDisallowed);
      layer->setSquashingDisallowedReasons(reasonsPreventingSquashing);
    }
  }

  CompositingStateTransitionType compositedLayerUpdate =
      computeCompositedLayerUpdate(layer);

  if (m_compositor->allocateOrClearCompositedLayerMapping(
          layer, compositedLayerUpdate)) {
    TRACE_LAYER_INVALIDATION(
        layer, InspectorLayerInvalidationTrackingEvent::NewCompositedLayer);
    layersNeedingPaintInvalidation.append(layer);
    m_layersChanged = true;
    if (ScrollingCoordinator* scrollingCoordinator =
            scrollingCoordinatorFromLayer(*layer)) {
      if (layer->layoutObject()->style()->hasViewportConstrainedPosition())
        scrollingCoordinator->frameViewFixedObjectsDidChange(
            layer->layoutObject()->view()->frameView());
    }
  }

  // Add this layer to a squashing backing if needed.
  updateSquashingAssignment(layer, squashingState, compositedLayerUpdate,
                            layersNeedingPaintInvalidation);

  const bool layerIsSquashed =
      compositedLayerUpdate == PutInSquashingLayer ||
      (compositedLayerUpdate == NoCompositingStateChange &&
       layer->groupedMapping());
  if (layerIsSquashed) {
    squashingState.nextSquashedLayerIndex++;
    IntRect layerBounds = layer->clippedAbsoluteBoundingBox();
    squashingState.totalAreaOfSquashedRects += layerBounds.size().area();
    squashingState.boundingRect.unite(layerBounds);
  }

  if (layer->stackingNode()->isStackingContext()) {
    PaintLayerStackingNodeIterator iterator(*layer->stackingNode(),
                                            NegativeZOrderChildren);
    while (PaintLayerStackingNode* curNode = iterator.next())
      assignLayersToBackingsInternal(curNode->layer(), squashingState,
                                     layersNeedingPaintInvalidation);
  }

  // At this point, if the layer is to be separately composited, then its
  // backing becomes the most recent in paint-order.
  if (layer->compositingState() == PaintsIntoOwnBacking) {
    ASSERT(!requiresSquashing(layer->getCompositingReasons()));
    squashingState.updateSquashingStateForNewMapping(
        layer->compositedLayerMapping(), layer->hasCompositedLayerMapping(),
        layersNeedingPaintInvalidation);
  }

  if (layer->scrollParent())
    layer->scrollParent()->getScrollableArea()->setTopmostScrollChild(layer);

  if (layer->needsCompositedScrolling())
    layer->getScrollableArea()->setTopmostScrollChild(nullptr);

  PaintLayerStackingNodeIterator iterator(
      *layer->stackingNode(), NormalFlowChildren | PositiveZOrderChildren);
  while (PaintLayerStackingNode* curNode = iterator.next())
    assignLayersToBackingsInternal(curNode->layer(), squashingState,
                                   layersNeedingPaintInvalidation);

  if (squashingState.hasMostRecentMapping &&
      &squashingState.mostRecentMapping->owningLayer() == layer)
    squashingState.haveAssignedBackingsToEntireSquashingLayerSubtree = true;
}

}  // namespace blink