ui/gfx/font_fallback_linux.cc

// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "ui/gfx/font_fallback_linux.h"

#include <fontconfig/fontconfig.h>

#include <map>
#include <memory>
#include <string>
#include <vector>

#include "base/lazy_instance.h"
#include "base/memory/ptr_util.h"
#include "ui/gfx/font.h"

namespace gfx {

namespace {

const char kFontFormatTrueType[] = "TrueType";
const char kFontFormatCFF[] = "CFF";

typedef std::map<std::string, std::vector<Font> > FallbackCache;
base::LazyInstance<FallbackCache>::Leaky g_fallback_cache =
    LAZY_INSTANCE_INITIALIZER;

}  // namespace

std::vector<Font> GetFallbackFonts(const Font& font) {
  std::string font_family = font.GetFontName();
  std::vector<Font>* fallback_fonts =
      &g_fallback_cache.Get()[font_family];
  if (!fallback_fonts->empty())
    return *fallback_fonts;

  FcPattern* pattern = FcPatternCreate();
  FcValue family;
  family.type = FcTypeString;
  family.u.s = reinterpret_cast<const FcChar8*>(font_family.c_str());
  FcPatternAdd(pattern, FC_FAMILY, family, FcFalse);
  if (FcConfigSubstitute(NULL, pattern, FcMatchPattern) == FcTrue) {
    FcDefaultSubstitute(pattern);
    FcResult result;
    FcFontSet* fonts = FcFontSort(NULL, pattern, FcTrue, NULL, &result);
    if (fonts) {
      for (int i = 0; i < fonts->nfont; ++i) {
        char* name = NULL;
        FcPatternGetString(fonts->fonts[i], FC_FAMILY, 0,
            reinterpret_cast<FcChar8**>(&name));
        // FontConfig returns multiple fonts with the same family name and
        // different configurations. Check to prevent duplicate family names.
        if (fallback_fonts->empty() ||
            fallback_fonts->back().GetFontName() != name) {
          fallback_fonts->push_back(Font(std::string(name), 13));
        }
      }
      FcFontSetDestroy(fonts);
    }
  }
  FcPatternDestroy(pattern);

  if (fallback_fonts->empty())
    fallback_fonts->push_back(Font(font_family, 13));

  return *fallback_fonts;
}

namespace {

class CachedFont {
 public:
  // Note: We pass the charset explicitly as callers
  // should not create CachedFont entries without knowing
  // that the FcPattern contains a valid charset.
  CachedFont(FcPattern* pattern, FcCharSet* char_set)
      : supported_characters_(char_set) {
    DCHECK(pattern);
    DCHECK(char_set);
    fallback_font_.name = GetFontName(pattern);
    fallback_font_.filename = GetFontFilename(pattern);
    fallback_font_.ttc_index = GetFontTtcIndex(pattern);
    fallback_font_.is_bold = IsFontBold(pattern);
    fallback_font_.is_italic = IsFontItalic(pattern);
  }

  const FallbackFontData& fallback_font() const { return fallback_font_; }

  bool HasGlyphForCharacter(UChar32 c) const {
    return supported_characters_ && FcCharSetHasChar(supported_characters_, c);
  }

 private:
  static std::string GetFontName(FcPattern* pattern) {
    FcChar8* familyName = nullptr;
    if (FcPatternGetString(pattern, FC_FAMILY, 0, &familyName) != FcResultMatch)
      return std::string();
    return std::string(reinterpret_cast<const char*>(familyName));
  }

  static std::string GetFontFilename(FcPattern* pattern) {
    FcChar8* c_filename = nullptr;
    if (FcPatternGetString(pattern, FC_FILE, 0, &c_filename) != FcResultMatch)
      return std::string();
    return std::string(reinterpret_cast<const char*>(c_filename));
  }

  static int GetFontTtcIndex(FcPattern* pattern) {
    int ttcIndex = -1;
    if (FcPatternGetInteger(pattern, FC_INDEX, 0, &ttcIndex) != FcResultMatch ||
        ttcIndex < 0)
      return 0;
    return ttcIndex;
  }

  static bool IsFontBold(FcPattern* pattern) {
    int weight = 0;
    if (FcPatternGetInteger(pattern, FC_WEIGHT, 0, &weight) != FcResultMatch)
      return false;
    return weight >= FC_WEIGHT_BOLD;
  }

  static bool IsFontItalic(FcPattern* pattern) {
    int slant = 0;
    if (FcPatternGetInteger(pattern, FC_SLANT, 0, &slant) != FcResultMatch)
      return false;
    return slant != FC_SLANT_ROMAN;
  }

  FallbackFontData fallback_font_;
  // supported_characters_ is owned by the parent
  // FcFontSet and should never be freed.
  FcCharSet* supported_characters_;
};

class CachedFontSet {
 public:
  // CachedFontSet takes ownership of the passed FcFontSet.
  static std::unique_ptr<CachedFontSet> CreateForLocale(
      const std::string& locale) {
    FcFontSet* font_set = CreateFcFontSetForLocale(locale);
    return base::WrapUnique(new CachedFontSet(font_set));
  }

  ~CachedFontSet() {
    fallback_list_.clear();
    FcFontSetDestroy(font_set_);
  }

  FallbackFontData GetFallbackFontForChar(UChar32 c) {
    for (const auto& cached_font : fallback_list_) {
      if (cached_font.HasGlyphForCharacter(c))
        return cached_font.fallback_font();
    }
    // The previous code just returned garbage if the user didn't
    // have the necessary fonts, this seems better than garbage.
    // Current callers happen to ignore any values with an empty family string.
    return FallbackFontData();
  }

 private:
  static FcFontSet* CreateFcFontSetForLocale(const std::string& locale) {
    FcPattern* pattern = FcPatternCreate();

    if (!locale.empty()) {
      // FcChar* is unsigned char* so we have to cast.
      FcPatternAddString(pattern, FC_LANG,
                         reinterpret_cast<const FcChar8*>(locale.c_str()));
    }

    FcPatternAddBool(pattern, FC_SCALABLE, FcTrue);

    FcConfigSubstitute(0, pattern, FcMatchPattern);
    FcDefaultSubstitute(pattern);

    if (locale.empty())
      FcPatternDel(pattern, FC_LANG);

    // The result parameter returns if any fonts were found.
    // We already handle 0 fonts correctly, so we ignore the param.
    FcResult result;
    FcFontSet* font_set = FcFontSort(0, pattern, 0, 0, &result);
    FcPatternDestroy(pattern);

    // The caller will take ownership of this FcFontSet.
    return font_set;
  }

  CachedFontSet(FcFontSet* font_set) : font_set_(font_set) {
    FillFallbackList();
  }

  void FillFallbackList() {
    DCHECK(fallback_list_.empty());
    if (!font_set_)
      return;

    for (int i = 0; i < font_set_->nfont; ++i) {
      FcPattern* pattern = font_set_->fonts[i];

      // Ignore any bitmap fonts users may still have installed from last
      // century.
      FcBool is_scalable;
      if (FcPatternGetBool(pattern, FC_SCALABLE, 0, &is_scalable) !=
              FcResultMatch ||
          !is_scalable)
        continue;

      // Ignore any fonts FontConfig knows about, but that we don't have
      // permission to read.
      FcChar8* c_filename;
      if (FcPatternGetString(pattern, FC_FILE, 0, &c_filename) != FcResultMatch)
        continue;
      if (access(reinterpret_cast<char*>(c_filename), R_OK))
        continue;

      // Take only supported font formats on board.
      FcChar8* font_format;
      if (FcPatternGetString(pattern, FC_FONTFORMAT, 0, &font_format) !=
          FcResultMatch) {
        continue;
      }
      if (font_format &&
          strcmp(reinterpret_cast<char*>(font_format), kFontFormatTrueType) &&
          strcmp(reinterpret_cast<char*>(font_format), kFontFormatCFF)) {
        continue;
      }

      // Make sure this font can tell us what characters it has glyphs for.
      FcCharSet* char_set;
      if (FcPatternGetCharSet(pattern, FC_CHARSET, 0, &char_set) !=
          FcResultMatch)
        continue;

      fallback_list_.emplace_back(pattern, char_set);
    }
  }

  FcFontSet* font_set_;  // Owned by this object.
  // CachedFont has a FcCharset* which points into the FcFontSet.
  // If the FcFontSet is ever destroyed, the fallback list
  // must be cleared first.
  std::vector<CachedFont> fallback_list_;

  DISALLOW_COPY_AND_ASSIGN(CachedFontSet);
};

typedef std::map<std::string, std::unique_ptr<CachedFontSet>> FontSetCache;
base::LazyInstance<FontSetCache>::Leaky g_font_sets_by_locale =
    LAZY_INSTANCE_INITIALIZER;

}  // namespace

FallbackFontData GetFallbackFontForChar(UChar32 c, const std::string& locale) {
  auto& cached_font_set = g_font_sets_by_locale.Get()[locale];
  if (!cached_font_set)
    cached_font_set = CachedFontSet::CreateForLocale(locale);
  return cached_font_set->GetFallbackFontForChar(c);
}

}  // namespace gfx