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 */
/* class that manages rules for positioning floats */
#ifndef nsFloatManager_h_
#define nsFloatManager_h_
#include "mozilla/Attributes.h"
#include "mozilla/TypedEnumBits.h"
#include "mozilla/UniquePtr.h"
#include "mozilla/WritingModes.h"
#include "nsCoord.h"
#include "nsFrameList.h" // for DEBUG_FRAME_DUMP
#include "nsIntervalSet.h"
#include "nsPoint.h"
#include "nsTArray.h"
class nsIFrame;
class nsPresContext;
namespace mozilla {
struct ReflowInput;
class PresShell;
} // namespace mozilla
enum class nsFlowAreaRectFlags : uint32_t {
NoFlags = 0,
HasFloats = 1 << 0,
MayWiden = 1 << 1,
ISizeIsActuallyNegative = 1 << 2,
* The available space for content not occupied by floats is divided
* into a sequence of rectangles in the block direction. However, we
* need to know not only the rectangle, but also whether it was reduced
* (from the content rectangle) by floats that actually intruded into
* the content rectangle. If it has been reduced by floats, then we also
* track whether the flow area might widen as the floats narrow in the
* block direction.
struct nsFlowAreaRect {
mozilla::LogicalRect mRect;
nsFlowAreaRectFlags mAreaFlags;
nsFlowAreaRect(mozilla::WritingMode aWritingMode, nscoord aICoord,
nscoord aBCoord, nscoord aISize, nscoord aBSize,
nsFlowAreaRectFlags aAreaFlags)
: mRect(aWritingMode, aICoord, aBCoord, aISize, aBSize),
mAreaFlags(aAreaFlags) {}
bool HasFloats() const {
return (bool)(mAreaFlags & nsFlowAreaRectFlags::HasFloats);
bool MayWiden() const {
return (bool)(mAreaFlags & nsFlowAreaRectFlags::MayWiden);
bool ISizeIsActuallyNegative() const {
return (bool)(mAreaFlags & nsFlowAreaRectFlags::ISizeIsActuallyNegative);
* nsFloatManager is responsible for implementing CSS's rules for
* positioning floats. An nsFloatManager object is created during reflow for
* any block with NS_BLOCK_BFC. During reflow, the float manager for the nearest
* such ancestor block is found in ReflowInput::mFloatManager.
* According to the line-relative mappings in CSS Writing Modes spec [1],
* line-right and line-left are calculated with respect to the writing mode
* of the containing block of the floats. All the writing modes passed to
* nsFloatManager methods should be the containing block's writing mode.
* However, according to the abstract-to-physical mappings table [2], the
* 'direction' property of the containing block doesn't affect the
* interpretation of line-right and line-left. We actually implement this by
* passing in the writing mode of the block formatting context (BFC), i.e.
* the of BlockReflowState's writing mode.
* nsFloatManager uses a special logical coordinate space with inline
* coordinates on the line-axis and block coordinates on the block-axis
* based on the writing mode of the block formatting context. All the
* physical types like nsRect, nsPoint, etc. use this coordinate space. See
* FloatInfo::mRect for an example.
class nsFloatManager {
explicit nsFloatManager(mozilla::PresShell* aPresShell,
mozilla::WritingMode aWM);
void* operator new(size_t aSize) noexcept(true);
void operator delete(void* aPtr, size_t aSize);
static void Shutdown();
* Get float region stored on the frame. (Defaults to mRect if it's
* not there.) The float region is the area impacted by this float;
* the coordinates are relative to the containing block frame.
static mozilla::LogicalRect GetRegionFor(mozilla::WritingMode aWM,
nsIFrame* aFloatFrame,
const nsSize& aContainerSize);
* Calculate the float region for this frame using aMargin and the
* frame's mRect. The region includes the margins around the float,
* but doesn't include the relative offsets.
* Note that if the frame is or has a continuation, aMargin's top
* and/or bottom must be zeroed by the caller.
static mozilla::LogicalRect CalculateRegionFor(
mozilla::WritingMode aWM, nsIFrame* aFloatFrame,
const mozilla::LogicalMargin& aMargin, const nsSize& aContainerSize);
* Store the float region on the frame. The region is stored
* as a delta against the mRect, so repositioning the frame will
* also reposition the float region.
static void StoreRegionFor(mozilla::WritingMode aWM, nsIFrame* aFloat,
const mozilla::LogicalRect& aRegion,
const nsSize& aContainerSize);
// Structure that stores the current state of a float manager for
// Save/Restore purposes.
struct SavedState {
explicit SavedState()
: mFloatInfoCount(0),
mSplitRightFloatAcrossBreak(false) {}
uint32_t mFloatInfoCount;
nscoord mLineLeft, mBlockStart;
bool mPushedLeftFloatPastBreak;
bool mPushedRightFloatPastBreak;
bool mSplitLeftFloatAcrossBreak;
bool mSplitRightFloatAcrossBreak;
friend class nsFloatManager;
* Translate the current origin by the specified offsets. This
* creates a new local coordinate space relative to the current
* coordinate space.
void Translate(nscoord aLineLeft, nscoord aBlockStart) {
mLineLeft += aLineLeft;
mBlockStart += aBlockStart;
* Returns the current translation from local coordinate space to
* world coordinate space. This represents the accumulated calls to
* Translate().
void GetTranslation(nscoord& aLineLeft, nscoord& aBlockStart) const {
aLineLeft = mLineLeft;
aBlockStart = mBlockStart;
* Get information about the area available to content that flows
* around floats. Two different types of space can be requested:
* BandFromPoint: returns the band containing block-dir coordinate
* |aBCoord| (though actually with the top truncated to begin at
* aBCoord), but up to at most |aBSize| (which may be nscoord_MAX).
* This will return the tallest rectangle whose block start is
* |aBCoord| and in which there are no changes in what floats are
* on the sides of that rectangle, but will limit the block size
* of the rectangle to |aBSize|. The inline start and end edges
* of the rectangle give the area available for line boxes in that
* space. The inline size of this resulting rectangle will not be
* negative.
* WidthWithinHeight: This returns a rectangle whose block start
* is aBCoord and whose block size is exactly aBSize. Its inline
* start and end edges give the corresponding edges of the space
* that can be used for line boxes *throughout* that space. (It
* is possible that more inline space could be used in part of the
* space if a float begins or ends in it.) The inline size of the
* resulting rectangle can be negative.
* ShapeType can be used to request two different types of flow areas.
* (This is the float area defined in CSS Shapes Module Level 1 ยง1.4):
* Margin: uses the float element's margin-box to request the flow area.
* ShapeOutside: uses the float element's shape-outside value to request
* the float area.
* @param aBCoord [in] block-dir coordinate for block start of available space
* desired, which are positioned relative to the current translation.
* @param aBSize [in] see above
* @param aContentArea [in] an nsRect representing the content area
* @param aState [in] If null, use the current state, otherwise, do
* computation based only on floats present in the given
* saved state.
* @return An nsFlowAreaRect whose:
* mRect is the resulting rectangle for line boxes. It will not
* extend beyond aContentArea's inline bounds, but may be
* narrower when floats are present.
* mHasFloats is whether there are floats at the sides of the
* return value including those that do not reduce the line box
* inline size at all (because they are entirely in the margins)
enum class BandInfoType { BandFromPoint, WidthWithinHeight };
enum class ShapeType { Margin, ShapeOutside };
nsFlowAreaRect GetFlowArea(mozilla::WritingMode aWM, nscoord aBCoord,
nscoord aBSize, BandInfoType aBandInfoType,
ShapeType aShapeType,
mozilla::LogicalRect aContentArea,
SavedState* aState,
const nsSize& aContainerSize) const;
* Add a float that comes after all floats previously added. Its
* block start must be even with or below the top of all previous
* floats.
* aMarginRect is relative to the current translation. The caller
* must ensure aMarginRect.height >= 0 and aMarginRect.width >= 0.
void AddFloat(nsIFrame* aFloatFrame, const mozilla::LogicalRect& aMarginRect,
mozilla::WritingMode aWM, const nsSize& aContainerSize);
* Notify that we tried to place a float that could not fit at all and
* had to be pushed to the next page/column? (If so, we can't place
* any more floats in this page/column because of the rule that the
* top of a float cannot be above the top of an earlier float. It
* also means that any clear needs to continue to the next column.)
void SetPushedLeftFloatPastBreak() { mPushedLeftFloatPastBreak = true; }
void SetPushedRightFloatPastBreak() { mPushedRightFloatPastBreak = true; }
* Notify that we split a float, with part of it needing to be pushed
* to the next page/column. (This means that any 'clear' needs to
* continue to the next page/column.)
void SetSplitLeftFloatAcrossBreak() { mSplitLeftFloatAcrossBreak = true; }
void SetSplitRightFloatAcrossBreak() { mSplitRightFloatAcrossBreak = true; }
* Remove the regions associated with this floating frame and its
* next-sibling list. Some of the frames may never have been added;
* we just skip those. This is not fully general; it only works as
* long as the N frames to be removed are the last N frames to have
* been added; if there's a frame in the middle of them that should
* not be removed, YOU LOSE.
nsresult RemoveTrailingRegions(nsIFrame* aFrameList);
bool HasAnyFloats() const { return !mFloats.IsEmpty(); }
* Methods for dealing with the propagation of float damage during
* reflow.
bool HasFloatDamage() const { return !mFloatDamage.IsEmpty(); }
void IncludeInDamage(nscoord aIntervalBegin, nscoord aIntervalEnd) {
mFloatDamage.IncludeInterval(aIntervalBegin + mBlockStart,
aIntervalEnd + mBlockStart);
bool IntersectsDamage(nscoord aIntervalBegin, nscoord aIntervalEnd) const {
return mFloatDamage.Intersects(aIntervalBegin + mBlockStart,
aIntervalEnd + mBlockStart);
* Saves the current state of the float manager into aState.
void PushState(SavedState* aState);
* Restores the float manager to the saved state.
* These states must be managed using stack discipline. PopState can only
* be used after PushState has been used to save the state, and it can only
* be used once --- although it can be omitted; saved states can be ignored.
* States must be popped in the reverse order they were pushed. A
* call to PopState invalidates any saved states Pushed after the
* state passed to PopState was pushed.
void PopState(SavedState* aState);
* Get the block start of the last float placed into the float
* manager, to enforce the rule that a float can't be above an earlier
* float. Returns the minimum nscoord value if there are no floats.
* The result is relative to the current translation.
nscoord LowestFloatBStart() const;
* Return the coordinate of the lowest float matching aClearType in
* this float manager. Returns aBCoord if there are no matching
* floats.
* Both aBCoord and the result are relative to the current translation.
nscoord ClearFloats(nscoord aBCoord, mozilla::StyleClear aClearType) const;
* Checks if clear would pass into the floats' BFC's next-in-flow,
* i.e. whether floats affecting this clear have continuations.
bool ClearContinues(mozilla::StyleClear aClearType) const;
void AssertStateMatches(SavedState* aState) const {
aState->mLineLeft == mLineLeft && aState->mBlockStart == mBlockStart &&
aState->mPushedLeftFloatPastBreak == mPushedLeftFloatPastBreak &&
aState->mPushedRightFloatPastBreak == mPushedRightFloatPastBreak &&
aState->mSplitLeftFloatAcrossBreak == mSplitLeftFloatAcrossBreak &&
aState->mSplitRightFloatAcrossBreak ==
mSplitRightFloatAcrossBreak &&
aState->mFloatInfoCount == mFloats.Length(),
"float manager state should match saved state");
* Dump the state of the float manager out to a file.
nsresult List(FILE* out) const;
class ShapeInfo;
class RoundedBoxShapeInfo;
class EllipseShapeInfo;
class PolygonShapeInfo;
class ImageShapeInfo;
struct FloatInfo {
nsIFrame* const mFrame;
// The lowest block-ends of left/right floats up to and including
// this one.
nscoord mLeftBEnd, mRightBEnd;
FloatInfo(nsIFrame* aFrame, nscoord aLineLeft, nscoord aBlockStart,
const mozilla::LogicalRect& aMarginRect, mozilla::WritingMode aWM,
const nsSize& aContainerSize);
nscoord LineLeft() const { return mRect.x; }
nscoord LineRight() const { return mRect.XMost(); }
nscoord ISize() const { return mRect.width; }
nscoord BStart() const { return mRect.y; }
nscoord BEnd() const { return mRect.YMost(); }
nscoord BSize() const { return mRect.height; }
bool IsEmpty() const { return mRect.IsEmpty(); }
// aBStart and aBEnd are the starting and ending coordinate of a band.
// LineLeft() and LineRight() return the innermost line-left extent and
// line-right extent within the given band, respectively.
nscoord LineLeft(ShapeType aShapeType, const nscoord aBStart,
const nscoord aBEnd) const;
nscoord LineRight(ShapeType aShapeType, const nscoord aBStart,
const nscoord aBEnd) const;
nscoord BStart(ShapeType aShapeType) const;
nscoord BEnd(ShapeType aShapeType) const;
bool IsEmpty(ShapeType aShapeType) const;
bool MayNarrowInBlockDirection(ShapeType aShapeType) const;
FloatInfo(FloatInfo&& aOther);
// NB! This is really a logical rect in a writing mode suitable for
// placing floats, which is not necessarily the actual writing mode
// either of the block which created the float manager or the block
// that is calling the float manager. The inline coordinates are in
// the line-relative axis of the float manager and its block
// coordinates are in the float manager's block direction.
nsRect mRect;
// Pointer to a concrete subclass of ShapeInfo or null, which means that
// there is no shape-outside.
mozilla::UniquePtr<ShapeInfo> mShapeInfo;
#ifdef DEBUG
// Store the writing mode from the block frame which establishes the block
// formatting context (BFC) when the nsFloatManager is created.
mozilla::WritingMode mWritingMode;
// Translation from local to global coordinate space.
nscoord mLineLeft, mBlockStart;
// We use 11 here in order to fill up the jemalloc allocatoed chunk nicely,
AutoTArray<FloatInfo, 11> mFloats;
nsIntervalSet mFloatDamage;
// Did we try to place a float that could not fit at all and had to be
// pushed to the next page/column? If so, we can't place any more
// floats in this page/column because of the rule that the top of a
// float cannot be above the top of an earlier float. And we also
// need to apply this information to 'clear', and thus need to
// separate left and right floats.
bool mPushedLeftFloatPastBreak;
bool mPushedRightFloatPastBreak;
// Did we split a float, with part of it needing to be pushed to the
// next page/column. This means that any 'clear' needs to continue to
// the next page/column.
bool mSplitLeftFloatAcrossBreak;
bool mSplitRightFloatAcrossBreak;
static int32_t sCachedFloatManagerCount;
static void* sCachedFloatManagers[NS_FLOAT_MANAGER_CACHE_SIZE];
nsFloatManager(const nsFloatManager&) = delete;
void operator=(const nsFloatManager&) = delete;
* A helper class to manage maintenance of the float manager during
* nsBlockFrame::Reflow. It automatically restores the old float
* manager in the reflow input when the object goes out of scope.
class nsAutoFloatManager {
using ReflowInput = mozilla::ReflowInput;
explicit nsAutoFloatManager(ReflowInput& aReflowInput)
: mReflowInput(aReflowInput), mOld(nullptr) {}
* Create a new float manager for the specified frame. This will
* `remember' the old float manager, and install the new float
* manager in the reflow input.
void CreateFloatManager(nsPresContext* aPresContext);
ReflowInput& mReflowInput;
mozilla::UniquePtr<nsFloatManager> mNew;
// A non-owning pointer, which points to the object owned by
// nsAutoFloatManager::mNew.
nsFloatManager* mOld;
#endif /* !defined(nsFloatManager_h_) */