From eff5e67356acbee22375de68007f6cdc294837f7 Mon Sep 17 00:00:00 2001
From: Gary Qian <garyq@google.com>
Date: Thu, 13 Dec 2018 10:39:09 -0800
Subject: [PATCH] Fallback font match caching to fix emoji lag. (#7208)

---
 third_party/txt/src/txt/font_collection.cc | 17 ++++++++++++++++-
 third_party/txt/src/txt/font_collection.h  | 12 ++++++++++++
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/third_party/txt/src/txt/font_collection.cc b/third_party/txt/src/txt/font_collection.cc
index 5503e54e03f..71e6a5178e6 100644
--- a/third_party/txt/src/txt/font_collection.cc
+++ b/third_party/txt/src/txt/font_collection.cc
@@ -202,6 +202,22 @@ std::shared_ptr<minikin::FontFamily> FontCollection::CreateMinikinFontFamily(
 const std::shared_ptr<minikin::FontFamily>& FontCollection::MatchFallbackFont(
     uint32_t ch,
     std::string locale) {
+  // Check if the ch's matched font has been cached. We cache the results of
+  // this method as repeated matchFamilyStyleCharacter calls can become
+  // extremely laggy when typing a large number of complex emojis.
+  auto lookup = fallback_match_cache_.find(ch);
+  if (lookup != fallback_match_cache_.end()) {
+    return *lookup->second;
+  }
+  const std::shared_ptr<minikin::FontFamily>* match =
+      &DoMatchFallbackFont(ch, locale);
+  fallback_match_cache_.insert(std::make_pair(ch, match));
+  return *match;
+}
+
+const std::shared_ptr<minikin::FontFamily>& FontCollection::DoMatchFallbackFont(
+    uint32_t ch,
+    std::string locale) {
   for (const sk_sp<SkFontMgr>& manager : GetFontManagerOrder()) {
     std::vector<const char*> bcp47;
     if (!locale.empty())
@@ -219,7 +235,6 @@ const std::shared_ptr<minikin::FontFamily>& FontCollection::MatchFallbackFont(
 
     return GetFallbackFontFamily(manager, family_name);
   }
-
   return g_null_family;
 }
 
diff --git a/third_party/txt/src/txt/font_collection.h b/third_party/txt/src/txt/font_collection.h
index d512a6dd3ae..e3dfaa8d007 100644
--- a/third_party/txt/src/txt/font_collection.h
+++ b/third_party/txt/src/txt/font_collection.h
@@ -49,6 +49,8 @@ class FontCollection : public std::enable_shared_from_this<FontCollection> {
       const std::string& family,
       const std::string& locale);
 
+  // Provides a FontFamily that contains glyphs for ch. This caches previously
+  // matched fonts. Also see FontCollection::DoMatchFallbackFont.
   const std::shared_ptr<minikin::FontFamily>& MatchFallbackFont(
       uint32_t ch,
       std::string locale);
@@ -80,12 +82,22 @@ class FontCollection : public std::enable_shared_from_this<FontCollection> {
                      std::shared_ptr<minikin::FontCollection>,
                      FamilyKey::Hasher>
       font_collections_cache_;
+  // Cache that stores the results of MatchFallbackFont to ensure lag-free emoji
+  // font fallback matching.
+  std::unordered_map<uint32_t, const std::shared_ptr<minikin::FontFamily>*>
+      fallback_match_cache_;
   std::unordered_map<std::string, std::shared_ptr<minikin::FontFamily>>
       fallback_fonts_;
   std::unordered_map<std::string, std::set<std::string>>
       fallback_fonts_for_locale_;
   bool enable_font_fallback_;
 
+  // Performs the actual work of MatchFallbackFont. The result is cached in
+  // fallback_match_cache_.
+  const std::shared_ptr<minikin::FontFamily>& DoMatchFallbackFont(
+      uint32_t ch,
+      std::string locale);
+
   std::vector<sk_sp<SkFontMgr>> GetFontManagerOrder() const;
 
   std::shared_ptr<minikin::FontFamily> CreateMinikinFontFamily(