feat: Enumerate fonts on Linux using Fontconfig when available (#1821)

### Problem description

The fonts list on Linux does not show all system fonts, and does not
show font names at all.

### Implementation description

Use Fontconfig to make the list less bad if Fontconfig headers are
available.

### Additional things

I like fonts.

---------

Co-authored-by: Nik <werwolv98@gmail.com>

main/gui/CMakeLists.txt

@@ -63,6 +63,15 @@ if (WIN32)
     target_link_libraries(main PRIVATE usp10 wsock32 ws2_32 Dwmapi.lib Winmm.lib)
 else ()
     target_link_libraries(main PRIVATE pthread)
+
+    if (NOT APPLE)
+        find_package(Fontconfig)
+        if (TARGET Fontconfig::Fontconfig)
+            message(STATUS "Using Fontconfig version: ${Fontconfig_VERSION}")
+            target_link_libraries(main PRIVATE Fontconfig::Fontconfig)
+            target_compile_definitions(main PRIVATE IMHEX_HAS_FONTCONFIG)
+        endif ()
+    endif ()
 endif ()
 
 precompileHeaders(main ${CMAKE_CURRENT_SOURCE_DIR}/include)

main/gui/source/window/linux_window.cpp

@@ -22,6 +22,10 @@
     #include <string.h>
     #include <ranges>
 
+    #if defined(IMHEX_HAS_FONTCONFIG)
+        #include <fontconfig/fontconfig.h>
+    #endif
+
 namespace hex {
 
     bool isFileInPath(const std::fs::path &filename) {
@@ -48,7 +52,43 @@ namespace hex {
         } // Hopefully one of these commands is installed
     }
 
+    #if defined(IMHEX_HAS_FONTCONFIG)
+        static bool enumerateFontConfig() {
+            if (!FcInit())
+                return false;
+
+            ON_SCOPE_EXIT { FcFini(); };
+
+            auto fonts = FcConfigGetFonts(nullptr, FcSetSystem);
+            if (fonts == nullptr)
+                return false;
+
+            for (int i = 0; i < fonts->nfont; ++i) {
+                auto font = fonts->fonts[i];
+                FcChar8 *file, *fullName;
+
+                if (FcPatternGetString(font, FC_FILE, 0, &file) != FcResultMatch) {
+                    continue;
+                }
+
+                if (FcPatternGetString(font, FC_FULLNAME, 0, &fullName) != FcResultMatch
+                    && FcPatternGetString(font, FC_FAMILY, 0, &fullName) != FcResultMatch) {
+                    continue;
+                }
+                
+                registerFont(reinterpret_cast<const char *>(fullName), reinterpret_cast<const char *>(file));
+            }
+
+            return true;
+        }
+    #endif
+
     void enumerateFonts() {
+        #if defined(IMHEX_HAS_FONTCONFIG)
+            if (enumerateFontConfig())
+                return;
+        #endif
+
         const std::array FontDirectories = {
             "/usr/share/fonts",
             "/usr/local/share/fonts",