gecko/layout/generic/nsAbsoluteContainingBlock.h

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/*
 * code for managing absolutely positioned children of a rendering
 * object that is a containing block for them
 */

#ifndef nsAbsoluteContainingBlock_h___
#define nsAbsoluteContainingBlock_h___

#include "nsFrameList.h"
#include "nsHTMLReflowState.h"
#include "nsGkAtoms.h"

class nsIAtom;
class nsIFrame;
class nsPresContext;

/**
 * This class contains the logic for being an absolute containing block.  This
 * class is used within viewport frames (for frames representing content with
 * fixed position) and blocks (for frames representing absolutely positioned
 * content), since each set of frames is absolutely positioned with respect to
 * its parent.
 *
 * There is no principal child list, just a named child list which contains
 * the absolutely positioned frames.
 *
 * All functions include as the first argument the frame that is delegating
 * the request.
 *
 * @see nsGkAtoms::absoluteList and nsGkAtoms::fixedList
 */
class nsAbsoluteContainingBlock
{
public:
  nsAbsoluteContainingBlock(nsIAtom* aChildListName)
#ifdef DEBUG
    : mChildListName(aChildListName)
#endif
  {
    NS_ASSERTION(mChildListName == nsGkAtoms::absoluteList ||
                 mChildListName == nsGkAtoms::fixedList,
                 "should either represent position:fixed or absolute content");
  }

#ifdef DEBUG
  nsIAtom* GetChildListName() const { return mChildListName; }
#endif

  nsresult FirstChild(const nsIFrame* aDelegatingFrame,
                      nsIAtom*        aListName,
                      nsIFrame**      aFirstChild) const;
  nsIFrame* GetFirstChild() { return mAbsoluteFrames.FirstChild(); }
  
  nsresult SetInitialChildList(nsIFrame*       aDelegatingFrame,
                               nsIAtom*        aListName,
                               nsIFrame*       aChildList);
  nsresult AppendFrames(nsIFrame*      aDelegatingFrame,
                        nsIAtom*       aListName,
                        nsIFrame*      aFrameList);
  nsresult InsertFrames(nsIFrame*      aDelegatingFrame,
                        nsIAtom*       aListName,
                        nsIFrame*      aPrevFrame,
                        nsIFrame*      aFrameList);
  nsresult RemoveFrame(nsIFrame*      aDelegatingFrame,
                       nsIAtom*       aListName,
                       nsIFrame*      aOldFrame);

  // Called by the delegating frame after it has done its reflow first. This
  // function will reflow any absolutely positioned child frames that need to
  // be reflowed, e.g., because the absolutely positioned child frame has
  // 'auto' for an offset, or a percentage based width or height.
  // If aChildBounds is set, it returns (in the local coordinate space) the 
  // bounding rect of the absolutely positioned child elements taking into 
  // account their overflow area (if it is visible).
  // @param aForceReflow if this is false, reflow for some absolutely
  //        positioned frames may be skipped based on whether they use
  //        placeholders for positioning and on whether the containing block
  //        width or height changed.
  nsresult Reflow(nsIFrame*                aDelegatingFrame,
                  nsPresContext*           aPresContext,
                  const nsHTMLReflowState& aReflowState,
                  nscoord                  aContainingBlockWidth,
                  nscoord                  aContainingBlockHeight,
                  PRBool                   aCBWidthChanged,
                  PRBool                   aCBHeightChanged,
                  nsRect*                  aChildBounds = nsnull);


  void DestroyFrames(nsIFrame* aDelegatingFrame);

  PRBool  HasAbsoluteFrames() {return mAbsoluteFrames.NotEmpty();}

protected:
  // Returns PR_TRUE if the position of f depends on the position of
  // its placeholder or if the position or size of f depends on a
  // containing block dimension that changed.
  PRBool FrameDependsOnContainer(nsIFrame* f, PRBool aCBWidthChanged,
                                 PRBool aCBHeightChanged);

  nsresult ReflowAbsoluteFrame(nsIFrame*                aDelegatingFrame,
                               nsPresContext*          aPresContext,
                               const nsHTMLReflowState& aReflowState,
                               nscoord                  aContainingBlockWidth,
                               nscoord                  aContainingBlockHeight,
                               nsIFrame*                aKidFrame,
                               nsReflowStatus&          aStatus,
                               nsRect*                  aChildBounds);

protected:
  nsFrameList mAbsoluteFrames;  // additional named child list

#ifdef DEBUG
  nsIAtom* const mChildListName; // nsGkAtoms::fixedList or nsGkAtoms::absoluteList

  // helper routine for debug printout
  void PrettyUC(nscoord aSize,
                char*   aBuf);
#endif
};

#endif /* nsnsAbsoluteContainingBlock_h___ */