Ladybird: Use fontconfig to choose generic fonts on non-Apple systems

If we get a suggestion from fontconfig, we try those fonts first, before
falling back on the hard coded list of known suitable fonts for each
generic family.

Ladybird/FontPlugin.cpp

@@ -13,11 +13,22 @@
 #include <LibGfx/Font/Emoji.h>
 #include <LibGfx/Font/FontDatabase.h>
 
+#ifdef USE_FONTCONFIG
+#    include <fontconfig/fontconfig.h>
+#endif
+
 namespace Ladybird {
 
 FontPlugin::FontPlugin(bool is_layout_test_mode)
     : m_is_layout_test_mode(is_layout_test_mode)
 {
+#ifdef USE_FONTCONFIG
+    {
+        auto fontconfig_initialized = FcInit();
+        VERIFY(fontconfig_initialized);
+    }
+#endif
+
     // Load anything we can find in the system's font directories
     for (auto const& path : Core::StandardPaths::font_directories().release_value_but_fixme_should_propagate_errors())
         Gfx::FontDatabase::the().load_all_fonts_from_uri(MUST(String::formatted("file://{}", path)));
@@ -50,6 +61,79 @@ Gfx::Font& FontPlugin::default_fixed_width_font()
     return *m_default_fixed_width_font;
 }
 
+#ifdef USE_FONTCONFIG
+static Optional<String> query_fontconfig_for_generic_family(Web::Platform::GenericFont generic_font)
+{
+    char const* pattern_string = nullptr;
+    switch (generic_font) {
+    case Web::Platform::GenericFont::Cursive:
+        pattern_string = "cursive";
+        break;
+    case Web::Platform::GenericFont::Fantasy:
+        pattern_string = "fantasy";
+        break;
+    case Web::Platform::GenericFont::Monospace:
+        pattern_string = "monospace";
+        break;
+    case Web::Platform::GenericFont::SansSerif:
+        pattern_string = "sans-serif";
+        break;
+    case Web::Platform::GenericFont::Serif:
+        pattern_string = "serif";
+        break;
+    case Web::Platform::GenericFont::UiMonospace:
+        pattern_string = "monospace";
+        break;
+    case Web::Platform::GenericFont::UiRounded:
+        pattern_string = "sans-serif";
+        break;
+    case Web::Platform::GenericFont::UiSansSerif:
+        pattern_string = "sans-serif";
+        break;
+    case Web::Platform::GenericFont::UiSerif:
+        pattern_string = "serif";
+        break;
+    default:
+        VERIFY_NOT_REACHED();
+    }
+
+    auto* config = FcConfigGetCurrent();
+    VERIFY(config);
+
+    FcPattern* pattern = FcNameParse(reinterpret_cast<FcChar8 const*>(pattern_string));
+    VERIFY(pattern);
+
+    auto success = FcConfigSubstitute(config, pattern, FcMatchPattern);
+    VERIFY(success);
+
+    FcDefaultSubstitute(pattern);
+
+    // Never select bitmap fonts.
+    success = FcPatternAddBool(pattern, FC_SCALABLE, FcTrue);
+    VERIFY(success);
+
+    // FIXME: Enable this once we can handle OpenType variable fonts.
+    success = FcPatternAddBool(pattern, FC_VARIABLE, FcFalse);
+    VERIFY(success);
+
+    Optional<String> name;
+    FcResult result {};
+
+    if (auto* matched = FcFontMatch(config, pattern, &result)) {
+        FcChar8* family = nullptr;
+        if (FcPatternGetString(matched, FC_FAMILY, 0, &family) == FcResultMatch) {
+            auto const* family_cstring = reinterpret_cast<char const*>(family);
+            if (auto string = String::from_utf8(StringView { family_cstring, strlen(family_cstring) }); !string.is_error()) {
+                name = string.release_value();
+            }
+        }
+        FcPatternDestroy(matched);
+    }
+    FcPatternDestroy(pattern);
+    return name;
+}
+#endif
+
 void FontPlugin::update_generic_fonts()
 {
     // How we choose which system font to use for each CSS font:
@@ -69,10 +153,19 @@ void FontPlugin::update_generic_fonts()
 
         RefPtr<Gfx::Font const> gfx_font;
 
-        for (auto& fallback : fallbacks) {
+#ifdef USE_FONTCONFIG
-            gfx_font = Gfx::FontDatabase::the().get(fallback, 16, 400, Gfx::FontWidth::Normal, 0);
+        auto name = query_fontconfig_for_generic_family(generic_font);
-            if (gfx_font)
+        if (name.has_value()) {
-                break;
+            gfx_font = Gfx::FontDatabase::the().get(name.value(), 16, 400, Gfx::FontWidth::Normal, 0);
+        }
+#endif
+
+        if (!gfx_font) {
+            for (auto const& fallback : fallbacks) {
+                gfx_font = Gfx::FontDatabase::the().get(fallback, 16, 400, Gfx::FontWidth::Normal, 0);
+                if (gfx_font)
+                    break;
+            }
         }
 
         m_generic_font_names[static_cast<size_t>(generic_font)] = gfx_font ? gfx_font->family() : String {};

Ladybird/WebContent/CMakeLists.txt

@@ -1,4 +1,6 @@
 include(accelerated_graphics)
+include(fontconfig)
+
 set(WEBCONTENT_SOURCE_DIR ${LADYBIRD_SOURCE_DIR}/Userland/Services/WebContent/)
 
 set(WEBCONTENT_SOURCES
@@ -70,6 +72,10 @@ else()
     add_executable(WebContent main.cpp)
 endif()
 
+if (HAS_FONTCONFIG)
+    target_link_libraries(webcontent PRIVATE Fontconfig::Fontconfig)
+endif()
+
 target_link_libraries(WebContent PRIVATE webcontent LibURL)
 
 target_sources(webcontent PUBLIC FILE_SET ladybird TYPE HEADERS

Ladybird/WebWorker/CMakeLists.txt

@@ -1,3 +1,5 @@
+include(fontconfig)
+
 set(WEBWORKER_SOURCE_DIR ${LADYBIRD_SOURCE_DIR}/Userland/Services/WebWorker)
 
 set(CMAKE_AUTOMOC OFF)
@@ -22,6 +24,10 @@ target_include_directories(webworker PRIVATE ${LADYBIRD_SOURCE_DIR}/Userland/)
 target_include_directories(webworker PRIVATE ${CMAKE_CURRENT_BINARY_DIR}/..)
 target_link_libraries(webworker PUBLIC LibCore LibFileSystem LibGfx LibIPC LibJS LibProtocol LibWeb LibWebView LibLocale LibImageDecoderClient LibMain LibURL)
 
+if (HAS_FONTCONFIG)
+    target_link_libraries(webworker PRIVATE Fontconfig::Fontconfig)
+endif()
+
 add_executable(WebWorker main.cpp)
 target_include_directories(WebWorker PRIVATE ${LADYBIRD_SOURCE_DIR}/Userland/)
 target_link_libraries(WebWorker PRIVATE webworker)

Meta/CMake/fontconfig.cmake

@@ -0,0 +1,5 @@
+if (NOT APPLE)
+    find_package(Fontconfig REQUIRED)
+    set(HAS_FONTCONFIG ON CACHE BOOL "" FORCE)
+    add_compile_definitions(USE_FONTCONFIG=1)
+endif()

vcpkg.json

@@ -2,7 +2,11 @@
   "builtin-baseline": "01f602195983451bc83e72f4214af2cbc495aa94",
   "dependencies": [
     "sqlite3",
-    "woff2"
+    "woff2",
+    {
+      "name": "fontconfig",
+      "platform": "linux | freebsd | openbsd"
+    }
   ],
   "overrides": [
     {
@@ -12,6 +16,10 @@
     {
       "name": "woff2",
       "version": "1.0.2#4"
+    },
+    {
+      "name": "fontconfig",
+      "version": "2.14.2#1"
     }
   ]
 }