Source code

Revision control

Copy as Markdown

Other Tools

/* -*- 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 */
/* struct containing the input to nsIFrame::Reflow */
#include "mozilla/ReflowInput.h"
#include <algorithm>
#include "CounterStyleManager.h"
#include "LayoutLogging.h"
#include "mozilla/dom/HTMLInputElement.h"
#include "mozilla/WritingModes.h"
#include "nsBlockFrame.h"
#include "nsFlexContainerFrame.h"
#include "nsFontInflationData.h"
#include "nsFontMetrics.h"
#include "nsGkAtoms.h"
#include "nsGridContainerFrame.h"
#include "nsIContent.h"
#include "nsIFrame.h"
#include "nsIFrameInlines.h"
#include "nsImageFrame.h"
#include "nsIPercentBSizeObserver.h"
#include "nsLayoutUtils.h"
#include "nsLineBox.h"
#include "nsPresContext.h"
#include "nsStyleConsts.h"
#include "nsTableFrame.h"
#include "StickyScrollContainer.h"
using namespace mozilla;
using namespace mozilla::css;
using namespace mozilla::dom;
using namespace mozilla::layout;
static bool CheckNextInFlowParenthood(nsIFrame* aFrame, nsIFrame* aParent) {
nsIFrame* frameNext = aFrame->GetNextInFlow();
nsIFrame* parentNext = aParent->GetNextInFlow();
return frameNext && parentNext && frameNext->GetParent() == parentNext;
* Adjusts the margin for a list (ol, ul), if necessary, depending on
* font inflation settings. Unfortunately, because bullets from a list are
* placed in the margin area, we only have ~40px in which to place the
* bullets. When they are inflated, however, this causes problems, since
* the text takes up more space than is available in the margin.
* This method will return a small amount (in app units) by which the
* margin can be adjusted, so that the space is available for list
* bullets to be rendered with font inflation enabled.
static nscoord FontSizeInflationListMarginAdjustment(const nsIFrame* aFrame) {
if (!aFrame->IsBlockFrameOrSubclass()) {
return 0;
// We only want to adjust the margins if we're dealing with an ordered list.
const nsBlockFrame* blockFrame = static_cast<const nsBlockFrame*>(aFrame);
if (!blockFrame->HasMarker()) {
return 0;
float inflation = nsLayoutUtils::FontSizeInflationFor(aFrame);
if (inflation <= 1.0f) {
return 0;
// The HTML spec states that the default padding for ordered lists
// begins at 40px, indicating that we have 40px of space to place a
// bullet. When performing font inflation calculations, we add space
// equivalent to this, but simply inflated at the same amount as the
// text, in app units.
auto margin = nsPresContext::CSSPixelsToAppUnits(40) * (inflation - 1);
auto* list = aFrame->StyleList();
if (!list->mCounterStyle.IsAtom()) {
return margin;
nsAtom* type = list->mCounterStyle.AsAtom();
if (type != nsGkAtoms::none && type != nsGkAtoms::disc &&
type != nsGkAtoms::circle && type != nsGkAtoms::square &&
type != nsGkAtoms::disclosure_closed &&
type != nsGkAtoms::disclosure_open) {
return margin;
return 0;
SizeComputationInput::SizeComputationInput(nsIFrame* aFrame,
gfxContext* aRenderingContext)
: mFrame(aFrame),
mComputedPadding(mWritingMode) {
nsIFrame* aFrame, gfxContext* aRenderingContext,
WritingMode aContainingBlockWritingMode, nscoord aContainingBlockISize,
const Maybe<LogicalMargin>& aBorder, const Maybe<LogicalMargin>& aPadding)
: SizeComputationInput(aFrame, aRenderingContext) {
InitOffsets(aContainingBlockWritingMode, aContainingBlockISize,
mFrame->Type(), {}, aBorder, aPadding);
// Initialize a <b>root</b> reflow input with a rendering context to
// use for measuring things.
ReflowInput::ReflowInput(nsPresContext* aPresContext, nsIFrame* aFrame,
gfxContext* aRenderingContext,
const LogicalSize& aAvailableSpace, InitFlags aFlags)
: SizeComputationInput(aFrame, aRenderingContext),
mAvailableSize(aAvailableSpace) {
MOZ_ASSERT(aRenderingContext, "no rendering context");
MOZ_ASSERT(aPresContext, "no pres context");
MOZ_ASSERT(aFrame, "no frame");
MOZ_ASSERT(aPresContext == aFrame->PresContext(), "wrong pres context");
if (aFlags.contains(InitFlag::DummyParentReflowInput)) {
mFlags.mDummyParentReflowInput = true;
if (aFlags.contains(InitFlag::StaticPosIsCBOrigin)) {
mFlags.mStaticPosIsCBOrigin = true;
if (!aFlags.contains(InitFlag::CallerWillInit)) {
// When we encounter a PageContent frame this will be set to true.
mFlags.mCanHaveClassABreakpoints = false;
// Initialize a reflow input for a child frame's reflow. Some state
// is copied from the parent reflow input; the remaining state is
// computed.
ReflowInput::ReflowInput(nsPresContext* aPresContext,
const ReflowInput& aParentReflowInput,
nsIFrame* aFrame, const LogicalSize& aAvailableSpace,
const Maybe<LogicalSize>& aContainingBlockSize,
InitFlags aFlags,
const StyleSizeOverrides& aSizeOverrides,
ComputeSizeFlags aComputeSizeFlags)
: SizeComputationInput(aFrame, aParentReflowInput.mRenderingContext),
mLineLayout(mFrame->IsLineParticipant() ? aParentReflowInput.mLineLayout
: nullptr),
(aParentReflowInput.mPercentBSizeObserver &&
? aParentReflowInput.mPercentBSizeObserver
: nullptr),
mReflowDepth(aParentReflowInput.mReflowDepth + 1),
mAvailableSize(aAvailableSpace) {
MOZ_ASSERT(aPresContext, "no pres context");
MOZ_ASSERT(aFrame, "no frame");
MOZ_ASSERT(aPresContext == aFrame->PresContext(), "wrong pres context");
MOZ_ASSERT(!mFlags.mSpecialBSizeReflow || !aFrame->IsSubtreeDirty(),
"frame should be clean when getting special bsize reflow");
if (mWritingMode.IsOrthogonalTo(aParentReflowInput.GetWritingMode())) {
// If we're setting up for an orthogonal flow, and the parent reflow input
// had a constrained ComputedBSize, we can use that as our AvailableISize
// in preference to leaving it unconstrained.
if (AvailableISize() == NS_UNCONSTRAINEDSIZE &&
aParentReflowInput.ComputedBSize() != NS_UNCONSTRAINEDSIZE) {
// Note: mFlags was initialized as a copy of aParentReflowInput.mFlags up in
// this constructor's init list, so the only flags that we need to explicitly
// initialize here are those that may need a value other than our parent's.
mFlags.mNextInFlowUntouched =
aParentReflowInput.mFlags.mNextInFlowUntouched &&
CheckNextInFlowParenthood(aFrame, aParentReflowInput.mFrame);
mFlags.mAssumingHScrollbar = mFlags.mAssumingVScrollbar = false;
mFlags.mIsColumnBalancing = false;
mFlags.mColumnSetWrapperHasNoBSizeLeft = false;
mFlags.mTreatBSizeAsIndefinite = false;
mFlags.mDummyParentReflowInput = false;
mFlags.mStaticPosIsCBOrigin = aFlags.contains(InitFlag::StaticPosIsCBOrigin);
mFlags.mIOffsetsNeedCSSAlign = mFlags.mBOffsetsNeedCSSAlign = false;
// aPresContext->IsPaginated() and the named pages pref should have been
// checked when constructing the root ReflowInput.
if (aParentReflowInput.mFlags.mCanHaveClassABreakpoints) {
"mCanHaveClassABreakpoints set during non-paginated reflow.");
using mozilla::LayoutFrameType;
switch (mFrame->Type()) {
case LayoutFrameType::PageContent:
// PageContent requires paginated reflow.
"nsPageContentFrame should not be in non-paginated reflow");
"mFlags.mCanHaveClassABreakpoints should have been "
"initalized to false before we found nsPageContentFrame");
mFlags.mCanHaveClassABreakpoints = true;
case LayoutFrameType::Block: // FALLTHROUGH
case LayoutFrameType::Canvas: // FALLTHROUGH
case LayoutFrameType::FlexContainer: // FALLTHROUGH
case LayoutFrameType::GridContainer:
if (mFrame->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW)) {
// Never allow breakpoints inside of out-of-flow frames.
mFlags.mCanHaveClassABreakpoints = false;
// This frame type can have class A breakpoints, inherit this flag
// from the parent (this is done for all flags during construction).
// This also includes Canvas frames, as each PageContent frame always
// has exactly one child which is a Canvas frame.
// Do NOT include the subclasses of BlockFrame here, as the ones for
// which this could be applicable (ColumnSetWrapper and the MathML
// frames) cannot have class A breakpoints.
MOZ_ASSERT(mFlags.mCanHaveClassABreakpoints ==
mFlags.mCanHaveClassABreakpoints = false;
if (aFlags.contains(InitFlag::DummyParentReflowInput) ||
(mParentReflowInput->mFlags.mDummyParentReflowInput &&
mFrame->IsTableFrame())) {
mFlags.mDummyParentReflowInput = true;
if (!aFlags.contains(InitFlag::CallerWillInit)) {
Init(aPresContext, aContainingBlockSize);
template <typename SizeOrMaxSize>
inline nscoord SizeComputationInput::ComputeISizeValue(
const WritingMode aWM, const LogicalSize& aContainingBlockSize,
const LogicalSize& aContentEdgeToBoxSizing, nscoord aBoxSizingToMarginEdge,
const SizeOrMaxSize& aSize) const {
return mFrame
->ComputeISizeValue(mRenderingContext, aWM, aContainingBlockSize,
aContentEdgeToBoxSizing, aBoxSizingToMarginEdge,
template <typename SizeOrMaxSize>
nscoord SizeComputationInput::ComputeISizeValue(
const LogicalSize& aContainingBlockSize, StyleBoxSizing aBoxSizing,
const SizeOrMaxSize& aSize) const {
WritingMode wm = GetWritingMode();
const auto borderPadding = ComputedLogicalBorderPadding(wm);
LogicalSize inside = aBoxSizing == StyleBoxSizing::Border
? borderPadding.Size(wm)
: LogicalSize(wm);
nscoord outside =
borderPadding.IStartEnd(wm) + ComputedLogicalMargin(wm).IStartEnd(wm);
outside -= inside.ISize(wm);
return ComputeISizeValue(wm, aContainingBlockSize, inside, outside, aSize);
nscoord SizeComputationInput::ComputeBSizeValue(
nscoord aContainingBlockBSize, StyleBoxSizing aBoxSizing,
const LengthPercentage& aSize) const {
WritingMode wm = GetWritingMode();
nscoord inside = 0;
if (aBoxSizing == StyleBoxSizing::Border) {
inside = ComputedLogicalBorderPadding(wm).BStartEnd(wm);
return nsLayoutUtils::ComputeBSizeValue(aContainingBlockBSize, inside, aSize);
nsSize ReflowInput::ComputedSizeAsContainerIfConstrained() const {
LogicalSize size = ComputedSize();
if (size.ISize(mWritingMode) == NS_UNCONSTRAINEDSIZE) {
size.ISize(mWritingMode) = 0;
} else {
size.ISize(mWritingMode) += mComputedBorderPadding.IStartEnd(mWritingMode);
if (size.BSize(mWritingMode) == NS_UNCONSTRAINEDSIZE) {
size.BSize(mWritingMode) = 0;
} else {
size.BSize(mWritingMode) += mComputedBorderPadding.BStartEnd(mWritingMode);
return size.GetPhysicalSize(mWritingMode);
bool ReflowInput::ShouldReflowAllKids() const {
// Note that we could make a stronger optimization for IsBResize if
// we use it in a ShouldReflowChild test that replaces the current
// were tested there along with NS_FRAME_CONTAINS_RELATIVE_BSIZE.
// This would need to be combined with a slight change in which
// frames NS_FRAME_CONTAINS_RELATIVE_BSIZE is marked on.
return mFrame->HasAnyStateBits(NS_FRAME_IS_DIRTY) || IsIResize() ||
(IsBResize() &&
void ReflowInput::SetComputedISize(nscoord aComputedISize,
ResetResizeFlags aFlags) {
// It'd be nice to assert that |frame| is not in reflow, but this fails
// because viewport frames reset the computed isize on a copy of their reflow
// input when reflowing fixed-pos kids. In that case we actually don't want
// to mess with the resize flags, because comparing the frame's rect to the
// munged computed isize is pointless.
NS_WARNING_ASSERTION(aComputedISize >= 0, "Invalid computed inline-size!");
if (ComputedISize() != aComputedISize) {
mComputedSize.ISize(mWritingMode) = std::max(0, aComputedISize);
if (aFlags == ResetResizeFlags::Yes) {
InitResizeFlags(mFrame->PresContext(), mFrame->Type());
void ReflowInput::SetComputedBSize(nscoord aComputedBSize,
ResetResizeFlags aFlags) {
// It'd be nice to assert that |frame| is not in reflow, but this fails
// for the same reason as above.
NS_WARNING_ASSERTION(aComputedBSize >= 0, "Invalid computed block-size!");
if (ComputedBSize() != aComputedBSize) {
mComputedSize.BSize(mWritingMode) = std::max(0, aComputedBSize);
if (aFlags == ResetResizeFlags::Yes) {
InitResizeFlags(mFrame->PresContext(), mFrame->Type());
void ReflowInput::Init(nsPresContext* aPresContext,
const Maybe<LogicalSize>& aContainingBlockSize,
const Maybe<LogicalMargin>& aBorder,
const Maybe<LogicalMargin>& aPadding) {
if (AvailableISize() == NS_UNCONSTRAINEDSIZE) {
// Look up the parent chain for an orthogonal inline limit,
// and reset AvailableISize() if found.
for (const ReflowInput* parent = mParentReflowInput; parent != nullptr;
parent = parent->mParentReflowInput) {
if (parent->GetWritingMode().IsOrthogonalTo(mWritingMode) &&
parent->mOrthogonalLimit != NS_UNCONSTRAINEDSIZE) {
"have unconstrained inline-size; this should only "
"result from very large sizes, not attempts at "
"intrinsic inline-size calculation");
mStylePosition = mFrame->StylePosition();
mStyleDisplay = mFrame->StyleDisplay();
mStyleBorder = mFrame->StyleBorder();
mStyleMargin = mFrame->StyleMargin();
LayoutFrameType type = mFrame->Type();
if (type == mozilla::LayoutFrameType::Placeholder) {
// Placeholders have a no-op Reflow method that doesn't need the rest of
// this initialization, so we bail out early.
mComputedSize.SizeTo(mWritingMode, 0, 0);
mFlags.mIsReplaced = mFrame->IsReplaced() || mFrame->IsReplacedWithBlock();
InitConstraints(aPresContext, aContainingBlockSize, aBorder, aPadding, type);
InitResizeFlags(aPresContext, type);
nsIFrame* parent = mFrame->GetParent();
if (parent && parent->HasAnyStateBits(NS_FRAME_IN_CONSTRAINED_BSIZE) &&
!(parent->IsScrollFrame() &&
parent->StyleDisplay()->mOverflowY != StyleOverflow::Hidden)) {
} else if (type == LayoutFrameType::SVGForeignObject) {
// An SVG foreignObject frame is inherently constrained block-size.
} else {
const auto& bSizeCoord = mStylePosition->BSize(mWritingMode);
const auto& maxBSizeCoord = mStylePosition->MaxBSize(mWritingMode);
if ((!bSizeCoord.BehavesLikeInitialValueOnBlockAxis() ||
!maxBSizeCoord.BehavesLikeInitialValueOnBlockAxis()) &&
// Don't set NS_FRAME_IN_CONSTRAINED_BSIZE on body or html elements.
(mFrame->GetContent() && !(mFrame->GetContent()->IsAnyOfHTMLElements(
nsGkAtoms::body, nsGkAtoms::html)))) {
// If our block-size was specified as a percentage, then this could
// actually resolve to 'auto', based on:
nsIFrame* containingBlk = mFrame;
while (containingBlk) {
const nsStylePosition* stylePos = containingBlk->StylePosition();
const auto& bSizeCoord = stylePos->BSize(mWritingMode);
const auto& maxBSizeCoord = stylePos->MaxBSize(mWritingMode);
if ((bSizeCoord.IsLengthPercentage() && !bSizeCoord.HasPercent()) ||
(maxBSizeCoord.IsLengthPercentage() &&
!maxBSizeCoord.HasPercent())) {
} else if (bSizeCoord.HasPercent() || maxBSizeCoord.HasPercent()) {
if (!(containingBlk = containingBlk->GetContainingBlock())) {
// If we've reached the top of the tree, then we don't have
// a constrained block-size.
} else {
} else {
if (mParentReflowInput &&
mParentReflowInput->GetWritingMode().IsOrthogonalTo(mWritingMode)) {
// Orthogonal frames are always reflowed with an unconstrained
// dimension to avoid incomplete reflow across an orthogonal
// boundary. Normally this is the block-size, but for column sets
// with auto-height it's the inline-size, so that they can add
// columns in the container's block direction
if (type == LayoutFrameType::ColumnSet &&
mStylePosition->ISize(mWritingMode).IsAuto()) {
SetComputedISize(NS_UNCONSTRAINEDSIZE, ResetResizeFlags::No);
} else {
if (mFrame->GetContainSizeAxes().mBContained) {
// In the case that a box is size contained in block axis, we want to ensure
// that it is also monolithic. We do this by setting AvailableBSize() to an
// unconstrained size to avoid fragmentation.
(mStyleDisplay->IsInlineOutsideStyle() && !mFrame->IsReplaced()) ||
type == LayoutFrameType::Text ||
"have unconstrained inline-size; this should only "
"result from very large sizes, not attempts at "
"intrinsic inline-size calculation");
static bool MightBeContainingBlockFor(nsIFrame* aMaybeContainingBlock,
nsIFrame* aFrame,
const nsStyleDisplay* aStyleDisplay) {
// Keep this in sync with nsIFrame::GetContainingBlock.
if (aFrame->IsAbsolutelyPositioned(aStyleDisplay) &&
aMaybeContainingBlock == aFrame->GetParent()) {
return true;
return aMaybeContainingBlock->IsBlockContainer();
void ReflowInput::InitCBReflowInput() {
if (!mParentReflowInput) {
mCBReflowInput = nullptr;
if (mParentReflowInput->mFlags.mDummyParentReflowInput) {
mCBReflowInput = mParentReflowInput;
// To avoid a long walk up the frame tree check if the parent frame can be a
// containing block for mFrame.
if (MightBeContainingBlockFor(mParentReflowInput->mFrame, mFrame,
mStyleDisplay) &&
mParentReflowInput->mFrame ==
mFrame->GetContainingBlock(0, mStyleDisplay)) {
// Inner table frames need to use the containing block of the outer
// table frame.
if (mFrame->IsTableFrame()) {
mCBReflowInput = mParentReflowInput->mCBReflowInput;
} else {
mCBReflowInput = mParentReflowInput;
} else {
mCBReflowInput = mParentReflowInput->mCBReflowInput;
/* Check whether CalcQuirkContainingBlockHeight would stop on the
* given reflow input, using its block as a height. (essentially
* returns false for any case in which CalcQuirkContainingBlockHeight
* has a "continue" in its main loop.)
* XXX Maybe refactor CalcQuirkContainingBlockHeight so it uses
* this function as well
static bool IsQuirkContainingBlockHeight(const ReflowInput* rs,
LayoutFrameType aFrameType) {
if (LayoutFrameType::Block == aFrameType ||
LayoutFrameType::Scroll == aFrameType) {
// Note: This next condition could change due to a style change,
// but that would cause a style reflow anyway, which means we're ok.
if (NS_UNCONSTRAINEDSIZE == rs->ComputedHeight()) {
if (!rs->mFrame->IsAbsolutelyPositioned(rs->mStyleDisplay)) {
return false;
return true;
void ReflowInput::InitResizeFlags(nsPresContext* aPresContext,
LayoutFrameType aFrameType) {
mFlags.mIsBResizeForPercentages = false;
const WritingMode wm = mWritingMode; // just a shorthand
// We should report that we have a resize in the inline dimension if
// *either* the border-box size or the content-box size in that
// dimension has changed. It might not actually be necessary to do
// this if the border-box size has changed and the content-box size
// has not changed, but since we've historically used the flag to mean
// border-box size change, continue to do that. It's possible for
// the content-box size to change without a border-box size change or
// a style change given (1) a fixed width (possibly fixed by max-width
// or min-width), box-sizing:border-box, and percentage padding;
// (2) box-sizing:content-box, M% width, and calc(Npx - M%) padding.
// However, we don't actually have the information at this point to tell
// whether the content-box size has changed, since both style data and the
// UsedPaddingProperty() have already been updated in
// SizeComputationInput::InitOffsets(). So, we check the HasPaddingChange()
// bit for the cases where it's possible for the content-box size to have
// changed without either (a) a change in the border-box size or (b) an
// nsChangeHint_NeedDirtyReflow change hint due to change in border or
// padding.
// We don't clear the HasPaddingChange() bit here, since sometimes we
// construct reflow input (e.g. in nsBlockFrame::ReflowBlockFrame to compute
// margin collapsing) without reflowing the frame. Instead, we clear it in
// nsIFrame::DidReflow().
bool isIResize =
// is the border-box resizing?
mFrame->ISize(wm) !=
ComputedISize() + ComputedLogicalBorderPadding(wm).IStartEnd(wm) ||
// or is the content-box resizing? (see comment above)
nsLayoutUtils::FontSizeInflationEnabled(aPresContext)) {
// Create our font inflation data if we don't have it already, and
// give it our current width information.
bool dirty = nsFontInflationData::UpdateFontInflationDataISizeFor(*this) &&
// Avoid running this at the box-to-block interface
// (where we shouldn't be inflating anyway, and where
// reflow input construction is probably to construct a
// dummy parent reflow input anyway).
if (dirty || (!mFrame->GetParent() && isIResize)) {
// When font size inflation is enabled, a change in either:
// * the effective width of a font inflation flow root
// * the width of the frame
// needs to cause a dirty reflow since they change the font size
// inflation calculations, which in turn change the size of text,
// line-heights, etc. This is relatively similar to a classic
// case of style change reflow, except that because inflation
// doesn't affect the intrinsic sizing codepath, there's no need
// to invalidate intrinsic sizes.
// Note that this makes horizontal resizing a good bit more
// expensive. However, font size inflation is targeted at a set of
// devices (zoom-and-pan devices) where the main use case for
// horizontal resizing needing to be efficient (window resizing) is
// not present. It does still increase the cost of dynamic changes
// caused by script where a style or content change in one place
// causes a resize in another (e.g., rebalancing a table).
// FIXME: This isn't so great for the cases where
// ReflowInput::SetComputedWidth is called, if the first time
// we go through InitResizeFlags we set IsHResize() to true, and then
// the second time we'd set it to false even without the
// NS_FRAME_IS_DIRTY bit already set.
if (mFrame->IsSVGForeignObjectFrame()) {
// Foreign object frames use dirty bits in a special way.
nsIFrame* kid = mFrame->PrincipalChildList().FirstChild();
if (kid) {
} else {
// Mark intrinsic widths on all descendants dirty. We need to do
// this (1) since we're changing the size of text and need to
// clear text runs on text frames and (2) since we actually are
// changing some intrinsic widths, but only those that live inside
// of containers.
// It makes sense to do this for descendants but not ancestors
// (which is unusual) because we're only changing the unusual
// inflation-dependent intrinsic widths (i.e., ones computed with
// nsPresContext::mInflationDisabledForShrinkWrap set to false),
// which should never affect anything outside of their inflation
// flow root (or, for that matter, even their inflation
// container).
// This is also different from what PresShell::FrameNeedsReflow
// does because it doesn't go through placeholders. It doesn't
// need to because we're actually doing something that cares about
// frame tree geometry (the width on an ancestor) rather than
// style.
AutoTArray<nsIFrame*, 32> stack;
do {
nsIFrame* f = stack.PopLastElement();
for (const auto& childList : f->ChildLists()) {
for (nsIFrame* kid : childList.mList) {
} while (stack.Length() != 0);
SetIResize(!mFrame->HasAnyStateBits(NS_FRAME_IS_DIRTY) && isIResize);
// XXX Should we really need to null check mCBReflowInput? (We do for
// at least nsBoxFrame).
if (mFrame->HasBSizeChange()) {
// When we have an nsChangeHint_UpdateComputedBSize, we'll set a bit
// on the frame to indicate we're resizing. This might catch cases,
// such as a change between auto and a length, where the box doesn't
// actually resize but children with percentages resize (since those
// percentages become auto if their containing block is auto).
mFlags.mIsBResizeForPercentages = true;
// We don't clear the HasBSizeChange state here, since sometimes we
// construct a ReflowInput (e.g. in nsBlockFrame::ReflowBlockFrame to
// compute margin collapsing) without reflowing the frame. Instead, we
// clear it in nsIFrame::DidReflow.
} else if (mCBReflowInput &&
mCBReflowInput->IsBResizeForPercentagesForWM(wm) &&
(mStylePosition->BSize(wm).HasPercent() ||
mStylePosition->MinBSize(wm).HasPercent() ||
mStylePosition->MaxBSize(wm).HasPercent())) {
// We have a percentage (or calc-with-percentage) block-size, and the
// value it's relative to has changed.
mFlags.mIsBResizeForPercentages = true;
} else if (aFrameType == LayoutFrameType::TableCell &&
(mFlags.mSpecialBSizeReflow ||
// Need to set the bit on the cell so that
// mCBReflowInput->IsBResize() is set correctly below when
// reflowing descendant.
mFlags.mIsBResizeForPercentages = true;
} else if (mCBReflowInput && mFrame->IsBlockWrapper()) {
// XXX Is this problematic for relatively positioned inlines acting
// as containing block for absolutely positioned elements?
// Possibly; in that case we should at least be checking
// IsSubtreeDirty(), I'd think.
mFlags.mIsBResizeForPercentages =
} else if (ComputedBSize() == NS_UNCONSTRAINEDSIZE) {
// We have an 'auto' block-size.
if (eCompatibility_NavQuirks == aPresContext->CompatibilityMode() &&
mCBReflowInput) {
// FIXME: This should probably also check IsIResize().
} else {
SetBResize(IsBResize() || mFrame->IsSubtreeDirty());
} else {
// We have a non-'auto' block-size, i.e., a length. Set the BResize
// flag to whether the size is actually different.
SetBResize(mFrame->BSize(wm) !=
ComputedBSize() +
bool dependsOnCBBSize = (mStylePosition->BSizeDependsOnContainer(wm) &&
// FIXME: condition this on not-abspos?
!mStylePosition->BSize(wm).IsAuto()) ||
mStylePosition->MinBSizeDependsOnContainer(wm) ||
mStylePosition->MaxBSizeDependsOnContainer(wm) ||
mStylePosition->mOffset.GetBStart(wm).HasPercent() ||
// If mFrame is a flex item, and mFrame's block axis is the flex container's
// main axis (e.g. in a column-oriented flex container with same
// writing-mode), then its block-size depends on its CB size, if its
// flex-basis has a percentage.
if (mFrame->IsFlexItem() &&
!nsFlexContainerFrame::IsItemInlineAxisMainAxis(mFrame)) {
const auto& flexBasis = mStylePosition->mFlexBasis;
dependsOnCBBSize |= (flexBasis.IsSize() && flexBasis.AsSize().HasPercent());
if (mFrame->StyleFont()->mLineHeight.IsMozBlockHeight()) {
// line-height depends on block bsize
// but only on containing blocks if this frame is not a suitable block
dependsOnCBBSize |= !nsLayoutUtils::IsNonWrapperBlock(mFrame);
// If we're the descendant of a table cell that performs special bsize
// reflows and we could be the child that requires them, always set
// the block-axis resize in case this is the first pass before the
// special bsize reflow. However, don't do this if it actually is
// the special bsize reflow, since in that case it will already be
// set correctly above if we need it set.
if (!IsBResize() && mCBReflowInput &&
(mCBReflowInput->mFrame->IsTableCellFrame() ||
mCBReflowInput->mFlags.mHeightDependsOnAncestorCell) &&
!mCBReflowInput->mFlags.mSpecialBSizeReflow && dependsOnCBBSize) {
mFlags.mHeightDependsOnAncestorCell = true;
// It would be nice to check that |ComputedBSize != NS_UNCONSTRAINEDSIZE|
// &&ed with the percentage bsize check. However, this doesn't get
// along with table special bsize reflows, since a special bsize
// reflow (a quirk that makes such percentage height work on children
// of table cells) can cause not just a single percentage height to
// become fixed, but an entire descendant chain of percentage height
// to become fixed.
if (dependsOnCBBSize && mCBReflowInput) {
const ReflowInput* rs = this;
bool hitCBReflowInput = false;
do {
rs = rs->mParentReflowInput;
if (!rs) {
if (rs->mFrame->HasAnyStateBits(NS_FRAME_CONTAINS_RELATIVE_BSIZE)) {
break; // no need to go further
// Keep track of whether we've hit the containing block, because
// we need to go at least that far.
if (rs == mCBReflowInput) {
hitCBReflowInput = true;
// XXX What about orthogonal flows? It doesn't make sense to
// keep propagating this bit across an orthogonal boundary,
// where the meaning of BSize changes. Bug 1175517.
} while (!hitCBReflowInput ||
(eCompatibility_NavQuirks == aPresContext->CompatibilityMode() &&
!IsQuirkContainingBlockHeight(rs, rs->mFrame->Type())));
// Note: We actually don't need to set the
// where we hit the early break statements in
// CalcQuirkContainingBlockHeight. But it doesn't hurt
// us to set the bit in these cases.
if (mFrame->HasAnyStateBits(NS_FRAME_IS_DIRTY)) {
// If we're reflowing everything, then we'll find out if we need
// to re-set this.
void ReflowInput::InitDynamicReflowRoot() {
if (mFrame->CanBeDynamicReflowRoot()) {
} else {
bool ReflowInput::ShouldApplyAutomaticMinimumOnBlockAxis() const {
return mFlags.mIsBSizeSetByAspectRatio &&
!mStyleDisplay->IsScrollableOverflow() &&
bool ReflowInput::IsInFragmentedContext() const {
// We consider mFrame with a prev-in-flow being in a fragmented context
// because nsColumnSetFrame can reflow its last column with an unconstrained
// available block-size.
return AvailableBSize() != NS_UNCONSTRAINEDSIZE || mFrame->GetPrevInFlow();
/* static */
LogicalMargin ReflowInput::ComputeRelativeOffsets(WritingMode aWM,
nsIFrame* aFrame,
const LogicalSize& aCBSize) {
LogicalMargin offsets(aWM);
const nsStylePosition* position = aFrame->StylePosition();
// Compute the 'inlineStart' and 'inlineEnd' values. 'inlineStart'
// moves the boxes to the end of the line, and 'inlineEnd' moves the
// boxes to the start of the line. The computed values are always:
// inlineStart=-inlineEnd
const auto& inlineStart = position->mOffset.GetIStart(aWM);
const auto& inlineEnd = position->mOffset.GetIEnd(aWM);
bool inlineStartIsAuto = inlineStart.IsAuto();
bool inlineEndIsAuto = inlineEnd.IsAuto();
// If neither 'inlineStart' nor 'inlineEnd' is auto, then we're
// over-constrained and we ignore one of them
if (!inlineStartIsAuto && !inlineEndIsAuto) {
inlineEndIsAuto = true;
if (inlineStartIsAuto) {
if (inlineEndIsAuto) {
// If both are 'auto' (their initial values), the computed values are 0
offsets.IStart(aWM) = offsets.IEnd(aWM) = 0;
} else {
// 'inlineEnd' isn't 'auto' so compute its value
offsets.IEnd(aWM) =
nsLayoutUtils::ComputeCBDependentValue(aCBSize.ISize(aWM), inlineEnd);
// Computed value for 'inlineStart' is minus the value of 'inlineEnd'
offsets.IStart(aWM) = -offsets.IEnd(aWM);
} else {
NS_ASSERTION(inlineEndIsAuto, "unexpected specified constraint");
// 'InlineStart' isn't 'auto' so compute its value
offsets.IStart(aWM) =
nsLayoutUtils::ComputeCBDependentValue(aCBSize.ISize(aWM), inlineStart);
// Computed value for 'inlineEnd' is minus the value of 'inlineStart'
offsets.IEnd(aWM) = -offsets.IStart(aWM);
// Compute the 'blockStart' and 'blockEnd' values. The 'blockStart'
// and 'blockEnd' properties move relatively positioned elements in
// the block progression direction. They also must be each other's
// negative
const auto& blockStart = position->mOffset.GetBStart(aWM);
const auto& blockEnd = position->mOffset.GetBEnd(aWM);
bool blockStartIsAuto = blockStart.IsAuto();
bool blockEndIsAuto = blockEnd.IsAuto();
// Check for percentage based values and a containing block block-size
// that depends on the content block-size. Treat them like 'auto'
if (blockStart.HasPercent()) {
blockStartIsAuto = true;
if (blockEnd.HasPercent()) {
blockEndIsAuto = true;
// If neither is 'auto', 'block-end' is ignored
if (!blockStartIsAuto && !blockEndIsAuto) {
blockEndIsAuto = true;
if (blockStartIsAuto) {
if (blockEndIsAuto) {
// If both are 'auto' (their initial values), the computed values are 0
offsets.BStart(aWM) = offsets.BEnd(aWM) = 0;
} else {
// 'blockEnd' isn't 'auto' so compute its value
offsets.BEnd(aWM) = nsLayoutUtils::ComputeBSizeDependentValue(
aCBSize.BSize(aWM), blockEnd);
// Computed value for 'blockStart' is minus the value of 'blockEnd'
offsets.BStart(aWM) = -offsets.BEnd(aWM);
} else {
NS_ASSERTION(blockEndIsAuto, "unexpected specified constraint");
// 'blockStart' isn't 'auto' so compute its value
offsets.BStart(aWM) = nsLayoutUtils::ComputeBSizeDependentValue(
aCBSize.BSize(aWM), blockStart);
// Computed value for 'blockEnd' is minus the value of 'blockStart'
offsets.BEnd(aWM) = -offsets.BStart(aWM);
// Convert the offsets to physical coordinates and store them on the frame
const nsMargin physicalOffsets = offsets.GetPhysicalMargin(aWM);
if (nsMargin* prop =
aFrame->GetProperty(nsIFrame::ComputedOffsetProperty())) {
*prop = physicalOffsets;
} else {
new nsMargin(physicalOffsets));
NS_ASSERTION(offsets.IStart(aWM) == -offsets.IEnd(aWM) &&
offsets.BStart(aWM) == -offsets.BEnd(aWM),
"ComputeRelativeOffsets should return valid results!");
return offsets;
/* static */
void ReflowInput::ApplyRelativePositioning(nsIFrame* aFrame,
const nsMargin& aComputedOffsets,
nsPoint* aPosition) {
if (!aFrame->IsRelativelyOrStickyPositioned()) {
"We assume that changing the 'position' property causes "
"frame reconstruction. If that ever changes, this code "
"should call "
// Store the normal position
aFrame->SetProperty(nsIFrame::NormalPositionProperty(), *aPosition);
const nsStyleDisplay* display = aFrame->StyleDisplay();
if (StylePositionProperty::Relative == display->mPosition) {
*aPosition += nsPoint(aComputedOffsets.left,;
} else if (StylePositionProperty::Sticky == display->mPosition &&
!aFrame->GetNextContinuation() && !aFrame->GetPrevContinuation() &&
!aFrame->HasAnyStateBits(NS_FRAME_PART_OF_IBSPLIT)) {
// Sticky positioning for elements with multiple frames needs to be
// computed all at once. We can't safely do that here because we might be
// partway through (re)positioning the frames, so leave it until the scroll
// container reflows and calls StickyScrollContainer::UpdatePositions.
// For single-frame sticky positioned elements, though, go ahead and apply
// it now to avoid unnecessary overflow updates later.
StickyScrollContainer* ssc =
if (ssc) {
*aPosition = ssc->ComputePosition(aFrame);
// static
void ReflowInput::ComputeAbsPosInlineAutoMargin(nscoord aAvailMarginSpace,
WritingMode aContainingBlockWM,
bool aIsMarginIStartAuto,
bool aIsMarginIEndAuto,
LogicalMargin& aMargin,
LogicalMargin& aOffsets) {
if (aIsMarginIStartAuto) {
if (aIsMarginIEndAuto) {
if (aAvailMarginSpace < 0) {
// Note that this case is different from the neither-'auto'
// case below, where the spec says to ignore 'left'/'right'.
// Ignore the specified value for 'margin-right'.
aMargin.IEnd(aContainingBlockWM) = aAvailMarginSpace;
} else {
// Both 'margin-left' and 'margin-right' are 'auto', so they get
// equal values
aMargin.IStart(aContainingBlockWM) = aAvailMarginSpace / 2;
aMargin.IEnd(aContainingBlockWM) =
aAvailMarginSpace - aMargin.IStart(aContainingBlockWM);
} else {
// Just 'margin-left' is 'auto'
aMargin.IStart(aContainingBlockWM) = aAvailMarginSpace;
} else {
if (aIsMarginIEndAuto) {
// Just 'margin-right' is 'auto'
aMargin.IEnd(aContainingBlockWM) = aAvailMarginSpace;
} else {
// We're over-constrained so use the direction of the containing
// block to dictate which value to ignore. (And note that the
// spec says to ignore 'left' or 'right' rather than
// 'margin-left' or 'margin-right'.)
// Note that this case is different from the both-'auto' case
// above, where the spec says to ignore
// 'margin-left'/'margin-right'.
// Ignore the specified value for 'right'.
aOffsets.IEnd(aContainingBlockWM) += aAvailMarginSpace;
// static
void ReflowInput::ComputeAbsPosBlockAutoMargin(nscoord aAvailMarginSpace,
WritingMode aContainingBlockWM,
bool aIsMarginBStartAuto,
bool aIsMarginBEndAuto,
LogicalMargin& aMargin,
LogicalMargin& aOffsets) {
if (aIsMarginBStartAuto) {
if (aIsMarginBEndAuto) {
// Both 'margin-top' and 'margin-bottom' are 'auto', so they get
// equal values
aMargin.BStart(aContainingBlockWM) = aAvailMarginSpace / 2;
aMargin.BEnd(aContainingBlockWM) =
aAvailMarginSpace - aMargin.BStart(aContainingBlockWM);
} else {
// Just margin-block-start is 'auto'
aMargin.BStart(aContainingBlockWM) = aAvailMarginSpace;
} else {
if (aIsMarginBEndAuto) {
// Just margin-block-end is 'auto'
aMargin.BEnd(aContainingBlockWM) = aAvailMarginSpace;
} else {
// We're over-constrained so ignore the specified value for
// block-end. (And note that the spec says to ignore 'bottom'
// rather than 'margin-bottom'.)
aOffsets.BEnd(aContainingBlockWM) += aAvailMarginSpace;
void ReflowInput::ApplyRelativePositioning(
nsIFrame* aFrame, mozilla::WritingMode aWritingMode,
const mozilla::LogicalMargin& aComputedOffsets,
mozilla::LogicalPoint* aPosition, const nsSize& aContainerSize) {
// Subtract the size of the frame from the container size that we
// use for converting between the logical and physical origins of
// the frame. This accounts for the fact that logical origins in RTL
// coordinate systems are at the top right of the frame instead of
// the top left.
nsSize frameSize = aFrame->GetSize();
nsPoint pos =
aPosition->GetPhysicalPoint(aWritingMode, aContainerSize - frameSize);
aFrame, aComputedOffsets.GetPhysicalMargin(aWritingMode), &pos);
*aPosition =
mozilla::LogicalPoint(aWritingMode, pos, aContainerSize - frameSize);
nsIFrame* ReflowInput::GetHypotheticalBoxContainer(nsIFrame* aFrame,
nscoord& aCBIStartEdge,
LogicalSize& aCBSize) const {
aFrame = aFrame->GetContainingBlock();
NS_ASSERTION(aFrame != mFrame, "How did that happen?");
/* Now aFrame is the containing block we want */
/* Check whether the containing block is currently being reflowed.
If so, use the info from the reflow input. */
const ReflowInput* reflowInput;
if (aFrame->HasAnyStateBits(NS_FRAME_IN_REFLOW)) {
for (reflowInput = mParentReflowInput;
reflowInput && reflowInput->mFrame != aFrame;
reflowInput = reflowInput->mParentReflowInput) {
/* do nothing */
} else {
reflowInput = nullptr;
if (reflowInput) {
WritingMode wm = reflowInput->GetWritingMode();
NS_ASSERTION(wm == aFrame->GetWritingMode(), "unexpected writing mode");
aCBIStartEdge = reflowInput->ComputedLogicalBorderPadding(wm).IStart(wm);
aCBSize = reflowInput->ComputedSize(wm);
} else {
/* Didn't find a reflow reflowInput for aFrame. Just compute the
information we want, on the assumption that aFrame already knows its
size. This really ought to be true by now. */
"aFrame shouldn't be in reflow; we'll lie if it is");
WritingMode wm = aFrame->GetWritingMode();
// Compute CB's offset & content-box size by subtracting borderpadding from
// frame size.
const auto& bp = aFrame->GetLogicalUsedBorderAndPadding(wm);
aCBIStartEdge = bp.IStart(wm);
aCBSize = aFrame->GetLogicalSize(wm) - bp.Size(wm);
return aFrame;
struct nsHypotheticalPosition {
// offset from inline-start edge of containing block (which is a padding edge)
nscoord mIStart;
// offset from block-start edge of containing block (which is a padding edge)
nscoord mBStart;
WritingMode mWritingMode;
* aInsideBoxSizing returns the part of the padding, border, and margin
* in the aAxis dimension that goes inside the edge given by box-sizing;
* aOutsideBoxSizing returns the rest.
void ReflowInput::CalculateBorderPaddingMargin(
LogicalAxis aAxis, nscoord aContainingBlockSize, nscoord* aInsideBoxSizing,
nscoord* aOutsideBoxSizing) const {
WritingMode wm = GetWritingMode();
mozilla::Side startSide =
wm.PhysicalSide(MakeLogicalSide(aAxis, LogicalEdge::Start));
mozilla::Side endSide =
wm.PhysicalSide(MakeLogicalSide(aAxis, LogicalEdge::End));
nsMargin styleBorder = mStyleBorder->GetComputedBorder();
nscoord borderStartEnd =
styleBorder.Side(startSide) + styleBorder.Side(endSide);
nscoord paddingStartEnd, marginStartEnd;
// See if the style system can provide us the padding directly
const auto* stylePadding = mFrame->StylePadding();
if (nsMargin padding; stylePadding->GetPadding(padding)) {
paddingStartEnd = padding.Side(startSide) + padding.Side(endSide);
} else {
// We have to compute the start and end values
nscoord start, end;
start = nsLayoutUtils::ComputeCBDependentValue(
aContainingBlockSize, stylePadding->mPadding.Get(startSide));
end = nsLayoutUtils::ComputeCBDependentValue(
aContainingBlockSize, stylePadding->mPadding.Get(endSide));
paddingStartEnd = start + end;
// See if the style system can provide us the margin directly
if (nsMargin margin; mStyleMargin->GetMargin(margin)) {
marginStartEnd = margin.Side(startSide) + margin.Side(endSide);
} else {
nscoord start, end;
// We have to compute the start and end values
if (mStyleMargin->mMargin.Get(startSide).IsAuto()) {
// We set this to 0 for now, and fix it up later in
// InitAbsoluteConstraints (which is caller of this function, via
// CalculateHypotheticalPosition).
start = 0;
} else {
start = nsLayoutUtils::ComputeCBDependentValue(
aContainingBlockSize, mStyleMargin->mMargin.Get(startSide));
if (mStyleMargin->mMargin.Get(endSide).IsAuto()) {
// We set this to 0 for now, and fix it up later in
// InitAbsoluteConstraints (which is caller of this function, via
// CalculateHypotheticalPosition).
end = 0;
} else {
end = nsLayoutUtils::ComputeCBDependentValue(
aContainingBlockSize, mStyleMargin->mMargin.Get(endSide));
marginStartEnd = start + end;
nscoord outside = paddingStartEnd + borderStartEnd + marginStartEnd;
nscoord inside = 0;
if (mStylePosition->mBoxSizing == StyleBoxSizing::Border) {
inside = borderStartEnd + paddingStartEnd;
outside -= inside;
*aInsideBoxSizing = inside;
*aOutsideBoxSizing = outside;
* Returns true iff a pre-order traversal of the normal child
* frames rooted at aFrame finds no non-empty frame before aDescendant.
static bool AreAllEarlierInFlowFramesEmpty(nsIFrame* aFrame,
nsIFrame* aDescendant,
bool* aFound) {
if (aFrame == aDescendant) {
*aFound = true;
return true;
if (aFrame->IsPlaceholderFrame()) {
auto ph = static_cast<nsPlaceholderFrame*>(aFrame);
MOZ_ASSERT(ph->IsSelfEmpty() && ph->PrincipalChildList().IsEmpty());
} else {
if (!aFrame->IsSelfEmpty()) {
*aFound = false;
return false;
for (nsIFrame* f : aFrame->PrincipalChildList()) {
bool allEmpty = AreAllEarlierInFlowFramesEmpty(f, aDescendant, aFound);
if (*aFound || !allEmpty) {
return allEmpty;
*aFound = false;
return true;
static bool AxisPolarityFlipped(LogicalAxis aThisAxis, WritingMode aThisWm,
WritingMode aOtherWm) {
if (MOZ_LIKELY(aThisWm == aOtherWm)) {
// Dedicated short circuit for the common case.
return false;
LogicalAxis otherAxis = aThisWm.IsOrthogonalTo(aOtherWm)
? GetOrthogonalAxis(aThisAxis)
: aThisAxis;
aThisWm.PhysicalAxis(aThisAxis) == aOtherWm.PhysicalAxis(otherAxis),
"Physical axes must match!");
Side thisStartSide =
aThisWm.PhysicalSide(MakeLogicalSide(aThisAxis, LogicalEdge::Start));
Side otherStartSide =
aOtherWm.PhysicalSide(MakeLogicalSide(otherAxis, LogicalEdge::Start));
return thisStartSide != otherStartSide;
static bool InlinePolarityFlipped(WritingMode aThisWm, WritingMode aOtherWm) {
return AxisPolarityFlipped(LogicalAxis::Inline, aThisWm, aOtherWm);
static bool BlockPolarityFlipped(WritingMode aThisWm, WritingMode aOtherWm) {
return AxisPolarityFlipped(LogicalAxis::Block, aThisWm, aOtherWm);
// Calculate the position of the hypothetical box that the element would have
// if it were in the flow.
// The values returned are relative to the padding edge of the absolute
// containing block. The writing-mode of the hypothetical box position will
// have the same block direction as the absolute containing block, but may
// differ in inline-bidi direction.
// In the code below, |aCBReflowInput->frame| is the absolute containing block,
// while |containingBlock| is the nearest block container of the placeholder
// frame, which may be different from the absolute containing block.
void ReflowInput::CalculateHypotheticalPosition(
nsPresContext* aPresContext, nsPlaceholderFrame* aPlaceholderFrame,
const ReflowInput* aCBReflowInput, nsHypotheticalPosition& aHypotheticalPos,
LayoutFrameType aFrameType) const {
NS_ASSERTION(mStyleDisplay->mOriginalDisplay != StyleDisplay::None,
"mOriginalDisplay has not been properly initialized");
// Find the nearest containing block frame to the placeholder frame,
// and its inline-start edge and width.
nscoord blockIStartContentEdge;
// Dummy writing mode for blockContentSize, will be changed as needed by
// GetHypotheticalBoxContainer.
WritingMode cbwm = aCBReflowInput->GetWritingMode();
LogicalSize blockContentSize(cbwm);
nsIFrame* containingBlock = GetHypotheticalBoxContainer(
aPlaceholderFrame, blockIStartContentEdge, blockContentSize);
// Now blockContentSize is in containingBlock's writing mode.
// If it's a replaced element and it has a 'auto' value for
//'inline size', see if we can get the intrinsic size. This will allow
// us to exactly determine both the inline edges
WritingMode wm = containingBlock->GetWritingMode();
const auto& styleISize = mStylePosition->ISize(wm);
bool isAutoISize = styleISize.IsAuto();
Maybe<nsSize> intrinsicSize;
if (mFlags.mIsReplaced && isAutoISize) {
// See if we can get the intrinsic size of the element
intrinsicSize = mFrame->GetIntrinsicSize().ToSize();
// See if we can calculate what the box inline size would have been if
// the element had been in the flow
Maybe<nscoord> boxISize;
if (mStyleDisplay->IsOriginalDisplayInlineOutside() && !mFlags.mIsReplaced) {
// For non-replaced inline-level elements the 'inline size' property
// doesn't apply, so we don't know what the inline size would have
// been without reflowing it
} else {
// It's either a replaced inline-level element or a block-level element
// Determine the total amount of inline direction
// border/padding/margin that the element would have had if it had
// been in the flow. Note that we ignore any 'auto' and 'inherit'
// values
nscoord insideBoxISizing, outsideBoxISizing;
blockContentSize.ISize(wm), &insideBoxISizing,
if (mFlags.mIsReplaced && isAutoISize) {
// It's a replaced element with an 'auto' inline size so the box inline
// size is its intrinsic size plus any border/padding/margin
if (intrinsicSize) {
boxISize.emplace(LogicalSize(wm, *intrinsicSize).ISize(wm) +
outsideBoxISizing + insideBoxISizing);
} else if (isAutoISize) {
// The box inline size is the containing block inline size
} else {
// We need to compute it. It's important we do this, because if it's
// percentage based this computed value may be different from the computed
// value calculated using the absolute containing block width
nscoord insideBoxBSizing, dummy;
&insideBoxBSizing, &dummy);
ComputeISizeValue(wm, blockContentSize,
LogicalSize(wm, insideBoxISizing, insideBoxBSizing),
outsideBoxISizing, styleISize) +
insideBoxISizing + outsideBoxISizing);
// Get the placeholder x-offset and y-offset in the coordinate
// space of its containing block
// XXXbz the placeholder is not fully reflowed yet if our containing block is
// relatively positioned...
nsSize containerSize =
? aCBReflowInput->ComputedSizeAsContainerIfConstrained()
: containingBlock->GetSize();
LogicalPoint placeholderOffset(
wm, aPlaceholderFrame->GetOffsetToIgnoringScrolling(containingBlock),
// First, determine the hypothetical box's mBStart. We want to check the
// content insertion frame of containingBlock for block-ness, but make
// sure to compute all coordinates in the coordinate system of
// containingBlock.
nsBlockFrame* blockFrame =
if (blockFrame) {
// Use a null containerSize to convert a LogicalPoint functioning as a
// vector into a physical nsPoint vector.
const nsSize nullContainerSize;
LogicalPoint blockOffset(
wm, blockFrame->GetOffsetToIgnoringScrolling(containingBlock),
bool isValid;
nsBlockInFlowLineIterator iter(blockFrame, aPlaceholderFrame, &isValid);
if (!isValid) {
// Give up. We're probably dealing with somebody using
// position:absolute inside native-anonymous content anyway.
aHypotheticalPos.mBStart = placeholderOffset.B(wm);
} else {
NS_ASSERTION(iter.GetContainer() == blockFrame,
"Found placeholder in wrong block!");
nsBlockFrame::LineIterator lineBox = iter.GetLine();
// How we determine the hypothetical box depends on whether the element
// would have been inline-level or block-level
LogicalRect lineBounds = lineBox->GetBounds().ConvertTo(
wm, lineBox->mWritingMode, lineBox->mContainerSize);
if (mStyleDisplay->IsOriginalDisplayInlineOutside()) {
// Use the block-start of the inline box which the placeholder lives in
// as the hypothetical box's block-start.
aHypotheticalPos.mBStart = lineBounds.BStart(wm) + blockOffset.B(wm);
} else {
// The element would have been block-level which means it would
// be below the line containing the placeholder frame, unless
// all the frames before it are empty. In that case, it would
// have been just before this line.
// XXXbz the line box is not fully reflowed yet if our
// containing block is relatively positioned...
if (lineBox != iter.End()) {
nsIFrame* firstFrame = lineBox->mFirstChild;
bool allEmpty = false;
if (firstFrame == aPlaceholderFrame) {
allEmpty = true;
} else {
auto prev = aPlaceholderFrame->GetPrevSibling();
if (prev && prev->IsPlaceholderFrame()) {
auto ph = static_cast<nsPlaceholderFrame*>(prev);
if (ph->GetLineIsEmptySoFar(&allEmpty)) {
if (!allEmpty) {
bool found = false;
while (firstFrame) { // See bug 223064
allEmpty = AreAllEarlierInFlowFramesEmpty(
firstFrame, aPlaceholderFrame, &found);
if (found || !allEmpty) {
firstFrame = firstFrame->GetNextSibling();
NS_ASSERTION(firstFrame, "Couldn't find placeholder!");
if (allEmpty) {
// The top of the hypothetical box is the top of the line
// containing the placeholder, since there is nothing in the
// line before our placeholder except empty frames.
aHypotheticalPos.mBStart =
lineBounds.BStart(wm) + blockOffset.B(wm);
} else {
// The top of the hypothetical box is just below the line
// containing the placeholder.
aHypotheticalPos.mBStart = lineBounds.BEnd(wm) + blockOffset.B(wm);
} else {
// Just use the placeholder's block-offset wrt the containing block
aHypotheticalPos.mBStart = placeholderOffset.B(wm);
} else {
// The containing block is not a block, so it's probably something
// like a XUL box, etc.
// Just use the placeholder's block-offset
aHypotheticalPos.mBStart = placeholderOffset.B(wm);
// Second, determine the hypothetical box's mIStart.
// How we determine the hypothetical box depends on whether the element
// would have been inline-level or block-level
if (mStyleDisplay->IsOriginalDisplayInlineOutside() ||
mFlags.mIOffsetsNeedCSSAlign) {
// The placeholder represents the IStart edge of the hypothetical box.
// (Or if mFlags.mIOffsetsNeedCSSAlign is set, it represents the IStart
// edge of the Alignment Container.)
aHypotheticalPos.mIStart = placeholderOffset.I(wm);
} else {
aHypotheticalPos.mIStart = blockIStartContentEdge;
// The current coordinate space is that of the nearest block to the
// placeholder. Convert to the coordinate space of the absolute containing
// block.
nsPoint cbOffset =
nsSize reflowSize = aCBReflowInput->ComputedSizeAsContainerIfConstrained();
LogicalPoint logCBOffs(wm, cbOffset, reflowSize - containerSize);
aHypotheticalPos.mIStart += logCBOffs.I(wm);
aHypotheticalPos.mBStart += logCBOffs.B(wm);
// If block direction doesn't match (whether orthogonal or antiparallel),
// we'll have to convert aHypotheticalPos to be in terms of cbwm.
// This upcoming conversion must be taken into account for border offsets.
const bool hypotheticalPosWillUseCbwm =
cbwm.GetBlockDir() != wm.GetBlockDir();
// The specified offsets are relative to the absolute containing block's
// padding edge and our current values are relative to the border edge, so
// translate.
const LogicalMargin border = aCBReflowInput->ComputedLogicalBorder(wm);
if (hypotheticalPosWillUseCbwm && InlinePolarityFlipped(wm, cbwm)) {
aHypotheticalPos.mIStart += border.IEnd(wm);
} else {
aHypotheticalPos.mIStart -= border.IStart(wm);
if (hypotheticalPosWillUseCbwm && BlockPolarityFlipped(wm, cbwm)) {
aHypotheticalPos.mBStart += border.BEnd(wm);
} else {
aHypotheticalPos.mBStart -= border.BStart(wm);
// At this point, we have computed aHypotheticalPos using the writing mode
// of the placeholder's containing block.
if (hypotheticalPosWillUseCbwm) {
// If the block direction we used in calculating aHypotheticalPos does not
// match the absolute containing block's, we need to convert here so that
// aHypotheticalPos is usable in relation to the absolute containing block.
// This requires computing or measuring the abspos frame's block-size,
// which is not otherwise required/used here (as aHypotheticalPos
// records only the block-start coordinate).
// This is similar to the inline-size calculation for a replaced
// inline-level element or a block-level element (above), except that
// 'auto' sizing is handled differently in the block direction for non-
// replaced elements and replaced elements lacking an intrinsic size.
// Determine the total amount of block direction
// border/padding/margin that the element would have had if it had
// been in the flow. Note that we ignore any 'auto' and 'inherit'
// values.
nscoord insideBoxSizing, outsideBoxSizing;
CalculateBorderPaddingMargin(LogicalAxis::Block, blockContentSize.BSize(wm),
&insideBoxSizing, &outsideBoxSizing);
nscoord boxBSize;
const auto& styleBSize = mStylePosition->BSize(wm);
if (styleBSize.BehavesLikeInitialValueOnBlockAxis()) {
if (mFlags.mIsReplaced && intrinsicSize) {
// It's a replaced element with an 'auto' block size so the box
// block size is its intrinsic size plus any border/padding/margin
boxBSize = LogicalSize(wm, *intrinsicSize).BSize(wm) +
outsideBoxSizing + insideBoxSizing;
} else {
// XXX Bug 1191801
// Figure out how to get the correct boxBSize here (need to reflow the
// positioned frame?)
boxBSize = 0;
} else {
// We need to compute it. It's important we do this, because if it's
// percentage-based this computed value may be different from the
// computed value calculated using the absolute containing block height.
boxBSize = nsLayoutUtils::ComputeBSizeValue(
blockContentSize.BSize(wm), insideBoxSizing,
styleBSize.AsLengthPercentage()) +
insideBoxSizing + outsideBoxSizing;