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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 */
* code for managing absolutely positioned children of a rendering
* object that is a containing block for them
#include "nsAbsoluteContainingBlock.h"
#include "nsContainerFrame.h"
#include "nsGkAtoms.h"
#include "mozilla/CSSAlignUtils.h"
#include "mozilla/PresShell.h"
#include "mozilla/ReflowInput.h"
#include "nsPlaceholderFrame.h"
#include "nsPresContext.h"
#include "nsCSSFrameConstructor.h"
#include "nsGridContainerFrame.h"
#include "mozilla/Sprintf.h"
#ifdef DEBUG
# include "nsBlockFrame.h"
static void PrettyUC(nscoord aSize, char* aBuf, int aBufSize) {
strcpy(aBuf, "UC");
} else {
if ((int32_t)0xdeadbeef == aSize) {
strcpy(aBuf, "deadbeef");
} else {
snprintf(aBuf, aBufSize, "%d", aSize);
using namespace mozilla;
typedef mozilla::CSSAlignUtils::AlignJustifyFlags AlignJustifyFlags;
void nsAbsoluteContainingBlock::SetInitialChildList(nsIFrame* aDelegatingFrame,
ChildListID aListID,
nsFrameList& aChildList) {
MOZ_ASSERT(mChildListID == aListID, "unexpected child list name");
#ifdef DEBUG
for (nsIFrame* f : aChildList) {
MOZ_ASSERT(f->GetParent() == aDelegatingFrame, "Unexpected parent");
void nsAbsoluteContainingBlock::AppendFrames(nsIFrame* aDelegatingFrame,
ChildListID aListID,
nsFrameList& aFrameList) {
NS_ASSERTION(mChildListID == aListID, "unexpected child list");
// Append the frames to our list of absolutely positioned frames
#ifdef DEBUG
mAbsoluteFrames.AppendFrames(nullptr, aFrameList);
// no damage to intrinsic widths, since absolutely positioned frames can't
// change them
aDelegatingFrame, IntrinsicDirty::Resize, NS_FRAME_HAS_DIRTY_CHILDREN);
void nsAbsoluteContainingBlock::InsertFrames(nsIFrame* aDelegatingFrame,
ChildListID aListID,
nsIFrame* aPrevFrame,
nsFrameList& aFrameList) {
NS_ASSERTION(mChildListID == aListID, "unexpected child list");
NS_ASSERTION(!aPrevFrame || aPrevFrame->GetParent() == aDelegatingFrame,
"inserting after sibling frame with different parent");
#ifdef DEBUG
mAbsoluteFrames.InsertFrames(nullptr, aPrevFrame, aFrameList);
// no damage to intrinsic widths, since absolutely positioned frames can't
// change them
aDelegatingFrame, IntrinsicDirty::Resize, NS_FRAME_HAS_DIRTY_CHILDREN);
void nsAbsoluteContainingBlock::RemoveFrame(nsIFrame* aDelegatingFrame,
ChildListID aListID,
nsIFrame* aOldFrame) {
NS_ASSERTION(mChildListID == aListID, "unexpected child list");
nsIFrame* nif = aOldFrame->GetNextInFlow();
if (nif) {
nif->GetParent()->DeleteNextInFlowChild(nif, false);
static void MaybeMarkAncestorsAsHavingDescendantDependentOnItsStaticPos(
nsIFrame* aFrame, nsIFrame* aContainingBlockFrame) {
if (!aFrame->StylePosition()->NeedsHypotheticalPositionIfAbsPos()) {
// We should have set the bit when reflowing the previous continuations
// already.
if (aFrame->GetPrevContinuation()) {
auto* placeholder = aFrame->GetPlaceholderFrame();
// Only fixed-pos frames can escape their containing block.
if (!placeholder->HasAnyStateBits(PLACEHOLDER_FOR_FIXEDPOS)) {
for (nsIFrame* ancestor = placeholder->GetParent(); ancestor;
ancestor = ancestor->GetParent()) {
// Walk towards the ancestor's first continuation. That's the only one that
// really matters, since it's the only one restyling will look at. We also
// flag the following continuations just so it's caught on the first
// early-return ones just to avoid walking them over and over.
do {
if (ancestor->DescendantMayDependOnItsStaticPosition()) {
// Moving the containing block or anything above it would move our static
// position as well, so no need to flag it or any of its ancestors.
if (aFrame == aContainingBlockFrame) {
nsIFrame* prev = ancestor->GetPrevContinuation();
if (!prev) {
ancestor = prev;
} while (true);
void nsAbsoluteContainingBlock::Reflow(nsContainerFrame* aDelegatingFrame,
nsPresContext* aPresContext,
const ReflowInput& aReflowInput,
nsReflowStatus& aReflowStatus,
const nsRect& aContainingBlock,
AbsPosReflowFlags aFlags,
OverflowAreas* aOverflowAreas) {
// PageContentFrame replicates fixed pos children so we really don't want
// them contributing to overflow areas because that means we'll create new
// pages ad infinitum if one of them overflows the page.
if (aDelegatingFrame->IsPageContentFrame()) {
MOZ_ASSERT(mChildListID == nsAtomicContainerFrame::kFixedList);
aOverflowAreas = nullptr;
nsReflowStatus reflowStatus;
const bool reflowAll = aReflowInput.ShouldReflowAllKids();
const bool isGrid = !!(aFlags & AbsPosReflowFlags::IsGridContainerCB);
nsIFrame* kidFrame;
nsOverflowContinuationTracker tracker(aDelegatingFrame, true);
for (kidFrame = mAbsoluteFrames.FirstChild(); kidFrame;
kidFrame = kidFrame->GetNextSibling()) {
bool kidNeedsReflow =
reflowAll || kidFrame->IsSubtreeDirty() ||
kidFrame, !!(aFlags & AbsPosReflowFlags::CBWidthChanged),
!!(aFlags & AbsPosReflowFlags::CBHeightChanged));
if (kidFrame->IsSubtreeDirty()) {
kidFrame, aDelegatingFrame);
nscoord availBSize = aReflowInput.AvailableBSize();
const nsRect& cb =
isGrid ? nsGridContainerFrame::GridItemCB(kidFrame) : aContainingBlock;
WritingMode containerWM = aReflowInput.GetWritingMode();
if (!kidNeedsReflow && availBSize != NS_UNCONSTRAINEDSIZE) {
// If we need to redo pagination on the kid, we need to reflow it.
// This can happen either if the available height shrunk and the
// kid (or its overflow that creates overflow containers) is now
// too large to fit in the available height, or if the available
// height has increased and the kid has a next-in-flow that we
// might need to pull from.
WritingMode kidWM = kidFrame->GetWritingMode();
if (containerWM.GetBlockDir() != kidWM.GetBlockDir()) {
// Not sure what the right test would be here.
kidNeedsReflow = true;
} else {
nscoord kidBEnd = kidFrame->GetLogicalRect(cb.Size()).BEnd(kidWM);
nscoord kidOverflowBEnd =
// Use ...RelativeToSelf to ignore transforms
kidFrame->ScrollableOverflowRectRelativeToSelf() +
NS_ASSERTION(kidOverflowBEnd >= kidBEnd,
"overflow area should be at least as large as frame rect");
if (kidOverflowBEnd > availBSize ||
(kidBEnd < availBSize && kidFrame->GetNextInFlow())) {
kidNeedsReflow = true;
if (kidNeedsReflow && !aPresContext->HasPendingInterrupt()) {
// Reflow the frame
nsReflowStatus kidStatus;
ReflowAbsoluteFrame(aDelegatingFrame, aPresContext, aReflowInput, cb,
aFlags, kidFrame, kidStatus, aOverflowAreas);
"ShouldAvoidBreakInside should prevent this from happening");
nsIFrame* nextFrame = kidFrame->GetNextInFlow();
if (!kidStatus.IsFullyComplete() &&
nsIFrame::eCanContainOverflowContainers)) {
// Need a continuation
if (!nextFrame) {
nextFrame = aPresContext->PresShell()
->CreateContinuingFrame(kidFrame, aDelegatingFrame);
// Add it as an overflow container.
// XXXfr This is a hack to fix some of our printing dataloss.
// See bug 154892. Not sure how to do it "right" yet; probably want
// to keep continuations within an nsAbsoluteContainingBlock eventually.
tracker.Insert(nextFrame, kidStatus);
} else {
// Delete any continuations
if (nextFrame) {
nsOverflowContinuationTracker::AutoFinish fini(&tracker, kidFrame);
nextFrame->GetParent()->DeleteNextInFlowChild(nextFrame, true);
} else {
tracker.Skip(kidFrame, reflowStatus);
if (aOverflowAreas) {
aDelegatingFrame->ConsiderChildOverflow(*aOverflowAreas, kidFrame);
// Make a CheckForInterrupt call, here, not just HasPendingInterrupt. That
// will make sure that we end up reflowing aDelegatingFrame in cases when
// one of our kids interrupted. Otherwise we'd set the dirty or
// dirty-children bit on the kid in the condition below, and then when
// reflow completes and we go to mark dirty bits on all ancestors of that
// kid we'll immediately bail out, because the kid already has a dirty bit.
// In particular, we won't set any dirty bits on aDelegatingFrame, so when
// the following reflow happens we won't reflow the kid in question. This
// might be slightly suboptimal in cases where |kidFrame| itself did not
// interrupt, since we'll trigger a reflow of it too when it's not strictly
// needed. But the logic to not do that is enough more complicated, and
// the case enough of an edge case, that this is probably better.
if (kidNeedsReflow && aPresContext->CheckForInterrupt(aDelegatingFrame)) {
if (aDelegatingFrame->HasAnyStateBits(NS_FRAME_IS_DIRTY)) {
} else {
// Abspos frames can't cause their parent to be incomplete,
// only overflow incomplete.
if (reflowStatus.IsIncomplete()) reflowStatus.SetOverflowIncomplete();
static inline bool IsFixedPaddingSize(const LengthPercentage& aCoord) {
return aCoord.ConvertsToLength();
static inline bool IsFixedMarginSize(const LengthPercentageOrAuto& aCoord) {
return aCoord.ConvertsToLength();
static inline bool IsFixedOffset(const LengthPercentageOrAuto& aCoord) {
return aCoord.ConvertsToLength();
bool nsAbsoluteContainingBlock::FrameDependsOnContainer(nsIFrame* f,
bool aCBWidthChanged,
bool aCBHeightChanged) {
const nsStylePosition* pos = f->StylePosition();
// See if f's position might have changed because it depends on a
// placeholder's position.
if (pos->NeedsHypotheticalPositionIfAbsPos()) {
return true;
if (!aCBWidthChanged && !aCBHeightChanged) {
// skip getting style data
return false;
const nsStylePadding* padding = f->StylePadding();
const nsStyleMargin* margin = f->StyleMargin();
WritingMode wm = f->GetWritingMode();
if (wm.IsVertical() ? aCBHeightChanged : aCBWidthChanged) {
// See if f's inline-size might have changed.
// If margin-inline-start/end, padding-inline-start/end,
// inline-size, min/max-inline-size are all lengths, 'none', or enumerated,
// then our frame isize does not depend on the parent isize.
// Note that borders never depend on the parent isize.
// XXX All of the enumerated values except -moz-available are ok too.
if (pos->ISizeDependsOnContainer(wm) ||
pos->MinISizeDependsOnContainer(wm) ||
pos->MaxISizeDependsOnContainer(wm) ||
!IsFixedPaddingSize(padding->mPadding.GetIStart(wm)) ||
!IsFixedPaddingSize(padding->mPadding.GetIEnd(wm))) {
return true;
// See if f's position might have changed. If we're RTL then the
// rules are slightly different. We'll assume percentage or auto
// margins will always induce a dependency on the size
if (!IsFixedMarginSize(margin->mMargin.GetIStart(wm)) ||
!IsFixedMarginSize(margin->mMargin.GetIEnd(wm))) {
return true;
if (wm.IsVertical() ? aCBWidthChanged : aCBHeightChanged) {
// See if f's block-size might have changed.
// If margin-block-start/end, padding-block-start/end,
// min-block-size, and max-block-size are all lengths or 'none',
// and bsize is a length or bsize and bend are auto and bstart is not auto,
// then our frame bsize does not depend on the parent bsize.
// Note that borders never depend on the parent bsize.
// FIXME(emilio): Should the BSize(wm).IsAuto() check also for the extremum
// lengths?
if ((pos->BSizeDependsOnContainer(wm) &&
!(pos->BSize(wm).IsAuto() && pos->mOffset.GetBEnd(wm).IsAuto() &&
!pos->mOffset.GetBStart(wm).IsAuto())) ||
pos->MinBSizeDependsOnContainer(wm) ||
pos->MaxBSizeDependsOnContainer(wm) ||
!IsFixedPaddingSize(padding->mPadding.GetBStart(wm)) ||
!IsFixedPaddingSize(padding->mPadding.GetBEnd(wm))) {
return true;
// See if f's position might have changed.
if (!IsFixedMarginSize(margin->mMargin.GetBStart(wm)) ||
!IsFixedMarginSize(margin->mMargin.GetBEnd(wm))) {
return true;
// Since we store coordinates relative to top and left, the position
// of a frame depends on that of its container if it is fixed relative
// to the right or bottom, or if it is positioned using percentages
// relative to the left or top. Because of the dependency on the
// sides (left and top) that we use to store coordinates, these tests
// are easier to do using physical coordinates rather than logical.
if (aCBWidthChanged) {
if (!IsFixedOffset(pos->mOffset.Get(eSideLeft))) {
return true;
// Note that even if 'left' is a length, our position can still
// depend on the containing block width, because if our direction or
// writing-mode moves from right to left (in either block or inline
// progression) and 'right' is not 'auto', we will discard 'left'
// and be positioned relative to the containing block right edge.
// 'left' length and 'right' auto is the only combination we can be
// sure of.
if ((wm.GetInlineDir() == WritingMode::eInlineRTL ||
wm.GetBlockDir() == WritingMode::eBlockRL) &&
!pos->mOffset.Get(eSideRight).IsAuto()) {
return true;
if (aCBHeightChanged) {
if (!IsFixedOffset(pos->mOffset.Get(eSideTop))) {
return true;
// See comment above for width changes.
if (wm.GetInlineDir() == WritingMode::eInlineBTT &&
!pos->mOffset.Get(eSideBottom).IsAuto()) {
return true;
return false;
void nsAbsoluteContainingBlock::DestroyFrames(
nsIFrame* aDelegatingFrame, nsIFrame* aDestructRoot,
PostDestroyData& aPostDestroyData) {
mAbsoluteFrames.DestroyFramesFrom(aDestructRoot, aPostDestroyData);
void nsAbsoluteContainingBlock::MarkSizeDependentFramesDirty() {
void nsAbsoluteContainingBlock::MarkAllFramesDirty() {
void nsAbsoluteContainingBlock::DoMarkFramesDirty(bool aMarkAllDirty) {
for (nsIFrame* kidFrame : mAbsoluteFrames) {
if (aMarkAllDirty) {
} else if (FrameDependsOnContainer(kidFrame, true, true)) {
// Add the weakest flags that will make sure we reflow this frame later
// Given an out-of-flow frame, this method returns the parent frame of its
// placeholder frame or null if it doesn't have a placeholder for some reason.
static nsContainerFrame* GetPlaceholderContainer(nsIFrame* aPositionedFrame) {
nsIFrame* placeholder = aPositionedFrame->GetPlaceholderFrame();
return placeholder ? placeholder->GetParent() : nullptr;
* This function returns the offset of an abs/fixed-pos child's static
* position, with respect to the "start" corner of its alignment container,
* according to CSS Box Alignment. This function only operates in a single
* axis at a time -- callers can choose which axis via the |aAbsPosCBAxis|
* parameter.
* @param aKidReflowInput The ReflowInput for the to-be-aligned abspos child.
* @param aKidSizeInAbsPosCBWM The child frame's size (after it's been given
* the opportunity to reflow), in terms of
* aAbsPosCBWM.
* @param aAbsPosCBSize The abspos CB size, in terms of aAbsPosCBWM.
* @param aPlaceholderContainer The parent of the child frame's corresponding
* placeholder frame, cast to a nsContainerFrame.
* (This will help us choose which alignment enum
* we should use for the child.)
* @param aAbsPosCBWM The child frame's containing block's WritingMode.
* @param aAbsPosCBAxis The axis (of the containing block) that we should
* be doing this computation for.
static nscoord OffsetToAlignedStaticPos(const ReflowInput& aKidReflowInput,
const LogicalSize& aKidSizeInAbsPosCBWM,
const LogicalSize& aAbsPosCBSize,
nsContainerFrame* aPlaceholderContainer,
WritingMode aAbsPosCBWM,
LogicalAxis aAbsPosCBAxis) {
if (!aPlaceholderContainer) {
// (The placeholder container should be the thing that kicks this whole
// process off, by setting PLACEHOLDER_STATICPOS_NEEDS_CSSALIGN. So it
// should exist... but bail gracefully if it doesn't.)
"Missing placeholder-container when computing a "
"CSS Box Alignment static position");
return 0;
// (Most of this function is simply preparing args that we'll pass to
// AlignJustifySelf at the end.)
// NOTE: Our alignment container is aPlaceholderContainer's content-box
// (or an area within it, if aPlaceholderContainer is a grid). So, we'll
// perform most of our arithmetic/alignment in aPlaceholderContainer's
// WritingMode. For brevity, we use the abbreviation "pc" for "placeholder
// container" in variables below.
WritingMode pcWM = aPlaceholderContainer->GetWritingMode();
// Find what axis aAbsPosCBAxis corresponds to, in placeholder's parent's
// writing-mode.
LogicalAxis pcAxis =
(pcWM.IsOrthogonalTo(aAbsPosCBWM) ? GetOrthogonalAxis(aAbsPosCBAxis)
: aAbsPosCBAxis);
const bool placeholderContainerIsContainingBlock =
aPlaceholderContainer == aKidReflowInput.mCBReflowInput->mFrame;
LayoutFrameType parentType = aPlaceholderContainer->Type();
LogicalSize alignAreaSize(pcWM);
if (parentType == LayoutFrameType::FlexContainer) {
// We store the frame rect in FinishAndStoreOverflow, which runs _after_
// reflowing the absolute frames, so handle the special case of the frame
// being the actual containing block here, by getting the size from
// aAbsPosCBSize.
// The alignment container is the flex container's content box.
if (placeholderContainerIsContainingBlock) {
alignAreaSize = aAbsPosCBSize.ConvertTo(pcWM, aAbsPosCBWM);
// aAbsPosCBSize is the padding-box, so substract the padding to get the
// content box.
alignAreaSize -=
} else {
alignAreaSize = aPlaceholderContainer->GetLogicalSize(pcWM);
LogicalMargin pcBorderPadding =
alignAreaSize -= pcBorderPadding.Size(pcWM);
} else if (parentType == LayoutFrameType::GridContainer) {
// This abspos elem's parent is a grid container. Per CSS Grid 10.1 & 10.2:
// - If the grid container *also* generates the abspos containing block (a
// grid area) for this abspos child, we use that abspos containing block as
// the alignment container, too. (And its size is aAbsPosCBSize.)
// - Otherwise, we use the grid's padding box as the alignment container.
if (placeholderContainerIsContainingBlock) {
// The alignment container is the grid area that we're using as the
// absolute containing block.
alignAreaSize = aAbsPosCBSize.ConvertTo(pcWM, aAbsPosCBWM);
} else {
// The alignment container is a the grid container's padding box (which
// we can get by subtracting away its border from frame's size):
alignAreaSize = aPlaceholderContainer->GetLogicalSize(pcWM);
LogicalMargin pcBorder =
alignAreaSize -= pcBorder.Size(pcWM);
} else {
NS_ERROR("Unsupported container for abpsos CSS Box Alignment");
return 0; // (leave the child at the start of its alignment container)
nscoord alignAreaSizeInAxis = (pcAxis == eLogicalAxisInline)
? alignAreaSize.ISize(pcWM)
: alignAreaSize.BSize(pcWM);
AlignJustifyFlags flags = AlignJustifyFlags::IgnoreAutoMargins;
StyleAlignFlags alignConst =
// If the safe bit in alignConst is set, set the safe flag in |flags|.
// Note: If no <overflow-position> is specified, we behave as 'unsafe'.
// This doesn't quite match the css-align spec, which has an [at-risk]
// "smart default" behavior with some extra nuance about scroll containers.
if (alignConst & StyleAlignFlags::SAFE) {
flags |= AlignJustifyFlags::OverflowSafe;
alignConst &= ~StyleAlignFlags::FLAG_BITS;
// Find out if placeholder-container & the OOF child have the same start-sides
// in the placeholder-container's pcAxis.
WritingMode kidWM = aKidReflowInput.GetWritingMode();
if (pcWM.ParallelAxisStartsOnSameSide(pcAxis, kidWM)) {
flags |= AlignJustifyFlags::SameSide;
// (baselineAdjust is unused. CSSAlignmentForAbsPosChild() should've
// converted 'baseline'/'last baseline' enums to their fallback values.)
const nscoord baselineAdjust = nscoord(0);
// AlignJustifySelf operates in the kid's writing mode, so we need to
// represent the child's size and the desired axis in that writing mode:
LogicalSize kidSizeInOwnWM =
aKidSizeInAbsPosCBWM.ConvertTo(kidWM, aAbsPosCBWM);
LogicalAxis kidAxis =
(kidWM.IsOrthogonalTo(aAbsPosCBWM) ? GetOrthogonalAxis(aAbsPosCBAxis)
: aAbsPosCBAxis);
nscoord offset = CSSAlignUtils::AlignJustifySelf(
alignConst, kidAxis, flags, baselineAdjust, alignAreaSizeInAxis,
aKidReflowInput, kidSizeInOwnWM);
// "offset" is in terms of the CSS Box Alignment container (i.e. it's in
// terms of pcWM). But our return value needs to in terms of the containing
// block's writing mode, which might have the opposite directionality in the
// given axis. In that case, we just need to negate "offset" when returning,
// to make it have the right effect as an offset for coordinates in the
// containing block's writing mode.
if (!pcWM.ParallelAxisStartsOnSameSide(pcAxis, aAbsPosCBWM)) {
return -offset;
return offset;
void nsAbsoluteContainingBlock::ResolveSizeDependentOffsets(
nsPresContext* aPresContext, ReflowInput& aKidReflowInput,
const LogicalSize& aKidSize, const LogicalMargin& aMargin,
LogicalMargin* aOffsets, LogicalSize* aLogicalCBSize) {
WritingMode wm = aKidReflowInput.GetWritingMode();
WritingMode outerWM = aKidReflowInput.mParentReflowInput->GetWritingMode();
// Now that we know the child's size, we resolve any sentinel values in its
// IStart/BStart offset coordinates that depend on that size.
// * NS_AUTOOFFSET indicates that the child's position in the given axis
// is determined by its end-wards offset property, combined with its size and
// available space. e.g.: "top: auto; height: auto; bottom: 50px"
// * m{I,B}OffsetsResolvedAfterSize indicate that the child is using its
// static position in that axis, *and* its static position is determined by
// the axis-appropriate css-align property (which may require the child's
// size, e.g. to center it within the parent).
if ((NS_AUTOOFFSET == aOffsets->IStart(outerWM)) ||
(NS_AUTOOFFSET == aOffsets->BStart(outerWM)) ||
aKidReflowInput.mFlags.mIOffsetsNeedCSSAlign ||
aKidReflowInput.mFlags.mBOffsetsNeedCSSAlign) {
if (-1 == aLogicalCBSize->ISize(wm)) {
// Get the containing block width/height
const ReflowInput* parentRI = aKidReflowInput.mParentReflowInput;
*aLogicalCBSize = aKidReflowInput.ComputeContainingBlockRectangle(
aPresContext, parentRI);
const LogicalSize logicalCBSizeOuterWM =
aLogicalCBSize->ConvertTo(outerWM, wm);
// placeholderContainer is used in each of the m{I,B}OffsetsNeedCSSAlign
// clauses. We declare it at this scope so we can avoid having to look
// it up twice (and only look it up if it's needed).
nsContainerFrame* placeholderContainer = nullptr;
if (NS_AUTOOFFSET == aOffsets->IStart(outerWM)) {
"Can't solve for both start and end");
aOffsets->IStart(outerWM) =
logicalCBSizeOuterWM.ISize(outerWM) - aOffsets->IEnd(outerWM) -
aMargin.IStartEnd(outerWM) - aKidSize.ISize(outerWM);
} else if (aKidReflowInput.mFlags.mIOffsetsNeedCSSAlign) {
placeholderContainer = GetPlaceholderContainer(aKidReflowInput.mFrame);
nscoord offset = OffsetToAlignedStaticPos(
aKidReflowInput, aKidSize, logicalCBSizeOuterWM, placeholderContainer,
outerWM, eLogicalAxisInline);
// Shift IStart from its current position (at start corner of the
// alignment container) by the returned offset. And set IEnd to the
// distance between the kid's end edge to containing block's end edge.
aOffsets->IStart(outerWM) += offset;
aOffsets->IEnd(outerWM) =
logicalCBSizeOuterWM.ISize(outerWM) -
(aOffsets->IStart(outerWM) + aKidSize.ISize(outerWM));
if (NS_AUTOOFFSET == aOffsets->BStart(outerWM)) {
aOffsets->BStart(outerWM) =
logicalCBSizeOuterWM.BSize(outerWM) - aOffsets->BEnd(outerWM) -
aMargin.BStartEnd(outerWM) - aKidSize.BSize(outerWM);
} else if (aKidReflowInput.mFlags.mBOffsetsNeedCSSAlign) {
if (!placeholderContainer) {
placeholderContainer = GetPlaceholderContainer(aKidReflowInput.mFrame);
nscoord offset = OffsetToAlignedStaticPos(
aKidReflowInput, aKidSize, logicalCBSizeOuterWM, placeholderContainer,
outerWM, eLogicalAxisBlock);
// Shift BStart from its current position (at start corner of the
// alignment container) by the returned offset. And set BEnd to the
// distance between the kid's end edge to containing block's end edge.
aOffsets->BStart(outerWM) += offset;
aOffsets->BEnd(outerWM) =
logicalCBSizeOuterWM.BSize(outerWM) -
(aOffsets->BStart(outerWM) + aKidSize.BSize(outerWM));
aKidReflowInput.SetComputedLogicalOffsets(outerWM, *aOffsets);
void nsAbsoluteContainingBlock::ResolveAutoMarginsAfterLayout(
ReflowInput& aKidReflowInput, const LogicalSize* aLogicalCBSize,
const LogicalSize& aKidSize, LogicalMargin& aMargin,
LogicalMargin& aOffsets) {
WritingMode wm = aKidReflowInput.GetWritingMode();
WritingMode outerWM = aKidReflowInput.mParentReflowInput->GetWritingMode();
const LogicalSize kidSizeInWM = aKidSize.ConvertTo(wm, outerWM);
LogicalMargin marginInWM = aMargin.ConvertTo(wm, outerWM);
LogicalMargin offsetsInWM = aOffsets.ConvertTo(wm, outerWM);
// No need to substract border sizes because aKidSize has it included
// already
nscoord availMarginSpace = aLogicalCBSize->BSize(wm) - kidSizeInWM.BSize(wm) -
offsetsInWM.BStartEnd(wm) -
if (availMarginSpace < 0) {
availMarginSpace = 0;
const auto& styleMargin = aKidReflowInput.mStyleMargin;
if (wm.IsOrthogonalTo(outerWM)) {
availMarginSpace, outerWM,
styleMargin->mMargin.GetIEnd(outerWM).IsAuto(), aMargin, aOffsets);
} else {
availMarginSpace, outerWM,
styleMargin->mMargin.GetBEnd(outerWM).IsAuto(), aMargin, aOffsets);
aKidReflowInput.SetComputedLogicalMargin(outerWM, aMargin);
aKidReflowInput.SetComputedLogicalOffsets(outerWM, aOffsets);
nsMargin* propValue =
// InitOffsets should've created a UsedMarginProperty for us, if any margin is
// auto.
MOZ_ASSERT_IF(styleMargin->HasInlineAxisAuto(outerWM) ||
if (propValue) {
*propValue = aMargin.GetPhysicalMargin(outerWM);
// XXX Optimize the case where it's a resize reflow and the absolutely
// positioned child has the exact same size and position and skip the
// reflow...
// When bug 154892 is checked in, make sure that when
// mChildListID == kFixedList, the height is unconstrained.
// since we don't allow replicated frames to split.
void nsAbsoluteContainingBlock::ReflowAbsoluteFrame(
nsIFrame* aDelegatingFrame, nsPresContext* aPresContext,
const ReflowInput& aReflowInput, const nsRect& aContainingBlock,
AbsPosReflowFlags aFlags, nsIFrame* aKidFrame, nsReflowStatus& aStatus,
OverflowAreas* aOverflowAreas) {
MOZ_ASSERT(aStatus.IsEmpty(), "Caller should pass a fresh reflow status!");
#ifdef DEBUG
if (nsBlockFrame::gNoisyReflow) {
nsIFrame::IndentBy(stdout, nsBlockFrame::gNoiseIndent);
printf("abs pos ");
nsAutoString name;
printf("%s ", NS_LossyConvertUTF16toASCII(name).get());
char width[16];
char height[16];
PrettyUC(aReflowInput.AvailableWidth(), width, 16);
PrettyUC(aReflowInput.AvailableHeight(), height, 16);
printf(" a=%s,%s ", width, height);
PrettyUC(aReflowInput.ComputedWidth(), width, 16);
PrettyUC(aReflowInput.ComputedHeight(), height, 16);
printf("c=%s,%s \n", width, height);
AutoNoisyIndenter indent(nsBlockFrame::gNoisy);
#endif // DEBUG
WritingMode wm = aKidFrame->GetWritingMode();
LogicalSize logicalCBSize(wm, aContainingBlock.Size());
nscoord availISize = logicalCBSize.ISize(wm);
if (availISize == -1) {
aReflowInput.ComputedSize(wm).ISize(wm) != NS_UNCONSTRAINEDSIZE,
"Must have a useful inline-size _somewhere_");
availISize = aReflowInput.ComputedSizeWithPadding(wm).ISize(wm);
ReflowInput::InitFlags initFlags;
if (aFlags & AbsPosReflowFlags::IsGridContainerCB) {
// When a grid container generates the abs.pos. CB for a *child* then
// the static position is determined via CSS Box Alignment within the
// abs.pos. CB (a grid area, i.e. a piece of the grid). In this scenario,
// due to the multiple coordinate spaces in play, we use a convenience flag
// to simply have the child's ReflowInput give it a static position at its
// abs.pos. CB origin, and then we'll align & offset it from there.
nsIFrame* placeholder = aKidFrame->GetPlaceholderFrame();
if (placeholder && placeholder->GetParent() == aDelegatingFrame) {
initFlags += ReflowInput::InitFlag::StaticPosIsCBOrigin;
bool constrainBSize =
(aReflowInput.AvailableBSize() != NS_UNCONSTRAINEDSIZE) &&
// Don't split if told not to (e.g. for fixed frames)
(aFlags & AbsPosReflowFlags::ConstrainHeight) &&
// XXX we don't handle splitting frames for inline absolute containing
// blocks yet
!aDelegatingFrame->IsInlineFrame() &&
// Bug 1588623: Support splitting absolute positioned multicol containers.
!aKidFrame->IsColumnSetWrapperFrame() &&
// Don't split things below the fold. (Ideally we shouldn't *have*
// anything totally below the fold, but we can't position frames
// across next-in-flow breaks yet.
(aKidFrame->GetLogicalRect(aContainingBlock.Size()).BStart(wm) <=
// Get the border values
const WritingMode outerWM = aReflowInput.GetWritingMode();
const LogicalMargin border = aDelegatingFrame->GetLogicalUsedBorder(outerWM);
const nscoord availBSize = constrainBSize
? aReflowInput.AvailableBSize() -
border.ConvertTo(wm, outerWM).BStart(wm)
ReflowInput kidReflowInput(aPresContext, aReflowInput, aKidFrame,
LogicalSize(wm, availISize, availBSize),
Some(logicalCBSize), initFlags);
if (kidReflowInput.AvailableBSize() != NS_UNCONSTRAINEDSIZE) {
// Shrink available block-size if it's constrained.
kidReflowInput.AvailableBSize() -=
const nscoord kidOffsetBStart =
if (NS_AUTOOFFSET != kidOffsetBStart) {
kidReflowInput.AvailableBSize() -= kidOffsetBStart;
// Do the reflow
ReflowOutput kidDesiredSize(kidReflowInput);
aKidFrame->Reflow(aPresContext, kidDesiredSize, kidReflowInput, aStatus);
const LogicalSize kidSize = kidDesiredSize.Size(outerWM);
LogicalMargin offsets = kidReflowInput.ComputedLogicalOffsets(outerWM);
LogicalMargin margin = kidReflowInput.ComputedLogicalMargin(outerWM);
// If we're doing CSS Box Alignment in either axis, that will apply the
// margin for us in that axis (since the thing that's aligned is the margin
// box). So, we clear out the margin here to avoid applying it twice.
if (kidReflowInput.mFlags.mIOffsetsNeedCSSAlign) {
margin.IStart(outerWM) = margin.IEnd(outerWM) = 0;
if (kidReflowInput.mFlags.mBOffsetsNeedCSSAlign) {
margin.BStart(outerWM) = margin.BEnd(outerWM) = 0;
// If we're solving for start in either inline or block direction,
// then compute it now that we know the dimensions.
ResolveSizeDependentOffsets(aPresContext, kidReflowInput, kidSize, margin,
&offsets, &logicalCBSize);
if (kidReflowInput.mFrame->HasIntrinsicKeywordForBSize()) {
ResolveAutoMarginsAfterLayout(kidReflowInput, &logicalCBSize, kidSize,
margin, offsets);
// Position the child relative to our padding edge
LogicalRect rect(
border.IStart(outerWM) + offsets.IStart(outerWM) + margin.IStart(outerWM),
border.BStart(outerWM) + offsets.BStart(outerWM) + margin.BStart(outerWM),
kidSize.ISize(outerWM), kidSize.BSize(outerWM));
nsRect r = rect.GetPhysicalRect(
outerWM, logicalCBSize.GetPhysicalSize(wm) +
// Offset the frame rect by the given origin of the absolute containing block.
r.x += aContainingBlock.x;
r.y += aContainingBlock.y;
nsView* view = aKidFrame->GetView();
if (view) {
// Size and position the view and set its opacity, visibility, content
// transparency, and clip
nsContainerFrame::SyncFrameViewAfterReflow(aPresContext, aKidFrame, view,
} else {
aKidFrame->DidReflow(aPresContext, &kidReflowInput);
#ifdef DEBUG
if (nsBlockFrame::gNoisyReflow) {
nsIFrame::IndentBy(stdout, nsBlockFrame::gNoiseIndent - 1);
printf("abs pos ");
nsAutoString name;
printf("%s ", NS_LossyConvertUTF16toASCII(name).get());
printf("%p rect=%d,%d,%d,%d\n", static_cast<void*>(aKidFrame), r.x, r.y,
r.width, r.height);
if (aOverflowAreas) {
aOverflowAreas->UnionWith(kidDesiredSize.mOverflowAreas + r.TopLeft());