tor-browser

nsFloatManager.h (18682B)

---

/* -*- 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 http://mozilla.org/MPL/2.0/. */

/* class that manages rules for positioning floats */

#ifndef nsFloatManager_h_
#define nsFloatManager_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,
};
MOZ_MAKE_ENUM_CLASS_BITWISE_OPERATORS(nsFlowAreaRectFlags)

/**
* 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);
 }
};

#define NS_FLOAT_MANAGER_CACHE_SIZE 64

/**
* 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.
*
* [1] https://drafts.csswg.org/css-writing-modes/#line-mappings
* [2] https://drafts.csswg.org/css-writing-modes/#logical-to-physical
*/
class nsFloatManager {
public:
 explicit nsFloatManager(mozilla::PresShell* aPresShell,
                         mozilla::WritingMode aWM);
 ~nsFloatManager();

 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),
         mLineLeft(0),
         mBlockStart(0),
         mPushedLeftFloatPastBreak(false),
         mPushedRightFloatPastBreak(false),
         mSplitLeftFloatAcrossBreak(false),
         mSplitRightFloatAcrossBreak(false) {}

  private:
   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 §1.4):
  *    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 aCBWM,
                            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::UsedClear 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::UsedClear aClearType) const;

 void AssertStateMatches(SavedState* aState) const {
   NS_ASSERTION(
       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");
 }

#ifdef DEBUG_FRAME_DUMP
 /**
  * Dump the state of the float manager out to a file.
  */
 nsresult List(FILE* out) const;
#endif

private:
 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;

#ifdef NS_BUILD_REFCNT_LOGGING
   FloatInfo(FloatInfo&& aOther);
   ~FloatInfo();
#endif

   // 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;
#endif

 // Translation from local to global coordinate space.
 nscoord mLineLeft, mBlockStart;
 // We use 11 here in order to fill up the jemalloc allocatoed chunk nicely,
 // see https://bugzilla.mozilla.org/show_bug.cgi?id=1362876#c6.
 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;

public:
 explicit nsAutoFloatManager(ReflowInput& aReflowInput)
     : mReflowInput(aReflowInput), mOld(nullptr) {}

 ~nsAutoFloatManager();

 /**
  * 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);

protected:
 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_) */