Fallback Font Cache and Character Hinting for VRShell

chrome/browser/android/vr_shell/font_fallback.cc

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/browser/android/vr_shell/font_fallback.h"
+
+#include <map>
+#include <set>
+#include <string>
+#include <vector>
+
+#include "base/lazy_instance.h"
+#include "base/memory/ptr_util.h"
+#include "third_party/icu/source/common/unicode/uscript.h"
+#include "third_party/skia/include/core/SkPaint.h"
+#include "third_party/skia/include/core/SkTypeface.h"
+#include "third_party/skia/include/ports/SkFontMgr.h"
+#include "ui/gfx/platform_font_linux.h"
+
+namespace vr_shell {
+
+namespace {
+
+enum KnownGlyph {
+  UNDEFINED,
+  UNKNOWN,
+  KNOWN,
+};
+
+class CachedFont {
+ public:
+  static std::unique_ptr<CachedFont> CreateForTypeface(
+      sk_sp<SkTypeface> typeface) {
+    return base::WrapUnique<CachedFont>(new CachedFont(std::move(typeface)));
+  }
+
+  bool HasGlyphForCharacter(UChar32 character) {
+    // In order to increase cache hits, the cache is script based rather than
+    // character based. This also limits the cache size to the number of Unicode
+    // scripts (174 at the time of writing).
+    UErrorCode err = UErrorCode::U_ZERO_ERROR;
+    UScriptCode script = uscript_getScript(character, &err);
+    if (!U_SUCCESS(err) || script == UScriptCode::USCRIPT_INVALID_CODE)
+      return false;
+    auto& supported = supported_scripts_[script];
+    if (supported != UNDEFINED)
+      return supported == KNOWN;
+    uint16_t glyph_id;
+    paint_.textToGlyphs(&character, sizeof(UChar32), &glyph_id);
+    supported = glyph_id ? KNOWN : UNKNOWN;
+    return glyph_id;
+  }
+  std::string GetFontName() { return name_; }
+
+ private:
+  explicit CachedFont(sk_sp<SkTypeface> skia_face) {
+    SkString sk_name;
+    skia_face->getFamilyName(&sk_name);
+    name_ = std::string(sk_name.c_str(), sk_name.size());
+    paint_.setTypeface(std::move(skia_face));
+    paint_.setTextEncoding(SkPaint::kUTF32_TextEncoding);
+  }
+
+  SkPaint paint_;
+  std::map<UScriptCode, KnownGlyph> supported_scripts_;
+  std::string name_;
+
+  DISALLOW_COPY_AND_ASSIGN(CachedFont);
+};
+
+using FontCache = std::map<SkFontID, std::unique_ptr<CachedFont>>;
+base::LazyInstance<FontCache>::Leaky g_fonts = LAZY_INSTANCE_INITIALIZER;
+
+class CachedFontSet {
+ public:
+  CachedFontSet() : locale_() {}
+  ~CachedFontSet() = default;
+
+  void SetLocale(const std::string& locale) {
+    // Store font list for one locale at a time.
+    if (locale != locale_) {
+      font_ids_.clear();
+      unknown_chars_.clear();
+      locale_ = locale;
+    }
+  }
+
+  std::string GetFallbackFontNameForChar(UChar32 c) {
+    if (unknown_chars_.find(c) != unknown_chars_.end())
+      return "";
+    for (SkFontID font_id : font_ids_) {
+      std::unique_ptr<CachedFont>& font = g_fonts.Get()[font_id];
+      if (font->HasGlyphForCharacter(c))
+        return font->GetFontName();
+    }
+    sk_sp<SkFontMgr> font_mgr(SkFontMgr::RefDefault());
+    const char* bcp47_locales[] = {locale_.c_str()};
+    sk_sp<SkTypeface> tf(font_mgr->matchFamilyStyleCharacter(
+        nullptr, SkFontStyle(), locale_.empty() ? nullptr : bcp47_locales,
+        locale_.empty() ? 0 : 1, c));
+    if (tf) {
+      SkFontID font_id = tf->uniqueID();
+      font_ids_.push_back(font_id);
+      std::unique_ptr<CachedFont>& cached_font = g_fonts.Get()[font_id];
+      if (!cached_font)
+        cached_font = CachedFont::CreateForTypeface(tf);
+      return cached_font->GetFontName();
+    }
+    unknown_chars_.insert(c);
+    return std::string();
+  }
+
+ private:
+  std::string locale_;
+  std::vector<SkFontID> font_ids_;
+  std::set<UChar32> unknown_chars_;
+
+  DISALLOW_COPY_AND_ASSIGN(CachedFontSet);
+};
+
+base::LazyInstance<CachedFontSet>::Leaky g_cached_font_set =
+    LAZY_INSTANCE_INITIALIZER;
+
+bool FontSupportsChar(const gfx::Font& font, UChar32 c) {
+  sk_sp<SkTypeface> typeface =
+      static_cast<gfx::PlatformFontLinux*>(font.platform_font())->typeface();
+  std::unique_ptr<CachedFont>& cached_font =
+      g_fonts.Get()[typeface->uniqueID()];
+  if (!cached_font)
+    cached_font = CachedFont::CreateForTypeface(std::move(typeface));
+  return cached_font->HasGlyphForCharacter(c);
+}
+
+}  // namespace
+
+std::string GetFallbackFontNameForChar(const gfx::Font& default_font,
+                                       UChar32 c,
+                                       const std::string& locale) {
+  if (FontSupportsChar(default_font, c))
+    return std::string();
+  CachedFontSet& cached_font_set = g_cached_font_set.Get();
+  cached_font_set.SetLocale(locale);
+  return cached_font_set.GetFallbackFontNameForChar(c);
+}
+
+}  // namespace vr_shell