layout/generic/nsPlaceholderFrame.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 /*
   8  * rendering object for the point that anchors out-of-flow rendering
   9  * objects such as floats and absolutely positioned elements
  10  */
  11
  12 /*
  13  * Destruction of a placeholder and its out-of-flow must observe the
  14  * following constraints:
  15  *
  16  * - The mapping from the out-of-flow to the placeholder must be
  17  *   removed from the frame manager before the placeholder is destroyed.
  18  * - The mapping from the out-of-flow to the placeholder must be
  19  *   removed from the frame manager before the out-of-flow is destroyed.
  20  * - The placeholder must be removed from the frame tree, or have the
  21  *   mapping from it to its out-of-flow cleared, before the out-of-flow
  22  *   is destroyed (so that the placeholder will not point to a destroyed
  23  *   frame while it's in the frame tree).
  24  *
  25  * Furthermore, some code assumes that placeholders point to something
  26  * useful, so placeholders without an associated out-of-flow should not
  27  * remain in the tree.
  28  *
  29  * The placeholder's Destroy() implementation handles the destruction of
  30  * the placeholder and its out-of-flow. To avoid crashes, frame removal
  31  * and destruction code that works with placeholders must not assume
  32  * that the placeholder points to its out-of-flow.
  33  */
  34
  35 #ifndef nsPlaceholderFrame_h___
  36 #define nsPlaceholderFrame_h___
  37
  38 #include "mozilla/Attributes.h"
  39 #include "nsIFrame.h"
  40 #include "nsGkAtoms.h"
  41
  42 namespace mozilla {
  43 class PresShell;
  44 }  // namespace mozilla
  45
  46 class nsPlaceholderFrame;
  47 nsPlaceholderFrame* NS_NewPlaceholderFrame(mozilla::PresShell* aPresShell,
  48                                            mozilla::ComputedStyle* aStyle,
  49                                            nsFrameState aTypeBits);
  50
  51 #define PLACEHOLDER_TYPE_MASK                                                  \
  52   (PLACEHOLDER_FOR_FLOAT | PLACEHOLDER_FOR_ABSPOS | PLACEHOLDER_FOR_FIXEDPOS | \
  53    PLACEHOLDER_FOR_TOPLAYER)
  54
  55 /**
  56  * Implementation of a frame that's used as a placeholder for a frame that
  57  * has been moved out of the flow.
  58  */
  59 class nsPlaceholderFrame final : public nsIFrame {
  60  public:
  61   NS_DECL_FRAMEARENA_HELPERS(nsPlaceholderFrame)
  62 #ifdef DEBUG
  63   NS_DECL_QUERYFRAME
  64 #endif
  65
  66   /**
  67    * Create a new placeholder frame.  aTypeBit must be one of the
  68    * PLACEHOLDER_FOR_* constants above.
  69    */
  70   friend nsPlaceholderFrame* NS_NewPlaceholderFrame(
  71       mozilla::PresShell* aPresShell, ComputedStyle* aStyle,
  72       nsFrameState aTypeBits);
  73
  74   nsPlaceholderFrame(ComputedStyle* aStyle, nsPresContext* aPresContext,
  75                      nsFrameState aTypeBits)
  76       : nsIFrame(aStyle, aPresContext, kClassID), mOutOfFlowFrame(nullptr) {
  77     MOZ_ASSERT(
  78         aTypeBits == PLACEHOLDER_FOR_FLOAT ||
  79             aTypeBits == PLACEHOLDER_FOR_ABSPOS ||
  80             aTypeBits == PLACEHOLDER_FOR_FIXEDPOS ||
  81             aTypeBits == (PLACEHOLDER_FOR_TOPLAYER | PLACEHOLDER_FOR_ABSPOS) ||
  82             aTypeBits == (PLACEHOLDER_FOR_TOPLAYER | PLACEHOLDER_FOR_FIXEDPOS),
  83         "Unexpected type bit");
  84     AddStateBits(aTypeBits);
  85   }
  86
  87   // Get/Set the associated out of flow frame
  88   nsIFrame* GetOutOfFlowFrame() const { return mOutOfFlowFrame; }
  89   void SetOutOfFlowFrame(nsIFrame* aFrame) {
  90     NS_ASSERTION(!aFrame || !aFrame->GetPrevContinuation(),
  91                  "OOF must be first continuation");
  92     mOutOfFlowFrame = aFrame;
  93   }
  94
  95   // nsIFrame overrides
  96   void AddInlineMinISize(gfxContext* aRenderingContext,
  97                          InlineMinISizeData* aData) override;
  98   void AddInlinePrefISize(gfxContext* aRenderingContext,
  99                           InlinePrefISizeData* aData) override;
 100
 101   void Reflow(nsPresContext* aPresContext, ReflowOutput& aDesiredSize,
 102               const ReflowInput& aReflowInput,
 103               nsReflowStatus& aStatus) override;
 104
 105   void Destroy(DestroyContext&) override;
 106
 107 #if defined(DEBUG) || (defined(MOZ_REFLOW_PERF_DSP) && defined(MOZ_REFLOW_PERF))
 108   void BuildDisplayList(nsDisplayListBuilder* aBuilder,
 109                         const nsDisplayListSet& aLists) 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 = "",
 114             ListFlags aFlags = ListFlags()) const override;
 115   nsresult GetFrameName(nsAString& aResult) const override;
 116 #endif  // DEBUG
 117
 118   bool IsEmpty() override { return true; }
 119   bool IsSelfEmpty() override { return true; }
 120
 121   bool CanContinueTextRun() const override;
 122
 123   void SetLineIsEmptySoFar(bool aValue) {
 124     AddOrRemoveStateBits(PLACEHOLDER_LINE_IS_EMPTY_SO_FAR, aValue);
 125     AddStateBits(PLACEHOLDER_HAVE_LINE_IS_EMPTY_SO_FAR);
 126   }
 127   bool GetLineIsEmptySoFar(bool* aResult) const {
 128     bool haveValue = HasAnyStateBits(PLACEHOLDER_HAVE_LINE_IS_EMPTY_SO_FAR);
 129     if (haveValue) {
 130       *aResult = HasAnyStateBits(PLACEHOLDER_LINE_IS_EMPTY_SO_FAR);
 131     }
 132     return haveValue;
 133   }
 134   void ForgetLineIsEmptySoFar() {
 135     RemoveStateBits(PLACEHOLDER_HAVE_LINE_IS_EMPTY_SO_FAR);
 136   }
 137
 138 #ifdef ACCESSIBILITY
 139   mozilla::a11y::AccType AccessibleType() override {
 140     nsIFrame* realFrame = GetRealFrameForPlaceholder(this);
 141     return realFrame ? realFrame->AccessibleType() : nsIFrame::AccessibleType();
 142   }
 143 #endif
 144
 145   ComputedStyle* GetParentComputedStyleForOutOfFlow(
 146       nsIFrame** aProviderFrame) const;
 147
 148   // Like GetParentComputedStyleForOutOfFlow, but ignores display:contents bits.
 149   ComputedStyle* GetLayoutParentStyleForOutOfFlow(
 150       nsIFrame** aProviderFrame) const;
 151
 152   bool RenumberFrameAndDescendants(int32_t* aOrdinal, int32_t aDepth,
 153                                    int32_t aIncrement,
 154                                    bool aForCounting) override {
 155     return mOutOfFlowFrame->RenumberFrameAndDescendants(
 156         aOrdinal, aDepth, aIncrement, aForCounting);
 157   }
 158
 159   /**
 160    * @return the out-of-flow for aFrame if aFrame is a placeholder; otherwise
 161    * aFrame
 162    */
 163   static nsIFrame* GetRealFrameFor(nsIFrame* aFrame) {
 164     MOZ_ASSERT(aFrame, "Must have a frame to work with");
 165     if (aFrame->IsPlaceholderFrame()) {
 166       return GetRealFrameForPlaceholder(aFrame);
 167     }
 168     return aFrame;
 169   }
 170
 171   /**
 172    * @return the out-of-flow for aFrame, which is known to be a placeholder
 173    */
 174   static nsIFrame* GetRealFrameForPlaceholder(nsIFrame* aFrame) {
 175     MOZ_ASSERT(aFrame->IsPlaceholderFrame(),
 176                "Must have placeholder frame as input");
 177     nsIFrame* outOfFlow =
 178         static_cast<nsPlaceholderFrame*>(aFrame)->GetOutOfFlowFrame();
 179     NS_ASSERTION(outOfFlow, "Null out-of-flow for placeholder?");
 180     return outOfFlow;
 181   }
 182
 183  protected:
 184   nsIFrame* mOutOfFlowFrame;
 185 };
 186
 187 #endif /* nsPlaceholderFrame_h___ */