renderblock.cpp

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            shadowTop = min(boxShadow->y - boxShadow->blur, shadowTop);
            shadowBottom = max(boxShadow->y + boxShadow->blur, shadowBottom);
        }

        box.move(shadowLeft, shadowTop);
        box.setWidth(box.width() - shadowLeft + shadowRight);
        box.setHeight(box.height() - shadowTop + shadowBottom);

        if (hasReflection()) {
            IntRect reflection(reflectionBox());
            int reflectTop = min(box.y(), reflection.y());
            int reflectBottom = max(box.bottom(), reflection.bottom());
            box.setHeight(reflectBottom - reflectTop);
            box.setY(reflectTop);
            
            int reflectLeft = min(box.x(), reflection.x());
            int reflectRight = max(box.right(), reflection.right());
            box.setWidth(reflectRight - reflectLeft);
            box.setX(reflectLeft);
        }
        return box;
    }

    if (!includeInterior && hasOverflowClip())
        return borderBoxRect();
    int l = overflowLeft(includeInterior);
    int t = overflowTop(includeInterior);
    return IntRect(l, t, overflowWidth(includeInterior) - l, max(overflowHeight(includeInterior), height()) - t);
}

bool RenderBlock::isSelfCollapsingBlock() const
{
    // We are not self-collapsing if we
    // (a) have a non-zero height according to layout (an optimization to avoid wasting time)
    // (b) are a table,
    // (c) have border/padding,
    // (d) have a min-height
    // (e) have specified that one of our margins can't collapse using a CSS extension
    if (height() > 0 ||
        isTable() || (borderBottom() + paddingBottom() + borderTop() + paddingTop()) != 0 ||
        style()->minHeight().isPositive() || 
        style()->marginTopCollapse() == MSEPARATE || style()->marginBottomCollapse() == MSEPARATE)
        return false;

    bool hasAutoHeight = style()->height().isAuto();
    if (style()->height().isPercent() && !style()->htmlHacks()) {
        hasAutoHeight = true;
        for (RenderBlock* cb = containingBlock(); !cb->isRenderView(); cb = cb->containingBlock()) {
            if (cb->style()->height().isFixed() || cb->isTableCell())
                hasAutoHeight = false;
        }
    }

    // If the height is 0 or auto, then whether or not we are a self-collapsing block depends
    // on whether we have content that is all self-collapsing or not.
    if (hasAutoHeight || ((style()->height().isFixed() || style()->height().isPercent()) && style()->height().isZero())) {
        // If the block has inline children, see if we generated any line boxes.  If we have any
        // line boxes, then we can't be self-collapsing, since we have content.
        if (childrenInline())
            return !firstLineBox();
        
        // Whether or not we collapse is dependent on whether all our normal flow children
        // are also self-collapsing.
        for (RenderBox* child = firstChildBox(); child; child = child->nextSiblingBox()) {
            if (child->isFloatingOrPositioned())
                continue;
            if (!child->isSelfCollapsingBlock())
                return false;
        }
        return true;
    }
    return false;
}

void RenderBlock::layout()
{
    // Update our first letter info now.
    updateFirstLetter();

    // Table cells call layoutBlock directly, so don't add any logic here.  Put code into
    // layoutBlock().
    layoutBlock(false);
    
    // It's safe to check for control clip here, since controls can never be table cells.
    if (hasControlClip()) {
        // Because of the lightweight clip, there can never be any overflow from children.
        m_overflowWidth = width();
        m_overflowHeight = height();
        m_overflowLeft = 0;
        m_overflowTop = 0;
    }
}

void RenderBlock::layoutBlock(bool relayoutChildren)
{
    ASSERT(needsLayout());

    if (isInline() && !isInlineBlockOrInlineTable()) // Inline <form>s inside various table elements can
        return;                                      // cause us to come in here.  Just bail.

    if (!relayoutChildren && layoutOnlyPositionedObjects())
        return;

    LayoutRepainter repainter(*this, m_everHadLayout && checkForRepaintDuringLayout());
    LayoutStateMaintainer statePusher(view(), this, IntSize(x(), y()), hasColumns() || hasTransform() || hasReflection());

    int oldWidth = width();
    int oldColumnWidth = desiredColumnWidth();

    calcWidth();
    calcColumnWidth();

    m_overflowWidth = width();
    m_overflowLeft = 0;

    if (oldWidth != width() || oldColumnWidth != desiredColumnWidth())
        relayoutChildren = true;

    clearFloats();

    int previousHeight = height();
    setHeight(0);

    m_overflowHeight = 0;

    // We use four values, maxTopPos, maxPosNeg, maxBottomPos, and maxBottomNeg, to track
    // our current maximal positive and negative margins.  These values are used when we
    // are collapsed with adjacent blocks, so for example, if you have block A and B
    // collapsing together, then you'd take the maximal positive margin from both A and B
    // and subtract it from the maximal negative margin from both A and B to get the
    // true collapsed margin.  This algorithm is recursive, so when we finish layout()
    // our block knows its current maximal positive/negative values.
    //
    // Start out by setting our margin values to our current margins.  Table cells have
    // no margins, so we don't fill in the values for table cells.
    bool isCell = isTableCell();
    if (!isCell) {
        initMaxMarginValues();

        setTopMarginQuirk(style()->marginTop().quirk());
        setBottomMarginQuirk(style()->marginBottom().quirk());

        Node* n = node();
        if (n && n->hasTagName(formTag) && static_cast<HTMLFormElement*>(n)->isMalformed()) {
            // See if this form is malformed (i.e., unclosed). If so, don't give the form
            // a bottom margin.
            setMaxBottomMargins(0, 0);
        }
    }

    // For overflow:scroll blocks, ensure we have both scrollbars in place always.
    if (scrollsOverflow()) {
        if (style()->overflowX() == OSCROLL)
            layer()->setHasHorizontalScrollbar(true);
        if (style()->overflowY() == OSCROLL)
            layer()->setHasVerticalScrollbar(true);
    }

    int repaintTop = 0;
    int repaintBottom = 0;
    int maxFloatBottom = 0;
    if (childrenInline())
        layoutInlineChildren(relayoutChildren, repaintTop, repaintBottom);
    else
        layoutBlockChildren(relayoutChildren, maxFloatBottom);

    // Expand our intrinsic height to encompass floats.
    int toAdd = borderBottom() + paddingBottom() + horizontalScrollbarHeight();
    if (floatBottom() > (height() - toAdd) && expandsToEncloseOverhangingFloats())
        setHeight(floatBottom() + toAdd);
    
    // Now lay out our columns within this intrinsic height, since they can slightly affect the intrinsic height as
    // we adjust for clean column breaks.
    int singleColumnBottom = layoutColumns();

    // Calculate our new height.
    int oldHeight = height();
    calcHeight();
    if (oldHeight != height()) {
        if (oldHeight > height() && maxFloatBottom > height() && !childrenInline()) {
            // One of our children's floats may have become an overhanging float for us. We need to look for it.
            for (RenderObject* child = firstChild(); child; child = child->nextSibling()) {
                if (child->isBlockFlow() && !child->isFloatingOrPositioned()) {
                    RenderBlock* block = toRenderBlock(child);
                    if (block->floatBottom() + block->y() > height())
                        addOverhangingFloats(block, -block->x(), -block->y(), false);
                }
            }
        }
        // We have to rebalance columns to the new height.
        layoutColumns(singleColumnBottom);

        // If the block got expanded in size, then increase our overflowheight to match.
        if (m_overflowHeight > height())
            m_overflowHeight -= toAdd;
        if (m_overflowHeight < height())
            m_overflowHeight = height();
    }
    if (previousHeight != height())
        relayoutChildren = true;

    if ((isCell || isInline() || isFloatingOrPositioned() || isRoot()) && !hasOverflowClip() && !hasControlClip())
        addVisualOverflow(floatRect());

    layoutPositionedObjects(relayoutChildren || isRoot());

    positionListMarker();

    // Always ensure our overflow width/height are at least as large as our width/height.
    m_overflowWidth = max(m_overflowWidth, width());
    m_overflowHeight = max(m_overflowHeight, height());

    if (!hasOverflowClip()) {
        for (ShadowData* boxShadow = style()->boxShadow(); boxShadow; boxShadow = boxShadow->next) {
            m_overflowLeft = min(m_overflowLeft, boxShadow->x - boxShadow->blur);
            m_overflowWidth = max(m_overflowWidth, width() + boxShadow->x + boxShadow->blur);
            m_overflowTop = min(m_overflowTop, boxShadow->y - boxShadow->blur);
            m_overflowHeight = max(m_overflowHeight, height() + boxShadow->y + boxShadow->blur);
        }
        
        if (hasReflection()) {
            m_overflowTop = min(m_overflowTop, reflectionBox().y());
            m_overflowHeight = max(m_overflowHeight, reflectionBox().bottom());
        }
    }

    statePusher.pop();

    // Update our scroll information if we're overflow:auto/scroll/hidden now that we know if
    // we overflow or not.
    if (hasOverflowClip())
        layer()->updateScrollInfoAfterLayout();

    // Repaint with our new bounds if they are different from our old bounds.
    bool didFullRepaint = repainter.repaintAfterLayout();
    if (!didFullRepaint && repaintTop != repaintBottom && (style()->visibility() == VISIBLE || enclosingLayer()->hasVisibleContent())) {
        IntRect repaintRect(m_overflowLeft, repaintTop, m_overflowWidth - m_overflowLeft, repaintBottom - repaintTop);

        // FIXME: Deal with multiple column repainting.  We have to split the repaint
        // rect up into multiple rects if it spans columns.

        repaintRect.inflate(maximalOutlineSize(PaintPhaseOutline));
        
        if (hasOverflowClip()) {
            // Adjust repaint rect for scroll offset
            int x = repaintRect.x();
            int y = repaintRect.y();
            layer()->subtractScrolledContentOffset(x, y);
            repaintRect.setX(x);
            repaintRect.setY(y);

            // Don't allow this rect to spill out of our overflow box.
            repaintRect.intersect(IntRect(0, 0, width(), height()));
        }

        // Make sure the rect is still non-empty after intersecting for overflow above
        if (!repaintRect.isEmpty()) {
            repaintRectangle(repaintRect); // We need to do a partial repaint of our content.
            if (hasReflection())
                layer()->reflection()->repaintRectangle(repaintRect);
        }
    }
    setNeedsLayout(false);
}

bool RenderBlock::expandsToEncloseOverhangingFloats() const
{
    return isInlineBlockOrInlineTable() || isFloatingOrPositioned() || hasOverflowClip() || (parent() && parent()->isFlexibleBox()) || hasColumns() || isTableCell() || isFieldset();
}

void RenderBlock::adjustPositionedBlock(RenderBox* child, const MarginInfo& marginInfo)
{
    if (child->style()->hasStaticX()) {
        if (style()->direction() == LTR)
            child->layer()->setStaticX(borderLeft() + paddingLeft());
        else
            child->layer()->setStaticX(borderRight() + paddingRight());
    }

    if (child->style()->hasStaticY()) {
        int y = height();
        if (!marginInfo.canCollapseWithTop()) {
            child->calcVerticalMargins();
            int marginTop = child->marginTop();
            int collapsedTopPos = marginInfo.posMargin();
            int collapsedTopNeg = marginInfo.negMargin();
            if (marginTop > 0) {
                if (marginTop > collapsedTopPos)
                    collapsedTopPos = marginTop;
            } else {
                if (-marginTop > collapsedTopNeg)
                    collapsedTopNeg = -marginTop;
            }
            y += (collapsedTopPos - collapsedTopNeg) - marginTop;
        }
        child->layer()->setStaticY(y);
    }
}

void RenderBlock::adjustFloatingBlock(const MarginInfo& marginInfo)
{
    // The float should be positioned taking into account the bottom margin
    // of the previous flow.  We add that margin into the height, get the
    // float positioned properly, and then subtract the margin out of the
    // height again.  In the case of self-collapsing blocks, we always just
    // use the top margins, since the self-collapsing block collapsed its
    // own bottom margin into its top margin.