gecko-dev/layout/generic/nsFloatManager.h

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
// vim:cindent:ts=2:et:sw=2:
/* 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/Attributes.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 nsIPresShell;
class nsIFrame;
class nsPresContext;
namespace mozilla {
struct ReflowInput;
class StyleBasicShape;
} // namespace mozilla

/**
 * 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.
 */
struct nsFlowAreaRect {
  mozilla::LogicalRect mRect;
  bool mHasFloats;

  nsFlowAreaRect(mozilla::WritingMode aWritingMode,
                 nscoord aICoord, nscoord aBCoord,
                 nscoord aISize, nscoord aBSize,
                 bool aHasFloats)
    : mRect(aWritingMode, aICoord, aBCoord, aISize, aBSize)
    , mHasFloats(aHasFloats) {}
};

#define NS_FLOAT_MANAGER_CACHE_SIZE 4

/**
 * nsFloatManager is responsible for implementing CSS's rules for
 * positioning floats. An nsFloatManager object is created during reflow for
 * any block with NS_BLOCK_FLOAT_MGR. 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 BlockReflowInput'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(nsIPresShell* aPresShell, mozilla::WritingMode aWM);
  ~nsFloatManager();

  void* operator new(size_t aSize) CPP_THROW_NEW;
  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() {}
  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 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 GetLowestFloatTop() const;

  /**
   * Return the coordinate of the lowest float matching aBreakType in
   * this float manager. Returns aBCoord if there are no matching
   * floats.
   *
   * Both aBCoord and the result are relative to the current translation.
   */
  enum {
    // Tell ClearFloats not to push to nscoord_MAX when floats have been
    // pushed to the next page/column.
    DONT_CLEAR_PUSHED_FLOATS = (1<<0)
  };
  nscoord ClearFloats(nscoord aBCoord, mozilla::StyleClear aBreakType,
                      uint32_t aFlags = 0) 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 aBreakType) 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:

  // ShapeInfo is an abstract class for implementing all the shapes in CSS
  // Shapes Module. A subclass needs to override all the methods to adjust
  // the flow area with respect to its shape.
  class ShapeInfo
  {
  public:
    virtual ~ShapeInfo() {}

    virtual nscoord LineLeft(mozilla::WritingMode aWM,
                             const nscoord aBStart,
                             const nscoord aBEnd) const = 0;
    virtual nscoord LineRight(mozilla::WritingMode aWM,
                              const nscoord aBStart,
                              const nscoord aBEnd) const = 0;
    virtual nscoord BStart() const = 0;
    virtual nscoord BEnd() const = 0;
    virtual bool IsEmpty() const = 0;

    // Translate the current origin by the specified offsets.
    virtual void Translate(nscoord aLineLeft, nscoord aBlockStart) = 0;

    static mozilla::UniquePtr<ShapeInfo> CreateCircleOrEllipse(
      mozilla::StyleBasicShape* const aBasicShape,
      const mozilla::LogicalRect& aShapeBoxRect,
      mozilla::WritingMode aWM,
      const nsSize& aContainerSize);

  protected:
    // Compute the minimum line-axis difference between the bounding shape
    // box and its rounded corner within the given band (block-axis region).
    // This is used as a helper function to compute the LineRight() and
    // LineLeft(). See the picture in the implementation for an example.
    // RadiusL and RadiusB stand for radius on the line-axis and block-axis.
    //
    // Returns radius-x diff on the line-axis, or 0 if there's no rounded
    // corner within the given band.
    static nscoord ComputeEllipseLineInterceptDiff(
      const nscoord aShapeBoxBStart, const nscoord aShapeBoxBEnd,
      const nscoord aBStartCornerRadiusL, const nscoord aBStartCornerRadiusB,
      const nscoord aBEndCornerRadiusL, const nscoord aBEndCornerRadiusB,
      const nscoord aBandBStart, const nscoord aBandBEnd);

    static nscoord XInterceptAtY(const nscoord aY, const nscoord aRadiusX,
                                 const nscoord aRadiusY);

    // Convert the coordinate space from physical to the logical space used
    // in nsFloatManager, which is the same as FloatInfo::mRect.
    static nsPoint ConvertPhysicalToLogical(mozilla::WritingMode aWM,
                                            const nsPoint& aPoint,
                                            const nsSize& aContainerSize);
  };

  // Implements shape-outside: <shape-box>.
  class BoxShapeInfo final : public ShapeInfo
  {
  public:
    BoxShapeInfo(const nsRect& aShapeBoxRect, nsIFrame* const aFrame)
      : mShapeBoxRect(aShapeBoxRect)
      , mFrame(aFrame)
    {
    }

    nscoord LineLeft(mozilla::WritingMode aWM,
                     const nscoord aBStart,
                     const nscoord aBEnd) const override;
    nscoord LineRight(mozilla::WritingMode aWM,
                      const nscoord aBStart,
                      const nscoord aBEnd) const override;
    nscoord BStart() const override { return mShapeBoxRect.y; }
    nscoord BEnd() const override { return mShapeBoxRect.YMost(); }
    bool IsEmpty() const override { return mShapeBoxRect.IsEmpty(); };

    void Translate(nscoord aLineLeft, nscoord aBlockStart) override
    {
      mShapeBoxRect.MoveBy(aLineLeft, aBlockStart);
    }

  private:
    // This is the reference box of css shape-outside if specified, which
    // implements the <shape-box> value in the CSS Shapes Module Level 1.
    // The coordinate space is the same as FloatInfo::mRect.
    nsRect mShapeBoxRect;
    // The frame of the float.
    nsIFrame* const mFrame;
  };

  // Implements shape-outside: circle() and shape-outside: ellipse().
  class EllipseShapeInfo : public ShapeInfo
  {
  public:
    EllipseShapeInfo(const nsPoint& aCenter,
                     const nsSize& aRadii)
      : mCenter(aCenter)
      , mRadii(aRadii)
    {}

    nscoord LineLeft(mozilla::WritingMode aWM,
                     const nscoord aBStart,
                     const nscoord aBEnd) const override;
    nscoord LineRight(mozilla::WritingMode aWM,
                      const nscoord aBStart,
                      const nscoord aBEnd) const override;
    nscoord BStart() const override { return mCenter.y - mRadii.height; }
    nscoord BEnd() const override { return mCenter.y + mRadii.height; }
    bool IsEmpty() const override { return mRadii.IsEmpty(); };

    void Translate(nscoord aLineLeft, nscoord aBlockStart) override
    {
      mCenter.MoveBy(aLineLeft, aBlockStart);
    }

  protected:
    // The position of the center of the ellipse. The coordinate space is the
    // same as FloatInfo::mRect.
    nsPoint mCenter;
    // The radii of the ellipse in app units. The width and height represent
    // the line-axis and block-axis radii of the ellipse.
    nsSize mRadii;
  };

  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(mozilla::WritingMode aWM, ShapeType aShapeType,
                     const nscoord aBStart, const nscoord aBEnd) const;
    nscoord LineRight(mozilla::WritingMode aWM, ShapeType aShapeType,
                      const nscoord aBStart, const nscoord aBEnd) const;
    nscoord BStart(ShapeType aShapeType) const;
    nscoord BEnd(ShapeType aShapeType) const;
    bool IsEmpty(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;
  nsTArray<FloatInfo> 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),
      mNew(nullptr),
      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;
  nsFloatManager *mNew;
  nsFloatManager *mOld;
};

#endif /* !defined(nsFloatManager_h_) */