gecko/layout/base/FrameLayerBuilder.h

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 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
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 * for the specific language governing rights and limitations under the
 * License.
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 * The Original Code is Mozilla Corporation code.
 *
 * The Initial Developer of the Original Code is Mozilla Foundation.
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 * Contributor(s):
 *   Robert O'Callahan <robert@ocallahan.org>
 *
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#ifndef FRAMELAYERBUILDER_H_
#define FRAMELAYERBUILDER_H_

#include "nsTHashtable.h"
#include "nsHashKeys.h"
#include "nsTArray.h"
#include "nsRegion.h"
#include "nsIFrame.h"
#include "Layers.h"

class nsDisplayListBuilder;
class nsDisplayList;
class nsDisplayItem;
class gfxContext;
class nsRootPresContext;

namespace mozilla {

enum LayerState {
  LAYER_NONE,
  LAYER_INACTIVE,
  LAYER_ACTIVE,
  // Force an active layer even if it causes incorrect rendering, e.g.
  // when the layer has rounded rect clips.
  LAYER_ACTIVE_FORCE,
  // Special layer that is metadata only.
  LAYER_ACTIVE_EMPTY
};

/**
 * The FrameLayerBuilder belongs to an nsDisplayListBuilder and is
 * responsible for converting display lists into layer trees.
 * 
 * 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
 * also updates userdata for the retained layer manager, and
 * DisplayItemDataProperty data for frames, to record 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 ThebesLayer 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 ThebesLayers so that 0,0 in the Thebes layer
 * corresponds to the (pixel-snapped) top-left of the aActiveScrolledRoot.
 * It sets up ContainerLayers so that 0,0 in the container layer
 * corresponds to the snapped top-left of the display list 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 ThebesLayer
 * 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:
  typedef layers::ContainerLayer ContainerLayer; 
  typedef layers::Layer Layer; 
  typedef layers::ThebesLayer ThebesLayer;
  typedef layers::LayerManager LayerManager;

  FrameLayerBuilder() :
    mRetainingManager(nsnull),
    mDetectedDOMModification(false),
    mInvalidateAllLayers(false)
  {
    mNewDisplayItemData.Init();
    mThebesLayerItems.Init();
  }

  void Init(nsDisplayListBuilder* aBuilder);

  /**
   * 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 on aManager. If aManager
   * is not the retained layer manager then it must be a temporary layer
   * manager that will not be used again.
   */
  void WillEndTransaction(LayerManager* aManager);

  /**
   * Call this after we end a transaction on aManager. If aManager
   * is not the retained layer manager then it must be a temporary layer
   * manager that will not be used again.
   */
  void DidEndTransaction(LayerManager* aManager);

  struct ContainerParameters {
    ContainerParameters() :
      mXScale(1), mYScale(1),
      mInTransformedSubtree(false), mInActiveTransformedSubtree(false),
      mDisableSubpixelAntialiasingInDescendants(false)
    {}
    ContainerParameters(float aXScale, float aYScale) :
      mXScale(aXScale), mYScale(aYScale),
      mInTransformedSubtree(false), mInActiveTransformedSubtree(false),
      mDisableSubpixelAntialiasingInDescendants(false)
    {}
    ContainerParameters(float aXScale, float aYScale,
                        const ContainerParameters& aParent) :
      mXScale(aXScale), mYScale(aYScale),
      mInTransformedSubtree(aParent.mInTransformedSubtree),
      mInActiveTransformedSubtree(aParent.mInActiveTransformedSubtree),
      mDisableSubpixelAntialiasingInDescendants(aParent.mDisableSubpixelAntialiasingInDescendants)
    {}
    float mXScale, mYScale;
    bool mInTransformedSubtree;
    bool mInActiveTransformedSubtree;
    bool mDisableSubpixelAntialiasingInDescendants;
    /**
     * When this is false, ThebesLayer 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
      // ThebesLayer to ensure that snapping exactly matches the ideal transform.
      return mInTransformedSubtree && !mInActiveTransformedSubtree;
    }
  };
  /**
   * 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.
   * aContainer 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
   * ThebesLayer 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.
   */
  already_AddRefed<ContainerLayer>
  BuildContainerLayerFor(nsDisplayListBuilder* aBuilder,
                         LayerManager* aManager,
                         nsIFrame* aContainerFrame,
                         nsDisplayItem* aContainerItem,
                         const nsDisplayList& aChildren,
                         const ContainerParameters& aContainerParameters,
                         const gfx3DMatrix* aTransform);

  /**
   * 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,
                         LayerManager* aManager,
                         nsDisplayItem* aItem);

  /**
   * Call this during invalidation if aFrame has
   * the NS_FRAME_HAS_CONTAINER_LAYER state bit. Only the nearest
   * ancestor frame of the damaged frame that has
   * NS_FRAME_HAS_CONTAINER_LAYER needs to be invalidated this way.
   */
  static void InvalidateThebesLayerContents(nsIFrame* aFrame,
                                            const nsRect& aRect);

  /**
   * For any descendant frame of aFrame (including across documents) that
   * has an associated container layer, invalidate all the contents of
   * all ThebesLayer children of the container. Useful when aFrame is
   * being moved and we need to invalidate everything in aFrame's subtree.
   */
  static void InvalidateThebesLayersInSubtree(nsIFrame* aFrame);

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

  /**
   * Call this to determine if a frame has a dedicated (non-Thebes) 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, PRUint32 aDisplayItemKey);

  /**
   * This callback must be provided to EndTransaction. The callback data
   * must be the nsDisplayListBuilder containing this FrameLayerBuilder.
   */
  static void DrawThebesLayer(ThebesLayer* aLayer,
                              gfxContext* aContext,
                              const nsIntRegion& aRegionToDraw,
                              const nsIntRegion& aRegionToInvalidate,
                              void* aCallbackData);

#ifdef MOZ_DUMP_PAINTING
  /**
   * Dumps this FrameLayerBuilder's retained layer manager's retained
   * layer tree to stderr.
   */
  void DumpRetainedLayerTree(FILE* aFile = stdout);
#endif

  /******* 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.
   */
  void AddLayerDisplayItem(Layer* aLayer,
                           nsDisplayItem* aItem,
                           LayerState aLayerState);

  /**
   * Record aItem as a display item that is rendered by the ThebesLayer
   * aLayer, with aClipRect, where aContainerLayerFrame is the frame
   * for the container layer this ThebesItem belongs to.
   * aItem must have an underlying frame.
   */
  struct Clip;
  void AddThebesDisplayItem(ThebesLayer* aLayer,
                            nsDisplayItem* aItem,
                            const Clip& aClip,
                            nsIFrame* aContainerLayerFrame,
                            LayerState aLayerState);

  /**
   * 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 ThebesLayer
   * that renders many display items.
   */
  Layer* GetOldLayerFor(nsIFrame* aFrame, PRUint32 aDisplayItemKey);

  /**
   * Try to determine whether the ThebesLayer aLayer paints an opaque
   * single color everywhere it's visible in aRect.
   * If successful, return that color, otherwise return NS_RGBA(0,0,0,0).
   */
  nscolor FindOpaqueColorCovering(nsDisplayListBuilder* aBuilder,
                                  ThebesLayer* aLayer, const nsRect& aRect);

  /**
   * Destroy any stored LayerManagerDataProperty and the associated data for
   * aFrame.
   */
  static void DestroyDisplayItemDataFor(nsIFrame* aFrame)
  {
    aFrame->Properties().Delete(LayerManagerDataProperty());
  }

  LayerManager* GetRetainingLayerManager() { return mRetainingManager; }

  /**
   * Returns true if the given item (which we assume here is
   * background-attachment:fixed) needs to be repainted as we scroll in its
   * document.
   * Returns false if it doesn't need to be repainted because the layer system
   * is ensuring its fixed-ness for us.
   */
  static bool NeedToInvalidateFixedDisplayItem(nsDisplayListBuilder* aBuilder,
                                                 nsDisplayItem* aItem);

  /**
   * Returns true if the given display item was rendered directly
   * into a retained layer.
   * Returns false if it was rendered into a temporary layer manager and then
   * into a retained layer.
   */
  static bool HasRetainedLayerFor(nsIFrame* aFrame, PRUint32 aDisplayItemKey);

  /**
   * Save transform that was in aLayer when we last painted. It must be an integer
   * translation.
   */
  void SaveLastPaintOffset(ThebesLayer* aLayer);
  /**
   * 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(ThebesLayer* aLayer);

  /**
   * Clip represents the intersection of an optional rectangle with a
   * list of rounded rectangles.
   */
  struct Clip {
    struct RoundedRect {
      nsRect mRect;
      // Indices into mRadii are the NS_CORNER_* constants in nsStyleConsts.h
      nscoord mRadii[8];

      bool operator==(const RoundedRect& aOther) const {
        if (!mRect.IsEqualInterior(aOther.mRect)) {
          return false;
        }

        NS_FOR_CSS_HALF_CORNERS(corner) {
          if (mRadii[corner] != aOther.mRadii[corner]) {
            return false;
          }
        }
        return true;
      }
      bool operator!=(const RoundedRect& aOther) const {
        return !(*this == aOther);
      }
    };
    nsRect mClipRect;
    nsTArray<RoundedRect> mRoundedClipRects;
    bool mHaveClipRect;

    Clip() : mHaveClipRect(false) {}

    // Construct as the intersection of aOther and aClipItem.
    Clip(const Clip& aOther, nsDisplayItem* aClipItem);

    // Apply this |Clip| to the given gfxContext.  Any saving of state
    // or clearing of other clips must be done by the caller.
    // See aBegin/aEnd note on ApplyRoundedRectsTo.
    void ApplyTo(gfxContext* aContext, nsPresContext* aPresContext,
                 PRUint32 aBegin = 0, PRUint32 aEnd = PR_UINT32_MAX);

    void ApplyRectTo(gfxContext* aContext, PRInt32 A2D) const;
    // Applies the rounded rects in this Clip to aContext
    // Will only apply rounded rects from aBegin (inclusive) to aEnd
    // (exclusive) or the number of rounded rects, whichever is smaller.
    void ApplyRoundedRectsTo(gfxContext* aContext, PRInt32 A2DPRInt32,
                             PRUint32 aBegin, PRUint32 aEnd) const;

    // Return a rectangle contained in the intersection of aRect with this
    // clip region. Tries to return the largest possible rectangle, but may
    // not succeed.
    nsRect ApproximateIntersect(const nsRect& aRect) const;

    // Returns false if aRect is definitely not clipped by a rounded corner in
    // this clip. Returns true if aRect is clipped by a rounded corner in this
    // clip or it can not be quickly determined that it is not clipped by a
    // rounded corner in this clip.
    bool IsRectClippedByRoundedCorner(const nsRect& aRect) const;

    // Intersection of all rects in this clip ignoring any rounded corners.
    nsRect NonRoundedIntersection() const;

    // Gets rid of any rounded corners in this clip.
    void RemoveRoundedCorners();

    bool operator==(const Clip& aOther) const {
      return mHaveClipRect == aOther.mHaveClipRect &&
             (!mHaveClipRect || mClipRect.IsEqualInterior(aOther.mClipRect)) &&
             mRoundedClipRects == aOther.mRoundedClipRects;
    }
    bool operator!=(const Clip& aOther) const {
      return !(*this == aOther);
    }
  };

protected:
  /**
   * We store an array of these for each frame that is associated with
   * one or more retained layers. Each DisplayItemData records the layer
   * used to render one of the frame's display items.
   */
  class DisplayItemData {
  public:
    DisplayItemData(Layer* aLayer, PRUint32 aKey, LayerState aLayerState)
      : mLayer(aLayer), mDisplayItemKey(aKey), mLayerState(aLayerState) {}

    nsRefPtr<Layer> mLayer;
    PRUint32        mDisplayItemKey;
    LayerState      mLayerState;
  };

  static void RemoveFrameFromLayerManager(nsIFrame* aFrame, void* aPropertyValue);

  NS_DECLARE_FRAME_PROPERTY_WITH_FRAME_IN_DTOR(LayerManagerDataProperty,
                                               RemoveFrameFromLayerManager)

  /**
   * We accumulate DisplayItemData elements in a hashtable during
   * the paint process, and store them in the frame property only when
   * paint is complete. This is the hashentry for that hashtable.
   */
  class DisplayItemDataEntry : public nsPtrHashKey<nsIFrame> {
  public:
    DisplayItemDataEntry(const nsIFrame *key) : nsPtrHashKey<nsIFrame>(key), mIsSharingContainerLayer(false) {}
    DisplayItemDataEntry(DisplayItemDataEntry &toCopy) :
      nsPtrHashKey<nsIFrame>(toCopy.mKey), mIsSharingContainerLayer(toCopy.mIsSharingContainerLayer)
    {
      // This isn't actually a copy-constructor; notice that it steals toCopy's
      // array.  Be careful.
      mData.SwapElements(toCopy.mData);
    }

    bool HasNonEmptyContainerLayer();

    nsAutoTArray<DisplayItemData, 1> mData;
    bool mIsSharingContainerLayer;

    enum { ALLOW_MEMMOVE = false };
  };

  // LayerManagerData needs to see DisplayItemDataEntry.
  friend class LayerManagerData;

  // 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.
   */
  static nsTArray<DisplayItemData>* GetDisplayItemDataArrayForFrame(nsIFrame *aFrame);

  /**
   * A useful hashtable iteration function that removes the
   * DisplayItemData property for the frame, clears its
   * NS_FRAME_HAS_CONTAINER_LAYER bit and returns PL_DHASH_REMOVE.
   * aClosure is ignored.
   */
  static PLDHashOperator RemoveDisplayItemDataForFrame(DisplayItemDataEntry* aEntry,
                                                       void* aClosure)
  {
    return UpdateDisplayItemDataForFrame(aEntry, nsnull);
  }

  /**
   * We store one of these for each display item associated with a
   * ThebesLayer, in a hashtable that maps each ThebesLayer to an array
   * of ClippedDisplayItems. (ThebesLayerItemsEntry is the hash entry
   * for that hashtable.)
   * These are only stored during the paint process, so that the
   * DrawThebesLayer callback can figure out which items to draw for the
   * ThebesLayer.
   * mItem always has an underlying frame.
   */
  struct ClippedDisplayItem {
    ClippedDisplayItem(nsDisplayItem* aItem, const Clip& aClip)
      : mItem(aItem), mClip(aClip)
    {
    }

    nsDisplayItem* mItem;
    Clip mClip;
    bool mInactiveLayer;
  };

  /**
   * We accumulate ClippedDisplayItem elements in a hashtable during
   * the paint process. This is the hashentry for that hashtable.
   */
public:
  class ThebesLayerItemsEntry : public nsPtrHashKey<ThebesLayer> {
  public:
    ThebesLayerItemsEntry(const ThebesLayer *key) :
        nsPtrHashKey<ThebesLayer>(key), mContainerLayerFrame(nsnull),
        mHasExplicitLastPaintOffset(false), mCommonClipCount(-1) {}
    ThebesLayerItemsEntry(const ThebesLayerItemsEntry &toCopy) :
      nsPtrHashKey<ThebesLayer>(toCopy.mKey), mItems(toCopy.mItems)
    {
      NS_ERROR("Should never be called, since we ALLOW_MEMMOVE");
    }

    nsTArray<ClippedDisplayItem> mItems;
    nsIFrame* mContainerLayerFrame;
    // The translation set on this ThebesLayer before we started updating the
    // layer tree.
    nsIntPoint mLastPaintOffset;
    bool mHasExplicitLastPaintOffset;
    /**
      * The first mCommonClipCount rounded rectangle clips are identical for
      * all items in the layer. Computed in ThebesLayerData.
      */
    PRUint32 mCommonClipCount;

    enum { ALLOW_MEMMOVE = true };
  };

  /**
   * Get the ThebesLayerItemsEntry object associated with aLayer in this
   * FrameLayerBuilder
   */
  ThebesLayerItemsEntry* GetThebesLayerItemsEntry(ThebesLayer* aLayer)
  {
    return mThebesLayerItems.GetEntry(aLayer);
  }

protected:
  void RemoveThebesItemsForLayerSubtree(Layer* aLayer);

  static PLDHashOperator UpdateDisplayItemDataForFrame(DisplayItemDataEntry* aEntry,
                                                       void* aUserArg);
  static PLDHashOperator StoreNewDisplayItemData(DisplayItemDataEntry* aEntry,
                                                 void* aUserArg);

  /**
   * 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
   */
  nsRootPresContext*                  mRootPresContext;
  /**
   * A map from frames to a list of (display item key, layer) pairs that
   * describes what layers various parts of the frame are assigned to.
   */
  nsTHashtable<DisplayItemDataEntry>  mNewDisplayItemData;
  /**
   * A map from ThebesLayers to the list of display items (plus
   * clipping data) to be rendered in the layer.
   */
  nsTHashtable<ThebesLayerItemsEntry> mThebesLayerItems;
  /**
   * Saved generation counter so we can detect DOM changes.
   */
  PRUint32                            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;
};

}

#endif /* FRAMELAYERBUILDER_H_ */