layout/base/FrameLayerBuilder.h
author Markus Stange <mstange@themasta.com>
Fri, 26 Feb 2016 01:29:41 +0100
changeset 323488 c690a0802e0007bb7e58bafeee672c816faa3cf5
parent 319078 75dfe10ec44a88bda2d9721d269ddf2429ac5426
child 325809 70f69c94da8c063217c1fdab25873edc22687c73
permissions -rw-r--r--
Bug 1247854 - Apply the correct scroll clips to the nsDisplayTransform and nsDisplayPerspective of a scrolled perspective item. r=mattwoodrow a=ritu I've decided to fix this in a very explicit way. The only "magic" part that's left is how we decide that the AGR of the perspective item is outside the scrolled frame (and I'm not sure myself how that works). I didn't want to change what scroll clips we set on what items, because the scroll clip really belongs on the perspective item, because that's the item that needs to be clipped, and it should also be the item that should be scrolled if it weren't for the fact that APZ wouldn't know that it should apply the perspective transform before the APZ transform. MozReview-Commit-ID: BBw8VPohQI4

/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef FRAMELAYERBUILDER_H_
#define FRAMELAYERBUILDER_H_

#include "nsTHashtable.h"
#include "nsHashKeys.h"
#include "nsTArray.h"
#include "nsRegion.h"
#include "nsIFrame.h"
#include "DisplayItemClip.h"
#include "mozilla/gfx/MatrixFwd.h"
#include "mozilla/layers/LayersTypes.h"
#include "LayerState.h"
#include "LayerUserData.h"

class nsDisplayListBuilder;
class nsDisplayList;
class nsDisplayItem;
class gfxContext;
class nsDisplayItemGeometry;

namespace mozilla {
class DisplayItemScrollClip;
namespace layers {
class ContainerLayer;
class LayerManager;
class BasicLayerManager;
class PaintedLayer;
class ImageLayer;
} // namespace layers

class FrameLayerBuilder;
class LayerManagerData;
class PaintedLayerData;
class ContainerState;

class RefCountedRegion {
private:
  ~RefCountedRegion() {}
public:
  NS_INLINE_DECL_REFCOUNTING(RefCountedRegion)

  RefCountedRegion() : mIsInfinite(false) {}
  nsRegion mRegion;
  bool mIsInfinite;
};

struct ContainerLayerParameters {
  ContainerLayerParameters()
    : mXScale(1)
    , mYScale(1)
    , mLayerContentsVisibleRect(nullptr)
    , mBackgroundColor(NS_RGBA(0,0,0,0))
    , mScrollClip(nullptr)
    , mScrollClipForPerspectiveChild(nullptr)
    , mInTransformedSubtree(false)
    , mInActiveTransformedSubtree(false)
    , mDisableSubpixelAntialiasingInDescendants(false)
    , mInLowPrecisionDisplayPort(false)
    , mForEventsOnly(false)
  {}
  ContainerLayerParameters(float aXScale, float aYScale)
    : mXScale(aXScale)
    , mYScale(aYScale)
    , mLayerContentsVisibleRect(nullptr)
    , mBackgroundColor(NS_RGBA(0,0,0,0))
    , mScrollClip(nullptr)
    , mScrollClipForPerspectiveChild(nullptr)
    , mInTransformedSubtree(false)
    , mInActiveTransformedSubtree(false)
    , mDisableSubpixelAntialiasingInDescendants(false)
    , mInLowPrecisionDisplayPort(false)
    , mForEventsOnly(false)
  {}
  ContainerLayerParameters(float aXScale, float aYScale,
                           const nsIntPoint& aOffset,
                           const ContainerLayerParameters& aParent)
    : mXScale(aXScale)
    , mYScale(aYScale)
    , mLayerContentsVisibleRect(nullptr)
    , mOffset(aOffset)
    , mBackgroundColor(aParent.mBackgroundColor)
    , mScrollClip(aParent.mScrollClip)
    , mScrollClipForPerspectiveChild(aParent.mScrollClipForPerspectiveChild)
    , mInTransformedSubtree(aParent.mInTransformedSubtree)
    , mInActiveTransformedSubtree(aParent.mInActiveTransformedSubtree)
    , mDisableSubpixelAntialiasingInDescendants(aParent.mDisableSubpixelAntialiasingInDescendants)
    , mInLowPrecisionDisplayPort(aParent.mInLowPrecisionDisplayPort)
    , mForEventsOnly(aParent.mForEventsOnly)
  {}

  float mXScale, mYScale;

  LayoutDeviceToLayerScale2D Scale() const {
    return LayoutDeviceToLayerScale2D(mXScale, mYScale);
  }

  /**
   * If non-null, the rectangle in which BuildContainerLayerFor stores the
   * visible rect of the layer, in the coordinate system of the created layer.
   */
  nsIntRect* mLayerContentsVisibleRect;

  /**
   * An offset to apply to all child layers created.
   */
  nsIntPoint mOffset;

  LayerIntPoint Offset() const {
    return LayerIntPoint::FromUnknownPoint(mOffset);
  }

  nscolor mBackgroundColor;
  const DisplayItemScrollClip* mScrollClip;

  // usually nullptr, except when building children of an nsDisplayPerspective
  const DisplayItemScrollClip* mScrollClipForPerspectiveChild;

  bool mInTransformedSubtree;
  bool mInActiveTransformedSubtree;
  bool mDisableSubpixelAntialiasingInDescendants;
  bool mInLowPrecisionDisplayPort;
  bool mForEventsOnly;
  /**
   * When this is false, PaintedLayer coordinates are drawn to with an integer
   * translation and the scale in mXScale/mYScale.
   */
  bool AllowResidualTranslation()
  {
    // If we're in a transformed subtree, but no ancestor transform is actively
    // changing, we'll use the residual translation when drawing into the
    // PaintedLayer to ensure that snapping exactly matches the ideal transform.
    return mInTransformedSubtree && !mInActiveTransformedSubtree;
  }
};

/**
 * The FrameLayerBuilder is responsible for converting display lists 
 * into layer trees. Every LayerManager needs a unique FrameLayerBuilder
 * to build layers.
 * 
 * The most important API in this class is BuildContainerLayerFor. This
 * method takes a display list as input and constructs a ContainerLayer
 * with child layers that render the contents of the display list. It
 * records the relationship between frames and layers.
 * 
 * That data enables us to retain layer trees. When constructing a
 * ContainerLayer, we first check to see if there's an existing
 * ContainerLayer for the same frame that can be recycled. If we recycle
 * it, we also try to reuse its existing PaintedLayer children to render
 * the display items without layers of their own. The idea is that by
 * recycling layers deterministically, we can ensure that when nothing
 * changes in a display list, we will reuse the existing layers without
 * changes.
 * 
 * We expose a GetLeafLayerFor method that can be called by display items
 * that make their own layers (e.g. canvas and video); this method
 * locates the last layer used to render the display item, if any, and
 * return it as a candidate for recycling.
 * 
 * FrameLayerBuilder sets up PaintedLayers so that 0,0 in the Painted layer
 * corresponds to the (pixel-snapped) top-left of the aAnimatedGeometryRoot.
 * It sets up ContainerLayers so that 0,0 in the container layer
 * corresponds to the snapped top-left of the display item reference frame.
 *
 * When we construct a container layer, we know the transform that will be
 * applied to the layer. If the transform scales the content, we can get
 * better results when intermediate buffers are used by pushing some scale
 * from the container's transform down to the children. For PaintedLayer
 * children, the scaling can be achieved by changing the size of the layer
 * and drawing into it with increased or decreased resolution. By convention,
 * integer types (nsIntPoint/nsIntSize/nsIntRect/nsIntRegion) are all in layer
 * coordinates, post-scaling, whereas appunit types are all pre-scaling.
 */
class FrameLayerBuilder : public layers::LayerUserData {
public:
  typedef layers::ContainerLayer ContainerLayer;
  typedef layers::Layer Layer;
  typedef layers::PaintedLayer PaintedLayer;
  typedef layers::ImageLayer ImageLayer;
  typedef layers::LayerManager LayerManager;
  typedef layers::BasicLayerManager BasicLayerManager;
  typedef layers::EventRegions EventRegions;

  FrameLayerBuilder();
  ~FrameLayerBuilder();

  static void Shutdown();

  void Init(nsDisplayListBuilder* aBuilder, LayerManager* aManager,
            PaintedLayerData* aLayerData = nullptr);

  /**
   * Call this to notify that we have just started a transaction on the
   * retained layer manager aManager.
   */
  void DidBeginRetainedLayerTransaction(LayerManager* aManager);

  /**
   * Call this just before we end a transaction.
   */
  void WillEndTransaction();

  /**
   * Call this after we end a transaction.
   */
  void DidEndTransaction();

  enum {
    CONTAINER_NOT_CLIPPED_BY_ANCESTORS = 0x01,

    /**
     * Set this when pulling an opaque background color from behind the
     * container layer into the container doesn't change the visual results,
     * given the effects you're going to apply to the container layer.
     * For example, this is compatible with opacity or clipping/masking, but
     * not with non-OVER blend modes or filters.
     */
    CONTAINER_ALLOW_PULL_BACKGROUND_COLOR = 0x02
  };
  /**
   * Build a container layer for a display item that contains a child
   * list, either reusing an existing one or creating a new one. It
   * sets the container layer children to layers which together render
   * the contents of the display list. It reuses existing layers from
   * the retained layer manager if possible.
   * aContainerItem may be null, in which case we construct a root layer.
   * This gets called by display list code. It calls BuildLayer on the
   * items in the display list, making items with their own layers
   * children of the new container, and assigning all other items to
   * PaintedLayer children created and managed by the FrameLayerBuilder.
   * Returns a layer with clip rect cleared; it is the
   * caller's responsibility to add any clip rect. The visible region
   * is set based on what's in the layer.
   * The container layer is transformed by aTransform (if non-null), and
   * the result is transformed by the scale factors in aContainerParameters.
   * aChildren is modified due to display item merging and flattening.
   * The visible region of the returned layer is set only if aContainerItem
   * is null.
   */
  already_AddRefed<ContainerLayer>
  BuildContainerLayerFor(nsDisplayListBuilder* aBuilder,
                         LayerManager* aManager,
                         nsIFrame* aContainerFrame,
                         nsDisplayItem* aContainerItem,
                         nsDisplayList* aChildren,
                         const ContainerLayerParameters& aContainerParameters,
                         const gfx::Matrix4x4* aTransform,
                         uint32_t aFlags = 0);

  /**
   * Get a retained layer for a display item that needs to create its own
   * layer for rendering (i.e. under nsDisplayItem::BuildLayer). Returns
   * null if no retained layer is available, which usually means that this
   * display item didn't have a layer before so the caller will
   * need to create one.
   * Returns a layer with clip rect cleared; it is the
   * caller's responsibility to add any clip rect and set the visible
   * region.
   */
  Layer* GetLeafLayerFor(nsDisplayListBuilder* aBuilder,
                         nsDisplayItem* aItem);

  /**
   * Call this to force all retained layers to be discarded and recreated at
   * the next paint.
   */
  static void InvalidateAllLayers(LayerManager* aManager);
  static void InvalidateAllLayersForFrame(nsIFrame *aFrame);

  /**
   * Call this to determine if a frame has a dedicated (non-Painted) layer
   * for the given display item key. If there isn't one, we return null,
   * otherwise we return the layer.
   */
  static Layer* GetDedicatedLayer(nsIFrame* aFrame, uint32_t aDisplayItemKey);

  /**
   * This callback must be provided to EndTransaction. The callback data
   * must be the nsDisplayListBuilder containing this FrameLayerBuilder.
   * This function can be called multiple times in a row to draw
   * different regions. This will occur when, for example, progressive paint is
   * enabled. In these cases aDirtyRegion can be used to specify a larger region
   * than aRegionToDraw that will be drawn during the transaction, possibly
   * allowing the callback to make optimizations.
   */
  static void DrawPaintedLayer(PaintedLayer* aLayer,
                              gfxContext* aContext,
                              const nsIntRegion& aRegionToDraw,
                              const nsIntRegion& aDirtyRegion,
                              mozilla::layers::DrawRegionClip aClip,
                              const nsIntRegion& aRegionToInvalidate,
                              void* aCallbackData);

  /**
   * Dumps this FrameLayerBuilder's retained layer manager's retained
   * layer tree. Defaults to dumping to stdout in non-HTML format.
   */
  static void DumpRetainedLayerTree(LayerManager* aManager, std::stringstream& aStream, bool aDumpHtml = false);

  /**
   * Returns the most recently allocated geometry item for the given display
   * item.
   *
   * XXX(seth): The current implementation must iterate through all display
   * items allocated for this display item's frame. This may lead to O(n^2)
   * behavior in some situations.
   */
  static nsDisplayItemGeometry* GetMostRecentGeometry(nsDisplayItem* aItem);


  /******* PRIVATE METHODS to FrameLayerBuilder.cpp ********/
  /* These are only in the public section because they need
   * to be called by file-scope helper functions in FrameLayerBuilder.cpp.
   */

  /**
   * Record aItem as a display item that is rendered by aLayer.
   *
   * @param aLayer Layer that the display item will be rendered into
   * @param aItem Display item to be drawn.
   * @param aLayerState What LayerState the item is using.
   * @param aManager If the layer is in the LAYER_INACTIVE state,
   * then this is the temporary layer manager to draw with.
   */
  void AddLayerDisplayItem(Layer* aLayer,
                           nsDisplayItem* aItem,
                           LayerState aLayerState,
                           BasicLayerManager* aManager);

  /**
   * Record aItem as a display item that is rendered by the PaintedLayer
   * aLayer, with aClipRect, where aContainerLayerFrame is the frame
   * for the container layer this ThebesItem belongs to.
   * aItem must have an underlying frame.
   * @param aTopLeft offset from active scrolled root to reference frame
   */
  void AddPaintedDisplayItem(PaintedLayerData* aLayer,
                            nsDisplayItem* aItem,
                            const DisplayItemClip& aClip,
                            ContainerState& aContainerState,
                            LayerState aLayerState,
                            const nsPoint& aTopLeft);

  /**
   * Calls GetOldLayerForFrame on the underlying frame of the display item,
   * and each subsequent merged frame if no layer is found for the underlying
   * frame.
   */
  Layer* GetOldLayerFor(nsDisplayItem* aItem, 
                        nsDisplayItemGeometry** aOldGeometry = nullptr, 
                        DisplayItemClip** aOldClip = nullptr);

  void ClearCachedGeometry(nsDisplayItem* aItem);

  static Layer* GetDebugOldLayerFor(nsIFrame* aFrame, uint32_t aDisplayItemKey);

  /**
   * Return the layer that all display items of aFrame were assigned to in the
   * last paint, or nullptr if there was no single layer assigned to all of the
   * frame's display items (i.e. zero, or more than one).
   * This function is for testing purposes and not performance sensitive.
   */
  static PaintedLayer* GetDebugSingleOldPaintedLayerForFrame(nsIFrame* aFrame);

  /**
   * Destroy any stored LayerManagerDataProperty and the associated data for
   * aFrame.
   */
  static void DestroyDisplayItemDataFor(nsIFrame* aFrame);

  LayerManager* GetRetainingLayerManager() { return mRetainingManager; }

  /**
   * Returns true if the given display item was rendered during the previous
   * paint. Returns false otherwise.
   */
  static bool HasRetainedDataFor(nsIFrame* aFrame, uint32_t aDisplayItemKey);

  class DisplayItemData;
  typedef void (*DisplayItemDataCallback)(nsIFrame *aFrame, DisplayItemData* aItem);

  static void IterateRetainedDataFor(nsIFrame* aFrame, DisplayItemDataCallback aCallback);

  /**
   * Save transform that was in aLayer when we last painted, and the position
   * of the active scrolled root frame. It must be an integer
   * translation.
   */
  void SavePreviousDataForLayer(PaintedLayer* aLayer, uint32_t aClipCount);
  /**
   * Get the translation transform that was in aLayer when we last painted. It's either
   * the transform saved by SaveLastPaintTransform, or else the transform
   * that's currently in the layer (which must be an integer translation).
   */
  nsIntPoint GetLastPaintOffset(PaintedLayer* aLayer);

  /**
   * Return the resolution at which we expect to render aFrame's contents,
   * assuming they are being painted to retained layers. This takes into account
   * the resolution the contents of the ContainerLayer containing aFrame are
   * being rendered at, as well as any currently-inactive transforms between
   * aFrame and that container layer.
   */
  static gfxSize GetPaintedLayerScaleForFrame(nsIFrame* aFrame);

  /**
   * Stores a Layer as the dedicated layer in the DisplayItemData for a given frame/key pair.
   *
   * Used when we optimize a PaintedLayer into an ImageLayer and want to retroactively update the 
   * DisplayItemData so we can retrieve the layer from within layout.
   */
  void StoreOptimizedLayerForFrame(nsDisplayItem* aItem, Layer* aLayer);
  
  NS_DECLARE_FRAME_PROPERTY_WITH_FRAME_IN_DTOR(LayerManagerDataProperty,
                                               nsTArray<DisplayItemData*>,
                                               RemoveFrameFromLayerManager)

  /**
   * Retained data storage:
   *
   * Each layer manager (widget, and inactive) stores a LayerManagerData object
   * that keeps a hash-set of DisplayItemData items that were drawn into it.
   * Each frame also keeps a list of DisplayItemData pointers that were
   * created for that frame. DisplayItemData objects manage these lists automatically.
   *
   * During layer construction we update the data in the LayerManagerData object, marking
   * items that are modified. At the end we sweep the LayerManagerData hash-set and remove
   * all items that haven't been modified.
   */

  /**
   * Retained data for a display item.
   */
  class DisplayItemData final {
  public:
    friend class FrameLayerBuilder;

    uint32_t GetDisplayItemKey() { return mDisplayItemKey; }
    Layer* GetLayer() { return mLayer; }
    nsDisplayItemGeometry* GetGeometry() const { return mGeometry.get(); }
    void Invalidate() { mIsInvalid = true; }
    void ClearAnimationCompositorState();

  private:
    DisplayItemData(LayerManagerData* aParent,
                    uint32_t aKey,
                    Layer* aLayer,
                    nsIFrame* aFrame = nullptr);

    /**
     * Removes any references to this object from frames
     * in mFrameList.
     */
    ~DisplayItemData();

    NS_INLINE_DECL_REFCOUNTING(DisplayItemData)


    /**
     * Associates this DisplayItemData with a frame, and adds it
     * to the LayerManagerDataProperty list on the frame.
     */
    void AddFrame(nsIFrame* aFrame);
    void RemoveFrame(nsIFrame* aFrame);
    const nsTArray<nsIFrame*>& GetFrameListChanges();

    /**
     * Updates the contents of this item to a new set of data, instead of allocating a new
     * object.
     * Set the passed in parameters, and clears the opt layer and inactive manager.
     * Parent, and display item key are assumed to be the same.
     *
     * EndUpdate must be called before the end of the transaction to complete the update.
     */
    void BeginUpdate(Layer* aLayer, LayerState aState,
                     uint32_t aContainerLayerGeneration, nsDisplayItem* aItem = nullptr);

    /**
     * Completes the update of this, and removes any references to data that won't live
     * longer than the transaction.
     *
     * Updates the geometry, frame list and clip.
     * For items within a PaintedLayer, a geometry object must be specified to retain
     * until the next transaction.
     *
     */
    void EndUpdate(nsAutoPtr<nsDisplayItemGeometry> aGeometry);
    void EndUpdate();

    LayerManagerData* mParent;
    RefPtr<Layer> mLayer;
    RefPtr<Layer> mOptLayer;
    RefPtr<BasicLayerManager> mInactiveManager;
    AutoTArray<nsIFrame*, 1> mFrameList;
    nsAutoPtr<nsDisplayItemGeometry> mGeometry;
    DisplayItemClip mClip;
    uint32_t        mDisplayItemKey;
    uint32_t        mContainerLayerGeneration;
    LayerState      mLayerState;

    /**
     * Temporary stoarage of the display item being referenced, only valid between
     * BeginUpdate and EndUpdate.
     */
    nsDisplayItem* mItem;
    AutoTArray<nsIFrame*, 1> mFrameListChanges;

    /**
     * Used to track if data currently stored in mFramesWithLayers (from an existing
     * paint) has been updated in the current paint.
     */
    bool            mUsed;
    bool            mIsInvalid;
  };

protected:

  friend class LayerManagerData;

  static void RemoveFrameFromLayerManager(const nsIFrame* aFrame,
                                          nsTArray<DisplayItemData*>* aArray);

  /**
   * Given a frame and a display item key that uniquely identifies a
   * display item for the frame, find the layer that was last used to
   * render that display item. Returns null if there is no such layer.
   * This could be a dedicated layer for the display item, or a PaintedLayer
   * that renders many display items.
   */
  DisplayItemData* GetOldLayerForFrame(nsIFrame* aFrame, uint32_t aDisplayItemKey);

  /**
   * Stores DisplayItemData associated with aFrame, stores the data in
   * mNewDisplayItemData.
   */
  DisplayItemData* StoreDataForFrame(nsDisplayItem* aItem, Layer* aLayer, LayerState aState);
  void StoreDataForFrame(nsIFrame* aFrame,
                         uint32_t aDisplayItemKey,
                         Layer* aLayer,
                         LayerState aState);

  // Flash the area within the context clip if paint flashing is enabled.
  static void FlashPaint(gfxContext *aContext);

  /*
   * Get the DisplayItemData array associated with this frame, or null if one
   * doesn't exist.
   *
   * Note that the pointer returned here is only valid so long as you don't
   * poke the LayerManagerData's mFramesWithLayers hashtable.
   */
  DisplayItemData* GetDisplayItemData(nsIFrame *aFrame, uint32_t aKey);

  /*
   * Get the DisplayItemData associated with this frame / display item pair,
   * using the LayerManager instead of FrameLayerBuilder.
   */
  static DisplayItemData* GetDisplayItemDataForManager(nsIFrame* aFrame, 
                                                       uint32_t aDisplayItemKey, 
                                                       LayerManager* aManager);
  static DisplayItemData* GetDisplayItemDataForManager(nsIFrame* aFrame, 
                                                       uint32_t aDisplayItemKey);
  static DisplayItemData* GetDisplayItemDataForManager(nsDisplayItem* aItem, LayerManager* aManager);
  static DisplayItemData* GetDisplayItemDataForManager(nsIFrame* aFrame, 
                                                       uint32_t aDisplayItemKey, 
                                                       LayerManagerData* aData);

  /**
   * We store one of these for each display item associated with a
   * PaintedLayer, in a hashtable that maps each PaintedLayer to an array
   * of ClippedDisplayItems. (PaintedLayerItemsEntry is the hash entry
   * for that hashtable.)
   * These are only stored during the paint process, so that the
   * DrawPaintedLayer callback can figure out which items to draw for the
   * PaintedLayer.
   */
  struct ClippedDisplayItem {
    ClippedDisplayItem(nsDisplayItem* aItem, uint32_t aGeneration);
    ~ClippedDisplayItem();

    nsDisplayItem* mItem;

    /**
     * If the display item is being rendered as an inactive
     * layer, then this stores the layer manager being
     * used for the inactive transaction.
     */
    RefPtr<LayerManager> mInactiveLayerManager;

    uint32_t mContainerLayerGeneration;

  };

  static void RecomputeVisibilityForItems(nsTArray<ClippedDisplayItem>& aItems,
                                          nsDisplayListBuilder* aBuilder,
                                          const nsIntRegion& aRegionToDraw,
                                          const nsIntPoint& aOffset,
                                          int32_t aAppUnitsPerDevPixel,
                                          float aXScale,
                                          float aYScale);

  void PaintItems(nsTArray<ClippedDisplayItem>& aItems,
                  const nsIntRect& aRect,
                  gfxContext* aContext,
                  nsRenderingContext* aRC,
                  nsDisplayListBuilder* aBuilder,
                  nsPresContext* aPresContext,
                  const nsIntPoint& aOffset,
                  float aXScale, float aYScale,
                  int32_t aCommonClipCount);

  /**
   * We accumulate ClippedDisplayItem elements in a hashtable during
   * the paint process. This is the hashentry for that hashtable.
   */
public:
  class PaintedLayerItemsEntry : public nsPtrHashKey<PaintedLayer> {
  public:
    explicit PaintedLayerItemsEntry(const PaintedLayer *key);
    PaintedLayerItemsEntry(const PaintedLayerItemsEntry&);
    ~PaintedLayerItemsEntry();

    nsTArray<ClippedDisplayItem> mItems;
    nsIFrame* mContainerLayerFrame;
    // The translation set on this PaintedLayer before we started updating the
    // layer tree.
    nsIntPoint mLastPaintOffset;
    uint32_t mLastCommonClipCount;

    uint32_t mContainerLayerGeneration;
    bool mHasExplicitLastPaintOffset;
    /**
      * The first mCommonClipCount rounded rectangle clips are identical for
      * all items in the layer. Computed in PaintedLayerData.
      */
    uint32_t mCommonClipCount;

    enum { ALLOW_MEMMOVE = true };
  };

  /**
   * Get the PaintedLayerItemsEntry object associated with aLayer in this
   * FrameLayerBuilder
   */
  PaintedLayerItemsEntry* GetPaintedLayerItemsEntry(PaintedLayer* aLayer)
  {
    return mPaintedLayerItems.GetEntry(aLayer);
  }

  PaintedLayerData* GetContainingPaintedLayerData()
  {
    return mContainingPaintedLayer;
  }

  bool IsBuildingRetainedLayers()
  {
    return !mContainingPaintedLayer && mRetainingManager;
  }

  /**
   * Attempt to build the most compressed layer tree possible, even if it means
   * throwing away existing retained buffers.
   */
  void SetLayerTreeCompressionMode() { mInLayerTreeCompressionMode = true; }
  bool CheckInLayerTreeCompressionMode();

  void ComputeGeometryChangeForItem(DisplayItemData* aData);

protected:
  /**
   * Returns true if the DOM has been modified since we started painting,
   * in which case we should bail out and not paint anymore. This should
   * never happen, but plugins can trigger it in some cases.
   */
  bool CheckDOMModified();

  /**
   * The layer manager belonging to the widget that is being retained
   * across paints.
   */
  LayerManager*                       mRetainingManager;
  /**
   * The root prescontext for the display list builder reference frame
   */
  RefPtr<nsRootPresContext>         mRootPresContext;

  /**
   * The display list builder being used.
   */
  nsDisplayListBuilder*               mDisplayListBuilder;
  /**
   * A map from PaintedLayers to the list of display items (plus
   * clipping data) to be rendered in the layer.
   */
  nsTHashtable<PaintedLayerItemsEntry> mPaintedLayerItems;

  /**
   * When building layers for an inactive layer, this is where the
   * inactive layer will be placed.
   */
  PaintedLayerData*                   mContainingPaintedLayer;

  /**
   * Saved generation counter so we can detect DOM changes.
   */
  uint32_t                            mInitialDOMGeneration;
  /**
   * Set to true if we have detected and reported DOM modification during
   * the current paint.
   */
  bool                                mDetectedDOMModification;
  /**
   * Indicates that the entire layer tree should be rerendered
   * during this paint.
   */
  bool                                mInvalidateAllLayers;

  bool                                mInLayerTreeCompressionMode;

  uint32_t                            mContainerLayerGeneration;
  uint32_t                            mMaxContainerLayerGeneration;
};

} // namespace mozilla

#endif /* FRAMELAYERBUILDER_H_ */