flutter_flutter/engine/core/rendering/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:
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 *    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 "config.h"
#include "core/rendering/compositing/CompositingLayerAssigner.h"

#include "core/rendering/compositing/CompositedLayerMapping.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(RenderLayerCompositor* compositor)
    : m_compositor(compositor)
    , m_layerSquashingEnabled(compositor->layerSquashingEnabled())
    , m_layersChanged(false)
{
}

CompositingLayerAssigner::~CompositingLayerAssigner()
{
}

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

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

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

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

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

    // If squashing is disabled, then layers that would have been squashed should just be separately composited.
    bool needsOwnBackingForDisabledSquashing = !m_layerSquashingEnabled && requiresSquashing(layer->compositingReasons());

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

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

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

CompositingReasons CompositingLayerAssigner::getReasonsPreventingSquashing(const RenderLayer* layer, const CompositingLayerAssigner::SquashingState& squashingState)
{
    if (!squashingState.haveAssignedBackingsToEntireSquashingLayerSubtree)
        return CompositingReasonSquashingWouldBreakPaintOrder;

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

    // FIXME: this is not efficient, since it walks up the tree . We should store these values on the CompositingInputsCache.
    ASSERT(squashingState.hasMostRecentMapping);
    const RenderLayer& squashingLayer = squashingState.mostRecentMapping->owningLayer();

    if (layer->clippingContainer() != squashingLayer.clippingContainer() && !squashingLayer.compositedLayerMapping()->containingSquashedLayer(layer->clippingContainer()))
        return CompositingReasonSquashingClippingContainerMismatch;

    // 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 CompositingReasonSquashedLayerClipsCompositingDescendants;

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

    const RenderLayer::AncestorDependentCompositingInputs& compositingInputs = layer->ancestorDependentCompositingInputs();
    const RenderLayer::AncestorDependentCompositingInputs& squashingLayerCompositingInputs = squashingLayer.ancestorDependentCompositingInputs();

    if (compositingInputs.opacityAncestor != squashingLayerCompositingInputs.opacityAncestor)
        return CompositingReasonSquashingOpacityAncestorMismatch;

    if (compositingInputs.transformAncestor != squashingLayerCompositingInputs.transformAncestor)
        return CompositingReasonSquashingTransformAncestorMismatch;

    if (compositingInputs.filterAncestor != squashingLayerCompositingInputs.filterAncestor)
        return CompositingReasonSquashingFilterAncestorMismatch;

    return CompositingReasonNone;
}

void CompositingLayerAssigner::updateSquashingAssignment(RenderLayer* layer, SquashingState& squashingState, const CompositingStateTransitionType compositedLayerUpdate,
    Vector<RenderLayer*>& 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 RenderLayer'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.mostRecentMapping->owningLayer(), 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.
        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(0);
        }

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

        layer->setLostGroupedMapping(false);
    }
}

void CompositingLayerAssigner::assignLayersToBackingsInternal(RenderLayer* layer, SquashingState& squashingState, Vector<RenderLayer*>& layersNeedingPaintInvalidation)
{
    if (m_layerSquashingEnabled && requiresSquashing(layer->compositingReasons())) {
        CompositingReasons reasonsPreventingSquashing = getReasonsPreventingSquashing(layer, squashingState);
        if (reasonsPreventingSquashing)
            layer->setCompositingReasons(layer->compositingReasons() | reasonsPreventingSquashing);
    }

    CompositingStateTransitionType compositedLayerUpdate = computeCompositedLayerUpdate(layer);

    if (m_compositor->allocateOrClearCompositedLayerMapping(layer, compositedLayerUpdate)) {
        layersNeedingPaintInvalidation.append(layer);
        m_layersChanged = true;
    }

    // Add this layer to a squashing backing if needed.
    if (m_layerSquashingEnabled) {
        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()) {
        RenderLayerStackingNodeIterator iterator(*layer->stackingNode(), NegativeZOrderChildren);
        while (RenderLayerStackingNode* curNode = iterator.next())
            assignLayersToBackingsInternal(curNode->layer(), squashingState, layersNeedingPaintInvalidation);
    }

    if (m_layerSquashingEnabled) {
        // 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 || layer->compositingState() == HasOwnBackingButPaintsIntoAncestor) {
            ASSERT(!requiresSquashing(layer->compositingReasons()));
            squashingState.updateSquashingStateForNewMapping(layer->compositedLayerMapping(), layer->hasCompositedLayerMapping());
        }
    }

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

    if (layer->needsCompositedScrolling())
        layer->scrollableArea()->setTopmostScrollChild(0);

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

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

}