path: root/src/ports/SkFontHost_android.cpp

/* libs/graphics/ports/SkFontHost_android.cpp
**
** Copyright 2006, The Android Open Source Project
**
** Licensed under the Apache License, Version 2.0 (the "License");
** you may not use this file except in compliance with the License.
** You may obtain a copy of the License at
**
**     http://www.apache.org/licenses/LICENSE-2.0
**
** Unless required by applicable law or agreed to in writing, software
** distributed under the License is distributed on an "AS IS" BASIS,
** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
** See the License for the specific language governing permissions and
** limitations under the License.
*/

#include "SkFontHost.h"
#include "SkDescriptor.h"
#include "SkMMapStream.h"
#include "SkPaint.h"
#include "SkString.h"
#include "SkStream.h"
#include "SkThread.h"
#include "SkTSearch.h"
#include "SkTypeface_android.h"
#include "FontHostConfiguration_android.h"
#include <stdio.h>

#define FONT_CACHE_MEMORY_BUDGET    (768 * 1024)

#ifndef SK_FONT_FILE_PREFIX
    #define SK_FONT_FILE_PREFIX          "/fonts/"
#endif

bool find_name_and_attributes(SkStream* stream, SkString* name,
                              SkTypeface::Style* style, bool* isFixedWidth);

static void GetFullPathForSysFonts(SkString* full, const char name[]) {
    full->set(getenv("ANDROID_ROOT"));
    full->append(SK_FONT_FILE_PREFIX);
    full->append(name);
}

///////////////////////////////////////////////////////////////////////////////

struct FamilyRec;

/*  This guy holds a mapping of a name -> family, used for looking up fonts.
    Since it is stored in a stretchy array that doesn't preserve object
    semantics, we don't use constructor/destructors, but just have explicit
    helpers to manage our internal bookkeeping.
*/
struct NameFamilyPair {
    const char* fName;      // we own this
    FamilyRec*  fFamily;    // we don't own this, we just reference it

    void construct(const char name[], FamilyRec* family) {
        fName = strdup(name);
        fFamily = family;   // we don't own this, so just record the referene
    }

    void destruct() {
        free((char*)fName);
        // we don't own family, so just ignore our reference
    }
};
typedef SkTDArray<NameFamilyPair> NameFamilyPairList;

// we use atomic_inc to grow this for each typeface we create
static int32_t gUniqueFontID;

// this is the mutex that protects gFamilyHead and GetNameList()
SK_DECLARE_STATIC_MUTEX(gFamilyHeadAndNameListMutex);
static FamilyRec* gFamilyHead;

static NameFamilyPairList& GetNameList() {
    /*
     *  It is assumed that the caller has already acquired a lock on
     *  gFamilyHeadAndNameListMutex before calling this.
     */
    static NameFamilyPairList* gNameList;
    if (NULL == gNameList) {
        gNameList = SkNEW(NameFamilyPairList);
        // register a delete proc with sk_atexit(..) when available
    }
    return *gNameList;
}

struct FamilyRec {
    FamilyRec*  fNext;
    SkTypeface* fFaces[4];

    FamilyRec()
    {
        fNext = gFamilyHead;
        memset(fFaces, 0, sizeof(fFaces));
        gFamilyHead = this;
    }
};

static SkTypeface* find_best_face(const FamilyRec* family,
                                  SkTypeface::Style style) {
    SkTypeface* const* faces = family->fFaces;

    if (faces[style] != NULL) { // exact match
        return faces[style];
    }
    // look for a matching bold
    style = (SkTypeface::Style)(style ^ SkTypeface::kItalic);
    if (faces[style] != NULL) {
        return faces[style];
    }
    // look for the plain
    if (faces[SkTypeface::kNormal] != NULL) {
        return faces[SkTypeface::kNormal];
    }
    // look for anything
    for (int i = 0; i < 4; i++) {
        if (faces[i] != NULL) {
            return faces[i];
        }
    }
    // should never get here, since the faces list should not be empty
    SkDEBUGFAIL("faces list is empty");
    return NULL;
}

static FamilyRec* find_family(const SkTypeface* member) {
    FamilyRec* curr = gFamilyHead;
    while (curr != NULL) {
        for (int i = 0; i < 4; i++) {
            if (curr->fFaces[i] == member) {
                return curr;
            }
        }
        curr = curr->fNext;
    }
    return NULL;
}

/*  Returns the matching typeface, or NULL. If a typeface is found, its refcnt
    is not modified.
 */
static SkTypeface* find_from_uniqueID(uint32_t uniqueID) {
    FamilyRec* curr = gFamilyHead;
    while (curr != NULL) {
        for (int i = 0; i < 4; i++) {
            SkTypeface* face = curr->fFaces[i];
            if (face != NULL && face->uniqueID() == uniqueID) {
                return face;
            }
        }
        curr = curr->fNext;
    }
    return NULL;
}

/*  Remove reference to this face from its family. If the resulting family
    is empty (has no faces), return that family, otherwise return NULL
*/
static FamilyRec* remove_from_family(const SkTypeface* face) {
    FamilyRec* family = find_family(face);
    if (family) {
        SkASSERT(family->fFaces[face->style()] == face);
        family->fFaces[face->style()] = NULL;

        for (int i = 0; i < 4; i++) {
            if (family->fFaces[i] != NULL) {    // family is non-empty
                return NULL;
            }
        }
    } else {
//        SkDebugf("remove_from_family(%p) face not found", face);
    }
    return family;  // return the empty family
}

// maybe we should make FamilyRec be doubly-linked
static void detach_and_delete_family(FamilyRec* family) {
    FamilyRec* curr = gFamilyHead;
    FamilyRec* prev = NULL;

    while (curr != NULL) {
        FamilyRec* next = curr->fNext;
        if (curr == family) {
            if (prev == NULL) {
                gFamilyHead = next;
            } else {
                prev->fNext = next;
            }
            SkDELETE(family);
            return;
        }
        prev = curr;
        curr = next;
    }
    SkASSERT(!"Yikes, couldn't find family in our list to remove/delete");
}

//  gFamilyHeadAndNameListMutex must already be acquired
static SkTypeface* find_typeface(const char name[], SkTypeface::Style style) {
    NameFamilyPairList& namelist = GetNameList();
    NameFamilyPair* list = namelist.begin();
    int             count = namelist.count();

    int index = SkStrLCSearch(&list[0].fName, count, name, sizeof(list[0]));

    if (index >= 0) {
        return find_best_face(list[index].fFamily, style);
    }
    return NULL;
}

//  gFamilyHeadAndNameListMutex must already be acquired
static SkTypeface* find_typeface(const SkTypeface* familyMember,
                                 SkTypeface::Style style) {
    const FamilyRec* family = find_family(familyMember);
    return family ? find_best_face(family, style) : NULL;
}

//  gFamilyHeadAndNameListMutex must already be acquired
static void add_name(const char name[], FamilyRec* family) {
    SkAutoAsciiToLC tolc(name);
    name = tolc.lc();

    NameFamilyPairList& namelist = GetNameList();
    NameFamilyPair* list = namelist.begin();
    int             count = namelist.count();

    int index = SkStrLCSearch(&list[0].fName, count, name, sizeof(list[0]));

    if (index < 0) {
        list = namelist.insert(~index);
        list->construct(name, family);
    }
}

//  gFamilyHeadAndNameListMutex must already be acquired
static void remove_from_names(FamilyRec* emptyFamily) {
#ifdef SK_DEBUG
    for (int i = 0; i < 4; i++) {
        SkASSERT(emptyFamily->fFaces[i] == NULL);
    }
#endif

    SkTDArray<NameFamilyPair>& list = GetNameList();

    // must go backwards when removing
    for (int i = list.count() - 1; i >= 0; --i) {
        NameFamilyPair* pair = &list[i];
        if (pair->fFamily == emptyFamily) {
            pair->destruct();
            list.remove(i);
        }
    }
}

///////////////////////////////////////////////////////////////////////////////

class FamilyTypeface : public SkTypeface {
public:
    FamilyTypeface(Style style, bool sysFont, SkTypeface* familyMember,
                   bool isFixedWidth)
    : SkTypeface(style, sk_atomic_inc(&gUniqueFontID) + 1, isFixedWidth) {
        fIsSysFont = sysFont;


        // our caller has acquired the gFamilyHeadAndNameListMutex so this is safe
        FamilyRec* rec = NULL;
        if (familyMember) {
            rec = find_family(familyMember);
            SkASSERT(rec);
        } else {
            rec = SkNEW(FamilyRec);
        }
        rec->fFaces[style] = this;
    }

    virtual ~FamilyTypeface() {
        SkAutoMutexAcquire  ac(gFamilyHeadAndNameListMutex);

        // remove us from our family. If the family is now empty, we return
        // that and then remove that family from the name list
        FamilyRec* family = remove_from_family(this);
        if (NULL != family) {
            remove_from_names(family);
            detach_and_delete_family(family);
        }
    }

    bool isSysFont() const { return fIsSysFont; }

    virtual SkStream* openStream() = 0;
    virtual const char* getUniqueString() const = 0;
    virtual const char* getFilePath() const = 0;

private:
    bool    fIsSysFont;

    typedef SkTypeface INHERITED;
};

///////////////////////////////////////////////////////////////////////////////

class StreamTypeface : public FamilyTypeface {
public:
    StreamTypeface(Style style, bool sysFont, SkTypeface* familyMember,
                   SkStream* stream, bool isFixedWidth)
    : INHERITED(style, sysFont, familyMember, isFixedWidth) {
        SkASSERT(stream);
        stream->ref();
        fStream = stream;
    }
    virtual ~StreamTypeface() {
        fStream->unref();
    }

    // overrides
    virtual SkStream* openStream() {
        // we just ref our existing stream, since the caller will call unref()
        // when they are through
        fStream->ref();
        // must rewind each time, since the caller assumes a "new" stream
        fStream->rewind();
        return fStream;
    }
    virtual const char* getUniqueString() const { return NULL; }
    virtual const char* getFilePath() const { return NULL; }

private:
    SkStream* fStream;

    typedef FamilyTypeface INHERITED;
};

class FileTypeface : public FamilyTypeface {
public:
    FileTypeface(Style style, bool sysFont, SkTypeface* familyMember,
                 const char path[], bool isFixedWidth)
    : INHERITED(style, sysFont, familyMember, isFixedWidth) {
        SkString fullpath;

        if (sysFont) {
            GetFullPathForSysFonts(&fullpath, path);
            path = fullpath.c_str();
        }
        fPath.set(path);
    }

    // overrides
    virtual SkStream* openStream() {
        SkStream* stream = SkNEW_ARGS(SkMMAPStream, (fPath.c_str()));

        // check for failure
        if (stream->getLength() <= 0) {
            SkDELETE(stream);
            // maybe MMAP isn't supported. try FILE
            stream = SkNEW_ARGS(SkFILEStream, (fPath.c_str()));
            if (stream->getLength() <= 0) {
                SkDELETE(stream);
                stream = NULL;
            }
        }
        return stream;
    }
    virtual const char* getUniqueString() const {
        const char* str = strrchr(fPath.c_str(), '/');
        if (str) {
            str += 1;   // skip the '/'
        }
        return str;
    }
    virtual const char* getFilePath() const {
        return fPath.c_str();
    }

private:
    SkString fPath;

    typedef FamilyTypeface INHERITED;
};

///////////////////////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////////////

static bool get_name_and_style(const char path[], SkString* name,
                               SkTypeface::Style* style,
                               bool* isFixedWidth, bool isExpected) {
    SkString        fullpath;
    GetFullPathForSysFonts(&fullpath, path);

    SkMMAPStream stream(fullpath.c_str());
    if (stream.getLength() > 0) {
        return find_name_and_attributes(&stream, name, style, isFixedWidth);
    }
    else {
        SkFILEStream stream(fullpath.c_str());
        if (stream.getLength() > 0) {
            return find_name_and_attributes(&stream, name, style, isFixedWidth);
        }
    }

    if (isExpected) {
        SkDebugf("---- failed to open <%s> as a font\n", fullpath.c_str());
    }
    return false;
}

// used to record our notion of the pre-existing fonts
struct FontInitRec {
    const char*         fFileName;
    const char* const*  fNames;     // null-terminated list
};

// deliberately empty, but we use the address to identify fallback fonts
static const char* gFBNames[] = { NULL };

static const struct {
    const char* fFileName;
    FallbackScripts fScript;
} gFBFileNames[] = {
    { "DroidNaskh-Regular.ttf", kArabic_FallbackScript },
    { "DroidSansEthiopic-Regular.ttf", kEthiopic_FallbackScript },
    { "DroidSansHebrew-Regular.ttf", kHebrewRegular_FallbackScript },
    { "DroidSansHebrew-Bold.ttf", kHebrewBold_FallbackScript },
    { "DroidSansThai.ttf", kThai_FallbackScript },
    { "DroidSansArmenian.ttf", kArmenian_FallbackScript },
    { "DroidSansGeorgian.ttf", kGeorgian_FallbackScript },
    { "Lohit-Devanagari.ttf", kDevanagari_FallbackScript },
    { "Lohit-Bengali.ttf", kBengali_FallbackScript },
    { "Lohit-Tamil.ttf", kTamil_FallbackScript },
};

/*  Fonts are grouped by family, with the first font in a family having the
    list of names (even if that list is empty), and the following members having
    null for the list. The names list must be NULL-terminated.
*/
static FontInitRec *gSystemFonts;
static size_t gNumSystemFonts = 0;

#define SYSTEM_FONTS_FILE "/system/etc/system_fonts.cfg"

// these globals are assigned (once) by load_system_fonts()
static FamilyRec* gDefaultFamily;
static SkTypeface* gDefaultNormal;
static char** gDefaultNames = NULL;
static uint32_t *gFallbackFonts;
static uint32_t *gFallbackScriptsMap;

/*  Load info from a configuration file that populates the system/fallback font structures
*/
static void load_font_info() {
//    load_font_info_xml("/system/etc/system_fonts.xml");
    SkTDArray<FontFamily*> fontFamilies;
    getFontFamilies(fontFamilies);

    SkTDArray<FontInitRec> fontInfo;
    bool firstInFamily = false;
    for (int i = 0; i < fontFamilies.count(); ++i) {
        FontFamily *family = fontFamilies[i];
        firstInFamily = true;
        for (int j = 0; j < family->fFileNames.count(); ++j) {
            FontInitRec fontInfoRecord;
            fontInfoRecord.fFileName = family->fFileNames[j];
            if (j == 0) {
                if (family->fNames.count() == 0) {
                    // Fallback font
                    fontInfoRecord.fNames = (char **)gFBNames;
                } else {
                    SkTDArray<const char*> names = family->fNames;
                    const char **nameList = (const char**)
                            malloc((names.count() + 1) * sizeof(char*));
                    if (nameList == NULL) {
                        // shouldn't get here
                        break;
                    }
                    if (gDefaultNames == NULL) {
                        gDefaultNames = (char**) nameList;
                    }
                    for (int i = 0; i < names.count(); ++i) {
                        nameList[i] = names[i];
                    }
                    nameList[names.count()] = NULL;
                    fontInfoRecord.fNames = nameList;
                }
            } else {
                fontInfoRecord.fNames = NULL;
            }
            *fontInfo.append() = fontInfoRecord;
        }
    }
    gNumSystemFonts = fontInfo.count();
    gSystemFonts = (FontInitRec*) malloc(gNumSystemFonts * sizeof(FontInitRec));
    gFallbackFonts = (uint32_t*) malloc((gNumSystemFonts + 1) * sizeof(uint32_t));
    gFallbackScriptsMap = (uint32_t*) calloc(kFallbackScriptNumber, sizeof(uint32_t));
    if (gSystemFonts == NULL) {
        // shouldn't get here
        gNumSystemFonts = 0;
    }
//    SkDebugf("---- We have %d system fonts", gNumSystemFonts);
    for (size_t i = 0; i < gNumSystemFonts; ++i) {
        gSystemFonts[i].fFileName = fontInfo[i].fFileName;
        gSystemFonts[i].fNames = fontInfo[i].fNames;
//        SkDebugf("---- gSystemFonts[%d] fileName=%s", i, fontInfo[i].fFileName);
    }
    fontFamilies.deleteAll();
}

/*
 *  Called once (ensured by the sentinel check at the beginning of our body).
 *  Initializes all the globals, and register the system fonts.
 *
 *  gFamilyHeadAndNameListMutex must already be acquired.
 */
static void load_system_fonts() {
    // check if we've already be called
    if (NULL != gDefaultNormal) {
        return;
    }

    load_font_info();

    const FontInitRec* rec = gSystemFonts;
    SkTypeface* firstInFamily = NULL;
    int fallbackCount = 0;

    for (size_t i = 0; i < gNumSystemFonts; i++) {
        // if we're the first in a new family, clear firstInFamily
        if (rec[i].fNames != NULL) {
            firstInFamily = NULL;
        }

        bool isFixedWidth;
        SkString name;
        SkTypeface::Style style;

        // we expect all the fonts, except the "fallback" fonts
        bool isExpected = (rec[i].fNames != gFBNames);
        if (!get_name_and_style(rec[i].fFileName, &name, &style,
                                &isFixedWidth, isExpected)) {
            continue;
        }

        SkTypeface* tf = SkNEW_ARGS(FileTypeface,
                                    (style,
                                     true,  // system-font (cannot delete)
                                     firstInFamily, // what family to join
                                     rec[i].fFileName,
                                     isFixedWidth) // filename
                                    );

//        SkDebugf("---- SkTypeface[%d] %s fontID %d\n", i, rec[i].fFileName, tf->uniqueID());

        FallbackScripts fallbackScript = SkGetFallbackScriptFromID(rec[i].fFileName);
        if (SkTypeface_ValidScript(fallbackScript)) {
            gFallbackScriptsMap[fallbackScript] = tf->uniqueID();
        }

        if (rec[i].fNames != NULL) {
            // see if this is one of our fallback fonts
            if (rec[i].fNames == gFBNames) {
//                SkDebugf("---- adding %s as fallback[%d] fontID %d\n",
//                         rec[i].fFileName, fallbackCount, tf->uniqueID());
                gFallbackFonts[fallbackCount++] = tf->uniqueID();
            }

            firstInFamily = tf;
            FamilyRec* family = find_family(tf);
            const char* const* names = rec[i].fNames;

            // record the default family if this is it
            if (names == gDefaultNames) {
                gDefaultFamily = family;
            }
            // add the names to map to this family
            while (*names) {
                add_name(*names, family);
                names += 1;
            }
        }
    }

    // do this after all fonts are loaded. This is our default font, and it
    // acts as a sentinel so we only execute load_system_fonts() once
    gDefaultNormal = find_best_face(gDefaultFamily, SkTypeface::kNormal);
    // now terminate our fallback list with the sentinel value
    gFallbackFonts[fallbackCount] = 0;
}

///////////////////////////////////////////////////////////////////////////////

void SkFontHost::Serialize(const SkTypeface* face, SkWStream* stream) {
    // lookup and record if the font is custom (i.e. not a system font)
    bool isCustomFont = !((FamilyTypeface*)face)->isSysFont();
    stream->writeBool(isCustomFont);

    if (isCustomFont) {
        SkStream* fontStream = ((FamilyTypeface*)face)->openStream();

        // store the length of the custom font
        uint32_t len = fontStream->getLength();
        stream->write32(len);

        // store the entire font in the serialized stream
        void* fontData = malloc(len);

        fontStream->read(fontData, len);
        stream->write(fontData, len);

        fontStream->unref();
        free(fontData);
//      SkDebugf("--- fonthost custom serialize %d %d\n", face->style(), len);

    } else {
        const char* name = ((FamilyTypeface*)face)->getUniqueString();

        stream->write8((uint8_t)face->style());

        if (NULL == name || 0 == *name) {
            stream->writePackedUInt(0);
//          SkDebugf("--- fonthost serialize null\n");
        } else {
            uint32_t len = strlen(name);
            stream->writePackedUInt(len);
            stream->write(name, len);
//          SkDebugf("--- fonthost serialize <%s> %d\n", name, face->style());
        }
    }
}

SkTypeface* SkFontHost::Deserialize(SkStream* stream) {
    SkAutoMutexAcquire  ac(gFamilyHeadAndNameListMutex);

    load_system_fonts();

    // check if the font is a custom or system font
    bool isCustomFont = stream->readBool();

    if (isCustomFont) {

        // read the length of the custom font from the stream
        uint32_t len = stream->readU32();

        // generate a new stream to store the custom typeface
        SkMemoryStream* fontStream = new SkMemoryStream(len);
        stream->read((void*)fontStream->getMemoryBase(), len);

        SkTypeface* face = CreateTypefaceFromStream(fontStream);

        fontStream->unref();

//      SkDebugf("--- fonthost custom deserialize %d %d\n", face->style(), len);
        return face;

    } else {
        int style = stream->readU8();

        int len = stream->readPackedUInt();
        if (len > 0) {
            SkString str;
            str.resize(len);
            stream->read(str.writable_str(), len);

            const FontInitRec* rec = gSystemFonts;
            for (size_t i = 0; i < gNumSystemFonts; i++) {
                if (strcmp(rec[i].fFileName, str.c_str()) == 0) {
                    // backup until we hit the fNames
                    for (int j = i; j >= 0; --j) {
                        if (rec[j].fNames != NULL) {
                            return SkFontHost::CreateTypeface(NULL,
                                        rec[j].fNames[0], NULL, 0,
                                        (SkTypeface::Style)style);
                        }
                    }
                }
            }
        }
    }
    return NULL;
}

///////////////////////////////////////////////////////////////////////////////

SkTypeface* SkFontHost::CreateTypeface(const SkTypeface* familyFace,
                                       const char familyName[],
                                       const void* data, size_t bytelength,
                                       SkTypeface::Style style) {
    SkAutoMutexAcquire  ac(gFamilyHeadAndNameListMutex);

    load_system_fonts();

    // clip to legal style bits
    style = (SkTypeface::Style)(style & SkTypeface::kBoldItalic);

    SkTypeface* tf = NULL;

    if (NULL != familyFace) {
        tf = find_typeface(familyFace, style);
    } else if (NULL != familyName) {
//        SkDebugf("======= familyName <%s>\n", familyName);
        tf = find_typeface(familyName, style);
    }

    if (NULL == tf) {
        tf = find_best_face(gDefaultFamily, style);
    }

    // we ref(), since the symantic is to return a new instance
    tf->ref();
    return tf;
}

SkTypeface* SkCreateTypefaceForScript(FallbackScripts script) {
    if (!SkTypeface_ValidScript(script)) {
        return NULL;
    }

    SkAutoMutexAcquire  ac(gFamilyHeadAndNameListMutex);

    load_system_fonts();

    if (gFallbackScriptsMap[script] == 0) {
        return NULL;
    }

    SkTypeface* tf = find_from_uniqueID(gFallbackScriptsMap[script]);
    // we ref(), since the symantic is to return a new instance
    tf->ref();
    return tf;
}

const char* SkGetFallbackScriptID(FallbackScripts script) {
    for (int i = 0; i < sizeof(gFBFileNames) / sizeof(gFBFileNames[0]); i++) {
        if (gFBFileNames[i].fScript == script) {
            return gFBFileNames[i].fFileName;
        }
    }
    return NULL;
}

FallbackScripts SkGetFallbackScriptFromID(const char* fileName) {
    for (int i = 0; i < sizeof(gFBFileNames) / sizeof(gFBFileNames[0]); i++) {
        if (strcmp(gFBFileNames[i].fFileName, fileName) == 0) {
            return gFBFileNames[i].fScript;
        }
    }
    return kFallbackScriptNumber; // Use SkTypeface_ValidScript as an invalid value.
}

SkStream* SkFontHost::OpenStream(uint32_t fontID) {
    SkAutoMutexAcquire  ac(gFamilyHeadAndNameListMutex);

    FamilyTypeface* tf = (FamilyTypeface*)find_from_uniqueID(fontID);
    SkStream* stream = tf ? tf->openStream() : NULL;

    if (stream && stream->getLength() == 0) {
        stream->unref();
        stream = NULL;
    }
    return stream;
}

size_t SkFontHost::GetFileName(SkFontID fontID, char path[], size_t length,
                               int32_t* index) {
    SkAutoMutexAcquire  ac(gFamilyHeadAndNameListMutex);

    FamilyTypeface* tf = (FamilyTypeface*)find_from_uniqueID(fontID);
    const char* src = tf ? tf->getFilePath() : NULL;

    if (src) {
        size_t size = strlen(src);
        if (path) {
            memcpy(path, src, SkMin32(size, length));
        }
        if (index) {
            *index = 0; // we don't have collections (yet)
        }
        return size;
    } else {
        return 0;
    }
}

SkFontID SkFontHost::NextLogicalFont(SkFontID currFontID, SkFontID origFontID) {
    SkAutoMutexAcquire  ac(gFamilyHeadAndNameListMutex);

    load_system_fonts();

    const SkTypeface* origTypeface = find_from_uniqueID(origFontID);
    const SkTypeface* currTypeface = find_from_uniqueID(currFontID);

    SkASSERT(origTypeface != 0);
    SkASSERT(currTypeface != 0);

    // Our fallback list always stores the id of the plain in each fallback
    // family, so we transform currFontID to its plain equivalent.
    currFontID = find_typeface(currTypeface, SkTypeface::kNormal)->uniqueID();

    /*  First see if fontID is already one of our fallbacks. If so, return
        its successor. If fontID is not in our list, then return the first one
        in our list. Note: list is zero-terminated, and returning zero means
        we have no more fonts to use for fallbacks.
     */
    const uint32_t* list = gFallbackFonts;
    for (int i = 0; list[i] != 0; i++) {
        if (list[i] == currFontID) {
            if (list[i+1] == 0)
                return 0;
            const SkTypeface* nextTypeface = find_from_uniqueID(list[i+1]);
            return find_typeface(nextTypeface, origTypeface->style())->uniqueID();
        }
    }

    // If we get here, currFontID was not a fallback, so we start at the
    // beginning of our list.
    const SkTypeface* firstTypeface = find_from_uniqueID(list[0]);
    return find_typeface(firstTypeface, origTypeface->style())->uniqueID();
}

///////////////////////////////////////////////////////////////////////////////

SkTypeface* SkFontHost::CreateTypefaceFromStream(SkStream* stream) {
    if (NULL == stream || stream->getLength() <= 0) {
        return NULL;
    }

    bool isFixedWidth;
    SkTypeface::Style style;

    if (find_name_and_attributes(stream, NULL, &style, &isFixedWidth)) {
        SkAutoMutexAcquire  ac(gFamilyHeadAndNameListMutex);
        return SkNEW_ARGS(StreamTypeface, (style, false, NULL, stream, isFixedWidth));
    } else {
        return NULL;
    }
}

SkTypeface* SkFontHost::CreateTypefaceFromFile(const char path[]) {
    SkStream* stream = SkNEW_ARGS(SkMMAPStream, (path));
    SkTypeface* face = SkFontHost::CreateTypefaceFromStream(stream);
    // since we created the stream, we let go of our ref() here
    stream->unref();
    return face;
}