/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * 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 GFX_FONT_H
#define GFX_FONT_H

#include "gfxTypes.h"
#include "nsString.h"
#include "gfxPoint.h"
#include "gfxFontFamilyList.h"
#include "gfxFontUtils.h"
#include "nsTArray.h"
#include "nsTHashtable.h"
#include "nsHashKeys.h"
#include "gfxSkipChars.h"
#include "gfxRect.h"
#include "nsExpirationTracker.h"
#include "gfxPlatform.h"
#include "nsIAtom.h"
#include "mozilla/HashFunctions.h"
#include "nsIMemoryReporter.h"
#include "nsIObserver.h"
#include "gfxFontFeatures.h"
#include "mozilla/MemoryReporting.h"
#include "mozilla/Attributes.h"
#include <algorithm>
#include "DrawMode.h"
#include "nsUnicodeScriptCodes.h"
#include "nsDataHashtable.h"
#include "harfbuzz/hb.h"
#include "mozilla/gfx/2D.h"

typedef struct _cairo_scaled_font cairo_scaled_font_t;
typedef struct gr_face            gr_face;

#ifdef DEBUG
#include <stdio.h>
#endif

class gfxContext;
class gfxTextRun;
class gfxFont;
class gfxFontFamily;
class gfxFontGroup;
class gfxGraphiteShaper;
class gfxHarfBuzzShaper;
class gfxUserFontSet;
class gfxUserFontData;
class gfxShapedText;
class gfxShapedWord;
class gfxSVGGlyphs;
class gfxMathTable;
class gfxTextContextPaint;
class FontInfoData;

class nsILanguageAtomService;

#define FONT_MAX_SIZE                  2000.0

#define NO_FONT_LANGUAGE_OVERRIDE      0

#define SMALL_CAPS_SCALE_FACTOR        0.8

struct FontListSizes;
struct gfxTextRunDrawCallbacks;

namespace mozilla {
namespace gfx {
class GlyphRenderingOptions;
}
}

struct gfxFontStyle {
    gfxFontStyle();
    gfxFontStyle(uint8_t aStyle, uint16_t aWeight, int16_t aStretch,
                 gfxFloat aSize, nsIAtom *aLanguage,
                 float aSizeAdjust, bool aSystemFont,
                 bool aPrinterFont,
                 bool aWeightSynthesis, bool aStyleSynthesis,
                 const nsString& aLanguageOverride);
    gfxFontStyle(const gfxFontStyle& aStyle);

    // the language (may be an internal langGroup code rather than an actual
    // language code) specified in the document or element's lang property,
    // or inferred from the charset
    nsRefPtr<nsIAtom> language;

    // Features are composed of (1) features from style rules (2) features
    // from feature setttings rules and (3) family-specific features.  (1) and
    // (3) are guaranteed to be mutually exclusive

    // custom opentype feature settings
    nsTArray<gfxFontFeature> featureSettings;

    // Some font-variant property values require font-specific settings
    // defined via @font-feature-values rules.  These are resolved after
    // font matching occurs.

    // -- list of value tags for specific alternate features
    nsTArray<gfxAlternateValue> alternateValues;

    // -- object used to look these up once the font is matched
    nsRefPtr<gfxFontFeatureValueSet> featureValueLookup;

    // The logical size of the font, in pixels
    gfxFloat size;

    // The aspect-value (ie., the ratio actualsize:actualxheight) that any
    // actual physical font created from this font structure must have when
    // rendering or measuring a string. A value of 0 means no adjustment
    // needs to be done.
    float sizeAdjust;

    // baseline offset, used when simulating sub/superscript glyphs
    float baselineOffset;

    // Language system tag, to override document language;
    // an OpenType "language system" tag represented as a 32-bit integer
    // (see http://www.microsoft.com/typography/otspec/languagetags.htm).
    // Normally 0, so font rendering will use the document or element language
    // (see above) to control any language-specific rendering, but the author
    // can override this for cases where the options implemented in the font
    // do not directly match the actual language. (E.g. lang may be Macedonian,
    // but the font in use does not explicitly support this; the author can
    // use font-language-override to request the Serbian option in the font
    // in order to get correct glyph shapes.)
    uint32_t languageOverride;

    // The weight of the font: 100, 200, ... 900.
    uint16_t weight;

    // The stretch of the font (the sum of various NS_FONT_STRETCH_*
    // constants; see gfxFontConstants.h).
    int8_t stretch;

    // Say that this font is a system font and therefore does not
    // require certain fixup that we do for fonts from untrusted
    // sources.
    bool systemFont : 1;

    // Say that this font is used for print or print preview.
    bool printerFont : 1;

    // Used to imitate -webkit-font-smoothing: antialiased
    bool useGrayscaleAntialiasing : 1;

    // The style of font (normal, italic, oblique)
    uint8_t style : 2;

    // Whether synthetic styles are allowed
    bool allowSyntheticWeight : 1;
    bool allowSyntheticStyle : 1;

    // some variant features require fallback which complicates the shaping
    // code, so set up a bool to indicate when shaping with fallback is needed
    bool noFallbackVariantFeatures : 1;

    // caps variant (small-caps, petite-caps, etc.)
    uint8_t variantCaps;

    // sub/superscript variant
    uint8_t variantSubSuper;

    // Return the final adjusted font size for the given aspect ratio.
    // Not meant to be called when sizeAdjust = 0.
    gfxFloat GetAdjustedSize(gfxFloat aspect) const {
        NS_ASSERTION(sizeAdjust != 0.0, "Not meant to be called when sizeAdjust = 0");
        gfxFloat adjustedSize = std::max(NS_round(size*(sizeAdjust/aspect)), 1.0);
        return std::min(adjustedSize, FONT_MAX_SIZE);
    }

    PLDHashNumber Hash() const {
        return ((style + (systemFont << 7) +
            (weight << 8)) + uint32_t(size*1000) + uint32_t(sizeAdjust*1000)) ^
            nsISupportsHashKey::HashKey(language);
    }

    int8_t ComputeWeight() const;

    // Adjust this style to simulate sub/superscript (as requested in the
    // variantSubSuper field) using size and baselineOffset instead.
    void AdjustForSubSuperscript(int32_t aAppUnitsPerDevPixel);

    bool Equals(const gfxFontStyle& other) const {
        return
            (*reinterpret_cast<const uint64_t*>(&size) ==
             *reinterpret_cast<const uint64_t*>(&other.size)) &&
            (style == other.style) &&
            (variantCaps == other.variantCaps) &&
            (variantSubSuper == other.variantSubSuper) &&
            (allowSyntheticWeight == other.allowSyntheticWeight) &&
            (allowSyntheticStyle == other.allowSyntheticStyle) &&
            (systemFont == other.systemFont) &&
            (printerFont == other.printerFont) &&
            (useGrayscaleAntialiasing == other.useGrayscaleAntialiasing) &&
            (weight == other.weight) &&
            (stretch == other.stretch) &&
            (language == other.language) &&
            (baselineOffset == other.baselineOffset) &&
            (*reinterpret_cast<const uint32_t*>(&sizeAdjust) ==
             *reinterpret_cast<const uint32_t*>(&other.sizeAdjust)) &&
            (featureSettings == other.featureSettings) &&
            (languageOverride == other.languageOverride) &&
            (alternateValues == other.alternateValues) &&
            (featureValueLookup == other.featureValueLookup);
    }

    static void ParseFontFeatureSettings(const nsString& aFeatureString,
                                         nsTArray<gfxFontFeature>& aFeatures);

    static uint32_t ParseFontLanguageOverride(const nsString& aLangTag);
};

class gfxCharacterMap : public gfxSparseBitSet {
public:
    nsrefcnt AddRef() {
        NS_PRECONDITION(int32_t(mRefCnt) >= 0, "illegal refcnt");
        ++mRefCnt;
        NS_LOG_ADDREF(this, mRefCnt, "gfxCharacterMap", sizeof(*this));
        return mRefCnt;
    }

    nsrefcnt Release() {
        NS_PRECONDITION(0 != mRefCnt, "dup release");
        --mRefCnt;
        NS_LOG_RELEASE(this, mRefCnt, "gfxCharacterMap");
        if (mRefCnt == 0) {
            NotifyReleased();
            // |this| has been deleted.
            return 0;
        }
        return mRefCnt;
    }

    gfxCharacterMap() :
        mHash(0), mBuildOnTheFly(false), mShared(false)
    { }

    void CalcHash() { mHash = GetChecksum(); }

    size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const {
        return gfxSparseBitSet::SizeOfExcludingThis(aMallocSizeOf);
    }

    // hash of the cmap bitvector
    uint32_t mHash;

    // if cmap is built on the fly it's never shared
    bool mBuildOnTheFly;

    // cmap is shared globally
    bool mShared;

protected:
    void NotifyReleased();

    nsAutoRefCnt mRefCnt;

private:
    gfxCharacterMap(const gfxCharacterMap&);
    gfxCharacterMap& operator=(const gfxCharacterMap&);
};

class gfxFontEntry {
public:
    NS_INLINE_DECL_REFCOUNTING(gfxFontEntry)

    gfxFontEntry(const nsAString& aName, bool aIsStandardFace = false);

    // unique name for the face, *not* the family; not necessarily the
    // "real" or user-friendly name, may be an internal identifier
    const nsString& Name() const { return mName; }

    // family name
    const nsString& FamilyName() const { return mFamilyName; }

    // The following two methods may be relatively expensive, as they
    // will (usually, except on Linux) load and parse the 'name' table;
    // they are intended only for the font-inspection API, not for
    // perf-critical layout/drawing work.

    // The "real" name of the face, if available from the font resource;
    // returns Name() if nothing better is available.
    virtual nsString RealFaceName();

    uint16_t Weight() const { return mWeight; }
    int16_t Stretch() const { return mStretch; }

    bool IsUserFont() const { return mIsUserFont; }
    bool IsLocalUserFont() const { return mIsLocalUserFont; }
    bool IsFixedPitch() const { return mFixedPitch; }
    bool IsItalic() const { return mItalic; }
    bool IsBold() const { return mWeight >= 600; } // bold == weights 600 and above
    bool IgnoreGDEF() const { return mIgnoreGDEF; }
    bool IgnoreGSUB() const { return mIgnoreGSUB; }

    // whether a feature is supported by the font (limited to a small set
    // of features for which some form of fallback needs to be implemented)
    bool SupportsOpenTypeFeature(int32_t aScript, uint32_t aFeatureTag);
    bool SupportsGraphiteFeature(uint32_t aFeatureTag);

    // returns a set containing all input glyph ids for a given feature
    const hb_set_t*
    InputsForOpenTypeFeature(int32_t aScript, uint32_t aFeatureTag);

    virtual bool IsSymbolFont();

    virtual bool HasFontTable(uint32_t aTableTag);

    inline bool HasGraphiteTables() {
        if (!mCheckedForGraphiteTables) {
            CheckForGraphiteTables();
            mCheckedForGraphiteTables = true;
        }
        return mHasGraphiteTables;
    }

    inline bool HasCmapTable() {
        if (!mCharacterMap) {
            ReadCMAP();
            NS_ASSERTION(mCharacterMap, "failed to initialize character map");
        }
        return mHasCmapTable;
    }

    inline bool HasCharacter(uint32_t ch) {
        if (mCharacterMap && mCharacterMap->test(ch)) {
            return true;
        }
        return TestCharacterMap(ch);
    }

    virtual bool SkipDuringSystemFallback() { return false; }
    virtual bool TestCharacterMap(uint32_t aCh);
    nsresult InitializeUVSMap();
    uint16_t GetUVSGlyph(uint32_t aCh, uint32_t aVS);

    // All concrete gfxFontEntry subclasses (except gfxProxyFontEntry) need
    // to override this, otherwise the font will never be used as it will
    // be considered to support no characters.
    // ReadCMAP() must *always* set the mCharacterMap pointer to a valid
    // gfxCharacterMap, even if empty, as other code assumes this pointer
    // can be safely dereferenced.
    virtual nsresult ReadCMAP(FontInfoData *aFontInfoData = nullptr);

    bool TryGetSVGData(gfxFont* aFont);
    bool HasSVGGlyph(uint32_t aGlyphId);
    bool GetSVGGlyphExtents(gfxContext *aContext, uint32_t aGlyphId,
                            gfxRect *aResult);
    bool RenderSVGGlyph(gfxContext *aContext, uint32_t aGlyphId, int aDrawMode,
                        gfxTextContextPaint *aContextPaint);
    // Call this when glyph geometry or rendering has changed
    // (e.g. animated SVG glyphs)
    void NotifyGlyphsChanged();

    enum MathConstant {
        // The order of the constants must match the order of the fields
        // defined in the MATH table.
        ScriptPercentScaleDown,
        ScriptScriptPercentScaleDown,
        DelimitedSubFormulaMinHeight,
        DisplayOperatorMinHeight,
        MathLeading,
        AxisHeight,
        AccentBaseHeight,
        FlattenedAccentBaseHeight,
        SubscriptShiftDown,
        SubscriptTopMax,
        SubscriptBaselineDropMin,
        SuperscriptShiftUp,
        SuperscriptShiftUpCramped,
        SuperscriptBottomMin,
        SuperscriptBaselineDropMax,
        SubSuperscriptGapMin,
        SuperscriptBottomMaxWithSubscript,
        SpaceAfterScript,
        UpperLimitGapMin,
        UpperLimitBaselineRiseMin,
        LowerLimitGapMin,
        LowerLimitBaselineDropMin,
        StackTopShiftUp,
        StackTopDisplayStyleShiftUp,
        StackBottomShiftDown,
        StackBottomDisplayStyleShiftDown,
        StackGapMin,
        StackDisplayStyleGapMin,
        StretchStackTopShiftUp,
        StretchStackBottomShiftDown,
        StretchStackGapAboveMin,
        StretchStackGapBelowMin,
        FractionNumeratorShiftUp,
        FractionNumeratorDisplayStyleShiftUp,
        FractionDenominatorShiftDown,
        FractionDenominatorDisplayStyleShiftDown,
        FractionNumeratorGapMin,
        FractionNumDisplayStyleGapMin,
        FractionRuleThickness,
        FractionDenominatorGapMin,
        FractionDenomDisplayStyleGapMin,
        SkewedFractionHorizontalGap,
        SkewedFractionVerticalGap,
        OverbarVerticalGap,
        OverbarRuleThickness,
        OverbarExtraAscender,
        UnderbarVerticalGap,
        UnderbarRuleThickness,
        UnderbarExtraDescender,
        RadicalVerticalGap,
        RadicalDisplayStyleVerticalGap,
        RadicalRuleThickness,
        RadicalExtraAscender,
        RadicalKernBeforeDegree,
        RadicalKernAfterDegree,
        RadicalDegreeBottomRaisePercent
    };

    // Call TryGetMathTable to try to load the Open Type MATH table. The other
    // functions forward the call to the gfxMathTable class. The GetMath...()
    // functions MUST NOT be called unless TryGetMathTable() has returned true.
    bool     TryGetMathTable();
    gfxFloat GetMathConstant(MathConstant aConstant);
    bool     GetMathItalicsCorrection(uint32_t aGlyphID,
                                      gfxFloat* aItalicCorrection);
    uint32_t GetMathVariantsSize(uint32_t aGlyphID, bool aVertical,
                                 uint16_t aSize);
    bool     GetMathVariantsParts(uint32_t aGlyphID, bool aVertical,
                                  uint32_t aGlyphs[4]);

    bool     TryGetColorGlyphs();
    bool     GetColorLayersInfo(uint32_t aGlyphId,
                                nsTArray<uint16_t>& layerGlyphs,
                                nsTArray<mozilla::gfx::Color>& layerColors);

    virtual bool MatchesGenericFamily(const nsACString& aGeneric) const {
        return true;
    }
    virtual bool SupportsLangGroup(nsIAtom *aLangGroup) const {
        return true;
    }

    // Access to raw font table data (needed for Harfbuzz):
    // returns a pointer to data owned by the fontEntry or the OS,
    // which will remain valid until the blob is destroyed.
    // The data MUST be treated as read-only; we may be getting a
    // reference to a shared system font cache.
    //
    // The default implementation uses CopyFontTable to get the data
    // into a byte array, and maintains a cache of loaded tables.
    //
    // Subclasses should override this if they can provide more efficient
    // access than copying table data into our own buffers.
    //
    // Get blob that encapsulates a specific font table, or nullptr if
    // the table doesn't exist in the font.
    //
    // Caller is responsible to call hb_blob_destroy() on the returned blob
    // (if non-nullptr) when no longer required. For transient access to a
    // table, use of AutoTable (below) is generally preferred.
    virtual hb_blob_t *GetFontTable(uint32_t aTag);

    // Stack-based utility to return a specified table, automatically releasing
    // the blob when the AutoTable goes out of scope.
    class AutoTable {
    public:
        AutoTable(gfxFontEntry* aFontEntry, uint32_t aTag)
        {
            mBlob = aFontEntry->GetFontTable(aTag);
        }
        ~AutoTable() {
            if (mBlob) {
                hb_blob_destroy(mBlob);
            }
        }
        operator hb_blob_t*() const { return mBlob; }
    private:
        hb_blob_t* mBlob;
        // not implemented:
        AutoTable(const AutoTable&) MOZ_DELETE;
        AutoTable& operator=(const AutoTable&) MOZ_DELETE;
    };

    already_AddRefed<gfxFont> FindOrMakeFont(const gfxFontStyle *aStyle,
                                             bool aNeedsBold);

    // Get an existing font table cache entry in aBlob if it has been
    // registered, or return false if not.  Callers must call
    // hb_blob_destroy on aBlob if true is returned.
    //
    // Note that some gfxFont implementations may not call this at all,
    // if it is more efficient to get the table from the OS at that level.
    bool GetExistingFontTable(uint32_t aTag, hb_blob_t** aBlob);

    // Elements of aTable are transferred (not copied) to and returned in a
    // new hb_blob_t which is registered on the gfxFontEntry, but the initial
    // reference is owned by the caller.  Removing the last reference
    // unregisters the table from the font entry.
    //
    // Pass nullptr for aBuffer to indicate that the table is not present and
    // nullptr will be returned.  Also returns nullptr on OOM.
    hb_blob_t *ShareFontTableAndGetBlob(uint32_t aTag,
                                        FallibleTArray<uint8_t>* aTable);

    // Get the font's unitsPerEm from the 'head' table, in the case of an
    // sfnt resource. Will return kInvalidUPEM for non-sfnt fonts,
    // if present on the platform.
    uint16_t UnitsPerEm();
    enum {
        kMinUPEM = 16,    // Limits on valid unitsPerEm range, from the
        kMaxUPEM = 16384, // OpenType spec
        kInvalidUPEM = uint16_t(-1)
    };

    // Shaper face accessors:
    // NOTE that harfbuzz and graphite handle ownership/lifetime of the face
    // object in completely different ways.

    // Get HarfBuzz face corresponding to this font file.
    // Caller must release with hb_face_destroy() when finished with it,
    // and the font entry will be notified via ForgetHBFace.
    hb_face_t* GetHBFace();
    virtual void ForgetHBFace();

    // Get Graphite face corresponding to this font file.
    // Caller must call gfxFontEntry::ReleaseGrFace when finished with it.
    gr_face* GetGrFace();
    virtual void ReleaseGrFace(gr_face* aFace);

    // Release any SVG-glyphs document this font may have loaded.
    void DisconnectSVG();

    // Called to notify that aFont is being destroyed. Needed when we're tracking
    // the fonts belonging to this font entry.
    void NotifyFontDestroyed(gfxFont* aFont);

    // For memory reporting
    virtual void AddSizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf,
                                        FontListSizes* aSizes) const;
    virtual void AddSizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf,
                                        FontListSizes* aSizes) const;

    // Used when checking for complex script support, to mask off cmap ranges
    struct ScriptRange {
        uint32_t         rangeStart;
        uint32_t         rangeEnd;
        hb_tag_t         tags[3]; // one or two OpenType script tags to check,
                                  // plus a NULL terminator
    };

    bool SupportsScriptInGSUB(const hb_tag_t* aScriptTags);

    nsString         mName;
    nsString         mFamilyName;

    bool             mItalic      : 1;
    bool             mFixedPitch  : 1;
    bool             mIsProxy     : 1;
    bool             mIsValid     : 1;
    bool             mIsBadUnderlineFont : 1;
    bool             mIsUserFont  : 1;
    bool             mIsLocalUserFont  : 1;
    bool             mStandardFace : 1;
    bool             mSymbolFont  : 1;
    bool             mIgnoreGDEF  : 1;
    bool             mIgnoreGSUB  : 1;
    bool             mSVGInitialized : 1;
    bool             mMathInitialized : 1;
    bool             mHasSpaceFeaturesInitialized : 1;
    bool             mHasSpaceFeatures : 1;
    bool             mHasSpaceFeaturesKerning : 1;
    bool             mHasSpaceFeaturesNonKerning : 1;
    bool             mSkipDefaultFeatureSpaceCheck : 1;
    bool             mHasGraphiteTables : 1;
    bool             mCheckedForGraphiteTables : 1;
    bool             mHasCmapTable : 1;
    bool             mGrFaceInitialized : 1;
    bool             mCheckedForColorGlyph : 1;

    // bitvector of substitution space features per script, one each
    // for default and non-default features
    uint32_t         mDefaultSubSpaceFeatures[(MOZ_NUM_SCRIPT_CODES + 31) / 32];
    uint32_t         mNonDefaultSubSpaceFeatures[(MOZ_NUM_SCRIPT_CODES + 31) / 32];

    uint16_t         mWeight;
    int16_t          mStretch;

    nsRefPtr<gfxCharacterMap> mCharacterMap;
    uint32_t         mUVSOffset;
    nsAutoArrayPtr<uint8_t> mUVSData;
    nsAutoPtr<gfxUserFontData> mUserFontData;
    nsAutoPtr<gfxSVGGlyphs> mSVGGlyphs;
    // list of gfxFonts that are using SVG glyphs
    nsTArray<gfxFont*> mFontsUsingSVGGlyphs;
    nsAutoPtr<gfxMathTable> mMathTable;
    nsTArray<gfxFontFeature> mFeatureSettings;
    nsAutoPtr<nsDataHashtable<nsUint32HashKey,bool>> mSupportedFeatures;
    nsAutoPtr<nsDataHashtable<nsUint32HashKey,hb_set_t*>> mFeatureInputs;
    uint32_t         mLanguageOverride;

    // Color Layer font support
    hb_blob_t*       mCOLR;
    hb_blob_t*       mCPAL;

protected:
    friend class gfxPlatformFontList;
    friend class gfxMacPlatformFontList;
    friend class gfxUserFcFontEntry;
    friend class gfxFontFamily;
    friend class gfxSingleFaceMacFontFamily;

    gfxFontEntry();

    // Protected destructor, to discourage deletion outside of Release():
    virtual ~gfxFontEntry();

    virtual gfxFont *CreateFontInstance(const gfxFontStyle *aFontStyle, bool aNeedsBold) {
        NS_NOTREACHED("oops, somebody didn't override CreateFontInstance");
        return nullptr;
    }

    virtual void CheckForGraphiteTables();

    // Copy a font table into aBuffer.
    // The caller will be responsible for ownership of the data.
    virtual nsresult CopyFontTable(uint32_t aTableTag,
                                   FallibleTArray<uint8_t>& aBuffer) {
        NS_NOTREACHED("forgot to override either GetFontTable or CopyFontTable?");
        return NS_ERROR_FAILURE;
    }

    // Return a blob that wraps a table found within a buffer of font data.
    // The blob does NOT own its data; caller guarantees that the buffer
    // will remain valid at least as long as the blob.
    // Returns null if the specified table is not found.
    // This method assumes aFontData is valid 'sfnt' data; before using this,
    // caller is responsible to do any sanitization/validation necessary.
    hb_blob_t* GetTableFromFontData(const void* aFontData, uint32_t aTableTag);

    // lookup the cmap in cached font data
    virtual already_AddRefed<gfxCharacterMap>
    GetCMAPFromFontInfo(FontInfoData *aFontInfoData,
                        uint32_t& aUVSOffset,
                        bool& aSymbolFont);

    // Font's unitsPerEm from the 'head' table, if available (will be set to
    // kInvalidUPEM for non-sfnt font formats)
    uint16_t mUnitsPerEm;

    // Shaper-specific face objects, shared by all instantiations of the same
    // physical font, regardless of size.
    // Usually, only one of these will actually be created for any given font
    // entry, depending on the font tables that are present.

    // hb_face_t is refcounted internally, so each shaper that's using it will
    // bump the ref count when it acquires the face, and "destroy" (release) it
    // in its destructor. The font entry has only this non-owning reference to
    // the face; when the face is deleted, it will tell the font entry to forget
    // it, so that a new face will be created next time it is needed.
    hb_face_t* mHBFace;

    static hb_blob_t* HBGetTable(hb_face_t *face, uint32_t aTag, void *aUserData);

    // Callback that the hb_face will use to tell us when it is being deleted.
    static void HBFaceDeletedCallback(void *aUserData);

    // gr_face is -not- refcounted, so it will be owned directly by the font
    // entry, and we'll keep a count of how many references we've handed out;
    // each shaper is responsible to call ReleaseGrFace on its entry when
    // finished with it, so that we know when it can be deleted.
    gr_face*   mGrFace;

    // hashtable to map raw table data ptr back to its owning blob, for use by
    // graphite table-release callback
    nsDataHashtable<nsPtrHashKey<const void>,void*>* mGrTableMap;

    // number of current users of this entry's mGrFace
    nsrefcnt mGrFaceRefCnt;

    static const void* GrGetTable(const void *aAppFaceHandle,
                                  unsigned int aName,
                                  size_t *aLen);
    static void GrReleaseTable(const void *aAppFaceHandle,
                               const void *aTableBuffer);

private:
    /**
     * Font table hashtable, to support GetFontTable for harfbuzz.
     *
     * The harfbuzz shaper (and potentially other clients) needs access to raw
     * font table data. This needs to be cached so that it can be used
     * repeatedly (each time we construct a text run; in some cases, for
     * each character/glyph within the run) without re-fetching large tables
     * every time.
     * 
     * Because we may instantiate many gfxFonts for the same physical font
     * file (at different sizes), we should ensure that they can share a
     * single cached copy of the font tables. To do this, we implement table
     * access and sharing on the fontEntry rather than the font itself.
     *
     * The default implementation uses GetFontTable() to read font table
     * data into byte arrays, and wraps them in blobs which are registered in
     * a hashtable.  The hashtable can then return pre-existing blobs to
     * harfbuzz.
     *
     * Harfbuzz will "destroy" the blobs when it is finished with them.  When
     * the last blob reference is removed, the FontTableBlobData user data
     * will remove the blob from the hashtable if still registered.
     */

    class FontTableBlobData;

    /**
     * FontTableHashEntry manages the entries of hb_blob_t's containing font
     * table data.
     *
     * This is used to share font tables across fonts with the same
     * font entry (but different sizes) for use by HarfBuzz.  The hashtable
     * does not own a strong reference to the blob, but keeps a weak pointer,
     * managed by FontTableBlobData.  Similarly FontTableBlobData keeps only a
     * weak pointer to the hashtable, managed by FontTableHashEntry.
     */

    class FontTableHashEntry : public nsUint32HashKey
    {
    public:
        // Declarations for nsTHashtable

        typedef nsUint32HashKey KeyClass;
        typedef KeyClass::KeyType KeyType;
        typedef KeyClass::KeyTypePointer KeyTypePointer;

        FontTableHashEntry(KeyTypePointer aTag)
            : KeyClass(aTag)
            , mSharedBlobData(nullptr)
            , mBlob(nullptr)
        { }

        // NOTE: This assumes the new entry belongs to the same hashtable as
        // the old, because the mHashtable pointer in mSharedBlobData (if
        // present) will not be updated.
        FontTableHashEntry(FontTableHashEntry&& toMove)
            : KeyClass(mozilla::Move(toMove))
            , mSharedBlobData(mozilla::Move(toMove.mSharedBlobData))
            , mBlob(mozilla::Move(toMove.mBlob))
        {
            toMove.mSharedBlobData = nullptr;
            toMove.mBlob = nullptr;
        }

        ~FontTableHashEntry() { Clear(); }

        // FontTable/Blob API

        // Transfer (not copy) elements of aTable to a new hb_blob_t and
        // return ownership to the caller.  A weak reference to the blob is
        // recorded in the hashtable entry so that others may use the same
        // table.
        hb_blob_t *
        ShareTableAndGetBlob(FallibleTArray<uint8_t>& aTable,
                             nsTHashtable<FontTableHashEntry> *aHashtable);

        // Return a strong reference to the blob.
        // Callers must hb_blob_destroy the returned blob.
        hb_blob_t *GetBlob() const;

        void Clear();

        static size_t
        SizeOfEntryExcludingThis(FontTableHashEntry *aEntry,
                                 mozilla::MallocSizeOf aMallocSizeOf,
                                 void* aUserArg);

    private:
        static void DeleteFontTableBlobData(void *aBlobData);
        // not implemented
        FontTableHashEntry& operator=(FontTableHashEntry& toCopy);

        FontTableBlobData *mSharedBlobData;
        hb_blob_t *mBlob;
    };

    nsAutoPtr<nsTHashtable<FontTableHashEntry> > mFontTableCache;

    gfxFontEntry(const gfxFontEntry&);
    gfxFontEntry& operator=(const gfxFontEntry&);
};


// used when iterating over all fonts looking for a match for a given character
struct GlobalFontMatch {
    GlobalFontMatch(const uint32_t aCharacter,
                    int32_t aRunScript,
                    const gfxFontStyle *aStyle) :
        mCh(aCharacter), mRunScript(aRunScript), mStyle(aStyle),
        mMatchRank(0), mCount(0), mCmapsTested(0)
        {

        }

    const uint32_t         mCh;          // codepoint to be matched
    int32_t                mRunScript;   // Unicode script for the codepoint
    const gfxFontStyle*    mStyle;       // style to match
    int32_t                mMatchRank;   // metric indicating closest match
    nsRefPtr<gfxFontEntry> mBestMatch;   // current best match
    nsRefPtr<gfxFontFamily> mMatchedFamily; // the family it belongs to
    uint32_t               mCount;       // number of fonts matched
    uint32_t               mCmapsTested; // number of cmaps tested
};

class gfxFontFamily {
public:
    NS_INLINE_DECL_REFCOUNTING(gfxFontFamily)

    gfxFontFamily(const nsAString& aName) :
        mName(aName),
        mOtherFamilyNamesInitialized(false),
        mHasOtherFamilyNames(false),
        mFaceNamesInitialized(false),
        mHasStyles(false),
        mIsSimpleFamily(false),
        mIsBadUnderlineFamily(false),
        mFamilyCharacterMapInitialized(false),
        mSkipDefaultFeatureSpaceCheck(false)
        { }

    const nsString& Name() { return mName; }

    virtual void LocalizedName(nsAString& aLocalizedName);
    virtual bool HasOtherFamilyNames();
    
    nsTArray<nsRefPtr<gfxFontEntry> >& GetFontList() { return mAvailableFonts; }
    
    void AddFontEntry(nsRefPtr<gfxFontEntry> aFontEntry) {
        // bug 589682 - set the IgnoreGDEF flag on entries for Italic faces
        // of Times New Roman, because of buggy table in those fonts
        if (aFontEntry->IsItalic() && !aFontEntry->IsUserFont() &&
            Name().EqualsLiteral("Times New Roman"))
        {
            aFontEntry->mIgnoreGDEF = true;
        }
        if (aFontEntry->mFamilyName.IsEmpty()) {
            aFontEntry->mFamilyName = Name();
        } else {
            MOZ_ASSERT(aFontEntry->mFamilyName.Equals(Name()));
        }
        aFontEntry->mSkipDefaultFeatureSpaceCheck = mSkipDefaultFeatureSpaceCheck;
        mAvailableFonts.AppendElement(aFontEntry);
    }

    // note that the styles for this family have been added
    bool HasStyles() { return mHasStyles; }
    void SetHasStyles(bool aHasStyles) { mHasStyles = aHasStyles; }

    // choose a specific face to match a style using CSS font matching
    // rules (weight matching occurs here).  may return a face that doesn't
    // precisely match (e.g. normal face when no italic face exists).
    // aNeedsSyntheticBold is set to true when synthetic bolding is
    // needed, false otherwise
    gfxFontEntry *FindFontForStyle(const gfxFontStyle& aFontStyle, 
                                   bool& aNeedsSyntheticBold);

    // checks for a matching font within the family
    // used as part of the font fallback process
    void FindFontForChar(GlobalFontMatch *aMatchData);

    // checks all fonts for a matching font within the family
    void SearchAllFontsForChar(GlobalFontMatch *aMatchData);

    // read in other family names, if any, and use functor to add each into cache
    virtual void ReadOtherFamilyNames(gfxPlatformFontList *aPlatformFontList);

    // helper method for reading localized family names from the name table
    // of a single face
    static void ReadOtherFamilyNamesForFace(const nsAString& aFamilyName,
                                            const char *aNameData,
                                            uint32_t aDataLength,
                                            nsTArray<nsString>& aOtherFamilyNames,
                                            bool useFullName);

    // set when other family names have been read in
    void SetOtherFamilyNamesInitialized() {
        mOtherFamilyNamesInitialized = true;
    }

    // read in other localized family names, fullnames and Postscript names
    // for all faces and append to lookup tables
    virtual void ReadFaceNames(gfxPlatformFontList *aPlatformFontList,
                               bool aNeedFullnamePostscriptNames,
                               FontInfoData *aFontInfoData = nullptr);

    // find faces belonging to this family (platform implementations override this;
    // should be made pure virtual once all subclasses have been updated)
    virtual void FindStyleVariations(FontInfoData *aFontInfoData = nullptr) { }

    // search for a specific face using the Postscript name
    gfxFontEntry* FindFont(const nsAString& aPostscriptName);

    // read in cmaps for all the faces
    void ReadAllCMAPs(FontInfoData *aFontInfoData = nullptr);

    bool TestCharacterMap(uint32_t aCh) {
        if (!mFamilyCharacterMapInitialized) {
            ReadAllCMAPs();
        }
        return mFamilyCharacterMap.test(aCh);
    }

    void ResetCharacterMap() {
        mFamilyCharacterMap.reset();
        mFamilyCharacterMapInitialized = false;
    }

    // mark this family as being in the "bad" underline offset blacklist
    void SetBadUnderlineFamily() {
        mIsBadUnderlineFamily = true;
        if (mHasStyles) {
            SetBadUnderlineFonts();
        }
    }

    bool IsBadUnderlineFamily() const { return mIsBadUnderlineFamily; }

    // sort available fonts to put preferred (standard) faces towards the end
    void SortAvailableFonts();

    // check whether the family fits into the simple 4-face model,
    // so we can use simplified style-matching;
    // if so set the mIsSimpleFamily flag (defaults to False before we've checked)
    void CheckForSimpleFamily();

    // For memory reporter
    virtual void AddSizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf,
                                        FontListSizes* aSizes) const;
    virtual void AddSizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf,
                                        FontListSizes* aSizes) const;

    // Only used for debugging checks - does a linear search
    bool ContainsFace(gfxFontEntry* aFontEntry) {
        uint32_t i, numFonts = mAvailableFonts.Length();
        for (i = 0; i < numFonts; i++) {
            if (mAvailableFonts[i] == aFontEntry) {
                return true;
            }
        }
        return false;
    }

    void SetSkipSpaceFeatureCheck(bool aSkipCheck) {
        mSkipDefaultFeatureSpaceCheck = aSkipCheck;
    }

protected:
    // Protected destructor, to discourage deletion outside of Release():
    virtual ~gfxFontFamily()
    {
    }

    // fills in an array with weights of faces that match style,
    // returns whether any matching entries found
    virtual bool FindWeightsForStyle(gfxFontEntry* aFontsForWeights[],
                                       bool anItalic, int16_t aStretch);

    bool ReadOtherFamilyNamesForFace(gfxPlatformFontList *aPlatformFontList,
                                     hb_blob_t           *aNameTable,
                                     bool                 useFullName = false);

    // set whether this font family is in "bad" underline offset blacklist.
    void SetBadUnderlineFonts() {
        uint32_t i, numFonts = mAvailableFonts.Length();
        for (i = 0; i < numFonts; i++) {
            if (mAvailableFonts[i]) {
                mAvailableFonts[i]->mIsBadUnderlineFont = true;
            }
        }
    }

    nsString mName;
    nsTArray<nsRefPtr<gfxFontEntry> >  mAvailableFonts;
    gfxSparseBitSet mFamilyCharacterMap;
    bool mOtherFamilyNamesInitialized : 1;
    bool mHasOtherFamilyNames : 1;
    bool mFaceNamesInitialized : 1;
    bool mHasStyles : 1;
    bool mIsSimpleFamily : 1;
    bool mIsBadUnderlineFamily : 1;
    bool mFamilyCharacterMapInitialized : 1;
    bool mSkipDefaultFeatureSpaceCheck : 1;

    enum {
        // for "simple" families, the faces are stored in mAvailableFonts
        // with fixed positions:
        kRegularFaceIndex    = 0,
        kBoldFaceIndex       = 1,
        kItalicFaceIndex     = 2,
        kBoldItalicFaceIndex = 3,
        // mask values for selecting face with bold and/or italic attributes
        kBoldMask   = 0x01,
        kItalicMask = 0x02
    };
};

struct gfxTextRange {
    enum {
        // flags for recording the kind of font-matching that was used
        kFontGroup      = 0x0001,
        kPrefsFallback  = 0x0002,
        kSystemFallback = 0x0004
    };
    gfxTextRange(uint32_t aStart, uint32_t aEnd,
                 gfxFont* aFont, uint8_t aMatchType)
        : start(aStart),
          end(aEnd),
          font(aFont),
          matchType(aMatchType)
    { }
    uint32_t Length() const { return end - start; }
    uint32_t start, end;
    nsRefPtr<gfxFont> font;
    uint8_t matchType;
};


/**
 * Font cache design:
 * 
 * The mFonts hashtable contains most fonts, indexed by (gfxFontEntry*, style).
 * It does not add a reference to the fonts it contains.
 * When a font's refcount decreases to zero, instead of deleting it we
 * add it to our expiration tracker.
 * The expiration tracker tracks fonts with zero refcount. After a certain
 * period of time, such fonts expire and are deleted.
 *
 * We're using 3 generations with a ten-second generation interval, so
 * zero-refcount fonts will be deleted 20-30 seconds after their refcount
 * goes to zero, if timer events fire in a timely manner.
 *
 * The font cache also handles timed expiration of cached ShapedWords
 * for "persistent" fonts: it has a repeating timer, and notifies
 * each cached font to "age" its shaped words. The words will be released
 * by the fonts if they get aged three times without being re-used in the
 * meantime.
 *
 * Note that the ShapedWord timeout is much larger than the font timeout,
 * so that in the case of a short-lived font, we'll discard the gfxFont
 * completely, with all its words, and avoid the cost of aging the words
 * individually. That only happens with longer-lived fonts.
 */
struct FontCacheSizes {
    FontCacheSizes()
        : mFontInstances(0), mShapedWords(0)
    { }

    size_t mFontInstances; // memory used by instances of gfxFont subclasses
    size_t mShapedWords; // memory used by the per-font shapedWord caches
};

class gfxFontCache MOZ_FINAL : public nsExpirationTracker<gfxFont,3> {
public:
    enum {
        FONT_TIMEOUT_SECONDS = 10,
        SHAPED_WORD_TIMEOUT_SECONDS = 60
    };

    gfxFontCache();
    ~gfxFontCache();

    /*
     * Get the global gfxFontCache.  You must call Init() before
     * calling this method --- the result will not be null.
     */
    static gfxFontCache* GetCache() {
        return gGlobalCache;
    }

    static nsresult Init();
    // It's OK to call this even if Init() has not been called.
    static void Shutdown();

    // Look up a font in the cache. Returns an addrefed pointer, or null
    // if there's nothing matching in the cache
    already_AddRefed<gfxFont> Lookup(const gfxFontEntry *aFontEntry,
                                     const gfxFontStyle *aStyle);
    // We created a new font (presumably because Lookup returned null);
    // put it in the cache. The font's refcount should be nonzero. It is
    // allowable to add a new font even if there is one already in the
    // cache with the same key; we'll forget about the old one.
    void AddNew(gfxFont *aFont);

    // The font's refcount has gone to zero; give ownership of it to
    // the cache. We delete it if it's not acquired again after a certain
    // amount of time.
    void NotifyReleased(gfxFont *aFont);

    // This gets called when the timeout has expired on a zero-refcount
    // font; we just delete it.
    virtual void NotifyExpired(gfxFont *aFont);

    // Cleans out the hashtable and removes expired fonts waiting for cleanup.
    // Other gfxFont objects may be still in use but they will be pushed
    // into the expiration queues and removed.
    void Flush() {
        mFonts.Clear();
        AgeAllGenerations();
    }

    void FlushShapedWordCaches() {
        mFonts.EnumerateEntries(ClearCachedWordsForFont, nullptr);
    }

    void AddSizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf,
                                FontCacheSizes* aSizes) const;
    void AddSizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf,
                                FontCacheSizes* aSizes) const;

protected:
    class MemoryReporter MOZ_FINAL : public nsIMemoryReporter
    {
        ~MemoryReporter() {}
    public:
        NS_DECL_ISUPPORTS
        NS_DECL_NSIMEMORYREPORTER
    };

    // Observer for notifications that the font cache cares about
    class Observer MOZ_FINAL
        : public nsIObserver
    {
        ~Observer() {}
    public:
        NS_DECL_ISUPPORTS
        NS_DECL_NSIOBSERVER
    };

    void DestroyFont(gfxFont *aFont);

    static gfxFontCache *gGlobalCache;

    struct Key {
        const gfxFontEntry* mFontEntry;
        const gfxFontStyle* mStyle;
        Key(const gfxFontEntry* aFontEntry, const gfxFontStyle* aStyle)
            : mFontEntry(aFontEntry), mStyle(aStyle) {}
    };

    class HashEntry : public PLDHashEntryHdr {
    public:
        typedef const Key& KeyType;
        typedef const Key* KeyTypePointer;

        // When constructing a new entry in the hashtable, we'll leave this
        // blank. The caller of Put() will fill this in.
        HashEntry(KeyTypePointer aStr) : mFont(nullptr) { }
        HashEntry(const HashEntry& toCopy) : mFont(toCopy.mFont) { }
        ~HashEntry() { }

        bool KeyEquals(const KeyTypePointer aKey) const;
        static KeyTypePointer KeyToPointer(KeyType aKey) { return &aKey; }
        static PLDHashNumber HashKey(const KeyTypePointer aKey) {
            return mozilla::HashGeneric(aKey->mStyle->Hash(), aKey->mFontEntry);
        }
        enum { ALLOW_MEMMOVE = true };

        gfxFont* mFont;
    };

    static size_t AddSizeOfFontEntryExcludingThis(HashEntry* aHashEntry,
                                                  mozilla::MallocSizeOf aMallocSizeOf,
                                                  void* aUserArg);

    nsTHashtable<HashEntry> mFonts;

    static PLDHashOperator ClearCachedWordsForFont(HashEntry* aHashEntry, void*);
    static PLDHashOperator AgeCachedWordsForFont(HashEntry* aHashEntry, void*);
    static void WordCacheExpirationTimerCallback(nsITimer* aTimer, void* aCache);
    nsCOMPtr<nsITimer>      mWordCacheExpirationTimer;
};

class gfxTextPerfMetrics {
public:

    struct TextCounts {
        uint32_t    numContentTextRuns;
        uint32_t    numChromeTextRuns;
        uint32_t    numChars;
        uint32_t    maxTextRunLen;
        uint32_t    wordCacheSpaceRules;
        uint32_t    wordCacheLong;
        uint32_t    wordCacheHit;
        uint32_t    wordCacheMiss;
        uint32_t    fallbackPrefs;
        uint32_t    fallbackSystem;
        uint32_t    textrunConst;
        uint32_t    textrunDestr;
    };

    uint32_t reflowCount;

    // counts per reflow operation
    TextCounts current;

    // totals for the lifetime of a document
    TextCounts cumulative;

    gfxTextPerfMetrics() {
        memset(this, 0, sizeof(gfxTextPerfMetrics));
    }

    // add current totals to cumulative ones
    void Accumulate() {
        if (current.numChars == 0) {
            return;
        }
        cumulative.numContentTextRuns += current.numContentTextRuns;
        cumulative.numChromeTextRuns += current.numChromeTextRuns;
        cumulative.numChars += current.numChars;
        if (current.maxTextRunLen > cumulative.maxTextRunLen) {
            cumulative.maxTextRunLen = current.maxTextRunLen;
        }
        cumulative.wordCacheSpaceRules += current.wordCacheSpaceRules;
        cumulative.wordCacheLong += current.wordCacheLong;
        cumulative.wordCacheHit += current.wordCacheHit;
        cumulative.wordCacheMiss += current.wordCacheMiss;
        cumulative.fallbackPrefs += current.fallbackPrefs;
        cumulative.fallbackSystem += current.fallbackSystem;
        cumulative.textrunConst += current.textrunConst;
        cumulative.textrunDestr += current.textrunDestr;
        memset(&current, 0, sizeof(current));
    }
};

class gfxTextRunFactory {
    NS_INLINE_DECL_REFCOUNTING(gfxTextRunFactory)

public:
    // Flags in the mask 0xFFFF0000 are reserved for textrun clients
    // Flags in the mask 0x0000F000 are reserved for per-platform fonts
    // Flags in the mask 0x00000FFF are set by the textrun creator.
    enum {
        CACHE_TEXT_FLAGS    = 0xF0000000,
        USER_TEXT_FLAGS     = 0x0FFF0000,
        PLATFORM_TEXT_FLAGS = 0x0000F000,
        TEXTRUN_TEXT_FLAGS  = 0x00000FFF,
        SETTABLE_FLAGS      = CACHE_TEXT_FLAGS | USER_TEXT_FLAGS,

        /**
         * When set, the text string pointer used to create the text run
         * is guaranteed to be available during the lifetime of the text run.
         */
        TEXT_IS_PERSISTENT           = 0x0001,
        /**
         * When set, the text is known to be all-ASCII (< 128).
         */
        TEXT_IS_ASCII                = 0x0002,
        /**
         * When set, the text is RTL.
         */
        TEXT_IS_RTL                  = 0x0004,
        /**
         * When set, spacing is enabled and the textrun needs to call GetSpacing
         * on the spacing provider.
         */
        TEXT_ENABLE_SPACING          = 0x0008,
        /**
         * When set, GetHyphenationBreaks may return true for some character
         * positions, otherwise it will always return false for all characters.
         */
        TEXT_ENABLE_HYPHEN_BREAKS    = 0x0010,
        /**
         * When set, the text has no characters above 255 and it is stored
         * in the textrun in 8-bit format.
         */
        TEXT_IS_8BIT                 = 0x0020,
        /**
         * When set, the RunMetrics::mBoundingBox field will be initialized
         * properly based on glyph extents, in particular, glyph extents that
         * overflow the standard font-box (the box defined by the ascent, descent
         * and advance width of the glyph). When not set, it may just be the
         * standard font-box even if glyphs overflow.
         */
        TEXT_NEED_BOUNDING_BOX       = 0x0040,
        /**
         * When set, optional ligatures are disabled. Ligatures that are
         * required for legible text should still be enabled.
         */
        TEXT_DISABLE_OPTIONAL_LIGATURES = 0x0080,
        /**
         * When set, the textrun should favour speed of construction over
         * quality. This may involve disabling ligatures and/or kerning or
         * other effects.
         */
        TEXT_OPTIMIZE_SPEED          = 0x0100,
        /**
         * For internal use by the memory reporter when accounting for
         * storage used by textruns.
         * Because the reporter may visit each textrun multiple times while
         * walking the frame trees and textrun cache, it needs to mark
         * textruns that have been seen so as to avoid multiple-accounting.
         */
        TEXT_RUN_SIZE_ACCOUNTED      = 0x0200,
        /**
         * When set, the textrun should discard control characters instead of
         * turning them into hexboxes.
         */
        TEXT_HIDE_CONTROL_CHARACTERS = 0x0400,

        /**
         * nsTextFrameThebes sets these, but they're defined here rather than
         * in nsTextFrameUtils.h because ShapedWord creation/caching also needs
         * to check the _INCOMING flag
         */
        TEXT_TRAILING_ARABICCHAR = 0x20000000,
        /**
         * When set, the previous character for this textrun was an Arabic
         * character.  This is used for the context detection necessary for
         * bidi.numeral implementation.
         */
        TEXT_INCOMING_ARABICCHAR = 0x40000000,

        // Set if the textrun should use the OpenType 'math' script.
        TEXT_USE_MATH_SCRIPT = 0x80000000,

        TEXT_UNUSED_FLAGS = 0x10000000
    };

    /**
     * This record contains all the parameters needed to initialize a textrun.
     */
    struct Parameters {
        // A reference context suggesting where the textrun will be rendered
        gfxContext   *mContext;
        // Pointer to arbitrary user data (which should outlive the textrun)
        void         *mUserData;
        // A description of which characters have been stripped from the original
        // DOM string to produce the characters in the textrun. May be null
        // if that information is not relevant.
        gfxSkipChars *mSkipChars;
        // A list of where linebreaks are currently placed in the textrun. May
        // be null if mInitialBreakCount is zero.
        uint32_t     *mInitialBreaks;
        uint32_t      mInitialBreakCount;
        // The ratio to use to convert device pixels to application layout units
        int32_t       mAppUnitsPerDevUnit;
    };

protected:
    // Protected destructor, to discourage deletion outside of Release():
    virtual ~gfxTextRunFactory() {}
};

/**
 * This stores glyph bounds information for a particular gfxFont, at
 * a particular appunits-per-dev-pixel ratio (because the compressed glyph
 * width array is stored in appunits).
 * 
 * We store a hashtable from glyph IDs to float bounding rects. For the
 * common case where the glyph has no horizontal left bearing, and no
 * y overflow above the font ascent or below the font descent, and tight
 * bounding boxes are not required, we avoid storing the glyph ID in the hashtable
 * and instead consult an array of 16-bit glyph XMost values (in appunits).
 * This array always has an entry for the font's space glyph --- the width is
 * assumed to be zero.
 */
class gfxGlyphExtents {
public:
    gfxGlyphExtents(int32_t aAppUnitsPerDevUnit) :
        mAppUnitsPerDevUnit(aAppUnitsPerDevUnit) {
        MOZ_COUNT_CTOR(gfxGlyphExtents);
    }
    ~gfxGlyphExtents();

    enum { INVALID_WIDTH = 0xFFFF };

    void NotifyGlyphsChanged() {
        mTightGlyphExtents.Clear();
    }

    // returns INVALID_WIDTH => not a contained glyph
    // Otherwise the glyph has no before-bearing or vertical bearings,
    // and the result is its width measured from the baseline origin, in
    // appunits.
    uint16_t GetContainedGlyphWidthAppUnits(uint32_t aGlyphID) const {
        return mContainedGlyphWidths.Get(aGlyphID);
    }

    bool IsGlyphKnown(uint32_t aGlyphID) const {
        return mContainedGlyphWidths.Get(aGlyphID) != INVALID_WIDTH ||
            mTightGlyphExtents.GetEntry(aGlyphID) != nullptr;
    }

    bool IsGlyphKnownWithTightExtents(uint32_t aGlyphID) const {
        return mTightGlyphExtents.GetEntry(aGlyphID) != nullptr;
    }

    // Get glyph extents; a rectangle relative to the left baseline origin
    // Returns true on success. Can fail on OOM or when aContext is null
    // and extents were not (successfully) prefetched.
    bool GetTightGlyphExtentsAppUnits(gfxFont *aFont, gfxContext *aContext,
            uint32_t aGlyphID, gfxRect *aExtents);

    void SetContainedGlyphWidthAppUnits(uint32_t aGlyphID, uint16_t aWidth) {
        mContainedGlyphWidths.Set(aGlyphID, aWidth);
    }
    void SetTightGlyphExtents(uint32_t aGlyphID, const gfxRect& aExtentsAppUnits);

    int32_t GetAppUnitsPerDevUnit() { return mAppUnitsPerDevUnit; }

    size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;
    size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;

private:
    class HashEntry : public nsUint32HashKey {
    public:
        // When constructing a new entry in the hashtable, we'll leave this
        // blank. The caller of Put() will fill this in.
        HashEntry(KeyTypePointer aPtr) : nsUint32HashKey(aPtr) {}
        HashEntry(const HashEntry& toCopy) : nsUint32HashKey(toCopy) {
          x = toCopy.x; y = toCopy.y; width = toCopy.width; height = toCopy.height;
        }

        float x, y, width, height;
    };

    enum { BLOCK_SIZE_BITS = 7, BLOCK_SIZE = 1 << BLOCK_SIZE_BITS }; // 128-glyph blocks

    class GlyphWidths {
    public:
        void Set(uint32_t aIndex, uint16_t aValue);
        uint16_t Get(uint32_t aIndex) const {
            uint32_t block = aIndex >> BLOCK_SIZE_BITS;
            if (block >= mBlocks.Length())
                return INVALID_WIDTH;
            uintptr_t bits = mBlocks[block];
            if (!bits)
                return INVALID_WIDTH;
            uint32_t indexInBlock = aIndex & (BLOCK_SIZE - 1);
            if (bits & 0x1) {
                if (GetGlyphOffset(bits) != indexInBlock)
                    return INVALID_WIDTH;
                return GetWidth(bits);
            }
            uint16_t *widths = reinterpret_cast<uint16_t *>(bits);
            return widths[indexInBlock];
        }

        uint32_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;
        
        ~GlyphWidths();

    private:
        static uint32_t GetGlyphOffset(uintptr_t aBits) {
            NS_ASSERTION(aBits & 0x1, "This is really a pointer...");
            return (aBits >> 1) & ((1 << BLOCK_SIZE_BITS) - 1);
        }
        static uint32_t GetWidth(uintptr_t aBits) {
            NS_ASSERTION(aBits & 0x1, "This is really a pointer...");
            return aBits >> (1 + BLOCK_SIZE_BITS);
        }
        static uintptr_t MakeSingle(uint32_t aGlyphOffset, uint16_t aWidth) {
            return (aWidth << (1 + BLOCK_SIZE_BITS)) + (aGlyphOffset << 1) + 1;
        }

        nsTArray<uintptr_t> mBlocks;
    };

    GlyphWidths             mContainedGlyphWidths;
    nsTHashtable<HashEntry> mTightGlyphExtents;
    int32_t                 mAppUnitsPerDevUnit;

private:
    // not implemented:
    gfxGlyphExtents(const gfxGlyphExtents& aOther) MOZ_DELETE;
    gfxGlyphExtents& operator=(const gfxGlyphExtents& aOther) MOZ_DELETE;
};

/**
 * gfxFontShaper
 *
 * This class implements text shaping (character to glyph mapping and
 * glyph layout). There is a gfxFontShaper subclass for each text layout
 * technology (uniscribe, core text, harfbuzz,....) we support.
 *
 * The shaper is responsible for setting up glyph data in gfxTextRuns.
 *
 * A generic, platform-independent shaper relies only on the standard
 * gfxFont interface and can work with any concrete subclass of gfxFont.
 *
 * Platform-specific implementations designed to interface to platform
 * shaping APIs such as Uniscribe or CoreText may rely on features of a
 * specific font subclass to access native font references
 * (such as CTFont, HFONT, DWriteFont, etc).
 */

class gfxFontShaper {
public:
    gfxFontShaper(gfxFont *aFont)
        : mFont(aFont)
    {
        NS_ASSERTION(aFont, "shaper requires a valid font!");
    }

    virtual ~gfxFontShaper() { }

    // Shape a piece of text and store the resulting glyph data into
    // aShapedText. Parameters aOffset/aLength indicate the range of
    // aShapedText to be updated; aLength is also the length of aText.
    virtual bool ShapeText(gfxContext     *aContext,
                           const char16_t *aText,
                           uint32_t        aOffset,
                           uint32_t        aLength,
                           int32_t         aScript,
                           gfxShapedText  *aShapedText) = 0;

    gfxFont *GetFont() const { return mFont; }

    // returns true if features exist in output, false otherwise
    static bool
    MergeFontFeatures(const gfxFontStyle *aStyle,
                      const nsTArray<gfxFontFeature>& aFontFeatures,
                      bool aDisableLigatures,
                      const nsAString& aFamilyName,
                      bool aAddSmallCaps,
                      nsDataHashtable<nsUint32HashKey,uint32_t>& aMergedFeatures);

protected:
    // the font this shaper is working with
    gfxFont * mFont;
};

/* a SPECIFIC single font family */
class gfxFont {

    friend class gfxHarfBuzzShaper;
    friend class gfxGraphiteShaper;

public:
    nsrefcnt AddRef(void) {
        NS_PRECONDITION(int32_t(mRefCnt) >= 0, "illegal refcnt");
        if (mExpirationState.IsTracked()) {
            gfxFontCache::GetCache()->RemoveObject(this);
        }
        ++mRefCnt;
        NS_LOG_ADDREF(this, mRefCnt, "gfxFont", sizeof(*this));
        return mRefCnt;
    }
    nsrefcnt Release(void) {
        NS_PRECONDITION(0 != mRefCnt, "dup release");
        --mRefCnt;
        NS_LOG_RELEASE(this, mRefCnt, "gfxFont");
        if (mRefCnt == 0) {
            NotifyReleased();
            // |this| may have been deleted.
            return 0;
        }
        return mRefCnt;
    }

    int32_t GetRefCount() { return mRefCnt; }

    // options to specify the kind of AA to be used when creating a font
    typedef enum {
        kAntialiasDefault,
        kAntialiasNone,
        kAntialiasGrayscale,
        kAntialiasSubpixel
    } AntialiasOption;

protected:
    nsAutoRefCnt mRefCnt;
    cairo_scaled_font_t *mScaledFont;

    void NotifyReleased() {
        gfxFontCache *cache = gfxFontCache::GetCache();
        if (cache) {
            // Don't delete just yet; return the object to the cache for
            // possibly recycling within some time limit
            cache->NotifyReleased(this);
        } else {
            // The cache may have already been shut down.
            delete this;
        }
    }

    gfxFont(gfxFontEntry *aFontEntry, const gfxFontStyle *aFontStyle,
            AntialiasOption anAAOption = kAntialiasDefault,
            cairo_scaled_font_t *aScaledFont = nullptr);

public:
    virtual ~gfxFont();

    bool Valid() const {
        return mIsValid;
    }

    // options for the kind of bounding box to return from measurement
    typedef enum {
        LOOSE_INK_EXTENTS,
            // A box that encloses all the painted pixels, and may
            // include sidebearings and/or additional ascent/descent
            // within the glyph cell even if the ink is smaller.
        TIGHT_INK_EXTENTS,
            // A box that tightly encloses all the painted pixels
            // (although actually on Windows, at least, it may be
            // slightly larger than strictly necessary because
            // we can't get precise extents with ClearType).
        TIGHT_HINTED_OUTLINE_EXTENTS
            // A box that tightly encloses the glyph outline,
            // ignoring possible antialiasing pixels that extend
            // beyond this.
            // NOTE: The default implementation of gfxFont::Measure(),
            // which works with the glyph extents cache, does not
            // differentiate between this and TIGHT_INK_EXTENTS.
            // Whether the distinction is important depends on the
            // antialiasing behavior of the platform; currently the
            // distinction is only implemented in the gfxWindowsFont
            // subclass, because of ClearType's tendency to paint
            // outside the hinted outline.
            // Also NOTE: it is relatively expensive to request this,
            // as it does not use cached glyph extents in the font.
    } BoundingBoxType;

    const nsString& GetName() const { return mFontEntry->Name(); }
    const gfxFontStyle *GetStyle() const { return &mStyle; }

    virtual cairo_scaled_font_t* GetCairoScaledFont() { return mScaledFont; }

    virtual gfxFont* CopyWithAntialiasOption(AntialiasOption anAAOption) {
        // platforms where this actually matters should override
        return nullptr;
    }

    virtual gfxFloat GetAdjustedSize() {
        return mAdjustedSize > 0.0 ? mAdjustedSize : mStyle.size;
    }

    float FUnitsToDevUnitsFactor() const {
        // check this was set up during font initialization
        NS_ASSERTION(mFUnitsConvFactor > 0.0f, "mFUnitsConvFactor not valid");
        return mFUnitsConvFactor;
    }

    // check whether this is an sfnt we can potentially use with harfbuzz
    bool FontCanSupportHarfBuzz() {
        return mFontEntry->HasCmapTable();
    }

    // check whether this is an sfnt we can potentially use with Graphite
    bool FontCanSupportGraphite() {
        return mFontEntry->HasGraphiteTables();
    }

    // whether a feature is supported by the font (limited to a small set
    // of features for which some form of fallback needs to be implemented)
    bool SupportsFeature(int32_t aScript, uint32_t aFeatureTag);

    // whether the font supports "real" small caps, petite caps etc.
    // aFallbackToSmallCaps true when petite caps should fallback to small caps
    bool SupportsVariantCaps(int32_t aScript, uint32_t aVariantCaps,
                             bool& aFallbackToSmallCaps,
                             bool& aSyntheticLowerToSmallCaps,
                             bool& aSyntheticUpperToSmallCaps);

    // whether the font supports subscript/superscript feature
    // for fallback, need to verify that all characters in the run
    // have variant substitutions
    bool SupportsSubSuperscript(uint32_t aSubSuperscript,
                                const uint8_t *aString,
                                uint32_t aLength, int32_t aRunScript);

    bool SupportsSubSuperscript(uint32_t aSubSuperscript,
                                const char16_t *aString,
                                uint32_t aLength, int32_t aRunScript);

    // Subclasses may choose to look up glyph ids for characters.
    // If they do not override this, gfxHarfBuzzShaper will fetch the cmap
    // table and use that.
    virtual bool ProvidesGetGlyph() const {
        return false;
    }
    // Map unicode character to glyph ID.
    // Only used if ProvidesGetGlyph() returns true.
    virtual uint32_t GetGlyph(uint32_t unicode, uint32_t variation_selector) {
        return 0;
    }
    // Return the horizontal advance of a glyph.
    gfxFloat GetGlyphHAdvance(gfxContext *aCtx, uint16_t aGID);

    // Return Azure GlyphRenderingOptions for drawing this font.
    virtual mozilla::TemporaryRef<mozilla::gfx::GlyphRenderingOptions>
      GetGlyphRenderingOptions() { return nullptr; }

    gfxFloat SynthesizeSpaceWidth(uint32_t aCh);

    // Font metrics
    struct Metrics {
        gfxFloat xHeight;
        gfxFloat strikeoutSize;
        gfxFloat strikeoutOffset;
        gfxFloat underlineSize;
        gfxFloat underlineOffset;

        gfxFloat internalLeading;
        gfxFloat externalLeading;

        gfxFloat emHeight;
        gfxFloat emAscent;
        gfxFloat emDescent;
        gfxFloat maxHeight;
        gfxFloat maxAscent;
        gfxFloat maxDescent;
        gfxFloat maxAdvance;

        gfxFloat aveCharWidth;
        gfxFloat spaceWidth;
        gfxFloat zeroOrAveCharWidth;  // width of '0', or if there is
                                      // no '0' glyph in this font,
                                      // equal to .aveCharWidth
    };
    virtual const gfxFont::Metrics& GetMetrics() = 0;

    /**
     * We let layout specify spacing on either side of any
     * character. We need to specify both before and after
     * spacing so that substring measurement can do the right things.
     * These values are in appunits. They're always an integral number of
     * appunits, but we specify them in floats in case very large spacing
     * values are required.
     */
    struct Spacing {
        gfxFloat mBefore;
        gfxFloat mAfter;
    };
    /**
     * Metrics for a particular string
     */
    struct RunMetrics {
        RunMetrics() {
            mAdvanceWidth = mAscent = mDescent = 0.0;
        }

        void CombineWith(const RunMetrics& aOther, bool aOtherIsOnLeft);

        // can be negative (partly due to negative spacing).
        // Advance widths should be additive: the advance width of the
        // (offset1, length1) plus the advance width of (offset1 + length1,
        // length2) should be the advance width of (offset1, length1 + length2)
        gfxFloat mAdvanceWidth;
        
        // For zero-width substrings, these must be zero!
        gfxFloat mAscent;  // always non-negative
        gfxFloat mDescent; // always non-negative
        
        // Bounding box that is guaranteed to include everything drawn.
        // If a tight boundingBox was requested when these metrics were
        // generated, this will tightly wrap the glyphs, otherwise it is
        // "loose" and may be larger than the true bounding box.
        // Coordinates are relative to the baseline left origin, so typically
        // mBoundingBox.y == -mAscent
        gfxRect  mBoundingBox;
    };

    /**
     * Draw a series of glyphs to aContext. The direction of aTextRun must
     * be honoured.
     * @param aStart the first character to draw
     * @param aEnd draw characters up to here
     * @param aBaselineOrigin the baseline origin; the left end of the baseline
     * for LTR textruns, the right end of the baseline for RTL textruns. On return,
     * this should be updated to the other end of the baseline. In application
     * units, really!
     * @param aSpacing spacing to insert before and after characters (for RTL
     * glyphs, before-spacing is inserted to the right of characters). There
     * are aEnd - aStart elements in this array, unless it's null to indicate
     * that there is no spacing.
     * @param aDrawMode specifies whether the fill or stroke of the glyph should be
     * drawn, or if it should be drawn into the current path
     * @param aContextPaint information about how to construct the fill and
     * stroke pattern. Can be nullptr if we are not stroking the text, which
     * indicates that the current source from aContext should be used for filling
     * 
     * Callers guarantee:
     * -- aStart and aEnd are aligned to cluster and ligature boundaries
     * -- all glyphs use this font
     * 
     * The default implementation builds a cairo glyph array and
     * calls cairo_show_glyphs or cairo_glyph_path.
     */
    virtual void Draw(gfxTextRun *aTextRun, uint32_t aStart, uint32_t aEnd,
                      gfxContext *aContext, DrawMode aDrawMode, gfxPoint *aBaselineOrigin,
                      Spacing *aSpacing, gfxTextContextPaint *aContextPaint,
                      gfxTextRunDrawCallbacks *aCallbacks);

    /**
     * Measure a run of characters. See gfxTextRun::Metrics.
     * @param aTight if false, then return the union of the glyph extents
     * with the font-box for the characters (the rectangle with x=0,width=
     * the advance width for the character run,y=-(font ascent), and height=
     * font ascent + font descent). Otherwise, we must return as tight as possible
     * an approximation to the area actually painted by glyphs.
     * @param aContextForTightBoundingBox when aTight is true, this must
     * be non-null.
     * @param aSpacing spacing to insert before and after glyphs. The bounding box
     * need not include the spacing itself, but the spacing affects the glyph
     * positions. null if there is no spacing.
     * 
     * Callers guarantee:
     * -- aStart and aEnd are aligned to cluster and ligature boundaries
     * -- all glyphs use this font
     * 
     * The default implementation just uses font metrics and aTextRun's
     * advances, and assumes no characters fall outside the font box. In
     * general this is insufficient, because that assumption is not always true.
     */
    virtual RunMetrics Measure(gfxTextRun *aTextRun,
                               uint32_t aStart, uint32_t aEnd,
                               BoundingBoxType aBoundingBoxType,
                               gfxContext *aContextForTightBoundingBox,
                               Spacing *aSpacing);
    /**
     * Line breaks have been changed at the beginning and/or end of a substring
     * of the text. Reshaping may be required; glyph updating is permitted.
     * @return true if anything was changed, false otherwise
     */
    bool NotifyLineBreaksChanged(gfxTextRun *aTextRun,
                                   uint32_t aStart, uint32_t aLength)
    { return false; }

    // Expiration tracking
    nsExpirationState *GetExpirationState() { return &mExpirationState; }

    // Get the glyphID of a space
    virtual uint32_t GetSpaceGlyph() = 0;

    gfxGlyphExtents *GetOrCreateGlyphExtents(int32_t aAppUnitsPerDevUnit);

    // You need to call SetupCairoFont on the aCR just before calling this
    virtual void SetupGlyphExtents(gfxContext *aContext, uint32_t aGlyphID,
                                   bool aNeedTight, gfxGlyphExtents *aExtents);

    // This is called by the default Draw() implementation above.
    virtual bool SetupCairoFont(gfxContext *aContext) = 0;

    virtual bool AllowSubpixelAA() { return true; }

    bool IsSyntheticBold() { return mApplySyntheticBold; }

    // Amount by which synthetic bold "fattens" the glyphs:
    // For size S up to a threshold size T, we use (0.25 + 3S / 4T),
    // so that the result ranges from 0.25 to 1.0; thereafter,
    // simply use (S / T).
    gfxFloat GetSyntheticBoldOffset() {
        gfxFloat size = GetAdjustedSize();
        const gfxFloat threshold = 48.0;
        return size < threshold ? (0.25 + 0.75 * size / threshold) :
                                  (size / threshold);
    }

    gfxFontEntry *GetFontEntry() { return mFontEntry.get(); }
    bool HasCharacter(uint32_t ch) {
        if (!mIsValid)
            return false;
        return mFontEntry->HasCharacter(ch); 
    }

    uint16_t GetUVSGlyph(uint32_t aCh, uint32_t aVS) {
        if (!mIsValid) {
            return 0;
        }
        return mFontEntry->GetUVSGlyph(aCh, aVS); 
    }

    bool InitFakeSmallCapsRun(gfxContext     *aContext,
                              gfxTextRun     *aTextRun,
                              const uint8_t  *aText,
                              uint32_t        aOffset,
                              uint32_t        aLength,
                              uint8_t         aMatchType,
                              int32_t         aScript,
                              bool            aSyntheticLower,
                              bool            aSyntheticUpper);

    bool InitFakeSmallCapsRun(gfxContext     *aContext,
                              gfxTextRun     *aTextRun,
                              const char16_t *aText,
                              uint32_t        aOffset,
                              uint32_t        aLength,
                              uint8_t         aMatchType,
                              int32_t         aScript,
                              bool            aSyntheticLower,
                              bool            aSyntheticUpper);

    // call the (virtual) InitTextRun method to do glyph generation/shaping,
    // limiting the length of text passed by processing the run in multiple
    // segments if necessary
    template<typename T>
    bool SplitAndInitTextRun(gfxContext *aContext,
                             gfxTextRun *aTextRun,
                             const T *aString,
                             uint32_t aRunStart,
                             uint32_t aRunLength,
                             int32_t aRunScript);

    // Get a ShapedWord representing the given text (either 8- or 16-bit)
    // for use in setting up a gfxTextRun.
    template<typename T>
    gfxShapedWord* GetShapedWord(gfxContext *aContext,
                                 const T *aText,
                                 uint32_t aLength,
                                 uint32_t aHash,
                                 int32_t aRunScript,
                                 int32_t aAppUnitsPerDevUnit,
                                 uint32_t aFlags,
                                 gfxTextPerfMetrics *aTextPerf);

    // Ensure the ShapedWord cache is initialized. This MUST be called before
    // any attempt to use GetShapedWord().
    void InitWordCache() {
        if (!mWordCache) {
            mWordCache = new nsTHashtable<CacheHashEntry>;
        }
    }

    // Called by the gfxFontCache timer to increment the age of all the words,
    // so that they'll expire after a sufficient period of non-use
    void AgeCachedWords() {
        if (mWordCache) {
            (void)mWordCache->EnumerateEntries(AgeCacheEntry, this);
        }
    }

    // Discard all cached word records; called on memory-pressure notification.
    void ClearCachedWords() {
        if (mWordCache) {
            mWordCache->Clear();
        }
    }

    // Glyph rendering/geometry has changed, so invalidate data as necessary.
    void NotifyGlyphsChanged();

    virtual void AddSizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf,
                                        FontCacheSizes* aSizes) const;
    virtual void AddSizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf,
                                        FontCacheSizes* aSizes) const;

    typedef enum {
        FONT_TYPE_DWRITE,
        FONT_TYPE_GDI,
        FONT_TYPE_FT2,
        FONT_TYPE_MAC,
        FONT_TYPE_OS2,
        FONT_TYPE_CAIRO
    } FontType;

    virtual FontType GetType() const = 0;

    virtual mozilla::TemporaryRef<mozilla::gfx::ScaledFont> GetScaledFont(mozilla::gfx::DrawTarget *aTarget)
    { return gfxPlatform::GetPlatform()->GetScaledFontForFont(aTarget, this); }

    bool KerningDisabled() {
        return mKerningSet && !mKerningEnabled;
    }

    /**
     * Subclass this object to be notified of glyph changes. Delete the object
     * when no longer needed.
     */
    class GlyphChangeObserver {
    public:
        virtual ~GlyphChangeObserver()
        {
            if (mFont) {
                mFont->RemoveGlyphChangeObserver(this);
            }
        }
        // This gets called when the gfxFont dies.
        void ForgetFont() { mFont = nullptr; }
        virtual void NotifyGlyphsChanged() = 0;
    protected:
        GlyphChangeObserver(gfxFont *aFont) : mFont(aFont)
        {
            mFont->AddGlyphChangeObserver(this);
        }
        gfxFont* mFont;
    };
    friend class GlyphChangeObserver;

    bool GlyphsMayChange()
    {
        // Currently only fonts with SVG glyphs can have animated glyphs
        return mFontEntry->TryGetSVGData(this);
    }

    static void DestroySingletons() {
        delete sScriptTagToCode;
        delete sDefaultFeatures;
    }

    // Get a font dimension from the MATH table, scaled to appUnits;
    // may only be called if mFontEntry->TryGetMathTable has succeeded
    // (i.e. the font is known to be a valid OpenType math font).
    nscoord GetMathConstant(gfxFontEntry::MathConstant aConstant,
                            uint32_t aAppUnitsPerDevPixel)
    {
        return NSToCoordRound(mFontEntry->GetMathConstant(aConstant) *
                              GetAdjustedSize() * aAppUnitsPerDevPixel);
    }

    // Get a dimensionless math constant (e.g. a percentage);
    // may only be called if mFontEntry->TryGetMathTable has succeeded
    // (i.e. the font is known to be a valid OpenType math font).
    float GetMathConstant(gfxFontEntry::MathConstant aConstant)
    {
        return mFontEntry->GetMathConstant(aConstant);
    }

    // return a cloned font resized and offset to simulate sub/superscript glyphs
    virtual already_AddRefed<gfxFont>
    GetSubSuperscriptFont(int32_t aAppUnitsPerDevPixel);

protected:

    // set the font size and offset used for
    // synthetic subscript/superscript glyphs
    void CalculateSubSuperSizeAndOffset(int32_t aAppUnitsPerDevPixel,
                                        gfxFloat& aSubSuperSizeRatio,
                                        float& aBaselineOffset);

    // Return a font that is a "clone" of this one, but reduced to 80% size
    // (and with variantCaps set to normal).
    // Default implementation relies on gfxFontEntry::CreateFontInstance;
    // backends that don't implement that will need to override this and use
    // an alternative technique. (gfxPangoFonts, I'm looking at you...)
    virtual already_AddRefed<gfxFont> GetSmallCapsFont();

    // subclasses may provide (possibly hinted) glyph widths (in font units);
    // if they do not override this, harfbuzz will use unhinted widths
    // derived from the font tables
    virtual bool ProvidesGlyphWidths() const {
        return false;
    }

    // The return value is interpreted as a horizontal advance in 16.16 fixed
    // point format.
    virtual int32_t GetGlyphWidth(gfxContext *aCtx, uint16_t aGID) {
        return -1;
    }

    void AddGlyphChangeObserver(GlyphChangeObserver *aObserver);
    void RemoveGlyphChangeObserver(GlyphChangeObserver *aObserver);

    // whether font contains substitution lookups containing spaces
    bool HasSubstitutionRulesWithSpaceLookups(int32_t aRunScript);

    // do spaces participate in shaping rules? if so, can't used word cache
    bool SpaceMayParticipateInShaping(int32_t aRunScript);

    // For 8-bit text, expand to 16-bit and then call the following method.
    bool ShapeText(gfxContext    *aContext,
                   const uint8_t *aText,
                   uint32_t       aOffset, // dest offset in gfxShapedText
                   uint32_t       aLength,
                   int32_t        aScript,
                   gfxShapedText *aShapedText); // where to store the result

    // Call the appropriate shaper to generate glyphs for aText and store
    // them into aShapedText.
    virtual bool ShapeText(gfxContext      *aContext,
                           const char16_t *aText,
                           uint32_t         aOffset,
                           uint32_t         aLength,
                           int32_t          aScript,
                           gfxShapedText   *aShapedText);

    // Helper to adjust for synthetic bold and set character-type flags
    // in the shaped text; implementations of ShapeText should call this
    // after glyph shaping has been completed.
    void PostShapingFixup(gfxContext      *aContext,
                          const char16_t *aText,
                          uint32_t         aOffset, // position within aShapedText
                          uint32_t         aLength,
                          gfxShapedText   *aShapedText);

    // Shape text directly into a range within a textrun, without using the
    // font's word cache. Intended for use when the font has layout features
    // that involve space, and therefore require shaping complete runs rather
    // than isolated words, or for long strings that are inefficient to cache.
    // This will split the text on "invalid" characters (tab/newline) that are
    // not handled via normal shaping, but does not otherwise divide up the
    // text.
    template<typename T>
    bool ShapeTextWithoutWordCache(gfxContext *aContext,
                                   const T    *aText,
                                   uint32_t    aOffset,
                                   uint32_t    aLength,
                                   int32_t     aScript,
                                   gfxTextRun *aTextRun);

    // Shape a fragment of text (a run that is known to contain only
    // "valid" characters, no newlines/tabs/other control chars).
    // All non-wordcache shaping goes through here; this is the function
    // that will ensure we don't pass excessively long runs to the various
    // platform shapers.
    template<typename T>
    bool ShapeFragmentWithoutWordCache(gfxContext *aContext,
                                       const T    *aText,
                                       uint32_t    aOffset,
                                       uint32_t    aLength,
                                       int32_t     aScript,
                                       gfxTextRun *aTextRun);

    void CheckForFeaturesInvolvingSpace();

    // whether a given feature is included in feature settings from both the
    // font and the style. aFeatureOn set if resolved feature value is non-zero
    bool HasFeatureSet(uint32_t aFeature, bool& aFeatureOn);

    // used when analyzing whether a font has space contextual lookups
    static nsDataHashtable<nsUint32HashKey, int32_t> *sScriptTagToCode;
    static nsTHashtable<nsUint32HashKey>             *sDefaultFeatures;

    nsRefPtr<gfxFontEntry> mFontEntry;

    struct CacheHashKey {
        union {
            const uint8_t   *mSingle;
            const char16_t *mDouble;
        }                mText;
        uint32_t         mLength;
        uint32_t         mFlags;
        int32_t          mScript;
        int32_t          mAppUnitsPerDevUnit;
        PLDHashNumber    mHashKey;
        bool             mTextIs8Bit;

        CacheHashKey(const uint8_t *aText, uint32_t aLength,
                     uint32_t aStringHash,
                     int32_t aScriptCode, int32_t aAppUnitsPerDevUnit,
                     uint32_t aFlags)
            : mLength(aLength),
              mFlags(aFlags),
              mScript(aScriptCode),
              mAppUnitsPerDevUnit(aAppUnitsPerDevUnit),
              mHashKey(aStringHash + aScriptCode +
                  aAppUnitsPerDevUnit * 0x100 + aFlags * 0x10000),
              mTextIs8Bit(true)
        {
            NS_ASSERTION(aFlags & gfxTextRunFactory::TEXT_IS_8BIT,
                         "8-bit flag should have been set");
            mText.mSingle = aText;
        }

        CacheHashKey(const char16_t *aText, uint32_t aLength,
                     uint32_t aStringHash,
                     int32_t aScriptCode, int32_t aAppUnitsPerDevUnit,
                     uint32_t aFlags)
            : mLength(aLength),
              mFlags(aFlags),
              mScript(aScriptCode),
              mAppUnitsPerDevUnit(aAppUnitsPerDevUnit),
              mHashKey(aStringHash + aScriptCode +
                  aAppUnitsPerDevUnit * 0x100 + aFlags * 0x10000),
              mTextIs8Bit(false)
        {
            // We can NOT assert that TEXT_IS_8BIT is false in aFlags here,
            // because this might be an 8bit-only word from a 16-bit textrun,
            // in which case the text we're passed is still in 16-bit form,
            // and we'll have to use an 8-to-16bit comparison in KeyEquals.
            mText.mDouble = aText;
        }
    };

    class CacheHashEntry : public PLDHashEntryHdr {
    public:
        typedef const CacheHashKey &KeyType;
        typedef const CacheHashKey *KeyTypePointer;

        // When constructing a new entry in the hashtable, the caller of Put()
        // will fill us in.
        CacheHashEntry(KeyTypePointer aKey) { }
        CacheHashEntry(const CacheHashEntry& toCopy) { NS_ERROR("Should not be called"); }
        ~CacheHashEntry() { }

        bool KeyEquals(const KeyTypePointer aKey) const;

        static KeyTypePointer KeyToPointer(KeyType aKey) { return &aKey; }

        static PLDHashNumber HashKey(const KeyTypePointer aKey) {
            return aKey->mHashKey;
        }

        enum { ALLOW_MEMMOVE = true };

        nsAutoPtr<gfxShapedWord> mShapedWord;
    };

    static size_t
    WordCacheEntrySizeOfExcludingThis(CacheHashEntry*   aHashEntry,
                                      mozilla::MallocSizeOf aMallocSizeOf,
                                      void*             aUserArg);

    nsAutoPtr<nsTHashtable<CacheHashEntry> > mWordCache;

    static PLDHashOperator AgeCacheEntry(CacheHashEntry *aEntry, void *aUserData);
    static const uint32_t  kShapedWordCacheMaxAge = 3;

    bool                       mIsValid;

    // use synthetic bolding for environments where this is not supported
    // by the platform
    bool                       mApplySyntheticBold;

    bool                       mKerningSet;     // kerning explicitly set?
    bool                       mKerningEnabled; // if set, on or off?

    nsExpirationState          mExpirationState;
    gfxFontStyle               mStyle;
    nsAutoTArray<gfxGlyphExtents*,1> mGlyphExtentsArray;
    nsAutoPtr<nsTHashtable<nsPtrHashKey<GlyphChangeObserver> > > mGlyphChangeObservers;

    gfxFloat                   mAdjustedSize;

    float                      mFUnitsConvFactor; // conversion factor from font units to dev units

    // the AA setting requested for this font - may affect glyph bounds
    AntialiasOption            mAntialiasOption;

    // a copy of the font without antialiasing, if needed for separate
    // measurement by mathml code
    nsAutoPtr<gfxFont>         mNonAAFont;

    // we create either or both of these shapers when needed, depending
    // whether the font has graphite tables, and whether graphite shaping
    // is actually enabled
    nsAutoPtr<gfxFontShaper>   mHarfBuzzShaper;
    nsAutoPtr<gfxFontShaper>   mGraphiteShaper;

    mozilla::RefPtr<mozilla::gfx::ScaledFont> mAzureScaledFont;

    // Helper for subclasses that want to initialize standard metrics from the
    // tables of sfnt (TrueType/OpenType) fonts.
    // This will use mFUnitsConvFactor if it is already set, else compute it
    // from mAdjustedSize and the unitsPerEm in the font's 'head' table.
    // Returns TRUE and sets mIsValid=TRUE if successful;
    // Returns TRUE but leaves mIsValid=FALSE if the font seems to be broken.
    // Returns FALSE if the font does not appear to be an sfnt at all,
    // and should be handled (if possible) using other APIs.
    bool InitMetricsFromSfntTables(Metrics& aMetrics);

    // Helper to calculate various derived metrics from the results of
    // InitMetricsFromSfntTables or equivalent platform code
    void CalculateDerivedMetrics(Metrics& aMetrics);

    // some fonts have bad metrics, this method sanitize them.
    // if this font has bad underline offset, aIsBadUnderlineFont should be true.
    void SanitizeMetrics(gfxFont::Metrics *aMetrics, bool aIsBadUnderlineFont);

    bool RenderSVGGlyph(gfxContext *aContext, gfxPoint aPoint, DrawMode aDrawMode,
                        uint32_t aGlyphId, gfxTextContextPaint *aContextPaint);
    bool RenderSVGGlyph(gfxContext *aContext, gfxPoint aPoint, DrawMode aDrawMode,
                        uint32_t aGlyphId, gfxTextContextPaint *aContextPaint,
                        gfxTextRunDrawCallbacks *aCallbacks,
                        bool& aEmittedGlyphs);

    bool RenderColorGlyph(gfxContext* aContext, gfxPoint& point, uint32_t aGlyphId);
    bool RenderColorGlyph(gfxContext* aContext,
                          mozilla::gfx::ScaledFont* scaledFont,
                          mozilla::gfx::GlyphRenderingOptions* renderingOptions,
                          mozilla::gfx::DrawOptions drawOptions,
                          const mozilla::gfx::Point& aPoint,
                          uint32_t aGlyphId);

    // Bug 674909. When synthetic bolding text by drawing twice, need to
    // render using a pixel offset in device pixels, otherwise text
    // doesn't appear bolded, it appears as if a bad text shadow exists
    // when a non-identity transform exists.  Use an offset factor so that
    // the second draw occurs at a constant offset in device pixels.
    // This helper calculates the scale factor we need to apply to the
    // synthetic-bold offset.
    static double CalcXScale(gfxContext *aContext);
};

// proportion of ascent used for x-height, if unable to read value from font
#define DEFAULT_XHEIGHT_FACTOR 0.56f

/*
 * gfxShapedText is an abstract superclass for gfxShapedWord and gfxTextRun.
 * These are objects that store a list of zero or more glyphs for each character.
 * For each glyph we store the glyph ID, the advance, and possibly x/y-offsets.
 * The idea is that a string is rendered by a loop that draws each glyph
 * at its designated offset from the current point, then advances the current
 * point by the glyph's advance in the direction of the textrun (LTR or RTL).
 * Each glyph advance is always rounded to the nearest appunit; this ensures
 * consistent results when dividing the text in a textrun into multiple text
 * frames (frame boundaries are always aligned to appunits). We optimize
 * for the case where a character has a single glyph and zero xoffset and yoffset,
 * and the glyph ID and advance are in a reasonable range so we can pack all
 * necessary data into 32 bits.
 *
 * gfxFontShaper can shape text into either a gfxShapedWord (cached by a gfxFont)
 * or directly into a gfxTextRun (for cases where we want to shape textruns in
 * their entirety rather than using cached words, because there may be layout
 * features that depend on the inter-word spaces).
 */
class gfxShapedText
{
public:
    gfxShapedText(uint32_t aLength, uint32_t aFlags,
                  int32_t aAppUnitsPerDevUnit)
        : mLength(aLength)
        , mFlags(aFlags)
        , mAppUnitsPerDevUnit(aAppUnitsPerDevUnit)
    { }

    virtual ~gfxShapedText() { }

    /**
     * This class records the information associated with a character in the
     * input string. It's optimized for the case where there is one glyph
     * representing that character alone.
     * 
     * A character can have zero or more associated glyphs. Each glyph
     * has an advance width and an x and y offset.
     * A character may be the start of a cluster.
     * A character may be the start of a ligature group.
     * A character can be "missing", indicating that the system is unable
     * to render the character.
     * 
     * All characters in a ligature group conceptually share all the glyphs
     * associated with the characters in a group.
     */
    class CompressedGlyph {
    public:
        CompressedGlyph() { mValue = 0; }

        enum {
            // Indicates that a cluster and ligature group starts at this
            // character; this character has a single glyph with a reasonable
            // advance and zero offsets. A "reasonable" advance
            // is one that fits in the available bits (currently 12) (specified
            // in appunits).
            FLAG_IS_SIMPLE_GLYPH  = 0x80000000U,

            // Indicates whether a linebreak is allowed before this character;
            // this is a two-bit field that holds a FLAG_BREAK_TYPE_xxx value
            // indicating the kind of linebreak (if any) allowed here.
            FLAGS_CAN_BREAK_BEFORE = 0x60000000U,

            FLAGS_CAN_BREAK_SHIFT = 29,
            FLAG_BREAK_TYPE_NONE   = 0,
            FLAG_BREAK_TYPE_NORMAL = 1,
            FLAG_BREAK_TYPE_HYPHEN = 2,

            FLAG_CHAR_IS_SPACE     = 0x10000000U,

            // The advance is stored in appunits
            ADVANCE_MASK  = 0x0FFF0000U,
            ADVANCE_SHIFT = 16,

            GLYPH_MASK = 0x0000FFFFU,

            // Non-simple glyphs may or may not have glyph data in the
            // corresponding mDetailedGlyphs entry. They have the following
            // flag bits:

            // When NOT set, indicates that this character corresponds to a
            // missing glyph and should be skipped (or possibly, render the character
            // Unicode value in some special way). If there are glyphs,
            // the mGlyphID is actually the UTF16 character code. The bit is
            // inverted so we can memset the array to zero to indicate all missing.
            FLAG_NOT_MISSING              = 0x01,
            FLAG_NOT_CLUSTER_START        = 0x02,
            FLAG_NOT_LIGATURE_GROUP_START = 0x04,

            FLAG_CHAR_IS_TAB              = 0x08,
            FLAG_CHAR_IS_NEWLINE          = 0x10,
            FLAG_CHAR_IS_LOW_SURROGATE    = 0x20,
            CHAR_IDENTITY_FLAGS_MASK      = 0x38,

            GLYPH_COUNT_MASK = 0x00FFFF00U,
            GLYPH_COUNT_SHIFT = 8
        };

        // "Simple glyphs" have a simple glyph ID, simple advance and their
        // x and y offsets are zero. Also the glyph extents do not overflow
        // the font-box defined by the font ascent, descent and glyph advance width.
        // These case is optimized to avoid storing DetailedGlyphs.

        // Returns true if the glyph ID aGlyph fits into the compressed representation
        static bool IsSimpleGlyphID(uint32_t aGlyph) {
            return (aGlyph & GLYPH_MASK) == aGlyph;
        }
        // Returns true if the advance aAdvance fits into the compressed representation.
        // aAdvance is in appunits.
        static bool IsSimpleAdvance(uint32_t aAdvance) {
            return (aAdvance & (ADVANCE_MASK >> ADVANCE_SHIFT)) == aAdvance;
        }

        bool IsSimpleGlyph() const { return (mValue & FLAG_IS_SIMPLE_GLYPH) != 0; }
        uint32_t GetSimpleAdvance() const { return (mValue & ADVANCE_MASK) >> ADVANCE_SHIFT; }
        uint32_t GetSimpleGlyph() const { return mValue & GLYPH_MASK; }

        bool IsMissing() const { return (mValue & (FLAG_NOT_MISSING|FLAG_IS_SIMPLE_GLYPH)) == 0; }
        bool IsClusterStart() const {
            return (mValue & FLAG_IS_SIMPLE_GLYPH) || !(mValue & FLAG_NOT_CLUSTER_START);
        }
        bool IsLigatureGroupStart() const {
            return (mValue & FLAG_IS_SIMPLE_GLYPH) || !(mValue & FLAG_NOT_LIGATURE_GROUP_START);
        }
        bool IsLigatureContinuation() const {
            return (mValue & FLAG_IS_SIMPLE_GLYPH) == 0 &&
                (mValue & (FLAG_NOT_LIGATURE_GROUP_START | FLAG_NOT_MISSING)) ==
                    (FLAG_NOT_LIGATURE_GROUP_START | FLAG_NOT_MISSING);
        }

        // Return true if the original character was a normal (breakable,
        // trimmable) space (U+0020). Not true for other characters that
        // may happen to map to the space glyph (U+00A0).
        bool CharIsSpace() const {
            return (mValue & FLAG_CHAR_IS_SPACE) != 0;
        }

        bool CharIsTab() const {
            return !IsSimpleGlyph() && (mValue & FLAG_CHAR_IS_TAB) != 0;
        }
        bool CharIsNewline() const {
            return !IsSimpleGlyph() && (mValue & FLAG_CHAR_IS_NEWLINE) != 0;
        }
        bool CharIsLowSurrogate() const {
            return !IsSimpleGlyph() && (mValue & FLAG_CHAR_IS_LOW_SURROGATE) != 0;
        }

        uint32_t CharIdentityFlags() const {
            return IsSimpleGlyph() ? 0 : (mValue & CHAR_IDENTITY_FLAGS_MASK);
        }

        void SetClusterStart(bool aIsClusterStart) {
            NS_ASSERTION(!IsSimpleGlyph(),
                         "can't call SetClusterStart on simple glyphs");
            if (aIsClusterStart) {
                mValue &= ~FLAG_NOT_CLUSTER_START;
            } else {
                mValue |= FLAG_NOT_CLUSTER_START;
            }
        }

        uint8_t CanBreakBefore() const {
            return (mValue & FLAGS_CAN_BREAK_BEFORE) >> FLAGS_CAN_BREAK_SHIFT;
        }
        // Returns FLAGS_CAN_BREAK_BEFORE if the setting changed, 0 otherwise
        uint32_t SetCanBreakBefore(uint8_t aCanBreakBefore) {
            NS_ASSERTION(aCanBreakBefore <= 2,
                         "Bogus break-before value!");
            uint32_t breakMask = (uint32_t(aCanBreakBefore) << FLAGS_CAN_BREAK_SHIFT);
            uint32_t toggle = breakMask ^ (mValue & FLAGS_CAN_BREAK_BEFORE);
            mValue ^= toggle;
            return toggle;
        }

        CompressedGlyph& SetSimpleGlyph(uint32_t aAdvanceAppUnits, uint32_t aGlyph) {
            NS_ASSERTION(IsSimpleAdvance(aAdvanceAppUnits), "Advance overflow");
            NS_ASSERTION(IsSimpleGlyphID(aGlyph), "Glyph overflow");
            NS_ASSERTION(!CharIdentityFlags(), "Char identity flags lost");
            mValue = (mValue & (FLAGS_CAN_BREAK_BEFORE | FLAG_CHAR_IS_SPACE)) |
                FLAG_IS_SIMPLE_GLYPH |
                (aAdvanceAppUnits << ADVANCE_SHIFT) | aGlyph;
            return *this;
        }
        CompressedGlyph& SetComplex(bool aClusterStart, bool aLigatureStart,
                uint32_t aGlyphCount) {
            mValue = (mValue & (FLAGS_CAN_BREAK_BEFORE | FLAG_CHAR_IS_SPACE)) |
                FLAG_NOT_MISSING |
                CharIdentityFlags() |
                (aClusterStart ? 0 : FLAG_NOT_CLUSTER_START) |
                (aLigatureStart ? 0 : FLAG_NOT_LIGATURE_GROUP_START) |
                (aGlyphCount << GLYPH_COUNT_SHIFT);
            return *this;
        }
        /**
         * Missing glyphs are treated as ligature group starts; don't mess with
         * the cluster-start flag (see bugs 618870 and 619286).
         */
        CompressedGlyph& SetMissing(uint32_t aGlyphCount) {
            mValue = (mValue & (FLAGS_CAN_BREAK_BEFORE | FLAG_NOT_CLUSTER_START |
                                FLAG_CHAR_IS_SPACE)) |
                CharIdentityFlags() |
                (aGlyphCount << GLYPH_COUNT_SHIFT);
            return *this;
        }
        uint32_t GetGlyphCount() const {
            NS_ASSERTION(!IsSimpleGlyph(), "Expected non-simple-glyph");
            return (mValue & GLYPH_COUNT_MASK) >> GLYPH_COUNT_SHIFT;
        }

        void SetIsSpace() {
            mValue |= FLAG_CHAR_IS_SPACE;
        }
        void SetIsTab() {
            NS_ASSERTION(!IsSimpleGlyph(), "Expected non-simple-glyph");
            mValue |= FLAG_CHAR_IS_TAB;
        }
        void SetIsNewline() {
            NS_ASSERTION(!IsSimpleGlyph(), "Expected non-simple-glyph");
            mValue |= FLAG_CHAR_IS_NEWLINE;
        }
        void SetIsLowSurrogate() {
            NS_ASSERTION(!IsSimpleGlyph(), "Expected non-simple-glyph");
            mValue |= FLAG_CHAR_IS_LOW_SURROGATE;
        }

    private:
        uint32_t mValue;
    };

    // Accessor for the array of CompressedGlyph records, which will be in
    // a different place in gfxShapedWord vs gfxTextRun
    virtual CompressedGlyph *GetCharacterGlyphs() = 0;

    /**
     * When the glyphs for a character don't fit into a CompressedGlyph record
     * in SimpleGlyph format, we use an array of DetailedGlyphs instead.
     */
    struct DetailedGlyph {
        /** The glyphID, or the Unicode character
         * if this is a missing glyph */
        uint32_t mGlyphID;
        /** The advance, x-offset and y-offset of the glyph, in appunits
         *  mAdvance is in the text direction (RTL or LTR)
         *  mXOffset is always from left to right
         *  mYOffset is always from top to bottom */   
        int32_t  mAdvance;
        float    mXOffset, mYOffset;
    };

    void SetGlyphs(uint32_t aCharIndex, CompressedGlyph aGlyph,
                   const DetailedGlyph *aGlyphs);

    void SetMissingGlyph(uint32_t aIndex, uint32_t aChar, gfxFont *aFont);

    void SetIsSpace(uint32_t aIndex) {
        GetCharacterGlyphs()[aIndex].SetIsSpace();
    }

    void SetIsLowSurrogate(uint32_t aIndex) {
        SetGlyphs(aIndex, CompressedGlyph().SetComplex(false, false, 0), nullptr);
        GetCharacterGlyphs()[aIndex].SetIsLowSurrogate();
    }

    bool HasDetailedGlyphs() const {
        return mDetailedGlyphs != nullptr;
    }

    bool IsClusterStart(uint32_t aPos) {
        NS_ASSERTION(aPos < GetLength(), "aPos out of range");
        return GetCharacterGlyphs()[aPos].IsClusterStart();
    }

    bool IsLigatureGroupStart(uint32_t aPos) {
        NS_ASSERTION(aPos < GetLength(), "aPos out of range");
        return GetCharacterGlyphs()[aPos].IsLigatureGroupStart();
    }

    // NOTE that this must not be called for a character offset that does
    // not have any DetailedGlyph records; callers must have verified that
    // GetCharacterGlyphs()[aCharIndex].GetGlyphCount() is greater than zero.
    DetailedGlyph *GetDetailedGlyphs(uint32_t aCharIndex) {
        NS_ASSERTION(GetCharacterGlyphs() && HasDetailedGlyphs() &&
                     !GetCharacterGlyphs()[aCharIndex].IsSimpleGlyph() &&
                     GetCharacterGlyphs()[aCharIndex].GetGlyphCount() > 0,
                     "invalid use of GetDetailedGlyphs; check the caller!");
        return mDetailedGlyphs->Get(aCharIndex);
    }

    void AdjustAdvancesForSyntheticBold(float aSynBoldOffset,
                                        uint32_t aOffset, uint32_t aLength);

    // Mark clusters in the CompressedGlyph records, starting at aOffset,
    // based on the Unicode properties of the text in aString.
    // This is also responsible to set the IsSpace flag for space characters.
    void SetupClusterBoundaries(uint32_t         aOffset,
                                const char16_t *aString,
                                uint32_t         aLength);
    // In 8-bit text, there won't actually be any clusters, but we still need
    // the space-marking functionality.
    void SetupClusterBoundaries(uint32_t       aOffset,
                                const uint8_t *aString,
                                uint32_t       aLength);

    uint32_t Flags() const {
        return mFlags;
    }

    bool IsRightToLeft() const {
        return (Flags() & gfxTextRunFactory::TEXT_IS_RTL) != 0;
    }

    float GetDirection() const {
        return IsRightToLeft() ? -1.0f : 1.0f;
    }

    bool DisableLigatures() const {
        return (Flags() & gfxTextRunFactory::TEXT_DISABLE_OPTIONAL_LIGATURES) != 0;
    }

    bool TextIs8Bit() const {
        return (Flags() & gfxTextRunFactory::TEXT_IS_8BIT) != 0;
    }

    int32_t GetAppUnitsPerDevUnit() const {
        return mAppUnitsPerDevUnit;
    }

    uint32_t GetLength() const {
        return mLength;
    }

    bool FilterIfIgnorable(uint32_t aIndex, uint32_t aCh);

protected:
    // Allocate aCount DetailedGlyphs for the given index
    DetailedGlyph *AllocateDetailedGlyphs(uint32_t aCharIndex,
                                          uint32_t aCount);

    // For characters whose glyph data does not fit the "simple" glyph criteria
    // in CompressedGlyph, we use a sorted array to store the association
    // between the source character offset and an index into an array 
    // DetailedGlyphs. The CompressedGlyph record includes a count of
    // the number of DetailedGlyph records that belong to the character,
    // starting at the given index.
    class DetailedGlyphStore {
    public:
        DetailedGlyphStore()
            : mLastUsed(0)
        { }

        // This is optimized for the most common calling patterns:
        // we rarely need random access to the records, access is most commonly
        // sequential through the textRun, so we record the last-used index
        // and check whether the caller wants the same record again, or the
        // next; if not, it's most likely we're starting over from the start
        // of the run, so we check the first entry before resorting to binary
        // search as a last resort.
        // NOTE that this must not be called for a character offset that does
        // not have any DetailedGlyph records; callers must have verified that
        // mCharacterGlyphs[aOffset].GetGlyphCount() is greater than zero
        // before calling this, otherwise the assertions here will fire (in a
        // debug build), and we'll probably crash.
        DetailedGlyph* Get(uint32_t aOffset) {
            NS_ASSERTION(mOffsetToIndex.Length() > 0,
                         "no detailed glyph records!");
            DetailedGlyph* details = mDetails.Elements();
            // check common cases (fwd iteration, initial entry, etc) first
            if (mLastUsed < mOffsetToIndex.Length() - 1 &&
                aOffset == mOffsetToIndex[mLastUsed + 1].mOffset) {
                ++mLastUsed;
            } else if (aOffset == mOffsetToIndex[0].mOffset) {
                mLastUsed = 0;
            } else if (aOffset == mOffsetToIndex[mLastUsed].mOffset) {
                // do nothing
            } else if (mLastUsed > 0 &&
                       aOffset == mOffsetToIndex[mLastUsed - 1].mOffset) {
                --mLastUsed;
            } else {
                mLastUsed =
                    mOffsetToIndex.BinaryIndexOf(aOffset, CompareToOffset());
            }
            NS_ASSERTION(mLastUsed != nsTArray<DGRec>::NoIndex,
                         "detailed glyph record missing!");
            return details + mOffsetToIndex[mLastUsed].mIndex;
        }

        DetailedGlyph* Allocate(uint32_t aOffset, uint32_t aCount) {
            uint32_t detailIndex = mDetails.Length();
            DetailedGlyph *details = mDetails.AppendElements(aCount);
            // We normally set up glyph records sequentially, so the common case
            // here is to append new records to the mOffsetToIndex array;
            // test for that before falling back to the InsertElementSorted
            // method.
            if (mOffsetToIndex.Length() == 0 ||
                aOffset > mOffsetToIndex[mOffsetToIndex.Length() - 1].mOffset) {
                mOffsetToIndex.AppendElement(DGRec(aOffset, detailIndex));
            } else {
                mOffsetToIndex.InsertElementSorted(DGRec(aOffset, detailIndex),
                                                   CompareRecordOffsets());
            }
            return details;
        }

        size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) {
            return aMallocSizeOf(this) +
                mDetails.SizeOfExcludingThis(aMallocSizeOf) +
                mOffsetToIndex.SizeOfExcludingThis(aMallocSizeOf);
        }

    private:
        struct DGRec {
            DGRec(const uint32_t& aOffset, const uint32_t& aIndex)
                : mOffset(aOffset), mIndex(aIndex) { }
            uint32_t mOffset; // source character offset in the textrun
            uint32_t mIndex;  // index where this char's DetailedGlyphs begin
        };

        struct CompareToOffset {
            bool Equals(const DGRec& a, const uint32_t& b) const {
                return a.mOffset == b;
            }
            bool LessThan(const DGRec& a, const uint32_t& b) const {
                return a.mOffset < b;
            }
        };

        struct CompareRecordOffsets {
            bool Equals(const DGRec& a, const DGRec& b) const {
                return a.mOffset == b.mOffset;
            }
            bool LessThan(const DGRec& a, const DGRec& b) const {
                return a.mOffset < b.mOffset;
            }
        };

        // Concatenated array of all the DetailedGlyph records needed for the
        // textRun; individual character offsets are associated with indexes
        // into this array via the mOffsetToIndex table.
        nsTArray<DetailedGlyph>     mDetails;

        // For each character offset that needs DetailedGlyphs, we record the
        // index in mDetails where the list of glyphs begins. This array is
        // sorted by mOffset.
        nsTArray<DGRec>             mOffsetToIndex;

        // Records the most recently used index into mOffsetToIndex, so that
        // we can support sequential access more quickly than just doing
        // a binary search each time.
        nsTArray<DGRec>::index_type mLastUsed;
    };

    nsAutoPtr<DetailedGlyphStore>   mDetailedGlyphs;

    // Number of char16_t characters and CompressedGlyph glyph records
    uint32_t                        mLength;

    // Shaping flags (direction, ligature-suppression)
    uint32_t                        mFlags;

    int32_t                         mAppUnitsPerDevUnit;
};

/*
 * gfxShapedWord: an individual (space-delimited) run of text shaped with a
 * particular font, without regard to external context.
 *
 * The glyph data is copied into gfxTextRuns as needed from the cache of
 * ShapedWords associated with each gfxFont instance.
 */
class gfxShapedWord : public gfxShapedText
{
public:
    // Create a ShapedWord that can hold glyphs for aLength characters,
    // with mCharacterGlyphs sized appropriately.
    //
    // Returns null on allocation failure (does NOT use infallible alloc)
    // so caller must check for success.
    //
    // This does NOT perform shaping, so the returned word contains no
    // glyph data; the caller must call gfxFont::ShapeText() with appropriate
    // parameters to set up the glyphs.
    static gfxShapedWord* Create(const uint8_t *aText, uint32_t aLength,
                                 int32_t aRunScript,
                                 int32_t aAppUnitsPerDevUnit,
                                 uint32_t aFlags) {
        NS_ASSERTION(aLength <= gfxPlatform::GetPlatform()->WordCacheCharLimit(),
                     "excessive length for gfxShapedWord!");

        // Compute size needed including the mCharacterGlyphs array
        // and a copy of the original text
        uint32_t size =
            offsetof(gfxShapedWord, mCharGlyphsStorage) +
            aLength * (sizeof(CompressedGlyph) + sizeof(uint8_t));
        void *storage = moz_malloc(size);
        if (!storage) {
            return nullptr;
        }

        // Construct in the pre-allocated storage, using placement new
        return new (storage) gfxShapedWord(aText, aLength, aRunScript,
                                           aAppUnitsPerDevUnit, aFlags);
    }

    static gfxShapedWord* Create(const char16_t *aText, uint32_t aLength,
                                 int32_t aRunScript,
                                 int32_t aAppUnitsPerDevUnit,
                                 uint32_t aFlags) {
        NS_ASSERTION(aLength <= gfxPlatform::GetPlatform()->WordCacheCharLimit(),
                     "excessive length for gfxShapedWord!");

        // In the 16-bit version of Create, if the TEXT_IS_8BIT flag is set,
        // then we convert the text to an 8-bit version and call the 8-bit
        // Create function instead.
        if (aFlags & gfxTextRunFactory::TEXT_IS_8BIT) {
            nsAutoCString narrowText;
            LossyAppendUTF16toASCII(nsDependentSubstring(aText, aLength),
                                    narrowText);
            return Create((const uint8_t*)(narrowText.BeginReading()),
                          aLength, aRunScript, aAppUnitsPerDevUnit, aFlags);
        }

        uint32_t size =
            offsetof(gfxShapedWord, mCharGlyphsStorage) +
            aLength * (sizeof(CompressedGlyph) + sizeof(char16_t));
        void *storage = moz_malloc(size);
        if (!storage) {
            return nullptr;
        }

        return new (storage) gfxShapedWord(aText, aLength, aRunScript,
                                           aAppUnitsPerDevUnit, aFlags);
    }

    // Override operator delete to properly free the object that was
    // allocated via moz_malloc.
    void operator delete(void* p) {
        moz_free(p);
    }

    CompressedGlyph *GetCharacterGlyphs() {
        return &mCharGlyphsStorage[0];
    }

    const uint8_t* Text8Bit() const {
        NS_ASSERTION(TextIs8Bit(), "invalid use of Text8Bit()");
        return reinterpret_cast<const uint8_t*>(mCharGlyphsStorage + GetLength());
    }

    const char16_t* TextUnicode() const {
        NS_ASSERTION(!TextIs8Bit(), "invalid use of TextUnicode()");
        return reinterpret_cast<const char16_t*>(mCharGlyphsStorage + GetLength());
    }

    char16_t GetCharAt(uint32_t aOffset) const {
        NS_ASSERTION(aOffset < GetLength(), "aOffset out of range");
        return TextIs8Bit() ?
            char16_t(Text8Bit()[aOffset]) : TextUnicode()[aOffset];
    }

    int32_t Script() const {
        return mScript;
    }

    void ResetAge() {
        mAgeCounter = 0;
    }
    uint32_t IncrementAge() {
        return ++mAgeCounter;
    }

private:
    // so that gfxTextRun can share our DetailedGlyphStore class
    friend class gfxTextRun;

    // Construct storage for a ShapedWord, ready to receive glyph data
    gfxShapedWord(const uint8_t *aText, uint32_t aLength,
                  int32_t aRunScript, int32_t aAppUnitsPerDevUnit,
                  uint32_t aFlags)
        : gfxShapedText(aLength, aFlags | gfxTextRunFactory::TEXT_IS_8BIT,
                        aAppUnitsPerDevUnit)
        , mScript(aRunScript)
        , mAgeCounter(0)
    {
        memset(mCharGlyphsStorage, 0, aLength * sizeof(CompressedGlyph));
        uint8_t *text = reinterpret_cast<uint8_t*>(&mCharGlyphsStorage[aLength]);
        memcpy(text, aText, aLength * sizeof(uint8_t));
    }

    gfxShapedWord(const char16_t *aText, uint32_t aLength,
                  int32_t aRunScript, int32_t aAppUnitsPerDevUnit,
                  uint32_t aFlags)
        : gfxShapedText(aLength, aFlags, aAppUnitsPerDevUnit)
        , mScript(aRunScript)
        , mAgeCounter(0)
    {
        memset(mCharGlyphsStorage, 0, aLength * sizeof(CompressedGlyph));
        char16_t *text = reinterpret_cast<char16_t*>(&mCharGlyphsStorage[aLength]);
        memcpy(text, aText, aLength * sizeof(char16_t));
        SetupClusterBoundaries(0, aText, aLength);
    }

    int32_t          mScript;

    uint32_t         mAgeCounter;

    // The mCharGlyphsStorage array is actually a variable-size member;
    // when the ShapedWord is created, its size will be increased as necessary
    // to allow the proper number of glyphs to be stored.
    // The original text, in either 8-bit or 16-bit form, will be stored
    // immediately following the CompressedGlyphs.
    CompressedGlyph  mCharGlyphsStorage[1];
};

/**
 * Callback for Draw() to use when drawing text with mode
 * DrawMode::GLYPH_PATH.
 */
struct gfxTextRunDrawCallbacks {

    /**
     * Constructs a new DrawCallbacks object.
     *
     * @param aShouldPaintSVGGlyphs If true, SVG glyphs will be
     *   painted and the NotifyBeforeSVGGlyphPainted/NotifyAfterSVGGlyphPainted
     *   callbacks will be invoked for each SVG glyph.  If false, SVG glyphs
     *   will not be painted; fallback plain glyphs are not emitted either.
     */
    gfxTextRunDrawCallbacks(bool aShouldPaintSVGGlyphs = false)
      : mShouldPaintSVGGlyphs(aShouldPaintSVGGlyphs)
    {
    }

    /**
     * Called when a path has been emitted to the gfxContext when
     * painting a text run.  This can be called any number of times,
     * due to partial ligatures and intervening SVG glyphs.
     */
    virtual void NotifyGlyphPathEmitted() = 0;

    /**
     * Called just before an SVG glyph has been painted to the gfxContext.
     */
    virtual void NotifyBeforeSVGGlyphPainted() { }

    /**
     * Called just after an SVG glyph has been painted to the gfxContext.
     */
    virtual void NotifyAfterSVGGlyphPainted() { }

    bool mShouldPaintSVGGlyphs;
};

/**
 * gfxTextRun is an abstraction for drawing and measuring substrings of a run
 * of text. It stores runs of positioned glyph data, each run having a single
 * gfxFont. The glyphs are associated with a string of source text, and the
 * gfxTextRun APIs take parameters that are offsets into that source text.
 * 
 * gfxTextRuns are not refcounted. They should be deleted when no longer required.
 * 
 * gfxTextRuns are mostly immutable. The only things that can change are
 * inter-cluster spacing and line break placement. Spacing is always obtained
 * lazily by methods that need it, it is not cached. Line breaks are stored
 * persistently (insofar as they affect the shaping of glyphs; gfxTextRun does
 * not actually do anything to explicitly account for line breaks). Initially
 * there are no line breaks. The textrun can record line breaks before or after
 * any given cluster. (Line breaks specified inside clusters are ignored.)
 * 
 * It is important that zero-length substrings are handled correctly. This will
 * be on the test!
 */
class gfxTextRun : public gfxShapedText {
public:

    // Override operator delete to properly free the object that was
    // allocated via moz_malloc.
    void operator delete(void* p) {
        moz_free(p);
    }

    virtual ~gfxTextRun();

    typedef gfxFont::RunMetrics Metrics;

    // Public textrun API for general use

    bool IsClusterStart(uint32_t aPos) {
        NS_ASSERTION(aPos < GetLength(), "aPos out of range");
        return mCharacterGlyphs[aPos].IsClusterStart();
    }
    bool IsLigatureGroupStart(uint32_t aPos) {
        NS_ASSERTION(aPos < GetLength(), "aPos out of range");
        return mCharacterGlyphs[aPos].IsLigatureGroupStart();
    }
    bool CanBreakLineBefore(uint32_t aPos) {
        NS_ASSERTION(aPos < GetLength(), "aPos out of range");
        return mCharacterGlyphs[aPos].CanBreakBefore() ==
            CompressedGlyph::FLAG_BREAK_TYPE_NORMAL;
    }
    bool CanHyphenateBefore(uint32_t aPos) {
        NS_ASSERTION(aPos < GetLength(), "aPos out of range");
        return mCharacterGlyphs[aPos].CanBreakBefore() ==
            CompressedGlyph::FLAG_BREAK_TYPE_HYPHEN;
    }

    bool CharIsSpace(uint32_t aPos) {
        NS_ASSERTION(aPos < GetLength(), "aPos out of range");
        return mCharacterGlyphs[aPos].CharIsSpace();
    }
    bool CharIsTab(uint32_t aPos) {
        NS_ASSERTION(aPos < GetLength(), "aPos out of range");
        return mCharacterGlyphs[aPos].CharIsTab();
    }
    bool CharIsNewline(uint32_t aPos) {
        NS_ASSERTION(aPos < GetLength(), "aPos out of range");
        return mCharacterGlyphs[aPos].CharIsNewline();
    }
    bool CharIsLowSurrogate(uint32_t aPos) {
        NS_ASSERTION(aPos < GetLength(), "aPos out of range");
        return mCharacterGlyphs[aPos].CharIsLowSurrogate();
    }

    uint32_t GetLength() { return mLength; }

    // All uint32_t aStart, uint32_t aLength ranges below are restricted to
    // grapheme cluster boundaries! All offsets are in terms of the string
    // passed into MakeTextRun.
    
    // All coordinates are in layout/app units

    /**
     * Set the potential linebreaks for a substring of the textrun. These are
     * the "allow break before" points. Initially, there are no potential
     * linebreaks.
     * 
     * This can change glyphs and/or geometry! Some textruns' shapes
     * depend on potential line breaks (e.g., title-case-converting textruns).
     * This function is virtual so that those textruns can reshape themselves.
     * 
     * @return true if this changed the linebreaks, false if the new line
     * breaks are the same as the old
     */
    virtual bool SetPotentialLineBreaks(uint32_t aStart, uint32_t aLength,
                                          uint8_t *aBreakBefore,
                                          gfxContext *aRefContext);

    /**
     * Layout provides PropertyProvider objects. These allow detection of
     * potential line break points and computation of spacing. We pass the data
     * this way to allow lazy data acquisition; for example BreakAndMeasureText
     * will want to only ask for properties of text it's actually looking at.
     * 
     * NOTE that requested spacing may not actually be applied, if the textrun
     * is unable to apply it in some context. Exception: spacing around a
     * whitespace character MUST always be applied.
     */
    class PropertyProvider {
    public:
        // Detect hyphenation break opportunities in the given range; breaks
        // not at cluster boundaries will be ignored.
        virtual void GetHyphenationBreaks(uint32_t aStart, uint32_t aLength,
                                          bool *aBreakBefore) = 0;

        // Returns the provider's hyphenation setting, so callers can decide
        // whether it is necessary to call GetHyphenationBreaks.
        // Result is an NS_STYLE_HYPHENS_* value.
        virtual int8_t GetHyphensOption() = 0;

        // Returns the extra width that will be consumed by a hyphen. This should
        // be constant for a given textrun.
        virtual gfxFloat GetHyphenWidth() = 0;

        typedef gfxFont::Spacing Spacing;

        /**
         * Get the spacing around the indicated characters. Spacing must be zero
         * inside clusters. In other words, if character i is not
         * CLUSTER_START, then character i-1 must have zero after-spacing and
         * character i must have zero before-spacing.
         */
        virtual void GetSpacing(uint32_t aStart, uint32_t aLength,
                                Spacing *aSpacing) = 0;

        // Returns a gfxContext that can be used to measure the hyphen glyph.
        // Only called if the hyphen width is requested.
        virtual already_AddRefed<gfxContext> GetContext() = 0;

        // Return the appUnitsPerDevUnit value to be used when measuring.
        // Only called if the hyphen width is requested.
        virtual uint32_t GetAppUnitsPerDevUnit() = 0;
    };

    class ClusterIterator {
    public:
        ClusterIterator(gfxTextRun *aTextRun);

        void Reset();

        bool NextCluster();

        uint32_t Position() const {
            return mCurrentChar;
        }

        uint32_t ClusterLength() const;

        gfxFloat ClusterAdvance(PropertyProvider *aProvider) const;

    private:
        gfxTextRun *mTextRun;
        uint32_t    mCurrentChar;
    };

    /**
     * Draws a substring. Uses only GetSpacing from aBreakProvider.
     * The provided point is the baseline origin on the left of the string
     * for LTR, on the right of the string for RTL.
     * @param aAdvanceWidth if non-null, the advance width of the substring
     * is returned here.
     * 
     * Drawing should respect advance widths in the sense that for LTR runs,
     * Draw(ctx, pt, offset1, length1, dirty, &provider, &advance) followed by
     * Draw(ctx, gfxPoint(pt.x + advance, pt.y), offset1 + length1, length2,
     *      dirty, &provider, nullptr) should have the same effect as
     * Draw(ctx, pt, offset1, length1+length2, dirty, &provider, nullptr).
     * For RTL runs the rule is:
     * Draw(ctx, pt, offset1 + length1, length2, dirty, &provider, &advance) followed by
     * Draw(ctx, gfxPoint(pt.x + advance, pt.y), offset1, length1,
     *      dirty, &provider, nullptr) should have the same effect as
     * Draw(ctx, pt, offset1, length1+length2, dirty, &provider, nullptr).
     * 
     * Glyphs should be drawn in logical content order, which can be significant
     * if they overlap (perhaps due to negative spacing).
     */
    void Draw(gfxContext *aContext, gfxPoint aPt,
              DrawMode aDrawMode,
              uint32_t aStart, uint32_t aLength,
              PropertyProvider *aProvider,
              gfxFloat *aAdvanceWidth, gfxTextContextPaint *aContextPaint,
              gfxTextRunDrawCallbacks *aCallbacks = nullptr);

    /**
     * Computes the ReflowMetrics for a substring.
     * Uses GetSpacing from aBreakProvider.
     * @param aBoundingBoxType which kind of bounding box (loose/tight)
     */
    Metrics MeasureText(uint32_t aStart, uint32_t aLength,
                        gfxFont::BoundingBoxType aBoundingBoxType,
                        gfxContext *aRefContextForTightBoundingBox,
                        PropertyProvider *aProvider);

    /**
     * Computes just the advance width for a substring.
     * Uses GetSpacing from aBreakProvider.
     */
    gfxFloat GetAdvanceWidth(uint32_t aStart, uint32_t aLength,
                             PropertyProvider *aProvider);

    /**
     * Clear all stored line breaks for the given range (both before and after),
     * and then set the line-break state before aStart to aBreakBefore and
     * after the last cluster to aBreakAfter.
     * 
     * We require that before and after line breaks be consistent. For clusters
     * i and i+1, we require that if there is a break after cluster i, a break
     * will be specified before cluster i+1. This may be temporarily violated
     * (e.g. after reflowing line L and before reflowing line L+1); to handle
     * these temporary violations, we say that there is a break betwen i and i+1
     * if a break is specified after i OR a break is specified before i+1.
     * 
     * This can change textrun geometry! The existence of a linebreak can affect
     * the advance width of the cluster before the break (when kerning) or the
     * geometry of one cluster before the break or any number of clusters
     * after the break. (The one-cluster-before-the-break limit is somewhat
     * arbitrary; if some scripts require breaking it, then we need to
     * alter nsTextFrame::TrimTrailingWhitespace, perhaps drastically becase
     * it could affect the layout of frames before it...)
     * 
     * We return true if glyphs or geometry changed, false otherwise. This
     * function is virtual so that gfxTextRun subclasses can reshape
     * properly.
     * 
     * @param aAdvanceWidthDelta if non-null, returns the change in advance
     * width of the given range.
     */
    virtual bool SetLineBreaks(uint32_t aStart, uint32_t aLength,
                                 bool aLineBreakBefore, bool aLineBreakAfter,
                                 gfxFloat *aAdvanceWidthDelta,
                                 gfxContext *aRefContext);

    /**
     * Finds the longest substring that will fit into the given width.
     * Uses GetHyphenationBreaks and GetSpacing from aBreakProvider.
     * Guarantees the following:
     * -- 0 <= result <= aMaxLength
     * -- result is the maximal value of N such that either
     *       N < aMaxLength && line break at N && GetAdvanceWidth(aStart, N) <= aWidth
     *   OR  N < aMaxLength && hyphen break at N && GetAdvanceWidth(aStart, N) + GetHyphenWidth() <= aWidth
     *   OR  N == aMaxLength && GetAdvanceWidth(aStart, N) <= aWidth
     * where GetAdvanceWidth assumes the effect of
     * SetLineBreaks(aStart, N, aLineBreakBefore, N < aMaxLength, aProvider)
     * -- if no such N exists, then result is the smallest N such that
     *       N < aMaxLength && line break at N
     *   OR  N < aMaxLength && hyphen break at N
     *   OR  N == aMaxLength
     *
     * The call has the effect of
     * SetLineBreaks(aStart, result, aLineBreakBefore, result < aMaxLength, aProvider)
     * and the returned metrics and the invariants above reflect this.
     *
     * @param aMaxLength this can be UINT32_MAX, in which case the length used
     * is up to the end of the string
     * @param aLineBreakBefore set to true if and only if there is an actual
     * line break at the start of this string.
     * @param aSuppressInitialBreak if true, then we assume there is no possible
     * linebreak before aStart. If false, then we will check the internal
     * line break opportunity state before deciding whether to return 0 as the
     * character to break before.
     * @param aTrimWhitespace if non-null, then we allow a trailing run of
     * spaces to be trimmed; the width of the space(s) will not be included in
     * the measured string width for comparison with the limit aWidth, and
     * trimmed spaces will not be included in returned metrics. The width
     * of the trimmed spaces will be returned in aTrimWhitespace.
     * Trimmed spaces are still counted in the "characters fit" result.
     * @param aMetrics if non-null, we fill this in for the returned substring.
     * If a hyphenation break was used, the hyphen is NOT included in the returned metrics.
     * @param aBoundingBoxType whether to make the bounding box in aMetrics tight
     * @param aRefContextForTightBoundingBox a reference context to get the
     * tight bounding box, if requested
     * @param aUsedHyphenation if non-null, records if we selected a hyphenation break
     * @param aLastBreak if non-null and result is aMaxLength, we set this to
     * the maximal N such that
     *       N < aMaxLength && line break at N && GetAdvanceWidth(aStart, N) <= aWidth
     *   OR  N < aMaxLength && hyphen break at N && GetAdvanceWidth(aStart, N) + GetHyphenWidth() <= aWidth
     * or UINT32_MAX if no such N exists, where GetAdvanceWidth assumes
     * the effect of
     * SetLineBreaks(aStart, N, aLineBreakBefore, N < aMaxLength, aProvider)
     *
     * @param aCanWordWrap true if we can break between any two grapheme
     * clusters. This is set by word-wrap: break-word
     *
     * @param aBreakPriority in/out the priority of the break opportunity
     * saved in the line. If we are prioritizing break opportunities, we will
     * not set a break with a lower priority. @see gfxBreakPriority.
     * 
     * Note that negative advance widths are possible especially if negative
     * spacing is provided.
     */
    uint32_t BreakAndMeasureText(uint32_t aStart, uint32_t aMaxLength,
                                 bool aLineBreakBefore, gfxFloat aWidth,
                                 PropertyProvider *aProvider,
                                 bool aSuppressInitialBreak,
                                 gfxFloat *aTrimWhitespace,
                                 Metrics *aMetrics,
                                 gfxFont::BoundingBoxType aBoundingBoxType,
                                 gfxContext *aRefContextForTightBoundingBox,
                                 bool *aUsedHyphenation,
                                 uint32_t *aLastBreak,
                                 bool aCanWordWrap,
                                 gfxBreakPriority *aBreakPriority);

    /**
     * Update the reference context.
     * XXX this is a hack. New text frame does not call this. Use only
     * temporarily for old text frame.
     */
    void SetContext(gfxContext *aContext) {}

    // Utility getters

    gfxFloat GetDirection() const { return (mFlags & gfxTextRunFactory::TEXT_IS_RTL) ? -1.0 : 1.0; }
    void *GetUserData() const { return mUserData; }
    void SetUserData(void *aUserData) { mUserData = aUserData; }
    uint32_t GetFlags() const { return mFlags; }
    void SetFlagBits(uint32_t aFlags) {
      NS_ASSERTION(!(aFlags & ~gfxTextRunFactory::SETTABLE_FLAGS),
                   "Only user flags should be mutable");
      mFlags |= aFlags;
    }
    void ClearFlagBits(uint32_t aFlags) {
      NS_ASSERTION(!(aFlags & ~gfxTextRunFactory::SETTABLE_FLAGS),
                   "Only user flags should be mutable");
      mFlags &= ~aFlags;
    }
    const gfxSkipChars& GetSkipChars() const { return mSkipChars; }
    gfxFontGroup *GetFontGroup() const { return mFontGroup; }


    // Call this, don't call "new gfxTextRun" directly. This does custom
    // allocation and initialization
    static gfxTextRun *Create(const gfxTextRunFactory::Parameters *aParams,
                              uint32_t aLength, gfxFontGroup *aFontGroup,
                              uint32_t aFlags);

    // The text is divided into GlyphRuns as necessary
    struct GlyphRun {
        nsRefPtr<gfxFont> mFont;   // never null
        uint32_t          mCharacterOffset; // into original UTF16 string
        uint8_t           mMatchType;
    };

    class GlyphRunIterator {
    public:
        GlyphRunIterator(gfxTextRun *aTextRun, uint32_t aStart, uint32_t aLength)
          : mTextRun(aTextRun), mStartOffset(aStart), mEndOffset(aStart + aLength) {
            mNextIndex = mTextRun->FindFirstGlyphRunContaining(aStart);
        }
        bool NextRun();
        GlyphRun *GetGlyphRun() { return mGlyphRun; }
        uint32_t GetStringStart() { return mStringStart; }
        uint32_t GetStringEnd() { return mStringEnd; }
    private:
        gfxTextRun *mTextRun;
        GlyphRun   *mGlyphRun;
        uint32_t    mStringStart;
        uint32_t    mStringEnd;
        uint32_t    mNextIndex;
        uint32_t    mStartOffset;
        uint32_t    mEndOffset;
    };

    class GlyphRunOffsetComparator {
    public:
        bool Equals(const GlyphRun& a,
                      const GlyphRun& b) const
        {
            return a.mCharacterOffset == b.mCharacterOffset;
        }

        bool LessThan(const GlyphRun& a,
                        const GlyphRun& b) const
        {
            return a.mCharacterOffset < b.mCharacterOffset;
        }
    };

    friend class GlyphRunIterator;
    friend class FontSelector;

    // API for setting up the textrun glyphs. Should only be called by
    // things that construct textruns.
    /**
     * We've found a run of text that should use a particular font. Call this
     * only during initialization when font substitution has been computed.
     * Call it before setting up the glyphs for the characters in this run;
     * SetMissingGlyph requires that the correct glyphrun be installed.
     *
     * If aForceNewRun, a new glyph run will be added, even if the
     * previously added run uses the same font.  If glyph runs are
     * added out of strictly increasing aStartCharIndex order (via
     * force), then SortGlyphRuns must be called after all glyph runs
     * are added before any further operations are performed with this
     * TextRun.
     */
    nsresult AddGlyphRun(gfxFont *aFont, uint8_t aMatchType,
                         uint32_t aStartCharIndex, bool aForceNewRun);
    void ResetGlyphRuns() { mGlyphRuns.Clear(); }
    void SortGlyphRuns();
    void SanitizeGlyphRuns();

    CompressedGlyph* GetCharacterGlyphs() {
        NS_ASSERTION(mCharacterGlyphs, "failed to initialize mCharacterGlyphs");
        return mCharacterGlyphs;
    }

    // clean out results from shaping in progress, used for fallback scenarios
    void ClearGlyphsAndCharacters();

    void SetSpaceGlyph(gfxFont *aFont, gfxContext *aContext, uint32_t aCharIndex);

    // Set the glyph data for the given character index to the font's
    // space glyph, IF this can be done as a "simple" glyph record
    // (not requiring a DetailedGlyph entry). This avoids the need to call
    // the font shaper and go through the shaped-word cache for most spaces.
    //
    // The parameter aSpaceChar is the original character code for which
    // this space glyph is being used; if this is U+0020, we need to record
    // that it could be trimmed at a run edge, whereas other kinds of space
    // (currently just U+00A0) would not be trimmable/breakable.
    //
    // Returns true if it was able to set simple glyph data for the space;
    // if it returns false, the caller needs to fall back to some other
    // means to create the necessary (detailed) glyph data.
    bool SetSpaceGlyphIfSimple(gfxFont *aFont, gfxContext *aContext,
                               uint32_t aCharIndex, char16_t aSpaceChar);

    // Record the positions of specific characters that layout may need to
    // detect in the textrun, even though it doesn't have an explicit copy
    // of the original text. These are recorded using flag bits in the
    // CompressedGlyph record; if necessary, we convert "simple" glyph records
    // to "complex" ones as the Tab and Newline flags are not present in
    // simple CompressedGlyph records.
    void SetIsTab(uint32_t aIndex) {
        CompressedGlyph *g = &mCharacterGlyphs[aIndex];
        if (g->IsSimpleGlyph()) {
            DetailedGlyph *details = AllocateDetailedGlyphs(aIndex, 1);
            details->mGlyphID = g->GetSimpleGlyph();
            details->mAdvance = g->GetSimpleAdvance();
            details->mXOffset = details->mYOffset = 0;
            SetGlyphs(aIndex, CompressedGlyph().SetComplex(true, true, 1), details);
        }
        g->SetIsTab();
    }
    void SetIsNewline(uint32_t aIndex) {
        CompressedGlyph *g = &mCharacterGlyphs[aIndex];
        if (g->IsSimpleGlyph()) {
            DetailedGlyph *details = AllocateDetailedGlyphs(aIndex, 1);
            details->mGlyphID = g->GetSimpleGlyph();
            details->mAdvance = g->GetSimpleAdvance();
            details->mXOffset = details->mYOffset = 0;
            SetGlyphs(aIndex, CompressedGlyph().SetComplex(true, true, 1), details);
        }
        g->SetIsNewline();
    }
    void SetIsLowSurrogate(uint32_t aIndex) {
        SetGlyphs(aIndex, CompressedGlyph().SetComplex(false, false, 0), nullptr);
        mCharacterGlyphs[aIndex].SetIsLowSurrogate();
    }

    /**
     * Prefetch all the glyph extents needed to ensure that Measure calls
     * on this textrun not requesting tight boundingBoxes will succeed. Note
     * that some glyph extents might not be fetched due to OOM or other
     * errors.
     */
    void FetchGlyphExtents(gfxContext *aRefContext);

    uint32_t CountMissingGlyphs();
    const GlyphRun *GetGlyphRuns(uint32_t *aNumGlyphRuns) {
        *aNumGlyphRuns = mGlyphRuns.Length();
        return mGlyphRuns.Elements();
    }
    // Returns the index of the GlyphRun containing the given offset.
    // Returns mGlyphRuns.Length() when aOffset is mCharacterCount.
    uint32_t FindFirstGlyphRunContaining(uint32_t aOffset);

    // Copy glyph data from a ShapedWord into this textrun.
    void CopyGlyphDataFrom(gfxShapedWord *aSource, uint32_t aStart);

    // Copy glyph data for a range of characters from aSource to this
    // textrun.
    void CopyGlyphDataFrom(gfxTextRun *aSource, uint32_t aStart,
                           uint32_t aLength, uint32_t aDest);

    nsExpirationState *GetExpirationState() { return &mExpirationState; }

    // Tell the textrun to release its reference to its creating gfxFontGroup
    // immediately, rather than on destruction. This is used for textruns
    // that are actually owned by a gfxFontGroup, so that they don't keep it
    // permanently alive due to a circular reference. (The caller of this is
    // taking responsibility for ensuring the textrun will not outlive its
    // mFontGroup.)
    void ReleaseFontGroup();

    struct LigatureData {
        // textrun offsets of the start and end of the containing ligature
        uint32_t mLigatureStart;
        uint32_t mLigatureEnd;
        // appunits advance to the start of the ligature part within the ligature;
        // never includes any spacing
        gfxFloat mPartAdvance;
        // appunits width of the ligature part; includes before-spacing
        // when the part is at the start of the ligature, and after-spacing
        // when the part is as the end of the ligature
        gfxFloat mPartWidth;
        
        bool mClipBeforePart;
        bool mClipAfterPart;
    };
    
    // return storage used by this run, for memory reporter;
    // nsTransformedTextRun needs to override this as it holds additional data
    virtual size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf)
      MOZ_MUST_OVERRIDE;
    virtual size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf)
      MOZ_MUST_OVERRIDE;

    // Get the size, if it hasn't already been gotten, marking as it goes.
    size_t MaybeSizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf)  {
        if (mFlags & gfxTextRunFactory::TEXT_RUN_SIZE_ACCOUNTED) {
            return 0;
        }
        mFlags |= gfxTextRunFactory::TEXT_RUN_SIZE_ACCOUNTED;
        return SizeOfIncludingThis(aMallocSizeOf);
    }
    void ResetSizeOfAccountingFlags() {
        mFlags &= ~gfxTextRunFactory::TEXT_RUN_SIZE_ACCOUNTED;
    }

    // shaping state - for some font features, fallback is required that
    // affects the entire run. for example, fallback for one script/font
    // portion of a textrun requires fallback to be applied to the entire run

    enum ShapingState {
        eShapingState_Normal,                 // default state
        eShapingState_ShapingWithFeature,     // have shaped with feature
        eShapingState_ShapingWithFallback,    // have shaped with fallback
        eShapingState_Aborted,                // abort initial iteration
        eShapingState_ForceFallbackFeature    // redo with fallback forced on
    };

    ShapingState GetShapingState() const { return mShapingState; }
    void SetShapingState(ShapingState aShapingState) {
        mShapingState = aShapingState;
    }

#ifdef DEBUG
    void Dump(FILE* aOutput);
#endif

protected:
    /**
     * Create a textrun, and set its mCharacterGlyphs to point immediately
     * after the base object; this is ONLY used in conjunction with placement
     * new, after allocating a block large enough for the glyph records to
     * follow the base textrun object.
     */
    gfxTextRun(const gfxTextRunFactory::Parameters *aParams,
               uint32_t aLength, gfxFontGroup *aFontGroup, uint32_t aFlags);

    /**
     * Helper for the Create() factory method to allocate the required
     * glyph storage for a textrun object with the basic size aSize,
     * plus room for aLength glyph records.
     */
    static void* AllocateStorageForTextRun(size_t aSize, uint32_t aLength);

    // Pointer to the array of CompressedGlyph records; must be initialized
    // when the object is constructed.
    CompressedGlyph *mCharacterGlyphs;

private:
    // **** general helpers **** 

    // Get the total advance for a range of glyphs.
    int32_t GetAdvanceForGlyphs(uint32_t aStart, uint32_t aEnd);

    // Spacing for characters outside the range aSpacingStart/aSpacingEnd
    // is assumed to be zero; such characters are not passed to aProvider.
    // This is useful to protect aProvider from being passed character indices
    // it is not currently able to handle.
    bool GetAdjustedSpacingArray(uint32_t aStart, uint32_t aEnd,
                                   PropertyProvider *aProvider,
                                   uint32_t aSpacingStart, uint32_t aSpacingEnd,
                                   nsTArray<PropertyProvider::Spacing> *aSpacing);

    //  **** ligature helpers ****
    // (Platforms do the actual ligaturization, but we need to do a bunch of stuff
    // to handle requests that begin or end inside a ligature)

    // if aProvider is null then mBeforeSpacing and mAfterSpacing are set to zero
    LigatureData ComputeLigatureData(uint32_t aPartStart, uint32_t aPartEnd,
                                     PropertyProvider *aProvider);
    gfxFloat ComputePartialLigatureWidth(uint32_t aPartStart, uint32_t aPartEnd,
                                         PropertyProvider *aProvider);
    void DrawPartialLigature(gfxFont *aFont, gfxContext *aCtx,
                             uint32_t aStart, uint32_t aEnd, gfxPoint *aPt,
                             PropertyProvider *aProvider,
                             gfxTextRunDrawCallbacks *aCallbacks);
    // Advance aStart to the start of the nearest ligature; back up aEnd
    // to the nearest ligature end; may result in *aStart == *aEnd
    void ShrinkToLigatureBoundaries(uint32_t *aStart, uint32_t *aEnd);
    // result in appunits
    gfxFloat GetPartialLigatureWidth(uint32_t aStart, uint32_t aEnd, PropertyProvider *aProvider);
    void AccumulatePartialLigatureMetrics(gfxFont *aFont,
                                          uint32_t aStart, uint32_t aEnd,
                                          gfxFont::BoundingBoxType aBoundingBoxType,
                                          gfxContext *aRefContext,
                                          PropertyProvider *aProvider,
                                          Metrics *aMetrics);

    // **** measurement helper ****
    void AccumulateMetricsForRun(gfxFont *aFont, uint32_t aStart, uint32_t aEnd,
                                 gfxFont::BoundingBoxType aBoundingBoxType,
                                 gfxContext *aRefContext,
                                 PropertyProvider *aProvider,
                                 uint32_t aSpacingStart, uint32_t aSpacingEnd,
                                 Metrics *aMetrics);

    // **** drawing helper ****
    void DrawGlyphs(gfxFont *aFont, gfxContext *aContext,
                    DrawMode aDrawMode, gfxPoint *aPt,
                    gfxTextContextPaint *aContextPaint, uint32_t aStart,
                    uint32_t aEnd, PropertyProvider *aProvider,
                    uint32_t aSpacingStart, uint32_t aSpacingEnd,
                    gfxTextRunDrawCallbacks *aCallbacks);

    // XXX this should be changed to a GlyphRun plus a maybe-null GlyphRun*,
    // for smaller size especially in the super-common one-glyphrun case
    nsAutoTArray<GlyphRun,1>        mGlyphRuns;

    void             *mUserData;
    gfxFontGroup     *mFontGroup; // addrefed on creation, but our reference
                                  // may be released by ReleaseFontGroup()
    gfxSkipChars      mSkipChars;
    nsExpirationState mExpirationState;

    bool              mSkipDrawing; // true if the font group we used had a user font
                                    // download that's in progress, so we should hide text
                                    // until the download completes (or timeout fires)
    bool              mReleasedFontGroup; // we already called NS_RELEASE on
                                          // mFontGroup, so don't do it again

    // shaping state for handling variant fallback features
    // such as subscript/superscript variant glyphs
    ShapingState      mShapingState;
};

class gfxFontGroup : public gfxTextRunFactory {
public:
    class FamilyFace {
    public:
        FamilyFace() { }

        FamilyFace(gfxFontFamily* aFamily, gfxFont* aFont)
            : mFamily(aFamily), mFont(aFont)
        {
            NS_ASSERTION(aFont, "font pointer must not be null");
            NS_ASSERTION(!aFamily ||
                         aFamily->ContainsFace(aFont->GetFontEntry()),
                         "font is not a member of the given family");
        }

        gfxFontFamily* Family() const { return mFamily.get(); }
        gfxFont* Font() const { return mFont.get(); }

    private:
        nsRefPtr<gfxFontFamily> mFamily;
        nsRefPtr<gfxFont>       mFont;
    };

    static void Shutdown(); // platform must call this to release the languageAtomService

    gfxFontGroup(const mozilla::FontFamilyList& aFontFamilyList,
                 const gfxFontStyle *aStyle,
                 gfxUserFontSet *aUserFontSet = nullptr);

    virtual ~gfxFontGroup();

    virtual gfxFont *GetFontAt(int32_t i) {
        // If it turns out to be hard for all clients that cache font
        // groups to call UpdateFontList at appropriate times, we could
        // instead consider just calling UpdateFontList from someplace
        // more central (such as here).
        NS_ASSERTION(!mUserFontSet || mCurrGeneration == GetGeneration(),
                     "Whoever was caching this font group should have "
                     "called UpdateFontList on it");
        NS_ASSERTION(mFonts.Length() > uint32_t(i) && mFonts[i].Font(), 
                     "Requesting a font index that doesn't exist");

        return mFonts[i].Font();
    }

    // Returns the first font in the font-group that has an OpenType MATH table,
    // or null if no such font is available. The GetMathConstant methods may be
    // called on the returned font.
    gfxFont *GetFirstMathFont();

    uint32_t FontListLength() const {
        return mFonts.Length();
    }

    const gfxFontStyle *GetStyle() const { return &mStyle; }

    virtual gfxFontGroup *Copy(const gfxFontStyle *aStyle);

    /**
     * The listed characters should be treated as invisible and zero-width
     * when creating textruns.
     */
    static bool IsInvalidChar(uint8_t ch);
    static bool IsInvalidChar(char16_t ch);

    /**
     * Make a textrun for a given string.
     * If aText is not persistent (aFlags & TEXT_IS_PERSISTENT), the
     * textrun will copy it.
     * This calls FetchGlyphExtents on the textrun.
     */
    virtual gfxTextRun *MakeTextRun(const char16_t *aString, uint32_t aLength,
                                    const Parameters *aParams, uint32_t aFlags);
    /**
     * Make a textrun for a given string.
     * If aText is not persistent (aFlags & TEXT_IS_PERSISTENT), the
     * textrun will copy it.
     * This calls FetchGlyphExtents on the textrun.
     */
    virtual gfxTextRun *MakeTextRun(const uint8_t *aString, uint32_t aLength,
                                    const Parameters *aParams, uint32_t aFlags);

    /**
     * Textrun creation helper for clients that don't want to pass
     * a full Parameters record.
     */
    template<typename T>
    gfxTextRun *MakeTextRun(const T *aString, uint32_t aLength,
                            gfxContext *aRefContext,
                            int32_t aAppUnitsPerDevUnit,
                            uint32_t aFlags)
    {
        gfxTextRunFactory::Parameters params = {
            aRefContext, nullptr, nullptr, nullptr, 0, aAppUnitsPerDevUnit
        };
        return MakeTextRun(aString, aLength, &params, aFlags);
    }

    /**
     * Get the (possibly-cached) width of the hyphen character.
     * The aCtx and aAppUnitsPerDevUnit parameters will be used only if
     * needed to initialize the cached hyphen width; otherwise they are
     * ignored.
     */
    gfxFloat GetHyphenWidth(gfxTextRun::PropertyProvider* aProvider);

    /**
     * Make a text run representing a single hyphen character.
     * This will use U+2010 HYPHEN if available in the first font,
     * otherwise fall back to U+002D HYPHEN-MINUS.
     * The caller is responsible for deleting the returned text run
     * when no longer required.
     */
    gfxTextRun *MakeHyphenTextRun(gfxContext *aCtx,
                                  uint32_t aAppUnitsPerDevUnit);

    /**
     * Check whether a given font (specified by its gfxFontEntry)
     * is already in the fontgroup's list of actual fonts
     */
    bool HasFont(const gfxFontEntry *aFontEntry);

    // This returns the preferred underline for this font group.
    // Some CJK fonts have wrong underline offset in its metrics.
    // If this group has such "bad" font, each platform's gfxFontGroup initialized mUnderlineOffset.
    // The value should be lower value of first font's metrics and the bad font's metrics.
    // Otherwise, this returns from first font's metrics.
    enum { UNDERLINE_OFFSET_NOT_SET = INT16_MAX };
    virtual gfxFloat GetUnderlineOffset() {
        if (mUnderlineOffset == UNDERLINE_OFFSET_NOT_SET)
            mUnderlineOffset = GetFontAt(0)->GetMetrics().underlineOffset;
        return mUnderlineOffset;
    }

    virtual already_AddRefed<gfxFont>
        FindFontForChar(uint32_t ch, uint32_t prevCh, int32_t aRunScript,
                        gfxFont *aPrevMatchedFont,
                        uint8_t *aMatchType);

    // search through pref fonts for a character, return nullptr if no matching pref font
    virtual already_AddRefed<gfxFont> WhichPrefFontSupportsChar(uint32_t aCh);

    virtual already_AddRefed<gfxFont>
        WhichSystemFontSupportsChar(uint32_t aCh, int32_t aRunScript);

    template<typename T>
    void ComputeRanges(nsTArray<gfxTextRange>& mRanges,
                       const T *aString, uint32_t aLength,
                       int32_t aRunScript);

    gfxUserFontSet* GetUserFontSet();

    // With downloadable fonts, the composition of the font group can change as fonts are downloaded
    // for each change in state of the user font set, the generation value is bumped to avoid picking up
    // previously created text runs in the text run word cache.  For font groups based on stylesheets
    // with no @font-face rule, this always returns 0.
    uint64_t GetGeneration();

    // used when logging text performance
    gfxTextPerfMetrics *GetTextPerfMetrics() { return mTextPerf; }
    void SetTextPerfMetrics(gfxTextPerfMetrics *aTextPerf) { mTextPerf = aTextPerf; }

    // This will call UpdateFontList() if the user font set is changed.
    void SetUserFontSet(gfxUserFontSet *aUserFontSet);

    // If there is a user font set, check to see whether the font list or any
    // caches need updating.
    virtual void UpdateFontList();

    bool ShouldSkipDrawing() const {
        return mSkipDrawing;
    }

    class LazyReferenceContextGetter {
    public:
      virtual already_AddRefed<gfxContext> GetRefContext() = 0;
    };
    // The gfxFontGroup keeps ownership of this textrun.
    // It is only guaranteed to exist until the next call to GetEllipsisTextRun
    // (which might use a different appUnitsPerDev value) for the font group,
    // or until UpdateFontList is called, or the fontgroup is destroyed.
    // Get it/use it/forget it :) - don't keep a reference that might go stale.
    gfxTextRun* GetEllipsisTextRun(int32_t aAppUnitsPerDevPixel,
                                   LazyReferenceContextGetter& aRefContextGetter);

    // helper method for resolving generic font families
    static void
    ResolveGenericFontNames(mozilla::FontFamilyType aGenericType,
                            nsIAtom *aLanguage,
                            nsTArray<nsString>& aGenericFamilies);

protected:
    mozilla::FontFamilyList mFamilyList;
    gfxFontStyle mStyle;
    nsTArray<FamilyFace> mFonts;
    gfxFloat mUnderlineOffset;
    gfxFloat mHyphenWidth;

    nsRefPtr<gfxUserFontSet> mUserFontSet;
    uint64_t mCurrGeneration;  // track the current user font set generation, rebuild font list if needed

    gfxTextPerfMetrics *mTextPerf;

    // Cache a textrun representing an ellipsis (useful for CSS text-overflow)
    // at a specific appUnitsPerDevPixel size
    nsAutoPtr<gfxTextRun>   mCachedEllipsisTextRun;

    // cache the most recent pref font to avoid general pref font lookup
    nsRefPtr<gfxFontFamily> mLastPrefFamily;
    nsRefPtr<gfxFont>       mLastPrefFont;
    eFontPrefLang           mLastPrefLang;       // lang group for last pref font
    eFontPrefLang           mPageLang;
    bool                    mLastPrefFirstFont;  // is this the first font in the list of pref fonts for this lang group?

    bool                    mSkipDrawing; // hide text while waiting for a font
                                          // download to complete (or fallback
                                          // timer to fire)

    /**
     * Textrun creation short-cuts for special cases where we don't need to
     * call a font shaper to generate glyphs.
     */
    gfxTextRun *MakeEmptyTextRun(const Parameters *aParams, uint32_t aFlags);
    gfxTextRun *MakeSpaceTextRun(const Parameters *aParams, uint32_t aFlags);
    gfxTextRun *MakeBlankTextRun(uint32_t aLength,
                                 const Parameters *aParams, uint32_t aFlags);

    // Initialize the list of fonts
    void BuildFontList();

    // Init this font group's font metrics. If there no bad fonts, you don't need to call this.
    // But if there are one or more bad fonts which have bad underline offset,
    // you should call this with the *first* bad font.
    void InitMetricsForBadFont(gfxFont* aBadFont);

    // Set up the textrun glyphs for an entire text run:
    // find script runs, and then call InitScriptRun for each
    template<typename T>
    void InitTextRun(gfxContext *aContext,
                     gfxTextRun *aTextRun,
                     const T *aString,
                     uint32_t aLength);

    // InitTextRun helper to handle a single script run, by finding font ranges
    // and calling each font's InitTextRun() as appropriate
    template<typename T>
    void InitScriptRun(gfxContext *aContext,
                       gfxTextRun *aTextRun,
                       const T *aString,
                       uint32_t aScriptRunStart,
                       uint32_t aScriptRunEnd,
                       int32_t aRunScript);

    // Helper for font-matching:
    // see if aCh is supported in any of the faces from aFamily;
    // if so return the best style match, else return null.
    already_AddRefed<gfxFont> TryAllFamilyMembers(gfxFontFamily* aFamily,
                                                  uint32_t aCh);

    // helper methods for looking up fonts

    // iterate over the fontlist, lookup names and expand generics
    void EnumerateFontList(nsIAtom *aLanguage, void *aClosure = nullptr);

    // expand a generic to a list of specific names based on prefs
    void FindGenericFonts(mozilla::FontFamilyType aGenericType,
                          nsIAtom *aLanguage,
                          void *aClosure);

    // lookup and add a font with a given name (i.e. *not* a generic!)
    virtual void FindPlatformFont(const nsAString& aName,
                                  bool aUseFontSet,
                                  void *aClosure);

    static nsILanguageAtomService* gLangService;
};
#endif
