From 0fece0650ec6298761f1ac4ab258a8ebf3f7feac Mon Sep 17 00:00:00 2001
From: Andreas Kling <andreas@ladybird.org>
Date: Mon, 14 Jul 2025 17:59:58 +0200
Subject: [PATCH] LibGfx: Let FontCascadeList quickly reject out-of-range code
 points

By keeping track of the enclosing range around all Unicode ranges of a
FontCascadeList entry, we can quickly reject any code point that's
outside all ranges.

This knocks font_for_code_point() from 7% to 3% in the profile when
scrolling on https://screenshotone.com/
---
 Libraries/LibGfx/FontCascadeList.cpp | 20 +++++++++++++++++---
 Libraries/LibGfx/FontCascadeList.h   |  8 +++++++-
 2 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/Libraries/LibGfx/FontCascadeList.cpp b/Libraries/LibGfx/FontCascadeList.cpp
index 7e8e17d8ad0..45cc71ceab3 100644
--- a/Libraries/LibGfx/FontCascadeList.cpp
+++ b/Libraries/LibGfx/FontCascadeList.cpp
@@ -15,7 +15,19 @@ void FontCascadeList::add(NonnullRefPtr<Font const> font)
 
 void FontCascadeList::add(NonnullRefPtr<Font const> font, Vector<UnicodeRange> unicode_ranges)
 {
-    m_fonts.append({ move(font), move(unicode_ranges) });
+    u32 lowest_code_point = 0xFFFFFFFF;
+    u32 highest_code_point = 0;
+
+    for (auto& range : unicode_ranges) {
+        lowest_code_point = min(lowest_code_point, range.min_code_point());
+        highest_code_point = max(highest_code_point, range.max_code_point());
+    }
+
+    m_fonts.append({ move(font),
+        Entry::RangeData {
+            { lowest_code_point, highest_code_point },
+            move(unicode_ranges),
+        } });
 }
 
 void FontCascadeList::extend(FontCascadeList const& other)
@@ -26,8 +38,10 @@ void FontCascadeList::extend(FontCascadeList const& other)
 Gfx::Font const& FontCascadeList::font_for_code_point(u32 code_point) const
 {
     for (auto const& entry : m_fonts) {
-        if (entry.unicode_ranges.has_value()) {
-            for (auto const& range : *entry.unicode_ranges) {
+        if (entry.range_data.has_value()) {
+            if (!entry.range_data->enclosing_range.contains(code_point))
+                continue;
+            for (auto const& range : entry.range_data->unicode_ranges) {
                 if (range.contains(code_point) && entry.font->contains_glyph(code_point))
                     return entry.font;
             }
diff --git a/Libraries/LibGfx/FontCascadeList.h b/Libraries/LibGfx/FontCascadeList.h
index e41a659bd22..36bc44840d8 100644
--- a/Libraries/LibGfx/FontCascadeList.h
+++ b/Libraries/LibGfx/FontCascadeList.h
@@ -40,7 +40,13 @@ public:
 
     struct Entry {
         NonnullRefPtr<Font const> font;
-        Optional<Vector<UnicodeRange>> unicode_ranges;
+        struct RangeData {
+            // The enclosing range is the union of all Unicode ranges. Used for fast skipping.
+            UnicodeRange enclosing_range;
+
+            Vector<UnicodeRange> unicode_ranges;
+        };
+        Optional<RangeData> range_data;
     };
 
     void set_last_resort_font(NonnullRefPtr<Font> font) { m_last_resort_font = move(font); }