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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at */
/* class that a parent frame uses to reflow a block frame */
#include "nsBlockReflowContext.h"
#include "BlockReflowState.h"
#include "nsFloatManager.h"
#include "nsColumnSetFrame.h"
#include "nsContainerFrame.h"
#include "nsBlockFrame.h"
#include "nsLineBox.h"
#include "nsLayoutUtils.h"
using namespace mozilla;
#ifdef DEBUG
# include "nsBlockDebugFlags.h" // For NOISY_BLOCK_DIR_MARGINS
nsBlockReflowContext::nsBlockReflowContext(nsPresContext* aPresContext,
const ReflowInput& aParentRI)
: mPresContext(aPresContext),
mMetrics(aParentRI) {}
static nsIFrame* DescendIntoBlockLevelFrame(nsIFrame* aFrame) {
LayoutFrameType type = aFrame->Type();
if (type == LayoutFrameType::ColumnSet) {
nsIFrame* child = aFrame->PrincipalChildList().FirstChild();
if (child) {
return DescendIntoBlockLevelFrame(child);
return aFrame;
bool nsBlockReflowContext::ComputeCollapsedBStartMargin(
const ReflowInput& aRI, nsCollapsingMargin* aMargin,
nsIFrame* aClearanceFrame, bool* aMayNeedRetry, bool* aBlockIsEmpty) {
WritingMode wm = aRI.GetWritingMode();
WritingMode parentWM = mMetrics.GetWritingMode();
// Include block-start element of frame's margin
// The inclusion of the block-end margin when empty is done by the caller
// since it doesn't need to be done by the top-level (non-recursive)
// caller.
printf(": %d => %d\n", aRI.ComputedLogicalMargin(wm).BStart(wm),
bool dirtiedLine = false;
bool setBlockIsEmpty = false;
// Calculate the frame's generational block-start-margin from its child
// blocks. Note that if the frame has a non-zero block-start-border or
// block-start-padding then this step is skipped because it will be a margin
// root. It is also skipped if the frame is a margin root for other
// reasons.
nsIFrame* frame = DescendIntoBlockLevelFrame(aRI.mFrame);
nsPresContext* prescontext = frame->PresContext();
nsBlockFrame* block = nullptr;
if (0 == aRI.ComputedLogicalBorderPadding(wm).BStart(wm)) {
block = do_QueryFrame(frame);
if (block) {
bool bStartMarginRoot, unused;
block->IsMarginRoot(&bStartMarginRoot, &unused);
if (bStartMarginRoot) {
block = nullptr;
// iterate not just through the lines of 'block' but also its
// overflow lines and the normal and overflow lines of its next in
// flows. Note that this will traverse some frames more than once:
// for example, if A contains B and A->nextinflow contains
// B->nextinflow, we'll traverse B->nextinflow twice. But this is
// OK because our traversal is idempotent.
for (; block; block = static_cast<nsBlockFrame*>(block->GetNextInFlow())) {
for (int overflowLines = 0; overflowLines <= 1; ++overflowLines) {
nsBlockFrame::LineIterator line;
nsBlockFrame::LineIterator line_end;
bool anyLines = true;
if (overflowLines) {
nsBlockFrame::FrameLines* frames = block->GetOverflowLines();
nsLineList* lines = frames ? &frames->mLines : nullptr;
if (!lines) {
anyLines = false;
} else {
line = lines->begin();
line_end = lines->end();
} else {
line = block->LinesBegin();
line_end = block->LinesEnd();
for (; anyLines && line != line_end; ++line) {
if (!aClearanceFrame && line->HasClearance()) {
// If we don't have a clearance frame, then we're computing
// the collapsed margin in the first pass, assuming that all
// lines have no clearance. So clear their clearance flags.
dirtiedLine = true;
bool isEmpty;
if (line->IsInline()) {
isEmpty = line->IsEmpty();
} else {
nsIFrame* kid = line->mFirstChild;
if (kid == aClearanceFrame) {
dirtiedLine = true;
if (!setBlockIsEmpty && aBlockIsEmpty) {
setBlockIsEmpty = true;
*aBlockIsEmpty = false;
goto done;
// Here is where we recur. Now that we have determined that a
// generational collapse is required we need to compute the
// child blocks margin and so in so that we can look into
// it. For its margins to be computed we need to have a reflow
// input for it.
// We may have to construct an extra reflow input here if
// we drilled down through a block wrapper. At the moment
// we can only drill down one level so we only have to support
// one extra reflow input.
const ReflowInput* outerReflowInput = &aRI;
if (frame != aRI.mFrame) {
NS_ASSERTION(frame->GetParent() == aRI.mFrame,
"Can only drill through one level of block wrapper");
LogicalSize availSpace = aRI.ComputedSize(frame->GetWritingMode());
outerReflowInput =
new ReflowInput(prescontext, aRI, frame, availSpace);
LogicalSize availSpace =
ReflowInput innerReflowInput(prescontext, *outerReflowInput, kid,
// Record that we're being optimistic by assuming the kid
// has no clearance
if (kid->StyleDisplay()->mClear != StyleClear::None ||
!nsBlockFrame::BlockCanIntersectFloats(kid)) {
*aMayNeedRetry = true;
if (ComputeCollapsedBStartMargin(innerReflowInput, aMargin,
aClearanceFrame, aMayNeedRetry,
&isEmpty)) {
dirtiedLine = true;
if (isEmpty) {
LogicalMargin innerMargin =
if (outerReflowInput != &aRI) {
delete const_cast<ReflowInput*>(outerReflowInput);
if (!isEmpty) {
if (!setBlockIsEmpty && aBlockIsEmpty) {
setBlockIsEmpty = true;
*aBlockIsEmpty = false;
goto done;
if (!setBlockIsEmpty && aBlockIsEmpty) {
// The first time we reach here is when this is the first block
// and we have processed all its normal lines.
setBlockIsEmpty = true;
// All lines are empty, or we wouldn't be here!
*aBlockIsEmpty = aRI.mFrame->IsSelfEmpty();
if (!setBlockIsEmpty && aBlockIsEmpty) {
*aBlockIsEmpty = aRI.mFrame->IsEmpty();
printf(": => %d\n", aMargin->get());
return dirtiedLine;
void nsBlockReflowContext::ReflowBlock(const LogicalRect& aSpace,
bool aApplyBStartMargin,
nsCollapsingMargin& aPrevMargin,
nscoord aClearance, nsLineBox* aLine,
ReflowInput& aFrameRI,
nsReflowStatus& aFrameReflowStatus,
BlockReflowState& aState) {
mFrame = aFrameRI.mFrame;
mWritingMode = aState.mReflowInput.GetWritingMode();
mContainerSize = aState.ContainerSize();
mSpace = aSpace;
if (!aState.IsAdjacentWithBStart()) {
aFrameRI.mFlags.mIsTopOfPage = false; // make sure this is cleared
if (aApplyBStartMargin) {
mBStartMargin = aPrevMargin;
printf(": reflowing ");
printf(" margin => %d, clearance => %d\n", mBStartMargin.get(), aClearance);
// Adjust the available size if it's constrained so that the
// child frame doesn't think it can reflow into its margin area.
if (mWritingMode.IsOrthogonalTo(mFrame->GetWritingMode())) {
if (NS_UNCONSTRAINEDSIZE != aFrameRI.AvailableISize()) {
0, aFrameRI.AvailableISize() - mBStartMargin.get() - aClearance));
} else {
if (NS_UNCONSTRAINEDSIZE != aFrameRI.AvailableBSize()) {
0, aFrameRI.AvailableBSize() - mBStartMargin.get() - aClearance));
} else {
// nsBlockFrame::ReflowBlock might call us multiple times with
// *different* values of aApplyBStartMargin.
nscoord tI = 0, tB = 0;
// The values of x and y do not matter for floats, so don't bother
// calculating them. Floats are guaranteed to have their own float
// manager, so tI and tB don't matter. mICoord and mBCoord don't
// matter becacuse they are only used in PlaceBlock, which is not used
// for floats.
if (aLine) {
// Compute inline/block coordinate where reflow will begin. Use the
// rules from 10.3.3 to determine what to apply. At this point in the
// reflow auto inline-start/end margins will have a zero value.
LogicalMargin usedMargin = aFrameRI.ComputedLogicalMargin(mWritingMode);
mICoord = mSpace.IStart(mWritingMode) + usedMargin.IStart(mWritingMode);
mBCoord = mSpace.BStart(mWritingMode) + mBStartMargin.get() + aClearance;
LogicalRect space(
mWritingMode, mICoord, mBCoord,
mSpace.ISize(mWritingMode) - usedMargin.IStartEnd(mWritingMode),
mSpace.BSize(mWritingMode) - usedMargin.BStartEnd(mWritingMode));
tI = space.LineLeft(mWritingMode, mContainerSize);
tB = mBCoord;
if (!mFrame->HasAnyStateBits(NS_BLOCK_BFC)) {
aFrameRI.mBlockDelta =
mOuterReflowInput.mBlockDelta + mBCoord - aLine->BStart();
#ifdef DEBUG
mMetrics.ISize(mWritingMode) = nscoord(0xdeadbeef);
mMetrics.BSize(mWritingMode) = nscoord(0xdeadbeef);
mOuterReflowInput.mFloatManager->Translate(tI, tB);
mFrame->Reflow(mPresContext, mMetrics, aFrameRI, aFrameReflowStatus);
mOuterReflowInput.mFloatManager->Translate(-tI, -tB);
#ifdef DEBUG
if (!aFrameReflowStatus.IsInlineBreakBefore()) {
if ((ABSURD_SIZE(mMetrics.ISize(mWritingMode)) ||
ABSURD_SIZE(mMetrics.BSize(mWritingMode))) &&
!mFrame->GetParent()->IsAbsurdSizeAssertSuppressed()) {
printf("nsBlockReflowContext: ");
printf(" metrics=%d,%d!\n", mMetrics.ISize(mWritingMode),
if ((mMetrics.ISize(mWritingMode) == nscoord(0xdeadbeef)) ||
(mMetrics.BSize(mWritingMode) == nscoord(0xdeadbeef))) {
printf("nsBlockReflowContext: ");
printf(" didn't set i/b %d,%d!\n", mMetrics.ISize(mWritingMode),
if (!mFrame->HasOverflowAreas()) {
if (!aFrameReflowStatus.IsInlineBreakBefore() &&
!aFrameRI.WillReflowAgainForClearance() &&
aFrameReflowStatus.IsFullyComplete()) {
// If mFrame is fully-complete and has a next-in-flow, we need to delete
// them now. Do not do this when a break-before is signaled or when a
// clearance frame is discovered in mFrame's subtree because mFrame is going
// to get reflowed again (whether the frame is (in)complete is undefined in
// that case anyway).
if (nsIFrame* kidNextInFlow = mFrame->GetNextInFlow()) {
// Remove all of the childs next-in-flows. Make sure that we ask
// the right parent to do the removal (it's possible that the
// parent is not this because we are executing pullup code).
// Floats will eventually be removed via nsBlockFrame::RemoveFloat
// which detaches the placeholder from the float.
nsOverflowContinuationTracker::AutoFinish fini(aState.mOverflowTracker,
nsIFrame::DestroyContext context(mPresContext->PresShell());
kidNextInFlow->GetParent()->DeleteNextInFlowChild(context, kidNextInFlow,
* Attempt to place the block frame within the available space. If
* it fits, apply inline-dir ("horizontal") positioning (CSS 10.3.3),
* collapse margins (CSS2 8.3.1). Also apply relative positioning.
bool nsBlockReflowContext::PlaceBlock(const ReflowInput& aReflowInput,
bool aForceFit, nsLineBox* aLine,
nsCollapsingMargin& aBEndMarginResult,
OverflowAreas& aOverflowAreas,
const nsReflowStatus& aReflowStatus) {
// Compute collapsed block-end margin value.
WritingMode parentWM = mMetrics.GetWritingMode();
// Don't apply the block-end margin if the block has a *later* sibling across
// column-span split.
if (aReflowStatus.IsComplete() && !mFrame->HasColumnSpanSiblings()) {
aBEndMarginResult = mMetrics.mCarriedOutBEndMargin;
} else {
// The used block-end-margin is set to zero before a break.
nscoord backupContainingBlockAdvance = 0;
// Check whether the block's block-end margin collapses with its block-start
// margin. See CSS 2.1 section 8.3.1; those rules seem to match
// nsBlockFrame::IsEmpty(). Any such block must have zero block-size so
// check that first. Note that a block can have clearance and still
// have adjoining block-start/end margins, because the clearance goes
// above the block-start margin.
// Mark the frame as non-dirty; it has been reflowed (or we wouldn't
// be here), and we don't want to assert in CachedIsEmpty()
bool empty = 0 == mMetrics.BSize(parentWM) && aLine->CachedIsEmpty();
if (empty) {
// Collapse the block-end margin with the block-start margin that was
// already applied.
printf(" ");
printf(": ");
" -- collapsing block start & end margin together; BStart=%d "
mBCoord, mSpace.BStart(mWritingMode));
// Section 8.3.1 of CSS 2.1 says that blocks with adjoining
// "top/bottom" (i.e. block-start/end) margins whose top margin collapses
// with their parent's top margin should have their top border-edge at the
// top border-edge of their parent. We actually don't have to do
// anything special to make this happen. In that situation,
// nsBlockFrame::ShouldApplyBStartMargin will have returned false,
// and mBStartMargin and aClearance will have been zero in
// ReflowBlock.
// If we did apply our block-start margin, but now we're collapsing it
// into the block-end margin, we need to back up the containing
// block's bCoord-advance by our block-start margin so that it doesn't get
// counted twice. Note that here we're allowing the line's bounds
// to become different from the block's position; we do this
// because the containing block will place the next line at the
// line's BEnd, and it must place the next line at a different
// point from where this empty block will be.
backupContainingBlockAdvance = mBStartMargin.get();
// See if the frame fit. If it's the first frame or empty then it
// always fits. If the block-size is unconstrained then it always fits,
// even if there's some sort of integer overflow that makes bCoord +
// mMetrics.BSize() appear to go beyond the available block size.
if (!empty && !aForceFit &&
mSpace.BSize(mWritingMode) != NS_UNCONSTRAINEDSIZE) {
nscoord bEnd =
mBCoord - backupContainingBlockAdvance + mMetrics.BSize(mWritingMode);
if (bEnd > mSpace.BEnd(mWritingMode)) {
// didn't fit, we must acquit.
mFrame->DidReflow(mPresContext, &aReflowInput);
return false;
aLine->SetBounds(mWritingMode, mICoord,
mBCoord - backupContainingBlockAdvance,
mMetrics.ISize(mWritingMode), mMetrics.BSize(mWritingMode),
// Now place the frame and complete the reflow process
mFrame, mPresContext, mMetrics, &aReflowInput, mWritingMode,
LogicalPoint(mWritingMode, mICoord, mBCoord), mContainerSize,
aOverflowAreas = mMetrics.mOverflowAreas + mFrame->GetPosition();
return true;