layout/generic/nsPlaceholderFrame.h

   1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* This Source Code Form is subject to the terms of the Mozilla Public
   3  * License, v. 2.0. If a copy of the MPL was not distributed with this
   4  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   5
   6 /*
   7  * rendering object for the point that anchors out-of-flow rendering
   8  * objects such as floats and absolutely positioned elements
   9  */
  10
  11 /*
  12  * Destruction of a placeholder and its out-of-flow must observe the
  13  * following constraints:
  14  *
  15  * - The mapping from the out-of-flow to the placeholder must be
  16  *   removed from the frame manager before the placeholder is destroyed.
  17  * - The mapping from the out-of-flow to the placeholder must be
  18  *   removed from the frame manager before the out-of-flow is destroyed.
  19  * - The placeholder must be removed from the frame tree, or have the
  20  *   mapping from it to its out-of-flow cleared, before the out-of-flow
  21  *   is destroyed (so that the placeholder will not point to a destroyed
  22  *   frame while it's in the frame tree).
  23  *
  24  * Furthermore, some code assumes that placeholders point to something
  25  * useful, so placeholders without an associated out-of-flow should not
  26  * remain in the tree.
  27  *
  28  * The placeholder's Destroy() implementation handles the destruction of
  29  * the placeholder and its out-of-flow. To avoid crashes, frame removal
  30  * and destruction code that works with placeholders must not assume
  31  * that the placeholder points to its out-of-flow.
  32  */
  33
  34 #ifndef nsPlaceholderFrame_h___
  35 #define nsPlaceholderFrame_h___
  36
  37 #include "mozilla/Attributes.h"
  38 #include "nsFrame.h"
  39 #include "nsGkAtoms.h"
  40
  41 nsIFrame* NS_NewPlaceholderFrame(nsIPresShell* aPresShell,
  42                                  nsStyleContext* aContext,
  43                                  nsFrameState aTypeBit);
  44
  45 #define PLACEHOLDER_TYPE_MASK    (PLACEHOLDER_FOR_FLOAT | \
  46                                   PLACEHOLDER_FOR_ABSPOS | \
  47                                   PLACEHOLDER_FOR_FIXEDPOS | \
  48                                   PLACEHOLDER_FOR_POPUP)
  49
  50 /**
  51  * Implementation of a frame that's used as a placeholder for a frame that
  52  * has been moved out of the flow.
  53  */
  54 class nsPlaceholderFrame MOZ_FINAL : public nsFrame {
  55 public:
  56   NS_DECL_FRAMEARENA_HELPERS
  57 #ifdef DEBUG
  58   NS_DECL_QUERYFRAME_TARGET(nsPlaceholderFrame)
  59   NS_DECL_QUERYFRAME
  60 #endif
  61
  62   /**
  63    * Create a new placeholder frame.  aTypeBit must be one of the
  64    * PLACEHOLDER_FOR_* constants above.
  65    */
  66   friend nsIFrame* NS_NewPlaceholderFrame(nsIPresShell* aPresShell,
  67                                           nsStyleContext* aContext,
  68                                           nsFrameState aTypeBit);
  69   nsPlaceholderFrame(nsStyleContext* aContext, nsFrameState aTypeBit)
  70     : nsFrame(aContext)
  71   {
  72     NS_PRECONDITION(aTypeBit == PLACEHOLDER_FOR_FLOAT ||
  73                     aTypeBit == PLACEHOLDER_FOR_ABSPOS ||
  74                     aTypeBit == PLACEHOLDER_FOR_FIXEDPOS ||
  75                     aTypeBit == PLACEHOLDER_FOR_POPUP,
  76                     "Unexpected type bit");
  77     AddStateBits(aTypeBit);
  78   }
  79
  80   // Get/Set the associated out of flow frame
  81   nsIFrame*  GetOutOfFlowFrame() const { return mOutOfFlowFrame; }
  82   void       SetOutOfFlowFrame(nsIFrame* aFrame) {
  83                NS_ASSERTION(!aFrame || !aFrame->GetPrevContinuation(),
  84                             "OOF must be first continuation");
  85                mOutOfFlowFrame = aFrame;
  86              }
  87
  88   // nsIFrame overrides
  89   // We need to override GetMinSize and GetPrefSize because XUL uses
  90   // placeholders not within lines.
  91   virtual void AddInlineMinISize(nsRenderingContext* aRenderingContext,
  92                                  InlineMinISizeData* aData) MOZ_OVERRIDE;
  93   virtual void AddInlinePrefISize(nsRenderingContext* aRenderingContext,
  94                                   InlinePrefISizeData* aData) MOZ_OVERRIDE;
  95   virtual nsSize GetMinSize(nsBoxLayoutState& aBoxLayoutState) MOZ_OVERRIDE;
  96   virtual nsSize GetPrefSize(nsBoxLayoutState& aBoxLayoutState) MOZ_OVERRIDE;
  97   virtual nsSize GetMaxSize(nsBoxLayoutState& aBoxLayoutState) MOZ_OVERRIDE;
  98
  99   virtual void Reflow(nsPresContext* aPresContext,
 100                       nsHTMLReflowMetrics& aDesiredSize,
 101                       const nsHTMLReflowState& aReflowState,
 102                       nsReflowStatus& aStatus) MOZ_OVERRIDE;
 103
 104   virtual void DestroyFrom(nsIFrame* aDestructRoot) MOZ_OVERRIDE;
 105
 106 #if defined(DEBUG) || (defined(MOZ_REFLOW_PERF_DSP) && defined(MOZ_REFLOW_PERF))
 107   virtual void BuildDisplayList(nsDisplayListBuilder*   aBuilder,
 108                                 const nsRect&           aDirtyRect,
 109                                 const nsDisplayListSet& aLists) MOZ_OVERRIDE;
 110 #endif // DEBUG || (MOZ_REFLOW_PERF_DSP && MOZ_REFLOW_PERF)
 111
 112 #ifdef DEBUG_FRAME_DUMP
 113   void List(FILE* out = stderr, const char* aPrefix = "", uint32_t aFlags = 0) const MOZ_OVERRIDE;
 114   virtual nsresult GetFrameName(nsAString& aResult) const MOZ_OVERRIDE;
 115 #endif // DEBUG
 116
 117   /**
 118    * Get the "type" of the frame
 119    *
 120    * @see nsGkAtoms::placeholderFrame
 121    */
 122   virtual nsIAtom* GetType() const MOZ_OVERRIDE;
 123
 124   virtual bool IsEmpty() MOZ_OVERRIDE { return true; }
 125   virtual bool IsSelfEmpty() MOZ_OVERRIDE { return true; }
 126
 127   virtual bool CanContinueTextRun() const MOZ_OVERRIDE;
 128
 129 #ifdef ACCESSIBILITY
 130   virtual mozilla::a11y::AccType AccessibleType() MOZ_OVERRIDE
 131   {
 132     nsIFrame* realFrame = GetRealFrameForPlaceholder(this);
 133     return realFrame ? realFrame->AccessibleType() :
 134                        nsFrame::AccessibleType();
 135   }
 136 #endif
 137
 138   virtual nsIFrame* GetParentStyleContextFrame() const MOZ_OVERRIDE;
 139
 140   /**
 141    * @return the out-of-flow for aFrame if aFrame is a placeholder; otherwise
 142    * aFrame
 143    */
 144   static nsIFrame* GetRealFrameFor(nsIFrame* aFrame) {
 145     NS_PRECONDITION(aFrame, "Must have a frame to work with");
 146     if (aFrame->GetType() == nsGkAtoms::placeholderFrame) {
 147       return GetRealFrameForPlaceholder(aFrame);
 148     }
 149     return aFrame;
 150   }
 151
 152   /**
 153    * @return the out-of-flow for aFrame, which is known to be a placeholder
 154    */
 155   static nsIFrame* GetRealFrameForPlaceholder(nsIFrame* aFrame) {
 156     NS_PRECONDITION(aFrame->GetType() == nsGkAtoms::placeholderFrame,
 157                     "Must have placeholder frame as input");
 158     nsIFrame* outOfFlow =
 159       static_cast<nsPlaceholderFrame*>(aFrame)->GetOutOfFlowFrame();
 160     NS_ASSERTION(outOfFlow, "Null out-of-flow for placeholder?");
 161     return outOfFlow;
 162   }
 163
 164 protected:
 165   nsIFrame* mOutOfFlowFrame;
 166 };
 167
 168 #endif /* nsPlaceholderFrame_h___ */