layout/generic/nsPlaceholderFrame.h

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  37
  38 /*
  39  * rendering object for the point that anchors out-of-flow rendering
  40  * objects such as floats and absolutely positioned elements
  41  */
  42
  43 /*
  44  * Destruction of a placeholder and its out-of-flow must observe the
  45  * following constraints:
  46  *
  47  * - The mapping from the out-of-flow to the placeholder must be
  48  *   removed from the frame manager before the placeholder is destroyed.
  49  * - The mapping from the out-of-flow to the placeholder must be
  50  *   removed from the frame manager before the out-of-flow is destroyed.
  51  * - The placeholder must be removed from the frame tree, or have the
  52  *   mapping from it to its out-of-flow cleared, before the out-of-flow
  53  *   is destroyed (so that the placeholder will not point to a destroyed
  54  *   frame while it's in the frame tree).
  55  *
  56  * Furthermore, some code assumes that placeholders point to something
  57  * useful, so placeholders without an associated out-of-flow should not
  58  * remain in the tree.
  59  *
  60  * The placeholder's Destroy() implementation handles the destruction of
  61  * the placeholder and its out-of-flow. To avoid crashes, frame removal
  62  * and destruction code that works with placeholders must not assume
  63  * that the placeholder points to its out-of-flow.
  64  */
  65
  66 #ifndef nsPlaceholderFrame_h___
  67 #define nsPlaceholderFrame_h___
  68
  69 #include "nsFrame.h"
  70 #include "nsGkAtoms.h"
  71
  72 nsIFrame* NS_NewPlaceholderFrame(nsIPresShell* aPresShell,
  73                                  nsStyleContext* aContext,
  74                                  nsFrameState aTypeBit);
  75
  76 // Frame state bits that are used to keep track of what this is a
  77 // placeholder for.
  78 #define PLACEHOLDER_FOR_FLOAT    NS_FRAME_STATE_BIT(20)
  79 #define PLACEHOLDER_FOR_ABSPOS   NS_FRAME_STATE_BIT(21)
  80 #define PLACEHOLDER_FOR_FIXEDPOS NS_FRAME_STATE_BIT(22)
  81 #define PLACEHOLDER_FOR_POPUP    NS_FRAME_STATE_BIT(23)
  82 #define PLACEHOLDER_TYPE_MASK    (PLACEHOLDER_FOR_FLOAT | \
  83                                   PLACEHOLDER_FOR_ABSPOS | \
  84                                   PLACEHOLDER_FOR_FIXEDPOS | \
  85                                   PLACEHOLDER_FOR_POPUP)
  86
  87 /**
  88  * Implementation of a frame that's used as a placeholder for a frame that
  89  * has been moved out of the flow
  90  */
  91 class nsPlaceholderFrame : public nsFrame {
  92 public:
  93   NS_DECL_FRAMEARENA_HELPERS
  94
  95   /**
  96    * Create a new placeholder frame.  aTypeBit must be one of the
  97    * PLACEHOLDER_FOR_* constants above.
  98    */
  99   friend nsIFrame* NS_NewPlaceholderFrame(nsIPresShell* aPresShell,
 100                                           nsStyleContext* aContext,
 101                                           nsFrameState aTypeBit);
 102   nsPlaceholderFrame(nsStyleContext* aContext, nsFrameState aTypeBit) :
 103     nsFrame(aContext)
 104   {
 105     NS_PRECONDITION(aTypeBit == PLACEHOLDER_FOR_FLOAT ||
 106                     aTypeBit == PLACEHOLDER_FOR_ABSPOS ||
 107                     aTypeBit == PLACEHOLDER_FOR_FIXEDPOS ||
 108                     aTypeBit == PLACEHOLDER_FOR_POPUP,
 109                     "Unexpected type bit");
 110     AddStateBits(aTypeBit);
 111   }
 112   virtual ~nsPlaceholderFrame();
 113
 114   // Get/Set the associated out of flow frame
 115   nsIFrame*  GetOutOfFlowFrame() const {return mOutOfFlowFrame;}
 116   void       SetOutOfFlowFrame(nsIFrame* aFrame) {
 117                NS_ASSERTION(!aFrame || !aFrame->GetPrevContinuation(),
 118                             "OOF must be first continuation");
 119                mOutOfFlowFrame = aFrame;
 120              }
 121
 122   // nsIHTMLReflow overrides
 123   // We need to override GetMinWidth and GetPrefWidth because XUL uses
 124   // placeholders not within lines.
 125   virtual nscoord GetMinWidth(nsIRenderingContext *aRenderingContext);
 126   virtual nscoord GetPrefWidth(nsIRenderingContext *aRenderingContext);
 127   virtual void AddInlineMinWidth(nsIRenderingContext *aRenderingContext,
 128                                  InlineMinWidthData *aData);
 129   virtual void AddInlinePrefWidth(nsIRenderingContext *aRenderingContext,
 130                                   InlinePrefWidthData *aData);
 131   virtual nsSize GetMinSize(nsBoxLayoutState& aBoxLayoutState);
 132   virtual nsSize GetPrefSize(nsBoxLayoutState& aBoxLayoutState);
 133   virtual nsSize GetMaxSize(nsBoxLayoutState& aBoxLayoutState);
 134   NS_IMETHOD Reflow(nsPresContext* aPresContext,
 135                     nsHTMLReflowMetrics& aDesiredSize,
 136                     const nsHTMLReflowState& aReflowState,
 137                     nsReflowStatus& aStatus);
 138
 139   virtual void DestroyFrom(nsIFrame* aDestructRoot);
 140
 141   // nsIFrame overrides
 142 #if defined(DEBUG) || (defined(MOZ_REFLOW_PERF_DSP) && defined(MOZ_REFLOW_PERF))
 143   NS_IMETHOD BuildDisplayList(nsDisplayListBuilder*   aBuilder,
 144                               const nsRect&           aDirtyRect,
 145                               const nsDisplayListSet& aLists);
 146 #endif // DEBUG || (MOZ_REFLOW_PERF_DSP && MOZ_REFLOW_PERF)
 147
 148 #ifdef DEBUG
 149   NS_IMETHOD List(FILE* out, PRInt32 aIndent) const;
 150 #endif // DEBUG
 151
 152   /**
 153    * Get the "type" of the frame
 154    *
 155    * @see nsGkAtoms::placeholderFrame
 156    */
 157   virtual nsIAtom* GetType() const;
 158
 159 #ifdef DEBUG
 160   NS_IMETHOD GetFrameName(nsAString& aResult) const;
 161 #endif
 162
 163   virtual PRBool IsEmpty() { return PR_TRUE; }
 164   virtual PRBool IsSelfEmpty() { return PR_TRUE; }
 165
 166   virtual PRBool CanContinueTextRun() const;
 167
 168 #ifdef ACCESSIBILITY
 169   virtual already_AddRefed<nsAccessible> CreateAccessible()
 170   {
 171     nsIFrame* realFrame = GetRealFrameForPlaceholder(this);
 172     return realFrame ? realFrame->CreateAccessible() :
 173                        nsFrame::CreateAccessible();
 174   }
 175 #endif
 176
 177   NS_IMETHOD GetParentStyleContextFrame(nsPresContext* aPresContext,
 178                                         nsIFrame**      aProviderFrame,
 179                                         PRBool*         aIsChild);
 180   /**
 181    * @return the out-of-flow for aFrame if aFrame is a placeholder; otherwise
 182    * aFrame
 183    */
 184   static nsIFrame* GetRealFrameFor(nsIFrame* aFrame) {
 185     NS_PRECONDITION(aFrame, "Must have a frame to work with");
 186     if (aFrame->GetType() == nsGkAtoms::placeholderFrame) {
 187       return GetRealFrameForPlaceholder(aFrame);
 188     }
 189     return aFrame;
 190   }
 191
 192   /**
 193    * @return the out-of-flow for aFrame, which is known to be a placeholder
 194    */
 195   static nsIFrame* GetRealFrameForPlaceholder(nsIFrame* aFrame) {
 196     NS_PRECONDITION(aFrame->GetType() == nsGkAtoms::placeholderFrame,
 197                     "Must have placeholder frame as input");
 198     nsIFrame* outOfFlow =
 199       static_cast<nsPlaceholderFrame*>(aFrame)->GetOutOfFlowFrame();
 200     NS_ASSERTION(outOfFlow, "Null out-of-flow for placeholder?");
 201     return outOfFlow;
 202   }
 203
 204 protected:
 205   nsIFrame* mOutOfFlowFrame;
 206 };
 207
 208 #endif /* nsPlaceholderFrame_h___ */