C++ FrameView::containsScrollableArea方法代码示例

bool CompositingReasonFinder::requiresCompositingForPosition(RenderObject* renderer, const RenderLayer* layer, RenderLayer::ViewportConstrainedNotCompositedReason* viewportConstrainedNotCompositedReason, bool* needToRecomputeCompositingRequirements) const
{
    // position:fixed elements that create their own stacking context (e.g. have an explicit z-index,
    // opacity, transform) can get their own composited layer. A stacking context is required otherwise
    // z-index and clipping will be broken.
    if (!renderer->isPositioned())
        return false;

    EPosition position = renderer->style()->position();
    bool isFixed = renderer->isOutOfFlowPositioned() && position == FixedPosition;
    // FIXME: The isStackingContainer check here is redundant. Fixed position elements are always stacking contexts.
    if (isFixed && !layer->stackingNode()->isStackingContainer())
        return false;

    bool isSticky = renderer->isInFlowPositioned() && position == StickyPosition;
    if (!isFixed && !isSticky)
        return false;

    // FIXME: acceleratedCompositingForFixedPositionEnabled should probably be renamed acceleratedCompositingForViewportConstrainedPositionEnabled().
    if (Settings* settings = m_renderView.document().settings()) {
        if (!settings->acceleratedCompositingForFixedPositionEnabled())
            return false;
    }

    if (isSticky)
        return isViewportConstrainedFixedOrStickyLayer(layer);

    RenderObject* container = renderer->container();
    // If the renderer is not hooked up yet then we have to wait until it is.
    if (!container) {
        *needToRecomputeCompositingRequirements = true;
        return false;
    }

    // Don't promote fixed position elements that are descendants of a non-view container, e.g. transformed elements.
    // They will stay fixed wrt the container rather than the enclosing frame.
    if (container != &m_renderView) {
        if (viewportConstrainedNotCompositedReason)
            *viewportConstrainedNotCompositedReason = RenderLayer::NotCompositedForNonViewContainer;
        return false;
    }

    // If the fixed-position element does not have any scrollable ancestor between it and
    // its container, then we do not need to spend compositor resources for it. Start by
    // assuming we can opt-out (i.e. no scrollable ancestor), and refine the answer below.
    bool hasScrollableAncestor = false;

    // The FrameView has the scrollbars associated with the top level viewport, so we have to
    // check the FrameView in addition to the hierarchy of ancestors.
    FrameView* frameView = m_renderView.frameView();
    if (frameView && frameView->isScrollable())
        hasScrollableAncestor = true;

    RenderLayer* ancestor = layer->parent();
    while (ancestor && !hasScrollableAncestor) {
        if (frameView->containsScrollableArea(ancestor->scrollableArea()))
            hasScrollableAncestor = true;
        if (ancestor->renderer() == &m_renderView)
            break;
        ancestor = ancestor->parent();
    }

    if (!hasScrollableAncestor) {
        if (viewportConstrainedNotCompositedReason)
            *viewportConstrainedNotCompositedReason = RenderLayer::NotCompositedForUnscrollableAncestors;
        return false;
    }

    // Subsequent tests depend on layout. If we can't tell now, just keep things the way they are until layout is done.
    if (m_renderView.document().lifecycle().state() < DocumentLifecycle::LayoutClean) {
        *needToRecomputeCompositingRequirements = true;
        return layer->hasCompositedLayerMapping();
    }

    bool paintsContent = layer->isVisuallyNonEmpty() || layer->hasVisibleDescendant();
    if (!paintsContent) {
        if (viewportConstrainedNotCompositedReason)
            *viewportConstrainedNotCompositedReason = RenderLayer::NotCompositedForNoVisibleContent;
        return false;
    }

    // Fixed position elements that are invisible in the current view don't get their own layer.
    if (FrameView* frameView = m_renderView.frameView()) {
        LayoutRect viewBounds = frameView->viewportConstrainedVisibleContentRect();
        LayoutRect layerBounds = layer->calculateLayerBounds(layer->compositor()->rootRenderLayer(), 0,
            RenderLayer::DefaultCalculateLayerBoundsFlags
            | RenderLayer::ExcludeHiddenDescendants
            | RenderLayer::DontConstrainForMask
            | RenderLayer::IncludeCompositedDescendants
            | RenderLayer::PretendLayerHasOwnBacking);
        if (!viewBounds.intersects(enclosingIntRect(layerBounds))) {
            if (viewportConstrainedNotCompositedReason) {
                *viewportConstrainedNotCompositedReason = RenderLayer::NotCompositedForBoundsOutOfView;
                *needToRecomputeCompositingRequirements = true;
            }
            return false;
        }
    }

    return true;
//.........这里部分代码省略.........