...

37 files changed, 145 insertions, 205 deletions

diff --git a/include/cru/common/Base.hpp b/include/cru/common/Base.hpp
index 409c2b0e..93d6f9a6 100644
--- a/include/cru/common/Base.hpp
+++ b/include/cru/common/Base.hpp
@@ -47,5 +47,5 @@ using Index = gsl::index;
 
 #define CRU_DEFINE_CLASS_LOG_TAG(tag) \
  private:                             \
-  constexpr static std::string_view log_tag = tag;
+  constexpr static std::u16string_view log_tag = tag;
 }  // namespace cru
diff --git a/include/cru/common/Logger.hpp b/include/cru/common/Logger.hpp
index f76e4626..f83ba8dc 100644
--- a/include/cru/common/Logger.hpp
+++ b/include/cru/common/Logger.hpp
@@ -15,30 +15,7 @@ enum class LogLevel { Debug, Info, Warn, Error };
 struct ILogSource : virtual Interface {
   // Write the string s. LogLevel is just a helper. It has no effect on the
   // content to write.
-  virtual void Write(LogLevel level, std::string_view s) = 0;
-};
-
-class StdioLogSource : public virtual ILogSource {
- public:
-  StdioLogSource() = default;
-
-  CRU_DELETE_COPY(StdioLogSource)
-  CRU_DELETE_MOVE(StdioLogSource)
-
-  ~StdioLogSource() override = default;
-
-  void Write(LogLevel level, std::string_view s) override {
-    // TODO: Emmm... Since it is buggy to use narrow char in UTF-8 on Windows. I
-    // think this implementation might be broken. (However, I didn't test it.)
-    // Maybe, I should detect Windows and use wide char (And I didn't test this
-    // either) or other more complicated implementation. Currently, I settled
-    // with this.
-    if (level == LogLevel::Error) {
-      std::cerr << s;
-    } else {
-      std::cout << s;
-    }
-  }
+  virtual void Write(LogLevel level, const std::u16string& s) = 0;
 };
 
 class Logger : public Object {
@@ -58,8 +35,8 @@ class Logger : public Object {
   void RemoveSource(ILogSource* source);
 
  public:
-  void Log(LogLevel level, std::string_view s);
-  void Log(LogLevel level, std::string_view tag, std::string_view s);
+  void Log(LogLevel level, std::u16string_view s);
+  void Log(LogLevel level, std::u16string_view tag, std::u16string_view s);
 
  public:
   std::list<std::unique_ptr<ILogSource>> sources_;
@@ -92,7 +69,7 @@ void Error(TArgs&&... args) {
 }
 
 template <typename... TArgs>
-void TagDebug([[maybe_unused]] std::string_view tag,
+void TagDebug([[maybe_unused]] std::u16string_view tag,
               [[maybe_unused]] TArgs&&... args) {
 #ifdef CRU_DEBUG
   Logger::GetInstance()->Log(LogLevel::Debug, tag,
@@ -101,19 +78,19 @@ void TagDebug([[maybe_unused]] std::string_view tag,
 }
 
 template <typename... TArgs>
-void TagInfo(std::string_view tag, TArgs&&... args) {
+void TagInfo(std::u16string_view tag, TArgs&&... args) {
   Logger::GetInstance()->Log(LogLevel::Info, tag,
                              fmt::format(std::forward<TArgs>(args)...));
 }
 
 template <typename... TArgs>
-void TagWarn(std::string_view tag, TArgs&&... args) {
+void TagWarn(std::u16string_view tag, TArgs&&... args) {
   Logger::GetInstance()->Log(LogLevel::Warn, tag,
                              fmt::format(std::forward<TArgs>(args)...));
 }
 
 template <typename... TArgs>
-void TagError(std::string_view tag, TArgs&&... args) {
+void TagError(std::u16string_view tag, TArgs&&... args) {
   Logger::GetInstance()->Log(LogLevel::Error, tag,
                              fmt::format(std::forward<TArgs>(args)...));
 }
diff --git a/include/cru/common/PreConfig.hpp b/include/cru/common/PreConfig.hpp
index 4bccef1d..802f17f8 100644
--- a/include/cru/common/PreConfig.hpp
+++ b/include/cru/common/PreConfig.hpp
@@ -6,3 +6,4 @@
 #endif
 
 #define _CRT_SECURE_NO_WARNINGS
+#define _SILENCE_CXX17_CODECVT_HEADER_DEPRECATION_WARNING
diff --git a/include/cru/common/StringUtil.hpp b/include/cru/common/StringUtil.hpp
index a44ae6b4..714f1d49 100644
--- a/include/cru/common/StringUtil.hpp
+++ b/include/cru/common/StringUtil.hpp
@@ -3,37 +3,90 @@
 
 namespace cru {
 using CodePoint = std::int32_t;
-constexpr CodePoint k_code_point_end = -1;
+constexpr CodePoint k_invalid_code_point = -1;
 
 class TextEncodeException : public std::runtime_error {
  public:
   using runtime_error::runtime_error;
 };
 
-class Utf8Iterator : public Object {
+inline bool IsSurrogatePair(char16_t c) { return c >= 0xD800 && c <= 0xDFFF; }
+
+inline bool IsSurrogatePairLeading(char16_t c) {
+  return c >= 0xD800 && c <= 0xDBFF;
+}
+
+inline bool IsSurrogatePairTrailing(char16_t c) {
+  return c >= 0xDC00 && c <= 0xDFFF;
+}
+
+class Utf16Iterator : public Object {
  public:
-  explicit Utf8Iterator(const std::string_view& string) : string_(string) {}
-  Utf8Iterator(const std::string_view& string, Index position)
-      : string_(string), position_(position) {}
+  explicit Utf16Iterator(std::u16string_view string)
+      : string_(std::move(string)) {}
+  Utf16Iterator(std::u16string_view string, Index position)
+      : string_(std::move(string)), position_(position) {}
 
-  CRU_DEFAULT_COPY(Utf8Iterator)
-  CRU_DEFAULT_MOVE(Utf8Iterator)
+  CRU_DEFAULT_COPY(Utf16Iterator)
+  CRU_DEFAULT_MOVE(Utf16Iterator)
 
-  ~Utf8Iterator() = default;
+  ~Utf16Iterator() = default;
 
  public:
-  void SetToHead() { position_ = 0; }
+  void SetPositionToHead() { position_ = 0; }
   void SetPosition(Index position) { position_ = position; }
 
-  // Advance current position and get next code point. Return k_code_point_end
-  // if there is no next code unit(point). Throw TextEncodeException if decoding
-  // fails.
+  // Backward current position and get previous code point. Return
+  // k_invalid_code_point if reach head. Throw TextEncodeException if encounter
+  // encoding problem.
+  CodePoint Previous();
+
+  // Advance current position and get next code point. Return
+  // k_invalid_code_point if reach tail. Throw TextEncodeException if encounter
+  // encoding problem.
   CodePoint Next();
 
   Index CurrentPosition() const { return this->position_; }
 
  private:
-  std::string_view string_;
+  std::u16string_view string_;
   Index position_ = 0;
 };
+
+Index PreviousIndex(std::u16string_view string, Index current);
+Index NextIndex(std::u16string_view string, Index current);
+
+std::string ToUtf8(const std::u16string& s);
+inline std::string ToUtf8(std::u16string_view s) {
+  return ToUtf8(std::u16string{s});
+}
+
+// class Utf8Iterator : public Object {
+//  public:
+//   explicit Utf8Iterator(const std::string_view& string) : string_(string) {}
+//   Utf8Iterator(const std::string_view& string, Index position)
+//       : string_(string), position_(position) {}
+
+//   CRU_DEFAULT_COPY(Utf8Iterator)
+//   CRU_DEFAULT_MOVE(Utf8Iterator)
+
+//   ~Utf8Iterator() = default;
+
+//  public:
+//   void SetToHead() { position_ = 0; }
+//   void SetPosition(Index position) { position_ = position; }
+
+//   // Advance current position and get next code point. Return
+//   k_invalid_code_point
+//   // if there is no next code unit(point). Throw TextEncodeException if
+//   decoding
+//   // fails.
+//   CodePoint Next();
+
+//   Index CurrentPosition() const { return this->position_; }
+
+//  private:
+//   std::string_view string_;
+//   Index position_ = 0;
+// };
 }  // namespace cru
diff --git a/include/cru/platform/Check.hpp b/include/cru/platform/Check.hpp
index f4bbcfe8..d3180582 100644
--- a/include/cru/platform/Check.hpp
+++ b/include/cru/platform/Check.hpp
@@ -2,6 +2,8 @@
 #include "Exception.hpp"
 #include "Resource.hpp"
 
+#include "cru/common/StringUtil.hpp"
+
 #include <fmt/format.h>
 #include <memory>
 #include <type_traits>
@@ -9,14 +11,14 @@
 namespace cru::platform {
 template <typename TTarget>
 TTarget* CheckPlatform(INativeResource* resource,
-                       const std::string_view& target_platform) {
+                       const std::u16string_view& target_platform) {
   Expects(resource);
   const auto result = dynamic_cast<TTarget*>(resource);
   if (result == nullptr) {
     throw UnsupportPlatformException(fmt::format(
         "Try to convert resource to target platform failed. Platform id of "
         "resource to convert: {} . Target platform id: {} .",
-        resource->GetPlatformId(), target_platform));
+        ToUtf8(resource->GetPlatformId()), ToUtf8(target_platform)));
   }
   return result;
 }
@@ -24,7 +26,7 @@ TTarget* CheckPlatform(INativeResource* resource,
 template <typename TTarget, typename TSource>
 std::shared_ptr<TTarget> CheckPlatform(
     const std::shared_ptr<TSource>& resource,
-    const std::string_view& target_platform) {
+    const std::u16string_view& target_platform) {
   static_assert(std::is_base_of_v<INativeResource, TSource>,
                 "TSource must be a subclass of INativeResource.");
   Expects(resource);
@@ -33,7 +35,7 @@ std::shared_ptr<TTarget> CheckPlatform(
     throw UnsupportPlatformException(fmt::format(
         "Try to convert resource to target platform failed. Platform id of "
         "resource to convert: {} . Target platform id: {} .",
-        resource->GetPlatformId(), target_platform));
+        ToUtf8(resource->GetPlatformId()), ToUtf8(target_platform)));
   }
   return result;
 }
diff --git a/include/cru/platform/Resource.hpp b/include/cru/platform/Resource.hpp
index 72cfaf52..7a85d9c1 100644
--- a/include/cru/platform/Resource.hpp
+++ b/include/cru/platform/Resource.hpp
@@ -5,6 +5,6 @@
 
 namespace cru::platform {
 struct INativeResource : virtual Interface {
-  virtual std::string_view GetPlatformId() const = 0;
+  virtual std::u16string_view GetPlatformId() const = 0;
 };
 }  // namespace cru::platform
diff --git a/include/cru/platform/graph/Factory.hpp b/include/cru/platform/graph/Factory.hpp
index 0a425d15..b4e68f12 100644
--- a/include/cru/platform/graph/Factory.hpp
+++ b/include/cru/platform/graph/Factory.hpp
@@ -16,10 +16,10 @@ struct IGraphFactory : virtual INativeResource {
 
   virtual std::unique_ptr<IGeometryBuilder> CreateGeometryBuilder() = 0;
 
-  virtual std::unique_ptr<IFont> CreateFont(const std::string_view& font_family,
+  virtual std::unique_ptr<IFont> CreateFont(std::u16string font_family,
                                             float font_size) = 0;
 
   virtual std::unique_ptr<ITextLayout> CreateTextLayout(
-      std::shared_ptr<IFont> font, std::string text) = 0;
+      std::shared_ptr<IFont> font, std::u16string text) = 0;
 };
 }  // namespace cru::platform::graph
diff --git a/include/cru/platform/graph/TextLayout.hpp b/include/cru/platform/graph/TextLayout.hpp
index 4086ac56..7dd20987 100644
--- a/include/cru/platform/graph/TextLayout.hpp
+++ b/include/cru/platform/graph/TextLayout.hpp
@@ -6,8 +6,8 @@
 
 namespace cru::platform::graph {
 struct ITextLayout : virtual IGraphResource {
-  virtual std::string GetText() = 0;
-  virtual void SetText(std::string new_text) = 0;
+  virtual std::u16string GetText() = 0;
+  virtual void SetText(std::u16string new_text) = 0;
 
   virtual std::shared_ptr<IFont> GetFont() = 0;
   virtual void SetFont(std::shared_ptr<IFont> font) = 0;
@@ -17,7 +17,7 @@ struct ITextLayout : virtual IGraphResource {
 
   virtual Rect GetTextBounds() = 0;
   virtual std::vector<Rect> TextRangeRect(const TextRange& text_range) = 0;
-  virtual Point TextSinglePoint(gsl::index position, bool trailing) = 0;
+  virtual Point TextSinglePoint(Index position, bool trailing) = 0;
   virtual TextHitTestResult HitTest(const Point& point) = 0;
 };
 }  // namespace cru::platform::graph
diff --git a/include/cru/platform/native/InputMethod.hpp b/include/cru/platform/native/InputMethod.hpp
index 1ede15b2..1c5b287e 100644
--- a/include/cru/platform/native/InputMethod.hpp
+++ b/include/cru/platform/native/InputMethod.hpp
@@ -18,28 +18,11 @@ struct CompositionClause {
 using CompositionClauses = std::vector<CompositionClause>;
 
 struct CompositionText {
-  std::string text;
+  std::u16string text;
   CompositionClauses clauses;
   TextRange selection;
 };
 
-inline std::ostream& operator<<(std::ostream& stream,
-                                const CompositionText& composition_text) {
-  stream << "text: " << composition_text.text << "\n"
-         << "clauses:\n";
-  for (int i = 0; i < static_cast<int>(composition_text.clauses.size()); i++) {
-    const auto& clause = composition_text.clauses[i];
-    stream << "\t" << i << ". start:" << clause.start << " end:" << clause.end;
-    if (clause.target) {
-      stream << " target";
-    }
-    stream << "\n";
-  }
-  stream << "selection: position:" << composition_text.selection.position
-         << " count:" << composition_text.selection.count;
-  return stream;
-}
-
 struct IInputMethodContext : virtual INativeResource {
   // Return true if you should draw composition text manually. Return false if
   // system will take care of that for you.
@@ -67,7 +50,7 @@ struct IInputMethodContext : virtual INativeResource {
   // Triggered every time composition text changes.
   virtual IEvent<std::nullptr_t>* CompositionEvent() = 0;
 
-  virtual IEvent<std::string_view>* TextEvent() = 0;
+  virtual IEvent<std::u16string_view>* TextEvent() = 0;
 };
 
 struct IInputMethodManager : virtual INativeResource {
diff --git a/include/cru/ui/ClickDetector.hpp b/include/cru/ui/ClickDetector.hpp
index 3977fb8e..4ffe5d05 100644
--- a/include/cru/ui/ClickDetector.hpp
+++ b/include/cru/ui/ClickDetector.hpp
@@ -36,7 +36,7 @@ enum class ClickState {
 };
 
 class ClickDetector : public Object {
-  CRU_DEFINE_CLASS_LOG_TAG("cru::ui::ClickDetector")
+  CRU_DEFINE_CLASS_LOG_TAG(u"cru::ui::ClickDetector")
 
  public:
   explicit ClickDetector(Control* control);
diff --git a/include/cru/ui/Control.hpp b/include/cru/ui/Control.hpp
index 347163be..bd86bc2f 100644
--- a/include/cru/ui/Control.hpp
+++ b/include/cru/ui/Control.hpp
@@ -22,7 +22,7 @@ class Control : public Object {
   ~Control() override = default;
 
  public:
-  virtual std::string_view GetControlType() const = 0;
+  virtual std::u16string_view GetControlType() const = 0;
 
   //*************** region: tree ***************
  public:
diff --git a/include/cru/ui/UiEvent.hpp b/include/cru/ui/UiEvent.hpp
index 39f26aee..5adace8a 100644
--- a/include/cru/ui/UiEvent.hpp
+++ b/include/cru/ui/UiEvent.hpp
@@ -212,7 +212,7 @@ class KeyEventArgs : public UiEventArgs {
 
 class CharEventArgs : public UiEventArgs {
  public:
-  CharEventArgs(Object* sender, Object* original_sender, std::string c)
+  CharEventArgs(Object* sender, Object* original_sender, std::u16string c)
       : UiEventArgs(sender, original_sender), c_(std::move(c)) {}
   CharEventArgs(const CharEventArgs& other) = default;
   CharEventArgs(CharEventArgs&& other) = default;
@@ -220,9 +220,9 @@ class CharEventArgs : public UiEventArgs {
   CharEventArgs& operator=(CharEventArgs&& other) = default;
   ~CharEventArgs() override = default;
 
-  std::string GetChar() const { return c_; }
+  std::u16string GetChar() const { return c_; }
 
  private:
-  std::string c_;
+  std::u16string c_;
 };
 }  // namespace cru::ui::event
diff --git a/include/cru/ui/UiHost.hpp b/include/cru/ui/UiHost.hpp
index 1a5c6302..b1658ef6 100644
--- a/include/cru/ui/UiHost.hpp
+++ b/include/cru/ui/UiHost.hpp
@@ -32,7 +32,7 @@ struct AfterLayoutEventArgs {};
 // 4. Delete Window when deleting_ is false and IsRetainAfterDestroy is false in
 // OnNativeDestroy.
 class UiHost : public Object, public SelfResolvable<UiHost> {
-  CRU_DEFINE_CLASS_LOG_TAG("cru::ui::UiHost")
+  CRU_DEFINE_CLASS_LOG_TAG(u"cru::ui::UiHost")
 
  public:
   // This will create root window render object and attach it to window.
diff --git a/include/cru/ui/Window.hpp b/include/cru/ui/Window.hpp
index eb2ecfbb..450ea97b 100644
--- a/include/cru/ui/Window.hpp
+++ b/include/cru/ui/Window.hpp
@@ -6,7 +6,7 @@ class Window final : public ContentControl {
   friend UiHost;
 
  public:
-  static constexpr std::string_view control_type = "Window";
+  static constexpr std::u16string_view control_type = u"Window";
 
  public:
   static Window* CreateOverlapped();
@@ -24,7 +24,7 @@ class Window final : public ContentControl {
   ~Window() override;
 
  public:
-  std::string_view GetControlType() const final;
+  std::u16string_view GetControlType() const final;
 
   render::RenderObject* GetRenderObject() const override;
 
diff --git a/include/cru/ui/controls/Button.hpp b/include/cru/ui/controls/Button.hpp
index 8a11409c..a4f727d6 100644
--- a/include/cru/ui/controls/Button.hpp
+++ b/include/cru/ui/controls/Button.hpp
@@ -7,7 +7,7 @@
 namespace cru::ui::controls {
 class Button : public ContentControl {
  public:
-  static constexpr std::string_view control_type = "Button";
+  static constexpr std::u16string_view control_type = u"Button";
 
   static Button* Create() { return new Button(); }
 
@@ -21,7 +21,7 @@ class Button : public ContentControl {
   Button& operator=(Button&& other) = delete;
   ~Button() override;
 
-  std::string_view GetControlType() const final { return control_type; }
+  std::u16string_view GetControlType() const final { return control_type; }
 
   render::RenderObject* GetRenderObject() const override;
 
diff --git a/include/cru/ui/controls/Container.hpp b/include/cru/ui/controls/Container.hpp
index e3d78365..304d402c 100644
--- a/include/cru/ui/controls/Container.hpp
+++ b/include/cru/ui/controls/Container.hpp
@@ -3,7 +3,7 @@
 
 namespace cru::ui::controls {
 class Container : public ContentControl {
-  static constexpr std::string_view control_type = "Container";
+  static constexpr std::u16string_view control_type = u"Container";
 
  protected:
   Container();
@@ -15,7 +15,7 @@ class Container : public ContentControl {
   ~Container() override;
 
  public:
-  std::string_view GetControlType() const final { return control_type; }
+  std::u16string_view GetControlType() const final { return control_type; }
 
   render::RenderObject* GetRenderObject() const override;
 
diff --git a/include/cru/ui/controls/FlexLayout.hpp b/include/cru/ui/controls/FlexLayout.hpp
index 3d6087c2..87162569 100644
--- a/include/cru/ui/controls/FlexLayout.hpp
+++ b/include/cru/ui/controls/FlexLayout.hpp
@@ -4,7 +4,7 @@
 namespace cru::ui::controls {
 class FlexLayout : public LayoutControl {
  public:
-  static constexpr std::string_view control_type = "FlexLayout";
+  static constexpr std::u16string_view control_type = u"FlexLayout";
 
   static FlexLayout* Create() { return new FlexLayout(); }
 
@@ -18,7 +18,7 @@ class FlexLayout : public LayoutControl {
   FlexLayout& operator=(FlexLayout&& other) = delete;
   ~FlexLayout() override;
 
-  std::string_view GetControlType() const final { return control_type; }
+  std::u16string_view GetControlType() const final { return control_type; }
 
   render::RenderObject* GetRenderObject() const override;
 
diff --git a/include/cru/ui/controls/StackLayout.hpp b/include/cru/ui/controls/StackLayout.hpp
index d5998cc4..c0b95044 100644
--- a/include/cru/ui/controls/StackLayout.hpp
+++ b/include/cru/ui/controls/StackLayout.hpp
@@ -4,7 +4,7 @@
 namespace cru::ui::controls {
 class StackLayout : public LayoutControl {
  public:
-  static constexpr std::string_view control_type = "StackLayout";
+  static constexpr std::u16string_view control_type = u"StackLayout";
 
   static StackLayout* Create() { return new StackLayout(); }
 
@@ -17,7 +17,7 @@ class StackLayout : public LayoutControl {
 
   ~StackLayout() override;
 
-  std::string_view GetControlType() const final { return control_type; }
+  std::u16string_view GetControlType() const final { return control_type; }
 
   render::RenderObject* GetRenderObject() const override;
 
diff --git a/include/cru/ui/controls/TextBlock.hpp b/include/cru/ui/controls/TextBlock.hpp
index 1b1b4a5c..8a9a3bff 100644
--- a/include/cru/ui/controls/TextBlock.hpp
+++ b/include/cru/ui/controls/TextBlock.hpp
@@ -7,7 +7,7 @@ class TextControlService;
 
 class TextBlock : public NoChildControl {
  public:
-  static constexpr std::string_view control_type = "TextBlock";
+  static constexpr std::u16string_view control_type = u"TextBlock";
 
   static TextBlock* Create() { return new TextBlock(); }
 
@@ -21,12 +21,12 @@ class TextBlock : public NoChildControl {
   TextBlock& operator=(TextBlock&& other) = delete;
   ~TextBlock() override;
 
-  std::string_view GetControlType() const final { return control_type; }
+  std::u16string_view GetControlType() const final { return control_type; }
 
   render::RenderObject* GetRenderObject() const override;
 
-  std::string GetText() const;
-  void SetText(std::string text);
+  std::u16string GetText() const;
+  void SetText(std::u16string text);
 
   gsl::not_null<render::TextRenderObject*> GetTextRenderObject();
   render::ScrollRenderObject* GetScrollRenderObject() { return nullptr; }
diff --git a/include/cru/ui/controls/TextBox.hpp b/include/cru/ui/controls/TextBox.hpp
index 3d4de7c0..5976f6da 100644
--- a/include/cru/ui/controls/TextBox.hpp
+++ b/include/cru/ui/controls/TextBox.hpp
@@ -10,7 +10,7 @@ class TextControlService;
 
 class TextBox : public NoChildControl {
  public:
-  static constexpr std::string_view control_type = "TextBox";
+  static constexpr std::u16string_view control_type = u"TextBox";
 
   static TextBox* Create() { return new TextBox(); }
 
@@ -23,7 +23,7 @@ class TextBox : public NoChildControl {
 
   ~TextBox() override;
 
-  std::string_view GetControlType() const final { return control_type; }
+  std::u16string_view GetControlType() const final { return control_type; }
 
   render::RenderObject* GetRenderObject() const override;
 
diff --git a/include/cru/ui/render/BorderRenderObject.hpp b/include/cru/ui/render/BorderRenderObject.hpp
index 94e888d4..587f051a 100644
--- a/include/cru/ui/render/BorderRenderObject.hpp
+++ b/include/cru/ui/render/BorderRenderObject.hpp
@@ -3,7 +3,7 @@
 
 namespace cru::ui::render {
 class BorderRenderObject : public RenderObject {
-  CRU_DEFINE_CLASS_LOG_TAG("cru::ui::render::BorderRenderObject")
+  CRU_DEFINE_CLASS_LOG_TAG(u"cru::ui::render::BorderRenderObject")
 
  public:
   BorderRenderObject();
diff --git a/include/cru/ui/render/FlexLayoutRenderObject.hpp b/include/cru/ui/render/FlexLayoutRenderObject.hpp
index 87a41c7e..ee29d1e4 100644
--- a/include/cru/ui/render/FlexLayoutRenderObject.hpp
+++ b/include/cru/ui/render/FlexLayoutRenderObject.hpp
@@ -74,7 +74,7 @@ namespace cru::ui::render {
 // and just fill the rest space with blank.
 //
 class FlexLayoutRenderObject : public LayoutRenderObject<FlexChildLayoutData> {
-  CRU_DEFINE_CLASS_LOG_TAG("cru::ui::render::FlexLayoutRenderObject")
+  CRU_DEFINE_CLASS_LOG_TAG(u"cru::ui::render::FlexLayoutRenderObject")
 
  public:
   FlexLayoutRenderObject() = default;
diff --git a/include/cru/ui/render/LayoutHelper.hpp b/include/cru/ui/render/LayoutHelper.hpp
index 3469ccf0..518dc5a3 100644
--- a/include/cru/ui/render/LayoutHelper.hpp
+++ b/include/cru/ui/render/LayoutHelper.hpp
@@ -9,6 +9,6 @@ float CalculateAnchorByAlignment(Alignment alignment, float start_point,
 
 MeasureLength StackLayoutCalculateChildMaxLength(
     MeasureLength parent_preferred_size, MeasureLength parent_max_size,
-    MeasureLength child_min_size, std::string_view log_tag,
-    std::string_view exceeds_message);
+    MeasureLength child_min_size, std::u16string_view log_tag,
+    std::u16string_view exceeds_message);
 }  // namespace cru::ui::render
diff --git a/include/cru/ui/render/RenderObject.hpp b/include/cru/ui/render/RenderObject.hpp
index 2e784afc..f820f029 100644
--- a/include/cru/ui/render/RenderObject.hpp
+++ b/include/cru/ui/render/RenderObject.hpp
@@ -37,7 +37,7 @@ namespace cru::ui::render {
 class RenderObject : public Object {
   friend WindowRenderObject;
 
-  CRU_DEFINE_CLASS_LOG_TAG("cru::ui::render::RenderObject")
+  CRU_DEFINE_CLASS_LOG_TAG(u"cru::ui::render::RenderObject")
 
  protected:
   enum class ChildMode {
diff --git a/include/cru/ui/render/StackLayoutRenderObject.hpp b/include/cru/ui/render/StackLayoutRenderObject.hpp
index 534d7f22..303241c5 100644
--- a/include/cru/ui/render/StackLayoutRenderObject.hpp
+++ b/include/cru/ui/render/StackLayoutRenderObject.hpp
@@ -23,7 +23,7 @@ namespace cru::ui::render {
 // to min size.
 class StackLayoutRenderObject
     : public LayoutRenderObject<StackChildLayoutData> {
-  CRU_DEFINE_CLASS_LOG_TAG("cru::ui::render:StackLayoutRenderObject")
+  CRU_DEFINE_CLASS_LOG_TAG(u"cru::ui::render:StackLayoutRenderObject")
 
  public:
   StackLayoutRenderObject() = default;
diff --git a/include/cru/ui/render/TextRenderObject.hpp b/include/cru/ui/render/TextRenderObject.hpp
index 77a92b4f..32d96797 100644
--- a/include/cru/ui/render/TextRenderObject.hpp
+++ b/include/cru/ui/render/TextRenderObject.hpp
@@ -18,7 +18,7 @@ namespace cru::ui::render {
 // If the result layout box is bigger than actual text box, then text is center
 // aligned.
 class TextRenderObject : public RenderObject {
-  CRU_DEFINE_CLASS_LOG_TAG("cru::ui::render::TextRenderObject")
+  CRU_DEFINE_CLASS_LOG_TAG(u"cru::ui::render::TextRenderObject")
 
  public:
   constexpr static float default_caret_width = 2;
@@ -34,8 +34,8 @@ class TextRenderObject : public RenderObject {
   TextRenderObject& operator=(TextRenderObject&& other) = delete;
   ~TextRenderObject() override;
 
-  std::string GetText() const;
-  void SetText(std::string new_text);
+  std::u16string GetText() const;
+  void SetText(std::u16string new_text);
 
   std::shared_ptr<platform::graph::IBrush> GetBrush() const { return brush_; }
   void SetBrush(std::shared_ptr<platform::graph::IBrush> new_brush);
diff --git a/include/cru/win/Exception.hpp b/include/cru/win/Exception.hpp
index 234aea69..3a95aa5d 100644
--- a/include/cru/win/Exception.hpp
+++ b/include/cru/win/Exception.hpp
@@ -10,7 +10,7 @@ namespace cru::platform::win {
 class HResultError : public platform::PlatformException {
  public:
   explicit HResultError(HRESULT h_result);
-  explicit HResultError(HRESULT h_result, const std::string_view& message);
+  explicit HResultError(HRESULT h_result, std::string_view message);
 
   CRU_DEFAULT_COPY(HResultError)
   CRU_DEFAULT_MOVE(HResultError)
@@ -27,8 +27,7 @@ inline void ThrowIfFailed(const HRESULT h_result) {
   if (FAILED(h_result)) throw HResultError(h_result);
 }
 
-inline void ThrowIfFailed(const HRESULT h_result,
-                          const std::string_view& message) {
+inline void ThrowIfFailed(const HRESULT h_result, std::string_view message) {
   if (FAILED(h_result)) throw HResultError(h_result, message);
 }
 
@@ -36,8 +35,8 @@ class Win32Error : public platform::PlatformException {
  public:
   // ::GetLastError is automatically called to get the error code.
   // The same as Win32Error(::GetLastError(), message)
-  explicit Win32Error(const std::string_view& message);
-  Win32Error(DWORD error_code, const std::string_view& message);
+  explicit Win32Error(std::string_view message);
+  Win32Error(DWORD error_code, std::string_view message);
 
   CRU_DEFAULT_COPY(Win32Error)
   CRU_DEFAULT_MOVE(Win32Error)
diff --git a/include/cru/win/String.hpp b/include/cru/win/String.hpp
deleted file mode 100644
index ac07f57b..00000000
--- a/include/cru/win/String.hpp
+++ /dev/null
@@ -1,75 +0,0 @@
-/*
-Because the text encoding problem on Windows, here I write some functions
-related to text encoding. The utf-8 and utf-16 conversion function is provided
-by win32 api. However win32 api does not provide any function about charactor
-iteration or index by code point. (At least I haven't found.) I don't use icu
-because it is not easy to build it on Windows and the bundled version in Windows
-(https://docs.microsoft.com/en-us/windows/win32/intl/international-components-for-unicode--icu-)
-is only available after Windows 10 Creators Update.
-
-Luckily, both utf-8 and utf-16 encoding are easy to learn and program with if we
-only do simple iteration rather than do much sophisticated work about
-complicated error situations. (And I learn the internal of the encoding by the
-way.)
-*/
-
-#pragma once
-#include "WinPreConfig.hpp"
-
-#include "cru/common/StringUtil.hpp"
-
-#include <cstdint>
-#include <stdexcept>
-#include <string>
-#include <string_view>
-
-namespace cru::platform::win {
-std::string ToUtf8String(const std::wstring_view& string);
-std::wstring ToUtf16String(const std::string_view& string);
-
-inline bool IsSurrogatePair(wchar_t c) { return c >= 0xD800 && c <= 0xDFFF; }
-
-inline bool IsSurrogatePairLeading(wchar_t c) {
-  return c >= 0xD800 && c <= 0xDBFF;
-}
-
-inline bool IsSurrogatePairTrailing(wchar_t c) {
-  return c >= 0xDC00 && c <= 0xDFFF;
-}
-
-class Utf16Iterator : public Object {
-  static_assert(
-      sizeof(wchar_t) == 2,
-      "Emmm, according to my knowledge, wchar_t should be 2-length on "
-      "Windows. If not, Utf16 will be broken.");
-
- public:
-  Utf16Iterator(const std::wstring_view& string) : string_(string) {}
-
-  CRU_DEFAULT_COPY(Utf16Iterator)
-  CRU_DEFAULT_MOVE(Utf16Iterator)
-
-  ~Utf16Iterator() = default;
-
- public:
-  void SetToHead() { position_ = 0; }
-
-  // Advance current position and get next code point. Return k_code_point_end
-  // if there is no next code unit(point). Throw TextEncodeException if decoding
-  // fails.
-  CodePoint Next();
-
-  Index CurrentPosition() const { return this->position_; }
-
- private:
-  std::wstring_view string_;
-  Index position_ = 0;
-};
-
-Index IndexUtf8ToUtf16(const std::string_view& utf8_string, Index utf8_index,
-                       const std::wstring_view& utf16_string);
-
-Index IndexUtf16ToUtf8(const std::wstring_view& utf16_string, Index utf16_index,
-                       const std::string_view& utf8_string);
-
-}  // namespace cru::platform::win
diff --git a/include/cru/win/graph/direct/Factory.hpp b/include/cru/win/graph/direct/Factory.hpp
index 763d4b2b..e70454f5 100644
--- a/include/cru/win/graph/direct/Factory.hpp
+++ b/include/cru/win/graph/direct/Factory.hpp
@@ -38,11 +38,11 @@ class DirectGraphFactory : public DirectResource, public virtual IGraphFactory {
 
   std::unique_ptr<IGeometryBuilder> CreateGeometryBuilder() override;
 
-  std::unique_ptr<IFont> CreateFont(const std::string_view& font_family,
+  std::unique_ptr<IFont> CreateFont(std::u16string font_family,
                                     float font_size) override;
 
   std::unique_ptr<ITextLayout> CreateTextLayout(std::shared_ptr<IFont> font,
-                                                std::string text) override;
+                                                std::u16string text) override;
 
  private:
   Microsoft::WRL::ComPtr<ID3D11Device> d3d11_device_;
diff --git a/include/cru/win/graph/direct/Font.hpp b/include/cru/win/graph/direct/Font.hpp
index ecf9fd81..2195f3e4 100644
--- a/include/cru/win/graph/direct/Font.hpp
+++ b/include/cru/win/graph/direct/Font.hpp
@@ -11,7 +11,7 @@ class DWriteFont : public DirectGraphResource,
                    public virtual IFont,
                    public virtual IComResource<IDWriteTextFormat> {
  public:
-  DWriteFont(DirectGraphFactory* factory, const std::string_view& font_family,
+  DWriteFont(DirectGraphFactory* factory, std::u16string font_family,
              float font_size);
 
   CRU_DELETE_COPY(DWriteFont)
@@ -27,6 +27,7 @@ class DWriteFont : public DirectGraphResource,
   float GetFontSize() override;
 
  private:
+  std::u16string font_family_;
   Microsoft::WRL::ComPtr<IDWriteTextFormat> text_format_;
 };
 }  // namespace cru::platform::graph::win::direct
diff --git a/include/cru/win/graph/direct/Resource.hpp b/include/cru/win/graph/direct/Resource.hpp
index d0a30dbd..6162ebd8 100644
--- a/include/cru/win/graph/direct/Resource.hpp
+++ b/include/cru/win/graph/direct/Resource.hpp
@@ -10,7 +10,7 @@ class DirectGraphFactory;
 
 class DirectResource : public Object, public virtual INativeResource {
  public:
-  static constexpr std::string_view k_platform_id = "Windows Direct";
+  static constexpr std::u16string_view k_platform_id = u"Windows Direct";
 
  protected:
   DirectResource() = default;
@@ -22,7 +22,7 @@ class DirectResource : public Object, public virtual INativeResource {
   ~DirectResource() override = default;
 
  public:
-  std::string_view GetPlatformId() const final { return k_platform_id; }
+  std::u16string_view GetPlatformId() const final { return k_platform_id; }
 };
 
 class DirectGraphResource : public DirectResource,
diff --git a/include/cru/win/graph/direct/TextLayout.hpp b/include/cru/win/graph/direct/TextLayout.hpp
index 40c63dbe..c53cf655 100644
--- a/include/cru/win/graph/direct/TextLayout.hpp
+++ b/include/cru/win/graph/direct/TextLayout.hpp
@@ -15,7 +15,7 @@ class DWriteTextLayout : public DirectGraphResource,
                          public virtual IComResource<IDWriteTextLayout> {
  public:
   DWriteTextLayout(DirectGraphFactory* factory, std::shared_ptr<IFont> font,
-                   std::string text);
+                   std::u16string text);
 
   CRU_DELETE_COPY(DWriteTextLayout)
   CRU_DELETE_MOVE(DWriteTextLayout)
@@ -28,8 +28,8 @@ class DWriteTextLayout : public DirectGraphResource,
   }
 
  public:
-  std::string GetText() override;
-  void SetText(std::string new_text) override;
+  std::u16string GetText() override;
+  void SetText(std::u16string new_text) override;
 
   std::shared_ptr<IFont> GetFont() override;
   void SetFont(std::shared_ptr<IFont> font) override;
@@ -41,12 +41,11 @@ class DWriteTextLayout : public DirectGraphResource,
   // Return empty vector if text_range.count is 0. Text range could be in
   // reverse direction, it should be normalized first in implementation.
   std::vector<Rect> TextRangeRect(const TextRange& text_range) override;
-  Point TextSinglePoint(gsl::index position, bool trailing) override;
+  Point TextSinglePoint(Index position, bool trailing) override;
   TextHitTestResult HitTest(const Point& point) override;
 
  private:
-  std::string text_;
-  std::wstring w_text_;
+  std::u16string text_;
   std::shared_ptr<DWriteFont> font_;
   float max_width_ = std::numeric_limits<float>::max();
   float max_height_ = std::numeric_limits<float>::max();
diff --git a/include/cru/win/native/Cursor.hpp b/include/cru/win/native/Cursor.hpp
index 44a6a362..373b9170 100644
--- a/include/cru/win/native/Cursor.hpp
+++ b/include/cru/win/native/Cursor.hpp
@@ -7,7 +7,7 @@
 
 namespace cru::platform::native::win {
 class WinCursor : public WinNativeResource, public virtual ICursor {
-  CRU_DEFINE_CLASS_LOG_TAG("cru::platform::native::win::WinCursor")
+  CRU_DEFINE_CLASS_LOG_TAG(u"cru::platform::native::win::WinCursor")
 
  public:
   WinCursor(HCURSOR handle, bool auto_destroy);
diff --git a/include/cru/win/native/GodWindow.hpp b/include/cru/win/native/GodWindow.hpp
index 0820bdb3..8b20e01f 100644
--- a/include/cru/win/native/GodWindow.hpp
+++ b/include/cru/win/native/GodWindow.hpp
@@ -5,7 +5,7 @@
 
 namespace cru::platform::native::win {
 class GodWindow : public Object {
-  CRU_DEFINE_CLASS_LOG_TAG("cru::platform::native::win::GodWindow")
+  CRU_DEFINE_CLASS_LOG_TAG(u"cru::platform::native::win::GodWindow")
 
  public:
   explicit GodWindow(WinUiApplication* application);
diff --git a/include/cru/win/native/InputMethod.hpp b/include/cru/win/native/InputMethod.hpp
index 45422ace..113f460d 100644
--- a/include/cru/win/native/InputMethod.hpp
+++ b/include/cru/win/native/InputMethod.hpp
@@ -12,7 +12,7 @@
 
 namespace cru::platform::native::win {
 class AutoHIMC : public Object {
-  CRU_DEFINE_CLASS_LOG_TAG("cru::platform::native::win::AutoHIMC")
+  CRU_DEFINE_CLASS_LOG_TAG(u"cru::platform::native::win::AutoHIMC")
 
  public:
   explicit AutoHIMC(HWND hwnd);
@@ -35,7 +35,7 @@ class AutoHIMC : public Object {
 
 class WinInputMethodContext : public WinNativeResource,
                               public virtual IInputMethodContext {
-  CRU_DEFINE_CLASS_LOG_TAG("cru::platform::native::win::WinInputMethodContext")
+  CRU_DEFINE_CLASS_LOG_TAG(u"cru::platform::native::win::WinInputMethodContext")
 
  public:
   WinInputMethodContext(gsl::not_null<WinNativeWindow*> window);
@@ -65,12 +65,12 @@ class WinInputMethodContext : public WinNativeResource,
 
   IEvent<std::nullptr_t>* CompositionEvent() override;
 
-  IEvent<std::string_view>* TextEvent() override;
+  IEvent<std::u16string_view>* TextEvent() override;
 
  private:
   void OnWindowNativeMessage(WindowNativeMessageEventArgs& args);
 
-  std::string GetResultString();
+  std::u16string GetResultString();
 
   std::optional<AutoHIMC> TryGetHIMC();
 
@@ -82,7 +82,7 @@ class WinInputMethodContext : public WinNativeResource,
   Event<std::nullptr_t> composition_start_event_;
   Event<std::nullptr_t> composition_end_event_;
   Event<std::nullptr_t> composition_event_;
-  Event<std::string_view> text_event_;
+  Event<std::u16string_view> text_event_;
 };
 
 class WinInputMethodManager : public WinNativeResource,
diff --git a/include/cru/win/native/Resource.hpp b/include/cru/win/native/Resource.hpp
index 7afaca0f..0de0e1a8 100644
--- a/include/cru/win/native/Resource.hpp
+++ b/include/cru/win/native/Resource.hpp
@@ -6,7 +6,7 @@
 namespace cru::platform::native::win {
 class WinNativeResource : public Object, public virtual INativeResource {
  public:
-  static constexpr std::string_view k_platform_id = "Windows";
+  static constexpr std::u16string_view k_platform_id = u"Windows";
 
  protected:
   WinNativeResource() = default;
@@ -18,6 +18,6 @@ class WinNativeResource : public Object, public virtual INativeResource {
   ~WinNativeResource() override = default;
 
  public:
-  std::string_view GetPlatformId() const final { return k_platform_id; }
+  std::u16string_view GetPlatformId() const final { return k_platform_id; }
 };
 }  // namespace cru::platform::native::win
diff --git a/include/cru/win/native/Window.hpp b/include/cru/win/native/Window.hpp
index 521a0a06..3e0b11cd 100644
--- a/include/cru/win/native/Window.hpp
+++ b/include/cru/win/native/Window.hpp
@@ -8,7 +8,7 @@
 
 namespace cru::platform::native::win {
 class WinNativeWindow : public WinNativeResource, public virtual INativeWindow {
-  CRU_DEFINE_CLASS_LOG_TAG("cru::platform::native::win::WinNativeWindow")
+  CRU_DEFINE_CLASS_LOG_TAG(u"cru::platform::native::win::WinNativeWindow")
 
  public:
   WinNativeWindow(WinUiApplication* application, WindowClass* window_class,