logmeow/fonts.cpp

#include <string>
#include <utility>
#include <exception>
#include <stdexcept>
#include <fontconfig/fontconfig.h>

#include <cstdio>
#include <cstdlib>

#include "fonts.h"

class FcResultException : public std::exception {
public:
    FcResultException(FcResult result) : _result(result) {}
    const char* what() const noexcept {
        switch (this->_result) {
            case FcResultMatch: return "FcResultException: Object exists with the specified ID";
            case FcResultNoMatch: return "FcResultException: Object doesn't exist at all";
            case FcResultTypeMismatch: return "FcResultException: Object exists, but the type doesn't match";
            case FcResultNoId: return "FcResultException: Object exists, but has fewer values than specified";
            case FcResultOutOfMemory: return "FcResultException: malloc failed";
        }
        return "FcResultException: Unknown result";
    }

private:
    FcResult _result;
};

static std::string get_filename(FcPattern* pattern, const char* family) {
    std::string filename;
    FcResult result;
    FcValue font_value;
    FcValue family_value = {
        .type = FcTypeString,
        .u = {
            .s = reinterpret_cast<const FcChar8*>(family)
        }
    };

    if (FcPatternAdd(pattern, FC_FAMILY, family_value, FcFalse) != FcTrue) {
        throw std::runtime_error(std::string("FcPatternAdd() for ") + family + " returned FcFalse");
    }
    FcConfigSubstitute(nullptr, pattern, FcMatchPattern);
    FcDefaultSubstitute(pattern);

    FcPattern* font_pattern = FcFontMatch(nullptr, pattern, &result);
    if (!font_pattern) {
        throw std::runtime_error(std::string("FcFontMatch() for ") + family + " returned nullptr");
    }
    if (result != FcResultMatch) {
        FcPatternDestroy(font_pattern);
        throw FcResultException(result);
    }

    result = FcPatternGet(font_pattern, FC_FILE, 0, &font_value);
    if (result != FcResultMatch) {
        FcPatternDestroy(font_pattern);
        throw FcResultException(result);
    }

    filename = reinterpret_cast<const char*>(font_value.u.s);
    FcPatternDestroy(font_pattern);
    return filename;
}

std::pair<std::string, std::string> get_fonts() {
    if (FcInit() != FcTrue) {
        throw std::runtime_error("FcInit() returned FcFalse");
    }

    std::string monospace_filename, sans_serif_filename;
    FcPattern* pattern = FcPatternCreate();
    if (!pattern) {
        FcFini();
        throw std::bad_alloc();
    }

    try {
        sans_serif_filename = get_filename(pattern, "sans-serif");
    } catch (const std::exception& e) {
        FcPatternDestroy(pattern);
        FcFini();
        throw;
    }
    FcPatternDel(pattern, FC_FAMILY);
    try {
        monospace_filename = get_filename(pattern, "monospace");
    } catch (const std::exception& e) {
        FcPatternDestroy(pattern);
        FcFini();
        throw;
    }

    FcPatternDestroy(pattern);
    FcFini();
    return std::make_pair(std::move(sans_serif_filename), std::move(monospace_filename));
}