From 6e70670e0be3591455dedb670c21a9f414fc35f6 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Fri, 8 Apr 2022 21:27:35 +0200
Subject: [PATCH] LibWeb: Load fonts from style sheet once when sheet is added

Previously, we were running the "load fonts if needed" machine at the
start of every style computation. That was a lot of unnecessary work,
especially on sites with lots of style rules, since we had to traverse
every style sheet to see if any @font-face rules needed loading.

With this patch, we now load fonts once per sheet, right after adding
it to a document's style sheet list.
---
 .../Libraries/LibWeb/CSS/StyleComputer.cpp    | 32 +++++++++----------
 Userland/Libraries/LibWeb/CSS/StyleComputer.h |  4 +--
 .../Libraries/LibWeb/CSS/StyleSheetList.cpp   |  3 +-
 3 files changed, 19 insertions(+), 20 deletions(-)

diff --git a/Userland/Libraries/LibWeb/CSS/StyleComputer.cpp b/Userland/Libraries/LibWeb/CSS/StyleComputer.cpp
index 5e49161bbc..d3074d4c5a 100644
--- a/Userland/Libraries/LibWeb/CSS/StyleComputer.cpp
+++ b/Userland/Libraries/LibWeb/CSS/StyleComputer.cpp
@@ -1120,7 +1120,6 @@ NonnullRefPtr<StyleProperties> StyleComputer::create_document_style() const
 
 NonnullRefPtr<StyleProperties> StyleComputer::compute_style(DOM::Element& element, Optional<CSS::Selector::PseudoElement> pseudo_element) const
 {
-    load_fonts_if_needed();
     build_rule_cache_if_needed();
 
     auto style = StyleProperties::create();
@@ -1268,23 +1267,22 @@ void StyleComputer::did_load_font([[maybe_unused]] FlyString const& family_name)
     document().invalidate_style();
 }
 
-void StyleComputer::load_fonts_if_needed() const
+void StyleComputer::load_fonts_from_sheet(CSSStyleSheet const& sheet)
 {
-    for_each_stylesheet(CascadeOrigin::Author, [&](StyleSheet const& sheet) {
-        for (auto const& rule : static_cast<CSSStyleSheet const&>(sheet).rules()) {
-            if (!is<CSSFontFaceRule>(rule))
-                continue;
-            auto const& font_face = static_cast<CSSFontFaceRule const&>(rule).font_face();
-            if (font_face.sources().is_empty())
-                continue;
-            if (m_loaded_fonts.contains(font_face.font_family()))
-                continue;
+    for (auto const& rule : static_cast<CSSStyleSheet const&>(sheet).rules()) {
+        if (!is<CSSFontFaceRule>(rule))
+            continue;
+        auto const& font_face = static_cast<CSSFontFaceRule const&>(rule).font_face();
+        if (font_face.sources().is_empty())
+            continue;
+        if (m_loaded_fonts.contains(font_face.font_family()))
+            continue;
 
-            LoadRequest request;
-            auto url = m_document.parse_url(font_face.sources().first().url.to_string());
-            auto loader = make<FontLoader>(const_cast<StyleComputer&>(*this), font_face.font_family(), move(url));
-            const_cast<StyleComputer&>(*this).m_loaded_fonts.set(font_face.font_family(), move(loader));
-        }
-    });
+        LoadRequest request;
+        auto url = m_document.parse_url(font_face.sources().first().url.to_string());
+        auto loader = make<FontLoader>(const_cast<StyleComputer&>(*this), font_face.font_family(), move(url));
+        const_cast<StyleComputer&>(*this).m_loaded_fonts.set(font_face.font_family(), move(loader));
+    }
 }
+
 }
diff --git a/Userland/Libraries/LibWeb/CSS/StyleComputer.h b/Userland/Libraries/LibWeb/CSS/StyleComputer.h
index aab5d88bfe..d54393ae88 100644
--- a/Userland/Libraries/LibWeb/CSS/StyleComputer.h
+++ b/Userland/Libraries/LibWeb/CSS/StyleComputer.h
@@ -74,6 +74,8 @@ public:
 
     void did_load_font(FlyString const& family_name);
 
+    void load_fonts_from_sheet(CSSStyleSheet const&);
+
 private:
     void compute_cascaded_values(StyleProperties&, DOM::Element&, Optional<CSS::Selector::PseudoElement>) const;
     void compute_font(StyleProperties&, DOM::Element const*, Optional<CSS::Selector::PseudoElement>) const;
@@ -113,8 +115,6 @@ private:
     };
     OwnPtr<RuleCache> m_rule_cache;
 
-    void load_fonts_if_needed() const;
-
     class FontLoader;
     HashMap<String, NonnullOwnPtr<FontLoader>> m_loaded_fonts;
 };
diff --git a/Userland/Libraries/LibWeb/CSS/StyleSheetList.cpp b/Userland/Libraries/LibWeb/CSS/StyleSheetList.cpp
index a43ab4711a..18f177009c 100644
--- a/Userland/Libraries/LibWeb/CSS/StyleSheetList.cpp
+++ b/Userland/Libraries/LibWeb/CSS/StyleSheetList.cpp
@@ -13,9 +13,10 @@ void StyleSheetList::add_sheet(NonnullRefPtr<CSSStyleSheet> sheet)
 {
     VERIFY(!m_sheets.contains_slow(sheet));
     sheet->set_style_sheet_list({}, this);
-    m_sheets.append(move(sheet));
+    m_sheets.append(sheet);
 
     m_document.style_computer().invalidate_rule_cache();
+    m_document.style_computer().load_fonts_from_sheet(*sheet);
     m_document.invalidate_style();
 }