font_unix.cpp

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/*
 * This file is part of OpenTTD.
 * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
 * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <https://www.gnu.org/licenses/old-licenses/gpl-2.0>.
 */

 
#include "../../stdafx.h"
 
#include "../../misc/autorelease.hpp"
#include "../../debug.h"
#include "../../fontcache.h"
#include "../../string_func.h"
#include "../../strings_func.h"
#include "font_unix.h"
 
#include <fontconfig/fontconfig.h>
#include <ft2build.h>
#include FT_FREETYPE_H
 
#include "../../safeguards.h"
 
extern FT_Library _ft_library;

static const FcChar8 *ToFcString(const std::string &str)
{
  return reinterpret_cast<const FcChar8 *>(str.c_str());
}

static const char *FromFcString(const FcChar8 *str)
{
  return reinterpret_cast<const char *>(str);
}

static std::tuple<std::string, std::string> SplitFontFamilyAndStyle(std::string_view font_name)
{
  auto separator = font_name.find(',');
  if (separator == std::string_view::npos) return { std::string(font_name), std::string() };
 
  auto begin = font_name.find_first_not_of("\t ", separator + 1);
  if (begin == std::string_view::npos) return { std::string(font_name.substr(0, separator)), std::string() };
 
  return { std::string(font_name.substr(0, separator)), std::string(font_name.substr(begin)) };
}

FT_Error GetFontByFaceName(std::string_view font_name, FT_Face *face)
{
  FT_Error err = FT_Err_Cannot_Open_Resource;
 
  if (!FcInit()) {
    ShowInfo("Unable to load font configuration");
    return err;
  }
 
  auto fc_instance = AutoRelease<FcConfig, FcConfigDestroy>(FcConfigReference(nullptr));
  assert(fc_instance != nullptr);
 
  /* Split & strip the font's style */
  auto [font_family, font_style] = SplitFontFamilyAndStyle(font_name);
 
  /* Resolve the name and populate the information structure */
  auto pat = AutoRelease<FcPattern, FcPatternDestroy>(FcPatternCreate());
  if (!font_family.empty()) FcPatternAddString(pat.get(), FC_FAMILY, ToFcString(font_family));
  if (!font_style.empty()) FcPatternAddString(pat.get(), FC_STYLE, ToFcString(font_style));
  FcConfigSubstitute(nullptr, pat.get(), FcMatchPattern);
  FcDefaultSubstitute(pat.get());
  auto fs = AutoRelease<FcFontSet, FcFontSetDestroy>(FcFontSetCreate());
  FcResult result;
  FcPattern *match = FcFontMatch(nullptr, pat.get(), &result);
 
  if (fs == nullptr || match == nullptr) return err;
 
  FcFontSetAdd(fs.get(), match);
 
  for (FcPattern *font : std::span(fs->fonts, fs->nfont)) {
    FcChar8 *family;
    FcChar8 *style;
    FcChar8 *file;
    int32_t index;
 
    /* Try the new filename */
    if (FcPatternGetString(font, FC_FILE, 0, &file) != FcResultMatch) continue;
    if (FcPatternGetString(font, FC_FAMILY, 0, &family) != FcResultMatch) continue;
    if (FcPatternGetString(font, FC_STYLE, 0, &style) != FcResultMatch) continue;
    if (FcPatternGetInteger(font, FC_INDEX, 0, &index) != FcResultMatch) continue;
 
    /* The correct style? */
    if (!font_style.empty() && !StrEqualsIgnoreCase(font_style, FromFcString(style))) continue;
 
    /* Font config takes the best shot, which, if the family name is spelled
     * wrongly a 'random' font, so check whether the family name is the
     * same as the supplied name */
    if (StrEqualsIgnoreCase(font_family, FromFcString(family))) {
      err = FT_New_Face(_ft_library, FromFcString(file), index, face);
      if (err == FT_Err_Ok) return err;
    }
  }
 
  return err;
}

static int GetPreferredWeightDistance(int weight)
{
  /* Prefer a font between normal and medium weight. */
  static constexpr int PREFERRED_WEIGHT_MIN = FC_WEIGHT_NORMAL;
  static constexpr int PREFERRED_WEIGHT_MAX = FC_WEIGHT_MEDIUM;
 
  if (weight < PREFERRED_WEIGHT_MIN) return std::abs(weight - PREFERRED_WEIGHT_MIN);
  if (weight > PREFERRED_WEIGHT_MAX) return weight - PREFERRED_WEIGHT_MAX;
  return 0;
}

bool FontConfigFindFallbackFont(const std::string &language_isocode, MissingGlyphSearcher *callback)
{
  bool ret = false;
 
  if (!FcInit()) return ret;
 
  auto fc_instance = AutoRelease<FcConfig, FcConfigDestroy>(FcConfigReference(nullptr));
  assert(fc_instance != nullptr);
 
  /* Fontconfig doesn't handle full language isocodes, only the part
   * before the _ of e.g. en_GB is used, so "remove" everything after
   * the _. */
  std::string lang = fmt::format(":lang={}", language_isocode.substr(0, language_isocode.find('_')));
 
  /* First create a pattern to match the wanted language. */
  auto pat = AutoRelease<FcPattern, FcPatternDestroy>(FcNameParse(ToFcString(lang)));
  /* We only want to know these attributes. */
  auto os = AutoRelease<FcObjectSet, FcObjectSetDestroy>(FcObjectSetBuild(FC_FILE, FC_INDEX, FC_SPACING, FC_SLANT, FC_WEIGHT, FC_CHARSET, nullptr));
  /* Get the list of filenames matching the wanted language. */
  auto fs = AutoRelease<FcFontSet, FcFontSetDestroy>(FcFontList(nullptr, pat.get(), os.get()));
 
  if (fs == nullptr) return ret;
 
  int best_weight = -1;
  const char *best_font = nullptr;
  int best_index = 0;
 
  for (FcPattern *font : std::span(fs->fonts, fs->nfont)) {
    FcChar8 *file = nullptr;
    FcResult res = FcPatternGetString(font, FC_FILE, 0, &file);
    if (res != FcResultMatch || file == nullptr) continue;
 
    /* Get a font with the right spacing .*/
    int value = 0;
    FcPatternGetInteger(font, FC_SPACING, 0, &value);
    if (callback->missing_fontsizes.Test(FontSize::Monospace) != (value == FC_MONO) && value != FC_DUAL) continue;
 
    /* Do not use those that explicitly say they're slanted. */
    FcPatternGetInteger(font, FC_SLANT, 0, &value);
    if (value != 0) continue;
 
    /* We want a font near to medium weight. */
    FcPatternGetInteger(font, FC_WEIGHT, 0, &value);
    int weight = GetPreferredWeightDistance(value);
    if (best_weight != -1 && weight > best_weight) continue;
 
    /* Test the font for matching glyphs. This is essentially the same as
     * calling TryFallback() but avoids having to reopen the font, etc. */
    size_t matching_chars = 0;
    FcCharSet *charset;
    FcPatternGetCharSet(font, FC_CHARSET, 0, &charset);
    for (const char32_t &c : callback->missing_glyphs) {
      if (FcCharSetHasChar(charset, c)) ++matching_chars;
    }
 
    if (matching_chars < callback->missing_glyphs.size()) {
      Debug(fontcache, 1, "Font \"{}\" misses {} glyphs", FromFcString(file), callback->missing_glyphs.size() - matching_chars);
      continue;
    }
 
    /* Possible match based on attributes, get index. */
    int32_t index;
    res = FcPatternGetInteger(font, FC_INDEX, 0, &index);
    if (res != FcResultMatch) continue;
 
    best_weight = weight;
    best_font = FromFcString(file);
    best_index = index;
  }
 
  if (best_font == nullptr) return false;
 
  FontCache::AddFallback(callback->missing_fontsizes, best_font, best_index);
 
  return true;
}