The Space Manager and related classes and structures are an important of the Gecko Layout system, specifically Block Layout. See the High Level Design document for an overview of the Space Manager, and as an introduction to the classes, structures and algorithms container in this, the Detailed Design Document.
The Space Manager is the central class is a group of classes that manage the occupied and available space that exists in horizontal bands across a canvas. The primary goal of the Space Manager is to provide information about those bands of space to support the CSS notion of floated elements.
There are three important parts to the Space Manager API: the parts that deal with the coordinate space of the Space Manager, the parts that deal with the regions managed by the Space Manager, and the parts that manage float impact intervals.
The class nsSpaceManager is declared in the file nsSpaceManger.h. The class is only used in the layout module and cannot be exported outside of that module (nor does it need to be). It is not a general purpose class, and is not intended to be subclasses .
Here is the class declaration, taken from the source file as of 01.08.02
/**
* Class for dealing with bands of available space. The space manager
* defines a coordinate space with an origin at (0, 0) that grows down
* and to the right.
*/
class nsSpaceManager {
public:
nsSpaceManager(nsIPresShell* aPresShell, nsIFrame* aFrame);
~nsSpaceManager();
void* operator new(size_t aSize);
void operator delete(void* aPtr, size_t aSize);
static void Shutdown();
/*
* Get the frame that's associated with the space manager. This frame
* created the space manager, and the world coordinate space is
* relative to this frame.
*
* You can use QueryInterface() on this frame to get any additional
* interfaces.
*/
nsIFrame* GetFrame() const { return mFrame; }
/**
* Translate the current origin by the specified (dx, dy). This
* creates a new local coordinate space relative to the current
* coordinate space.
*/
void Translate(nscoord aDx, nscoord aDy) { mX += aDx; mY += aDy; }
/**
* Returns the current translation from local coordinate space to
* world coordinate space. This represents the accumulated calls to
* Translate().
*/
void GetTranslation(nscoord& aX, nscoord& aY) const { aX = mX; aY = mY; }
/**
* Returns the y-most of the bottommost band or 0 if there are no bands.
*
* @return PR_TRUE if there are bands and PR_FALSE if there are no bands
*/
PRBool YMost(nscoord& aYMost) const;
/**
* Returns a band starting at the specified y-offset. The band data
* indicates which parts of the band are available, and which parts
* are unavailable
*
* The band data that is returned is in the coordinate space of the
* local coordinate system.
*
* The local coordinate space origin, the y-offset, and the max size
* describe a rectangle that's used to clip the underlying band of
* available space, i.e.
* {0, aYOffset, aMaxSize.width, aMaxSize.height} in the local
* coordinate space
*
* @param aYOffset the y-offset of where the band begins. The coordinate is
* relative to the upper-left corner of the local coordinate space
* @param aMaxSize the size to use to constrain the band data
* @param aBandData [in,out] used to return the list of trapezoids that
* describe the available space and the unavailable space
* @return NS_OK if successful and NS_ERROR_FAILURE if the band data is not
* not large enough. The 'count' member of the band data struct
* indicates how large the array of trapezoids needs to be
*/
nsresult GetBandData(nscoord aYOffset,
const nsSize& aMaxSize,
nsBandData& aBandData) const;
/**
* Add a rectangular region of unavailable space. The space is
* relative to the local coordinate system.
*
* The region is tagged with a frame
*
* @param aFrame the frame used to identify the region. Must not be NULL
* @param aUnavailableSpace the bounding rect of the unavailable space
* @return NS_OK if successful
* NS_ERROR_FAILURE if there is already a region tagged with aFrame
*/
nsresult AddRectRegion(nsIFrame* aFrame,
const nsRect& aUnavailableSpace);
/**
* Resize the rectangular region associated with aFrame by the specified
* deltas. The height change always applies to the bottom edge or the existing
* rect. You specify whether the width change applies to the left or right edge
*
* Returns NS_OK if successful, NS_ERROR_INVALID_ARG if there is no region
* tagged with aFrame
*/
enum AffectedEdge {LeftEdge, RightEdge};
nsresult ResizeRectRegion(nsIFrame* aFrame,
nscoord aDeltaWidth,
nscoord aDeltaHeight,
AffectedEdge aEdge = RightEdge);
/**
* Offset the region associated with aFrame by the specified amount.
*
* Returns NS_OK if successful, NS_ERROR_INVALID_ARG if there is no region
* tagged with aFrame
*/
nsresult OffsetRegion(nsIFrame* aFrame, nscoord dx, nscoord dy);
/**
* Remove the region associated with aFrane.
*
* Returns NS_OK if successful and NS_ERROR_INVALID_ARG if there is no region
* tagged with aFrame
*/
nsresult RemoveRegion(nsIFrame* aFrame);
/**
* Clears the list of regions representing the unavailable space.
*/
void ClearRegions();
/**
* Methods for dealing with the propagation of float damage during
* reflow.
*/
PRBool HasFloatDamage()
{
return !mFloatDamage.IsEmpty();
}
void IncludeInDamage(nscoord aIntervalBegin, nscoord aIntervalEnd)
{
mFloatDamage.IncludeInterval(aIntervalBegin + mY, aIntervalEnd + mY);
}
PRBool IntersectsDamage(nscoord aIntervalBegin, nscoord aIntervalEnd)
{
return mFloatDamage.Intersects(aIntervalBegin + mY, aIntervalEnd + mY);
}
#ifdef DEBUG
/**
* Dump the state of the spacemanager out to a file
*/
nsresult List(FILE* out);
void SizeOf(nsISizeOfHandler* aHandler, PRUint32* aResult) const;
#endif
private:
// Structure that maintains information about the region associated
// with a particular frame
struct FrameInfo {
nsIFrame* const mFrame;
nsRect mRect; // rectangular region
FrameInfo* mNext;
FrameInfo(nsIFrame* aFrame, const nsRect& aRect);
#ifdef NS_BUILD_REFCNT_LOGGING
~FrameInfo();
#endif
};
// Doubly linked list of band rects
struct BandRect : PRCListStr {
nscoord mLeft, mTop;
nscoord mRight, mBottom;
PRIntn mNumFrames; // number of frames occupying this rect
union {
nsIFrame* mFrame; // single frame occupying the space
nsVoidArray* mFrames; // list of frames occupying the space
};
BandRect(nscoord aLeft, nscoord aTop,
nscoord aRight, nscoord aBottom,
nsIFrame*);
BandRect(nscoord aLeft, nscoord aTop,
nscoord aRight, nscoord aBottom,
nsVoidArray*);
~BandRect();
// List operations
BandRect* Next() const {return (BandRect*)PR_NEXT_LINK(this);}
BandRect* Prev() const {return (BandRect*)PR_PREV_LINK(this);}
void InsertBefore(BandRect* aBandRect) {PR_INSERT_BEFORE(aBandRect, this);}
void InsertAfter(BandRect* aBandRect) {PR_INSERT_AFTER(aBandRect, this);}
void Remove() {PR_REMOVE_LINK(this);}
// Split the band rect into two vertically, with this band rect becoming
// the top part, and a new band rect being allocated and returned for the
// bottom part
//
// Does not insert the new band rect into the linked list
BandRect* SplitVertically(nscoord aBottom);
// Split the band rect into two horizontally, with this band rect becoming
// the left part, and a new band rect being allocated and returned for the
// right part
//
// Does not insert the new band rect into the linked list
BandRect* SplitHorizontally(nscoord aRight);
// Accessor functions
PRBool IsOccupiedBy(const nsIFrame*) const;
void AddFrame(const nsIFrame*);
void RemoveFrame(const nsIFrame*);
PRBool HasSameFrameList(const BandRect* aBandRect) const;
PRInt32 Length() const;
};
// Circular linked list of band rects
struct BandList : BandRect {
BandList();
// Accessors
PRBool IsEmpty() const {return PR_CLIST_IS_EMPTY((PRCListStr*)this);}
BandRect* Head() const {return (BandRect*)PR_LIST_HEAD(this);}
BandRect* Tail() const {return (BandRect*)PR_LIST_TAIL(this);}
// Operations
void Append(BandRect* aBandRect) {PR_APPEND_LINK(aBandRect, this);}
// Remove and delete all the band rects in the list
void Clear();
};
FrameInfo* GetFrameInfoFor(nsIFrame* aFrame);
FrameInfo* CreateFrameInfo(nsIFrame* aFrame, const nsRect& aRect);
void DestroyFrameInfo(FrameInfo*);
void ClearFrameInfo();
void ClearBandRects();
BandRect* GetNextBand(const BandRect* aBandRect) const;
void DivideBand(BandRect* aBand, nscoord aBottom);
PRBool CanJoinBands(BandRect* aBand, BandRect* aPrevBand);
PRBool JoinBands(BandRect* aBand, BandRect* aPrevBand);
void AddRectToBand(BandRect* aBand, BandRect* aBandRect);
void InsertBandRect(BandRect* aBandRect);
nsresult GetBandAvailableSpace(const BandRect* aBand,
nscoord aY,
const nsSize& aMaxSize,
nsBandData& aAvailableSpace) const;
nsIFrame* const mFrame; // frame associated with the space manager
nscoord mX, mY; // translation from local to global coordinate space
BandList mBandList; // header/sentinel for circular linked list of band rects
FrameInfo* mFrameInfoMap;
nsIntervalSet mFloatDamage;
static PRInt32 sCachedSpaceManagerCount;
static void* sCachedSpaceManagers[NS_SPACE_MANAGER_CACHE_SIZE];
nsSpaceManager(const nsSpaceManager&); // no implementation
void operator=(const nsSpaceManager&); // no implementation
};
The Constructor requires a Presentation Shell, used for arena allocations mostly, and a frame that this Space Manager is rooted on. The coordinate space of this Space Manager is relative to the frame passed in to the constructor.
nsSpaceManager(nsIPresShell* aPresShell, nsIFrame* aFrame); ~nsSpaceManager();
Operators 'new' and 'delete' are overridden to support a recycler. Space Manager instances come and go pretty frequently, and this recycler prevents excessive heap allocations and the performance penalties associated with it. The #define NS_SPACE_MANAGER_CACHE_SIZE is used to control the number of Space Manager instances that can be present in the recycler, currently 4. If more than NS_SPACE_MANAGER_CACHE_SIZE are allocated at a time,then standard allocation is used.
void* operator new(size_t aSize); void operator delete(void* aPtr, size_t aSize);
A Static method is used to shutdown the Space Manager recycling. This method deletes all of the Space Mangers in the recycler,and prevents further recycling. It is meant to be called only when the layout module is being terminated.
static void Shutdown();
/**
* Translate the current origin by the specified (dx, dy). This
* creates a new local coordinate space relative to the current
* coordinate space.
*/
void Translate(nscoord aDx, nscoord aDy) { mX += aDx; mY += aDy; }
/**
* Returns the current translation from local coordinate space to
* world coordinate space. This represents the accumulated calls to
* Translate().
*/
void GetTranslation(nscoord& aX, nscoord& aY) const { aX = mX; aY = mY; }
/**
* Returns the y-most of the bottommost band or 0 if there are no bands.
*
* @return PR_TRUE if there are bands and PR_FALSE if there are no bands
*/
PRBool YMost(nscoord& aYMost) const;
/**
* Returns a band starting at the specified y-offset. The band data
* indicates which parts of the band are available, and which parts
* are unavailable
*
* The band data that is returned is in the coordinate space of the
* local coordinate system.
*
* The local coordinate space origin, the y-offset, and the max size
* describe a rectangle that's used to clip the underlying band of
* available space, i.e.
* {0, aYOffset, aMaxSize.width, aMaxSize.height} in the local
* coordinate space
*
* @param aYOffset the y-offset of where the band begins. The coordinate is
* relative to the upper-left corner of the local coordinate space
* @param aMaxSize the size to use to constrain the band data
* @param aBandData [in,out] used to return the list of trapezoids that
* describe the available space and the unavailable space
* @return NS_OK if successful and NS_ERROR_FAILURE if the band data is not
* not large enough. The 'count' member of the band data struct
* indicates how large the array of trapezoids needs to be
*/
nsresult GetBandData(nscoord aYOffset,
const nsSize& aMaxSize,
nsBandData& aBandData) const;
/**
* Add a rectangular region of unavailable space. The space is
* relative to the local coordinate system.
*
* The region is tagged with a frame
*
* @param aFrame the frame used to identify the region. Must not be NULL
* @param aUnavailableSpace the bounding rect of the unavailable space
* @return NS_OK if successful
* NS_ERROR_FAILURE if there is already a region tagged with aFrame
*/
nsresult AddRectRegion(nsIFrame* aFrame,
const nsRect& aUnavailableSpace);
/**
* Resize the rectangular region associated with aFrame by the specified
* deltas. The height change always applies to the bottom edge or the existing
* rect. You specify whether the width change applies to the left or right edge
*
* Returns NS_OK if successful, NS_ERROR_INVALID_ARG if there is no region
* tagged with aFrame
*/
enum AffectedEdge {LeftEdge, RightEdge};
nsresult ResizeRectRegion(nsIFrame* aFrame,
nscoord aDeltaWidth,
nscoord aDeltaHeight,
AffectedEdge aEdge = RightEdge);
/**
* Offset the region associated with aFrame by the specified amount.
*
* Returns NS_OK if successful, NS_ERROR_INVALID_ARG if there is no region
* tagged with aFrame
*/
nsresult OffsetRegion(nsIFrame* aFrame, nscoord dx, nscoord dy);
/**
* Remove the region associated with aFrane.
*
* Returns NS_OK if successful and NS_ERROR_INVALID_ARG if there is no region
* tagged with aFrame
*/
nsresult RemoveRegion(nsIFrame* aFrame);
/**
* Clears the list of regions representing the unavailable space.
*/
void ClearRegions();
/**
* Methods for dealing with the propagation of float damage during
* reflow.
*/
PRBool HasFloatDamage()
{
return !mFloatDamage.IsEmpty();
}
void IncludeInDamage(nscoord aIntervalBegin, nscoord aIntervalEnd)
{
mFloatDamage.IncludeInterval(aIntervalBegin + mY, aIntervalEnd + mY);
}
PRBool IntersectsDamage(nscoord aIntervalBegin, nscoord aIntervalEnd)
{
return mFloatDamage.Intersects(aIntervalBegin + mY, aIntervalEnd + mY);
}
/** * Dump the state of the spacemanager out to a file */ nsresult List(FILE* out); void SizeOf(nsISizeOfHandler* aHandler, PRUint32* aResult) const;
/*
* Get the frame that's associated with the space manager. This frame
* created the space manager, and the world coordinate space is
* relative to this frame.
*
* You can use QueryInterface() on this frame to get any additional
* interfaces.
*/
nsIFrame* GetFrame() const { return mFrame; }
GetBandData is used to provide information to clients about what space if available and unavailable in a band of space. The client provides a vertical offset, the yOffset, that corresponds to the band that is of interest. This will be the y offset of the frame that is being reflowed. The caller also provides a collection of BandData objects (an array) and the number of items that the collection can handle. If the collection is too small, then an error is returned and the count is updated to indicate the size required.
The algorithm to provide the band data is as follows:
This method is called from GetBandData only. It walks all of the bands in the space manager and determines which bands intersect with the band passed in, and if within those bands there are regions that are available or occupied.
Clients call into this method to notify the Space Manager that a new frame is occupying some space.
Internal method to insert a band rect into the BandList in the correct location. There are several cases it has to handle, as specified in the source file comments:
// When comparing a rect to a band there are seven cases to consider. // 'R' is the rect and 'B' is the band. // // Case 1 Case 2 Case 3 Case 4 // ------ ------ ------ ------ // +-----+ +-----+ +-----+ +-----+ // | R | | R | +-----+ +-----+ | | | | // +-----+ +-----+ | | | R | | B | | B | // +-----+ | B | +-----+ | | +-----+ | | // | | | | +-----+ | R | +-----+ // | B | +-----+ +-----+ // | | // +-----+ // // // // Case 5 Case 6 Case 7 // ------ ------ ------ // +-----+ +-----+ +-----+ +-----+ // | | | R | | B | | | +-----+ // | B | +-----+ +-----+ | R | | B | // | | | | +-----+ // +-----+ +-----+ // +-----+ // | R | // +-----+ //
This algorithm is pretty confusing - basically what needs to happen is that rects and bands need to be divided up so that complicated cases like#2, #4, and #7, are reduced to simpler cases where the rects is totally above,below, or between a band rect. From the current implementation, it might be worth verifying that the final result of the inserts is a correctly ordered list of bandRects (debug mode only).
When a float is removed, the Space Manager is notified by a call to RemoveRegion,passing in the frame that is being removed.