C++ PaintLayer::setCompositingReasons方法代码示例

//.........这里部分代码省略.........
        ASSERT(willBeCompositedOrSquashed);
        // A foreground layer effectively is a new backing for all subsequent children, so
        // we don't need to test for overlap with anything behind this. So, we can finish
        // the previous context that was accumulating rects for the negative z-index
        // children, and start with a fresh new empty context.
        overlapMap.finishCurrentOverlapTestingContext();
        overlapMap.beginNewOverlapTestingContext();
        // This layer is going to be composited, so children can safely ignore the fact that there's an
        // animation running behind this layer, meaning they can rely on the overlap map testing again
        childRecursionData.m_testingOverlap = true;
    }

    PaintLayerStackingNodeIterator iterator(*layer->stackingNode(), NormalFlowChildren | PositiveZOrderChildren);
    while (PaintLayerStackingNode* curNode = iterator.next()) {
        IntRect absoluteChildDescendantBoundingBox;
        updateRecursive(layer, curNode->layer(), overlapMap, childRecursionData, anyDescendantHas3DTransform, unclippedDescendants, absoluteChildDescendantBoundingBox);
        absoluteDescendantBoundingBox.unite(absoluteChildDescendantBoundingBox);
    }

    // Now that the subtree has been traversed, we can check for compositing reasons that depended on the state of the subtree.

    if (layer->stackingNode()->isStackingContext()) {
        layer->setShouldIsolateCompositedDescendants(childRecursionData.m_hasUnisolatedCompositedBlendingDescendant);
    } else {
        layer->setShouldIsolateCompositedDescendants(false);
        currentRecursionData.m_hasUnisolatedCompositedBlendingDescendant = childRecursionData.m_hasUnisolatedCompositedBlendingDescendant;
    }

    // Subsequent layers in the parent's stacking context may also need to composite.
    if (childRecursionData.m_subtreeIsCompositing)
        currentRecursionData.m_subtreeIsCompositing = true;

    // Set the flag to say that this SC has compositing children.
    layer->setHasCompositingDescendant(childRecursionData.m_subtreeIsCompositing);

    if (layer->isRootLayer()) {
        // The root layer needs to be composited if anything else in the tree is composited.
        // Otherwise, we can disable compositing entirely.
        if (childRecursionData.m_subtreeIsCompositing || requiresCompositingOrSquashing(reasonsToComposite) || compositor->rootShouldAlwaysComposite()) {
            reasonsToComposite |= CompositingReasonRoot;
            currentRecursionData.m_subtreeIsCompositing = true;
        } else {
            compositor->setCompositingModeEnabled(false);
            reasonsToComposite = CompositingReasonNone;
        }
    } else {
        // All layers (even ones that aren't being composited) need to get added to
        // the overlap map. Layers that are not separately composited will paint into their
        // compositing ancestor's backing, and so are still considered for overlap.
        if (childRecursionData.m_compositingAncestor && !childRecursionData.m_compositingAncestor->isRootLayer())
            overlapMap.add(layer, absBounds);

        // Now check for reasons to become composited that depend on the state of descendant layers.
        CompositingReasons subtreeCompositingReasons = subtreeReasonsForCompositing(layer, childRecursionData.m_subtreeIsCompositing, anyDescendantHas3DTransform);
        reasonsToComposite |= subtreeCompositingReasons;
        if (!willBeCompositedOrSquashed && canBeComposited && requiresCompositingOrSquashing(subtreeCompositingReasons)) {
            childRecursionData.m_compositingAncestor = layer;
            // FIXME: this context push is effectively a no-op but needs to exist for
            // now, because the code is designed to push overlap information to the
            // second-from-top context of the stack.
            overlapMap.beginNewOverlapTestingContext();
            overlapMap.add(layer, absoluteDescendantBoundingBox);
            willBeCompositedOrSquashed = true;
        }

        if (willBeCompositedOrSquashed)
            reasonsToComposite |= layer->potentialCompositingReasonsFromStyle() & CompositingReasonInlineTransform;

        // If the original layer is composited, the reflection needs to be, too.
        if (layer->reflectionInfo()) {
            // FIXME: Shouldn't we call computeCompositingRequirements to handle a reflection overlapping with another layoutObject?
            PaintLayer* reflectionLayer = layer->reflectionInfo()->reflectionLayer();
            CompositingReasons reflectionCompositingReason = willBeCompositedOrSquashed ? CompositingReasonReflectionOfCompositedParent : CompositingReasonNone;
            reflectionLayer->setCompositingReasons(reflectionCompositingReason, CompositingReasonReflectionOfCompositedParent);
        }

        if (willBeCompositedOrSquashed && layer->layoutObject()->style()->hasBlendMode())
            currentRecursionData.m_hasUnisolatedCompositedBlendingDescendant = true;

        // Tell the parent it has compositing descendants.
        if (willBeCompositedOrSquashed)
            currentRecursionData.m_subtreeIsCompositing = true;

        // Turn overlap testing off for later layers if it's already off, or if we have an animating transform.
        // Note that if the layer clips its descendants, there's no reason to propagate the child animation to the parent layers. That's because
        // we know for sure the animation is contained inside the clipping rectangle, which is already added to the overlap map.
        bool isCompositedClippingLayer = canBeComposited && (reasonsToComposite & CompositingReasonClipsCompositingDescendants);
        bool isCompositedWithInlineTransform = reasonsToComposite & CompositingReasonInlineTransform;
        if ((!childRecursionData.m_testingOverlap && !isCompositedClippingLayer) || layer->layoutObject()->style()->hasCurrentTransformAnimation() || isCompositedWithInlineTransform)
            currentRecursionData.m_testingOverlap = false;

        if (childRecursionData.m_compositingAncestor == layer)
            overlapMap.finishCurrentOverlapTestingContext();

        descendantHas3DTransform |= anyDescendantHas3DTransform || layer->has3DTransform();
    }

    // At this point we have finished collecting all reasons to composite this layer.
    layer->setCompositingReasons(reasonsToComposite);
}