Add: Automatically load fonts for missing glyphs. (#14856)

src/console_cmds.cpp

@@ -2326,7 +2326,7 @@ static bool ConContent(std::span<std::string_view> argv)
  */
 static std::string_view FontLoadReasonToName(FontLoadReason load_reason)
 {
-	static const std::string_view LOAD_REASON_TO_NAME[] = { "default", "configured", "language" };
+	static const std::string_view LOAD_REASON_TO_NAME[] = { "default", "configured", "language", "missing" };
 	static_assert(std::size(LOAD_REASON_TO_NAME) == to_underlying(FontLoadReason::End));
 	return LOAD_REASON_TO_NAME[to_underlying(load_reason)];
 }

src/fontcache.cpp

@@ -75,6 +75,7 @@ int FontCache::GetDefaultFontHeight(FontSize fs)
 
 	for (const auto &fc : FontCache::caches) {
 		if (fc == nullptr || fc->fs != fs) continue;
+		if (fc->load_reason == FontLoadReason::MissingFallback) continue; // Avoid dynamically loaded fonts affecting widget sizes.
 		ascender = std::max(ascender, fc->ascender);
 		descender = std::min(descender, fc->descender);
 	}
@@ -269,10 +270,11 @@ std::string GetFontCacheFontName(FontSize fs)
 	}
 }
 
-/* static */ void FontCache::LoadFallbackFonts(FontSize fs)
+/* static */ void FontCache::LoadFallbackFonts(FontSize fs, FontLoadReason load_reason)
 {
 	const FontCacheSubSetting *setting = GetFontCacheSubSetting(fs);
 	for (auto it = setting->fallback_fonts.rbegin(); it != setting->fallback_fonts.rend(); ++it) {
+		if (it->load_reason != load_reason) continue;
 		FontCache::Register(FontProviderManager::LoadFont(fs, FontType::TrueType, false, it->name, it->os_handle), it->load_reason);
 	}
 }
@@ -318,12 +320,15 @@ std::string GetFontCacheFontName(FontSize fs)
 			if (std::ranges::find(fontnames, extra_font) == std::end(fontnames)) fontnames.push_back(extra_font);
 		}
 
+		/* First load fonts for missing glyphs discovered during string formatting. */
+		FontCache::LoadFallbackFonts(fs, FontLoadReason::MissingFallback);
+
 		/* Load configured fonts in reverse order so that the first entry has priority. */
 		for (auto it = fontnames.rbegin(); it != fontnames.rend(); ++it) {
 			if (*it == DEFAULT_FONT) {
 				FontCache::LoadDefaultFonts(fs);
 			} else if (*it == FALLBACK_FONT) {
-				FontCache::LoadFallbackFonts(fs);
+				FontCache::LoadFallbackFonts(fs, FontLoadReason::LanguageFallback);
 			} else {
 				FontCache::Register(FontProviderManager::LoadFont(fs, FontType::TrueType, true, std::string{*it}, {}), FontLoadReason::Configured);
 			}

src/fontcache.h

@@ -24,6 +24,7 @@ enum class FontLoadReason : uint8_t {
 	Default,
 	Configured,
 	LanguageFallback,
+	MissingFallback,
 	End,
 };
 
@@ -51,7 +52,7 @@ protected:
 	FontCache(FontSize fs) : fs(fs) {}
 	static void Register(std::unique_ptr<FontCache> &&fc, FontLoadReason load_reason);
 	static void LoadDefaultFonts(FontSize fs);
-	static void LoadFallbackFonts(FontSize fs);
+	static void LoadFallbackFonts(FontSize fs, FontLoadReason load_reason);
 
 public:
 	virtual ~FontCache() = default;

src/gfx_layout.cpp

@@ -10,10 +10,15 @@
 #include "stdafx.h"
 #include "core/math_func.hpp"
 #include "gfx_layout.h"
+#include "gfx_func.h"
 #include "string_func.h"
 #include "strings_func.h"
 #include "core/utf8.hpp"
 #include "debug.h"
+#include "timer/timer.h"
+#include "timer/timer_window.h"
+#include "viewport_func.h"
+#include "window_func.h"
 
 #include "table/control_codes.h"
 
@@ -37,6 +42,50 @@
 /** Cache of ParagraphLayout lines. */
 std::unique_ptr<Layouter::LineCache> Layouter::linecache;
 
+class RuntimeMissingGlyphSearcher : public MissingGlyphSearcher {
+	std::array<std::set<char32_t>, FS_END> glyphs{};
+public:
+	RuntimeMissingGlyphSearcher() : MissingGlyphSearcher(FONTSIZES_ALL) {}
+
+	FontLoadReason GetLoadReason() override { return FontLoadReason::MissingFallback; }
+
+	inline void Insert(FontSize fs, char32_t c)
+	{
+		this->glyphs[fs].insert(c);
+		this->search_timeout.Reset();
+	}
+
+	std::set<char32_t> GetRequiredGlyphs(FontSizes fontsizes) override
+	{
+		std::set<char32_t> r;
+		for (FontSize fs : fontsizes) {
+			r.merge(this->glyphs[fs]);
+		}
+		return r;
+	}
+
+	TimeoutTimer<TimerWindow> search_timeout{std::chrono::milliseconds(250), [this]()
+	{
+		FontSizes changed_fontsizes{};
+		for (FontSize fs = FS_BEGIN; fs != FS_END; ++fs) {
+			auto &missing = this->glyphs[fs];
+			if (missing.empty()) continue;
+
+			if (FontProviderManager::FindFallbackFont({}, fs, this)) changed_fontsizes.Set(fs);
+			missing.clear();
+		}
+
+		if (!changed_fontsizes.Any()) return;
+
+		FontCache::LoadFontCaches(changed_fontsizes);
+		LoadStringWidthTable(changed_fontsizes);
+		UpdateAllVirtCoords();
+		ReInitAllWindows(true);
+	}};
+};
+
+static RuntimeMissingGlyphSearcher _missing_glyphs;
+
 /**
  * Helper for getting a ParagraphLayouter of the given type.
  *
@@ -98,6 +147,7 @@ static inline void GetLayouter(Layouter::LineCacheItem &line, std::string_view s
 			FontIndex font_index = FontCache::GetFontIndexForCharacter(state.fontsize, c);
 
 			if (font_index == INVALID_FONT_INDEX) {
+				_missing_glyphs.Insert(state.fontsize, c);
 				font_index = FontCache::GetDefaultFontIndex(state.fontsize);
 			}