Rework windows font collector

meson.build

@@ -317,7 +317,7 @@ if host_machine.system() == 'windows'
             # Windows 8 not required if XAudio2 fails to be found. revert for compat.
             add_project_arguments('-D_WIN32_WINNT=0x0601', language: 'cpp')
         endif
-        
+
         if not have_dsound_h and get_option('xaudio2').enabled()
             error('xaudio2 enabled but xaudio2.h not found')
         endif
@@ -327,6 +327,10 @@ if host_machine.system() == 'windows'
     endif
 endif
 
+if host_machine.system() == 'windows' and cc.has_header('dwrite_3.h')
+    conf.set('HAVE_DWRITE_3', 1)
+endif
+
 if host_machine.system() == 'darwin'
     frameworks_dep = dependency('appleframeworks', modules : ['CoreText', 'CoreFoundation', 'AppKit', 'Carbon', 'IOKit', 'QuartzCore'])
     deps += frameworks_dep

src/dialog_fonts_collector.cpp

@@ -94,7 +94,14 @@ void FontsCollectorThread(AssFile *subs, agi::fs::path const& destination, FcMod
 			collector->AddPendingEvent(ValueEvent<color_str_pair>(EVT_ADD_TEXT, -1, {colour, text.Clone()}));
 		};
 
-		auto paths = FontCollector(AppendText).GetFontPaths(subs);
+		std::vector<agi::fs::path> paths;
+		try {
+			paths = FontCollector(AppendText).GetFontPaths(subs);
+		}
+		catch (agi::EnvironmentError const& err) {
+			AppendText(fmt_tl("* An error occurred when enumerating the used fonts: %s.\n", err.GetMessage()), 2);
+		}
+
 		if (paths.empty()) {
 			collector->AddPendingEvent(wxThreadEvent(EVT_COLLECTION_DONE));
 			return;

src/font_file_lister.h

@@ -41,17 +41,17 @@ struct CollectionResult {
 };
 
 #ifdef _WIN32
+#include <dwrite.h>
 class GdiFontFileLister {
-	std::unordered_multimap<uint32_t, agi::fs::path> index;
-	agi::scoped_holder<HDC> dc;
-	std::string buffer;
-
-	bool ProcessLogFont(LOGFONTW const& expected, LOGFONTW const& actual, std::vector<int> const& characters);
+	agi::scoped_holder<HDC> dc_sh;
+	agi::scoped_holder<IDWriteFactory*> dwrite_factory_sh;
+	agi::scoped_holder<IDWriteFontCollection*> font_collection_sh;
+	agi::scoped_holder<IDWriteGdiInterop*> gdi_interop_sh;
 
 public:
 	/// Constructor
-	/// @param cb Callback for status logging
-	GdiFontFileLister(FontCollectorStatusCallback &cb);
+	/// @throws agi::EnvironmentError if an error occurs during construction.
+	GdiFontFileLister(FontCollectorStatusCallback &);
 
 	/// @brief Get the path to the font with the given styles
 	/// @param facename Name of font face