Remove String stage 1.

56 files changed, 248 insertions, 230 deletions

diff --git a/include/cru/base/StringUtil.h b/include/cru/base/StringUtil.h
index 0ce3802f..2b1b5914 100644
--- a/include/cru/base/StringUtil.h
+++ b/include/cru/base/StringUtil.h
@@ -269,4 +269,28 @@ Utf8CodePointIterator CRU_BASE_API CreateUtf8Iterator(const std::byte* buffer,
 Utf8CodePointIterator CRU_BASE_API
 CreateUtf8Iterator(const std::vector<std::byte>& buffer);
 
+CodePoint CRU_BASE_API Utf8NextCodePoint(std::string_view str, Index current,
+                                         Index* next_position);
+CodePoint CRU_BASE_API Utf8PreviousCodePoint(std::string_view str,
+                                             Index current,
+                                             Index* next_position);
+// Return position after the character making predicate returns true or 0 if no
+// character doing so.
+Index CRU_BASE_API
+Utf8BackwardUntil(std::string_view str, Index position,
+                  const std::function<bool(CodePoint)>& predicate);
+// Return position before the character making predicate returns true or
+// str.size() if no character doing so.
+Index CRU_BASE_API
+Utf8ForwardUntil(std::string_view str, Index position,
+                 const std::function<bool(CodePoint)>& predicate);
+
+bool CRU_BASE_API Utf8IsValidInsertPosition(std::string_view str,
+                                            Index position);
+
+Index CRU_BASE_API Utf8PreviousWord(std::string_view str, Index position,
+                                    bool* is_space = nullptr);
+Index CRU_BASE_API Utf8NextWord(std::string_view str, Index position,
+                                bool* is_space = nullptr);
+
 }  // namespace cru
diff --git a/include/cru/platform/Check.h b/include/cru/platform/Check.h
index b36b7fc1..6b002c0c 100644
--- a/include/cru/platform/Check.h
+++ b/include/cru/platform/Check.h
@@ -13,7 +13,7 @@ TTarget* CheckPlatform(IPlatformResource* resource,
   const auto result = dynamic_cast<TTarget*>(resource);
   if (result == nullptr) {
     throw PlatformNotMatchException(
-        resource->GetPlatformIdUtf8(), target_platform,
+        resource->GetPlatformId(), target_platform,
         "Try to convert resource to target platform failed.");
   }
   return result;
@@ -28,7 +28,7 @@ std::shared_ptr<TTarget> CheckPlatform(const std::shared_ptr<TSource>& resource,
   const auto result = std::dynamic_pointer_cast<TTarget>(resource);
   if (result == nullptr) {
     throw PlatformNotMatchException(
-        resource->GetPlatformIdUtf8(), target_platform,
+        resource->GetPlatformId(), target_platform,
         "Try to convert resource to target platform failed.");
   }
   return result;
diff --git a/include/cru/platform/Resource.h b/include/cru/platform/Resource.h
index a16a9dbd..35a401be 100644
--- a/include/cru/platform/Resource.h
+++ b/include/cru/platform/Resource.h
@@ -1,17 +1,13 @@
 #pragma once
 #include "Base.h"
 
-#include "cru/base/Base.h"
-#include "cru/base/String.h"
+#include <cru/base/Base.h>
+
+#include <string>
 
 namespace cru::platform {
 struct CRU_PLATFORM_API IPlatformResource : virtual Interface {
-  CRU_DEFAULT_CONSTRUCTOR_DESTRUCTOR(IPlatformResource)
-
-  virtual String GetPlatformId() const = 0;
-
-  virtual String GetDebugString() { return String(); }
-
-  virtual std::string GetPlatformIdUtf8() const;
+  virtual std::string GetPlatformId() const = 0;
+  virtual std::string GetDebugString() { return {}; }
 };
 }  // namespace cru::platform
diff --git a/include/cru/platform/graphics/Base.h b/include/cru/platform/graphics/Base.h
index a61eb2a7..c3381394 100644
--- a/include/cru/platform/graphics/Base.h
+++ b/include/cru/platform/graphics/Base.h
@@ -1,8 +1,8 @@
 #pragma once
-#include "../Color.h"
-#include "../GraphicsBase.h"
-#include "../Matrix.h"
-#include "../Resource.h"
+#include <cru/platform/Base.h>          // IWYU pragma: export
+#include <cru/platform/Color.h>         // IWYU pragma: export
+#include <cru/platform/GraphicsBase.h>  // IWYU pragma: export
+#include <cru/platform/Matrix.h>        // IWYU pragma: export
 
 #ifdef CRU_IS_DLL
 #ifdef CRU_PLATFORM_GRAPHICS_EXPORT_API
diff --git a/include/cru/platform/graphics/Factory.h b/include/cru/platform/graphics/Factory.h
index d197d821..fa9a3a95 100644
--- a/include/cru/platform/graphics/Factory.h
+++ b/include/cru/platform/graphics/Factory.h
@@ -1,10 +1,9 @@
 #pragma once
-#include "Resource.h"
+#include "Base.h"
 
 #include "Brush.h"
 #include "Font.h"
 #include "Geometry.h"
-#include "Image.h"
 #include "ImageFactory.h"
 #include "TextLayout.h"
 
@@ -15,11 +14,11 @@ struct CRU_PLATFORM_GRAPHICS_API IGraphicsFactory : virtual IPlatformResource {
 
   virtual std::unique_ptr<IGeometryBuilder> CreateGeometryBuilder() = 0;
 
-  virtual std::unique_ptr<IFont> CreateFont(String font_family,
+  virtual std::unique_ptr<IFont> CreateFont(std::string font_family,
                                             float font_size) = 0;
 
   virtual std::unique_ptr<ITextLayout> CreateTextLayout(
-      std::shared_ptr<IFont> font, String text) = 0;
+      std::shared_ptr<IFont> font, std::string text) = 0;
 
   std::unique_ptr<ISolidColorBrush> CreateSolidColorBrush(const Color& color) {
     std::unique_ptr<ISolidColorBrush> brush = CreateSolidColorBrush();
diff --git a/include/cru/platform/graphics/Font.h b/include/cru/platform/graphics/Font.h
index 7144fdc2..de24222c 100644
--- a/include/cru/platform/graphics/Font.h
+++ b/include/cru/platform/graphics/Font.h
@@ -1,9 +1,11 @@
 #pragma once
 #include "Resource.h"
 
+#include <string>
+
 namespace cru::platform::graphics {
 struct CRU_PLATFORM_GRAPHICS_API IFont : virtual IGraphicsResource {
-  virtual String GetFontName() = 0;
+  virtual std::string GetFontName() = 0;
   virtual float GetFontSize() = 0;
 };
 }  // namespace cru::platform::graphics
diff --git a/include/cru/platform/graphics/Geometry.h b/include/cru/platform/graphics/Geometry.h
index b4b05194..2b251495 100644
--- a/include/cru/platform/graphics/Geometry.h
+++ b/include/cru/platform/graphics/Geometry.h
@@ -95,9 +95,10 @@ struct CRU_PLATFORM_GRAPHICS_API IGeometryBuilder : virtual IGraphicsResource {
 
   virtual std::unique_ptr<IGeometry> Build() = 0;
 
-  virtual void ParseAndApplySvgPathData(StringView path_d);
+  virtual void ParseAndApplySvgPathData(std::string_view path_d);
 };
 
 std::unique_ptr<IGeometry> CRU_PLATFORM_GRAPHICS_API
-CreateGeometryFromSvgPathData(IGraphicsFactory* factory, StringView path_d);
+CreateGeometryFromSvgPathData(IGraphicsFactory* factory,
+                              std::string_view path_d);
 }  // namespace cru::platform::graphics
diff --git a/include/cru/platform/graphics/NullPainter.h b/include/cru/platform/graphics/NullPainter.h
index 27cb6393..74d71c16 100644
--- a/include/cru/platform/graphics/NullPainter.h
+++ b/include/cru/platform/graphics/NullPainter.h
@@ -14,9 +14,9 @@ class CRU_PLATFORM_GRAPHICS_API NullPainter : public Object,
   ~NullPainter() override = default;
 
  public:
-  String GetPlatformId() const override { return u"NULL"; }
+  std::string GetPlatformId() const override { return "NULL"; }
 
-  String GetDebugString() override { return u"NullPainter"; }
+  std::string GetDebugString() override { return "NullPainter"; }
 
   Matrix GetTransform() override { return Matrix(); }
   void SetTransform(const Matrix& matrix) override { CRU_UNUSED(matrix) }
diff --git a/include/cru/platform/graphics/Resource.h b/include/cru/platform/graphics/Resource.h
index ab1b8de6..f910ca8a 100644
--- a/include/cru/platform/graphics/Resource.h
+++ b/include/cru/platform/graphics/Resource.h
@@ -1,6 +1,8 @@
 #pragma once
 #include "Base.h"
 
+#include <cru/platform/Resource.h>
+
 namespace cru::platform::graphics {
 struct IGraphicsFactory;
 
diff --git a/include/cru/platform/graphics/SvgGeometryBuilderMixin.h b/include/cru/platform/graphics/SvgGeometryBuilderMixin.h
index 32b665a5..586872b0 100644
--- a/include/cru/platform/graphics/SvgGeometryBuilderMixin.h
+++ b/include/cru/platform/graphics/SvgGeometryBuilderMixin.h
@@ -45,25 +45,24 @@ class CRU_PLATFORM_GRAPHICS_API SvgGeometryBuilderMixin
 
   void CloseFigure(bool close) override;
 
-  void ParseAndApplySvgPathData(StringView path_d) override;
+  void ParseAndApplySvgPathData(std::string_view path_d) override;
 
  protected:
-  String GetPathData() const { return current_; }
+  std::string GetPathData() const { return current_; }
 
  private:
   template <typename... Args>
-  void Append(StringView format, Args&&... args) {
-    current_ += String::FromUtf8(
-        std::format(format.ToUtf8(), std::forward<Args>(args)...));
-    current_ += u' ';
+  void Append(std::string_view format, Args&&... args) {
+    current_ += std::format(format, std::forward<Args>(args)...);
+    current_ += ' ';
   }
 
-  void AppendCommand(StringView command);
+  void AppendCommand(std::string_view command);
   void Append(bool flag);
   void Append(float number);
   void Append(const Point& point);
 
  private:
-  String current_;
+  std::string current_;
 };
 }  // namespace cru::platform::graphics
diff --git a/include/cru/platform/graphics/TextLayout.h b/include/cru/platform/graphics/TextLayout.h
index e060186b..4c5302eb 100644
--- a/include/cru/platform/graphics/TextLayout.h
+++ b/include/cru/platform/graphics/TextLayout.h
@@ -8,8 +8,8 @@ namespace cru::platform::graphics {
 // Requirement:
 // All text must be left-top aligned.
 struct CRU_PLATFORM_GRAPHICS_API ITextLayout : virtual IGraphicsResource {
-  virtual String GetText() = 0;
-  virtual void SetText(String new_text) = 0;
+  virtual std::string GetText() = 0;
+  virtual void SetText(std::string new_text) = 0;
 
   virtual std::shared_ptr<IFont> GetFont() = 0;
   virtual void SetFont(std::shared_ptr<IFont> font) = 0;
diff --git a/include/cru/platform/graphics/cairo/CairoGraphicsFactory.h b/include/cru/platform/graphics/cairo/CairoGraphicsFactory.h
index f0f7ecc5..563c6b40 100644
--- a/include/cru/platform/graphics/cairo/CairoGraphicsFactory.h
+++ b/include/cru/platform/graphics/cairo/CairoGraphicsFactory.h
@@ -26,11 +26,11 @@ class CRU_PLATFORM_GRAPHICS_CAIRO_API CairoGraphicsFactory
 
   std::unique_ptr<IGeometryBuilder> CreateGeometryBuilder() override;
 
-  std::unique_ptr<IFont> CreateFont(String font_family,
+  std::unique_ptr<IFont> CreateFont(std::string font_family,
                                     float font_size) override;
 
   std::unique_ptr<ITextLayout> CreateTextLayout(std::shared_ptr<IFont> font,
-                                                String text) override;
+                                                std::string text) override;
 
   IImageFactory* GetImageFactory() override;
 
diff --git a/include/cru/platform/graphics/cairo/CairoResource.h b/include/cru/platform/graphics/cairo/CairoResource.h
index bf35ab26..14730e8a 100644
--- a/include/cru/platform/graphics/cairo/CairoResource.h
+++ b/include/cru/platform/graphics/cairo/CairoResource.h
@@ -17,7 +17,7 @@ class CRU_PLATFORM_GRAPHICS_CAIRO_API CairoResource
 
   ~CairoResource() override;
 
-  String GetPlatformId() const override;
+  std::string GetPlatformId() const override;
   IGraphicsFactory* GetGraphicsFactory() override;
   CairoGraphicsFactory* GetCairoGraphicsFactory() const { return factory_; }
 
diff --git a/include/cru/platform/graphics/cairo/PangoFont.h b/include/cru/platform/graphics/cairo/PangoFont.h
index 3014739d..e8dbf3ec 100644
--- a/include/cru/platform/graphics/cairo/PangoFont.h
+++ b/include/cru/platform/graphics/cairo/PangoFont.h
@@ -9,12 +9,12 @@ namespace cru::platform::graphics::cairo {
 class CRU_PLATFORM_GRAPHICS_CAIRO_API PangoFont : public CairoResource,
                                                   public virtual IFont {
  public:
-  PangoFont(CairoGraphicsFactory* factory, String font_family, float font_size);
+  PangoFont(CairoGraphicsFactory* factory, std::string font_family, float font_size);
 
   ~PangoFont() override;
 
  public:
-  String GetFontName() override;
+  std::string GetFontName() override;
   float GetFontSize() override;
 
   PangoFontDescription* GetPangoFontDescription() {
@@ -22,7 +22,7 @@ class CRU_PLATFORM_GRAPHICS_CAIRO_API PangoFont : public CairoResource,
   }
 
  private:
-  String font_family_;
+  std::string font_family_;
   float font_size_;
   PangoFontDescription* pango_font_description_;
 };
diff --git a/include/cru/platform/graphics/cairo/PangoTextLayout.h b/include/cru/platform/graphics/cairo/PangoTextLayout.h
index cdc54e8d..270022ee 100644
--- a/include/cru/platform/graphics/cairo/PangoTextLayout.h
+++ b/include/cru/platform/graphics/cairo/PangoTextLayout.h
@@ -15,8 +15,8 @@ class CRU_PLATFORM_GRAPHICS_CAIRO_API PangoTextLayout
   ~PangoTextLayout() override;
 
  public:
-  String GetText() override;
-  void SetText(String new_text) override;
+  std::string GetText() override;
+  void SetText(std::string new_text) override;
 
   std::shared_ptr<IFont> GetFont() override;
   void SetFont(std::shared_ptr<IFont> font) override;
@@ -40,12 +40,7 @@ class CRU_PLATFORM_GRAPHICS_CAIRO_API PangoTextLayout
   PangoLayout* GetPangoLayout() { return pango_layout_; }
 
  private:
-  Index FromUtf8IndexToUtf16Index(Index index);
-  Index FromUtf16IndexToUtf8Index(Index index);
-
- private:
-  String text_;
-  std::string utf8_text_;
+  std::string text_;
 
   bool edit_mode_ = false;
 
diff --git a/include/cru/platform/gui/Base.h b/include/cru/platform/gui/Base.h
index affce4cd..f8ffbc51 100644
--- a/include/cru/platform/gui/Base.h
+++ b/include/cru/platform/gui/Base.h
@@ -1,9 +1,6 @@
 #pragma once
-#include "cru/base/Base.h"
-#include "cru/base/Bitmask.h"
-#include "cru/platform/graphics/Base.h"
-
-#include "../Resource.h"
+#include <cru/platform/Base.h>      // IWYU pragma: export
+#include <cru/platform/Resource.h>  // IWYU pragma: export
 
 #ifdef CRU_IS_DLL
 #ifdef CRU_PLATFORM_GUI_EXPORT_API
@@ -14,30 +11,3 @@
 #else
 #define CRU_PLATFORM_GUI_API
 #endif
-
-namespace cru::platform::gui {
-struct ICursor;
-struct ICursorManager;
-struct IUiApplication;
-struct INativeWindow;
-struct IInputMethodContext;
-struct IClipboard;
-
-namespace details {
-struct TagMouseButton {};
-}  // namespace details
-
-using MouseButton = Bitmask<details::TagMouseButton>;
-struct MouseButtons {
-  constexpr static MouseButton None = MouseButton::FromOffset(0);
-  constexpr static MouseButton Left = MouseButton::FromOffset(1);
-  constexpr static MouseButton Middle = MouseButton::FromOffset(2);
-  constexpr static MouseButton Right = MouseButton::FromOffset(3);
-};
-
-namespace mouse_buttons {
-constexpr MouseButton left{MouseButtons::Left};
-constexpr MouseButton middle{MouseButtons::Middle};
-constexpr MouseButton right{MouseButtons::Right};
-}  // namespace mouse_buttons
-}  // namespace cru::platform::gui
diff --git a/include/cru/platform/gui/Clipboard.h b/include/cru/platform/gui/Clipboard.h
index 47267895..63932683 100644
--- a/include/cru/platform/gui/Clipboard.h
+++ b/include/cru/platform/gui/Clipboard.h
@@ -3,7 +3,7 @@
 
 namespace cru::platform::gui {
 struct IClipboard : virtual IPlatformResource {
-  virtual String GetText() = 0;
-  virtual void SetText(String text) = 0;
+  virtual std::string GetText() = 0;
+  virtual void SetText(std::string text) = 0;
 };
 }  // namespace cru::platform::gui
diff --git a/include/cru/platform/gui/Keyboard.h b/include/cru/platform/gui/Input.h
index 97665e41..dca064d4 100644
--- a/include/cru/platform/gui/Keyboard.h
+++ b/include/cru/platform/gui/Input.h
@@ -1,8 +1,23 @@
 #pragma once
-#include "cru/base/Bitmask.h"
-#include "cru/platform/gui/Base.h"
+#include "Base.h"
+
+#include <cru/base/Bitmask.h>
+
+#include <string>
 
 namespace cru::platform::gui {
+namespace details {
+struct TagMouseButton {};
+}  // namespace details
+
+using MouseButton = Bitmask<details::TagMouseButton>;
+struct MouseButtons {
+  constexpr static MouseButton None = MouseButton::FromOffset(0);
+  constexpr static MouseButton Left = MouseButton::FromOffset(1);
+  constexpr static MouseButton Middle = MouseButton::FromOffset(2);
+  constexpr static MouseButton Right = MouseButton::FromOffset(3);
+};
+
 // Because of the complexity of keyboard layout, I only add code in US keyboard
 // layout, the most widely used layout in China. We should try to make it easy
 // to add new keyboard layout.
@@ -123,20 +138,15 @@ struct KeyModifiers {
   static constexpr KeyModifier Ctrl = KeyModifier::FromOffset(2);
   static constexpr KeyModifier Alt = KeyModifier::FromOffset(3);
   static constexpr KeyModifier Command = KeyModifier::FromOffset(4);
-  static constexpr KeyModifier none = None;
-  static constexpr KeyModifier shift = Shift;
-  static constexpr KeyModifier ctrl = Ctrl;
-  static constexpr KeyModifier alt = Alt;
-  static constexpr KeyModifier command = Command;
 };
 
 #ifdef CRU_PLATFORM_OSX
-constexpr KeyModifier kKeyModifierCommand = KeyModifiers::command;
+constexpr KeyModifier kKeyModifierCommand = KeyModifiers::Command;
 #else
-constexpr KeyModifier kKeyModifierCommand = KeyModifiers::ctrl;
+constexpr KeyModifier kKeyModifierCommand = KeyModifiers::Ctrl;
 #endif
 
-CRU_PLATFORM_GUI_API String ToString(KeyCode key_code);
-CRU_PLATFORM_GUI_API String ToString(KeyModifier key_modifier,
-                                     StringView separator = u"+");
+CRU_PLATFORM_GUI_API std::string ToString(KeyCode key_code);
+CRU_PLATFORM_GUI_API std::string ToString(KeyModifier key_modifier,
+                                          std::string_view separator = "+");
 }  // namespace cru::platform::gui
diff --git a/include/cru/platform/gui/InputMethod.h b/include/cru/platform/gui/InputMethod.h
index b4a1e9d9..d178cb8a 100644
--- a/include/cru/platform/gui/InputMethod.h
+++ b/include/cru/platform/gui/InputMethod.h
@@ -1,9 +1,9 @@
 #pragma once
 #include "Base.h"
 
-#include "cru/base/Event.h"
+#include <cru/base/Event.h>
+#include <cru/platform/GraphicsBase.h>
 
-#include <memory>
 #include <vector>
 
 namespace cru::platform::gui {
@@ -16,7 +16,7 @@ struct CompositionClause {
 using CompositionClauses = std::vector<CompositionClause>;
 
 struct CompositionText {
-  String text;
+  std::string text;
   CompositionClauses clauses;
   TextRange selection;
 };
@@ -61,6 +61,6 @@ struct IInputMethodContext : virtual IPlatformResource {
   virtual IEvent<std::nullptr_t>* CompositionStartEvent() = 0;
   virtual IEvent<std::nullptr_t>* CompositionEndEvent() = 0;
   virtual IEvent<std::nullptr_t>* CompositionEvent() = 0;
-  virtual IEvent<StringView>* TextEvent() = 0;
+  virtual IEvent<std::string>* TextEvent() = 0;
 };
 }  // namespace cru::platform::gui
diff --git a/include/cru/platform/gui/Menu.h b/include/cru/platform/gui/Menu.h
index 6e2a8902..d076ca69 100644
--- a/include/cru/platform/gui/Menu.h
+++ b/include/cru/platform/gui/Menu.h
@@ -1,7 +1,6 @@
 #pragma once
 #include "Base.h"
-
-#include "Keyboard.h"
+#include "Input.h"
 
 #include <functional>
 
@@ -9,8 +8,8 @@ namespace cru::platform::gui {
 struct IMenu;
 
 struct CRU_PLATFORM_GUI_API IMenuItem : virtual IPlatformResource {
-  virtual String GetTitle() = 0;
-  virtual void SetTitle(String title) = 0;
+  virtual std::string GetTitle() = 0;
+  virtual void SetTitle(std::string title) = 0;
   virtual bool IsEnabled() = 0;
   virtual void SetEnabled(bool enabled) = 0;
   virtual IMenu* GetParentMenu() = 0;
diff --git a/include/cru/platform/gui/SaveOpenDialogOptions.h b/include/cru/platform/gui/SaveOpenDialogOptions.h
index cff4a44f..484a1552 100644
--- a/include/cru/platform/gui/SaveOpenDialogOptions.h
+++ b/include/cru/platform/gui/SaveOpenDialogOptions.h
@@ -1,12 +1,15 @@
 #pragma once
 #include "Base.h"
 
+#include <string>
+#include <vector>
+
 namespace cru::platform::gui {
 struct CRU_PLATFORM_GUI_API SaveDialogOptions {
-  String title;
-  String prompt;
-  String message;
-  std::vector<String> allowed_file_types;
+  std::string title;
+  std::string prompt;
+  std::string message;
+  std::vector<std::string> allowed_file_types;
   bool allow_all_file_types = false;
 };
 
@@ -20,29 +23,29 @@ template <typename T>
 struct CRU_PLATFORM_GUI_API SaveDialogOptionsBuilderTemplate {
   T options;
 
-  SaveDialogOptionsBuilderTemplate& SetTitle(String title) {
+  SaveDialogOptionsBuilderTemplate& SetTitle(std::string title) {
     options.title = std::move(title);
     return *this;
   }
 
-  SaveDialogOptionsBuilderTemplate& SetPrompt(String prompt) {
+  SaveDialogOptionsBuilderTemplate& SetPrompt(std::string prompt) {
     options.prompt = std::move(prompt);
     return *this;
   }
 
-  SaveDialogOptionsBuilderTemplate& SetMessage(String message) {
+  SaveDialogOptionsBuilderTemplate& SetMessage(std::string message) {
     options.message = std::move(message);
     return *this;
   }
 
   SaveDialogOptionsBuilderTemplate& SetAllowedFileTypes(
-      std::vector<String> allowed_file_types) {
+      std::vector<std::string> allowed_file_types) {
     options.allowed_file_types = std::move(allowed_file_types);
     return *this;
   }
 
   SaveDialogOptionsBuilderTemplate& AddAllowedFileType(
-      String allowed_file_type) {
+      std::string allowed_file_type) {
     options.allowed_file_types.push_back(allowed_file_type);
     return *this;
   }
diff --git a/include/cru/platform/gui/UiApplication.h b/include/cru/platform/gui/UiApplication.h
index b44a450f..d15a3c72 100644
--- a/include/cru/platform/gui/UiApplication.h
+++ b/include/cru/platform/gui/UiApplication.h
@@ -1,17 +1,20 @@
 #pragma once
 #include "Base.h"
-
-#include "cru/base/Bitmask.h"
-#include "cru/platform/gui/Menu.h"
-
+#include "Menu.h"
 #include "SaveOpenDialogOptions.h"
 
+#include <cru/platform/graphics/Factory.h>
+
 #include <chrono>
 #include <functional>
-#include <memory>
 #include <vector>
 
 namespace cru::platform::gui {
+struct ICursorManager;
+struct INativeWindow;
+struct IInputMethodContext;
+struct IClipboard;
+
 // The entry point of a ui application.
 struct CRU_PLATFORM_GUI_API IUiApplication : public virtual IPlatformResource {
  public:
@@ -63,12 +66,12 @@ struct CRU_PLATFORM_GUI_API IUiApplication : public virtual IPlatformResource {
   /**
    * \todo Implement on Windows/X11.
    */
-  virtual std::optional<String> ShowSaveDialog(SaveDialogOptions options);
+  virtual std::optional<std::string> ShowSaveDialog(SaveDialogOptions options);
 
   /**
    * \todo Implement on Windows/X11.
    */
-  virtual std::optional<std::vector<String>> ShowOpenDialog(
+  virtual std::optional<std::vector<std::string>> ShowOpenDialog(
       OpenDialogOptions options);
 };
 }  // namespace cru::platform::gui
diff --git a/include/cru/platform/gui/Window.h b/include/cru/platform/gui/Window.h
index 06fbdb65..3be5b21b 100644
--- a/include/cru/platform/gui/Window.h
+++ b/include/cru/platform/gui/Window.h
@@ -1,11 +1,16 @@
 #pragma once
 #include "Base.h"
 
-#include "Keyboard.h"
+#include "Input.h"
 
-#include "cru/base/Event.h"
+#include <cru/base/Event.h>
+#include <cru/platform/GraphicsBase.h>
+#include <cru/platform/graphics/Painter.h>
 
 namespace cru::platform::gui {
+class ICursor;
+class IInputMethodContext;
+
 namespace details {
 struct WindowStyleFlagTag;
 }
@@ -53,8 +58,8 @@ struct CRU_PLATFORM_GUI_API INativeWindow : virtual IPlatformResource {
   virtual WindowStyleFlag GetStyleFlag() = 0;
   virtual void SetStyleFlag(WindowStyleFlag flag) = 0;
 
-  virtual String GetTitle() = 0;
-  virtual void SetTitle(String title) = 0;
+  virtual std::string GetTitle() = 0;
+  virtual void SetTitle(std::string title) = 0;
 
   virtual WindowVisibilityType GetVisibility() = 0;
   virtual void SetVisibility(WindowVisibilityType visibility) = 0;
diff --git a/include/cru/platform/gui/osx/Keyboard.h b/include/cru/platform/gui/osx/Keyboard.h
index 89e0fa05..619fdd1f 100644
--- a/include/cru/platform/gui/osx/Keyboard.h
+++ b/include/cru/platform/gui/osx/Keyboard.h
@@ -1,5 +1,5 @@
 #pragma once
-#include "cru/platform/gui/Keyboard.h"
+#include <cru/platform/gui/Input.h>
 
 namespace cru::platform::gui::osx {
 KeyCode KeyCodeFromOsxToCru(unsigned short n);
diff --git a/include/cru/platform/gui/sdl/Base.h b/include/cru/platform/gui/sdl/Base.h
index 9dd2eff6..0de2fd1f 100644
--- a/include/cru/platform/gui/sdl/Base.h
+++ b/include/cru/platform/gui/sdl/Base.h
@@ -8,13 +8,13 @@
 namespace cru::platform::gui::sdl {
 class SdlResource : public Object, public virtual IPlatformResource {
  public:
-  static constexpr const char16_t* kPlatformId = u"SDL";
+  static constexpr const char* kPlatformId = "SDL";
 
  protected:
   SdlResource() = default;
 
  public:
-  String GetPlatformId() const final { return String(kPlatformId); }
+  std::string GetPlatformId() const final { return kPlatformId; }
 };
 
 class SdlException : public PlatformException {
diff --git a/include/cru/platform/gui/sdl/Window.h b/include/cru/platform/gui/sdl/Window.h
index 1bcd42bf..4eb0a11d 100644
--- a/include/cru/platform/gui/sdl/Window.h
+++ b/include/cru/platform/gui/sdl/Window.h
@@ -29,8 +29,8 @@ class SdlWindow : public SdlResource, public virtual INativeWindow {
   WindowStyleFlag GetStyleFlag() override;
   void SetStyleFlag(WindowStyleFlag flag) override;
 
-  String GetTitle() override;
-  void SetTitle(String title) override;
+  std::string GetTitle() override;
+  void SetTitle(std::string title) override;
 
   WindowVisibilityType GetVisibility() override;
   void SetVisibility(WindowVisibilityType visibility) override;
diff --git a/include/cru/platform/gui/win/Keyboard.h b/include/cru/platform/gui/win/Keyboard.h
index 18b37b60..c98c49a3 100644
--- a/include/cru/platform/gui/win/Keyboard.h
+++ b/include/cru/platform/gui/win/Keyboard.h
@@ -1,7 +1,7 @@
 #pragma once
 #include "Base.h"
 
-#include "cru/platform/gui/Keyboard.h"
+#include <cru/platform/gui/Input.h>
 
 namespace cru::platform::gui::win {
 KeyCode CRU_WIN_GUI_API VirtualKeyToKeyCode(int virtual_key);
diff --git a/include/cru/platform/gui/xcb/Base.h b/include/cru/platform/gui/xcb/Base.h
index ad571a40..71007f87 100644
--- a/include/cru/platform/gui/xcb/Base.h
+++ b/include/cru/platform/gui/xcb/Base.h
@@ -1,19 +1,19 @@
 #pragma once
 
 #include <cru/base/Exception.h>
-
-#include "../../Resource.h"
+#include <cru/platform/Resource.h>
+#include <cru/platform/gui/Base.h>
 
 namespace cru::platform::gui::xcb {
 class XcbResource : public Object, public virtual IPlatformResource {
  public:
-  static constexpr const char16_t* kPlatformId = u"XCB";
+  static constexpr const char* kPlatformId = "XCB";
 
  protected:
   XcbResource() = default;
 
  public:
-  String GetPlatformId() const final { return String(kPlatformId); }
+  std::string GetPlatformId() const final { return std::string(kPlatformId); }
 };
 
 class XcbException : public PlatformException {
diff --git a/include/cru/platform/gui/xcb/Clipboard.h b/include/cru/platform/gui/xcb/Clipboard.h
index 44294cbc..690cd2b1 100644
--- a/include/cru/platform/gui/xcb/Clipboard.h
+++ b/include/cru/platform/gui/xcb/Clipboard.h
@@ -10,8 +10,8 @@ class XcbClipboard : public XcbResource, public virtual IClipboard {
   explicit XcbClipboard(XcbUiApplication* application);
   ~XcbClipboard() override;
 
-  String GetText() override;
-  void SetText(String text) override;
+  std::string GetText() override;
+  void SetText(std::string text) override;
 
  private:
   XcbUiApplication* application_;
diff --git a/include/cru/platform/gui/xcb/Cursor.h b/include/cru/platform/gui/xcb/Cursor.h
index 02ede7dd..03399333 100644
--- a/include/cru/platform/gui/xcb/Cursor.h
+++ b/include/cru/platform/gui/xcb/Cursor.h
@@ -1,9 +1,10 @@
 #pragma once
 
-#include <cru/base/io/Stream.h>
-#include "../Cursor.h"
 #include "Base.h"
 
+#include <cru/base/io/Stream.h>
+#include <cru/platform/gui/Cursor.h>
+
 #include <xcb/xcb.h>
 #include <xcb/xcb_cursor.h>
 #include <memory>
diff --git a/include/cru/platform/gui/xcb/Keyboard.h b/include/cru/platform/gui/xcb/Input.h
index adff95c1..77e213de 100644
--- a/include/cru/platform/gui/xcb/Keyboard.h
+++ b/include/cru/platform/gui/xcb/Input.h
@@ -1,6 +1,6 @@
 #pragma once
 
-#include <cru/platform/gui/Keyboard.h>
+#include <cru/platform/gui/Input.h>
 
 #include <xcb/xcb.h>
 #include <xkbcommon/xkbcommon.h>
diff --git a/include/cru/platform/gui/xcb/InputMethod.h b/include/cru/platform/gui/xcb/InputMethod.h
index c5ffd416..e32ed63e 100644
--- a/include/cru/platform/gui/xcb/InputMethod.h
+++ b/include/cru/platform/gui/xcb/InputMethod.h
@@ -1,9 +1,10 @@
 #pragma once
 
-#include <cru/base/Base.h>
-#include "../InputMethod.h"
 #include "Base.h"
 
+#include <cru/base/Base.h>
+#include <cru/platform/gui/InputMethod.h>
+
 #include <xcb-imdkit/imclient.h>
 #include <xcb/xcb.h>
 #include <optional>
@@ -66,7 +67,7 @@ class XcbXimInputMethodContext : public XcbResource,
   IEvent<std::nullptr_t>* CompositionStartEvent() override;
   IEvent<std::nullptr_t>* CompositionEndEvent() override;
   IEvent<std::nullptr_t>* CompositionEvent() override;
-  IEvent<StringView>* TextEvent() override;
+  IEvent<std::string>* TextEvent() override;
 
  private:
   void CreateIc(xcb_window_t window);
@@ -83,6 +84,6 @@ class XcbXimInputMethodContext : public XcbResource,
   Event<std::nullptr_t> composition_start_event_;
   Event<std::nullptr_t> composition_end_event_;
   Event<std::nullptr_t> composition_event_;
-  Event<StringView> text_event_;
+  Event<std::string> text_event_;
 };
 }  // namespace cru::platform::gui::xcb
diff --git a/include/cru/platform/gui/xcb/UiApplication.h b/include/cru/platform/gui/xcb/UiApplication.h
index ab481c79..55138fd3 100644
--- a/include/cru/platform/gui/xcb/UiApplication.h
+++ b/include/cru/platform/gui/xcb/UiApplication.h
@@ -1,9 +1,9 @@
 #pragma once
-#include "../UiApplication.h"
 #include "Base.h"
 
 #include <cru/base/platform/unix/EventLoop.h>
 #include <cru/platform/graphics/cairo/CairoGraphicsFactory.h>
+#include <cru/platform/gui/UiApplication.h>
 
 #include <xcb/xcb.h>
 #include <functional>
diff --git a/include/cru/platform/gui/xcb/Window.h b/include/cru/platform/gui/xcb/Window.h
index 5f1fd66e..bfd86297 100644
--- a/include/cru/platform/gui/xcb/Window.h
+++ b/include/cru/platform/gui/xcb/Window.h
@@ -1,11 +1,10 @@
 
 #pragma once
-#include <cru/base/Base.h>
-#include "../../GraphicsBase.h"
-#include "../TimerHelper.h"
-#include "../Window.h"
 #include "Base.h"
 
+#include <cru/platform/gui/TimerHelper.h>
+#include <cru/platform/gui/Window.h>
+
 #include <cairo.h>
 #include <xcb/xcb.h>
 #include <cstddef>
@@ -34,8 +33,8 @@ class XcbWindow : public XcbResource, public virtual INativeWindow {
   WindowStyleFlag GetStyleFlag() override;
   void SetStyleFlag(WindowStyleFlag flag) override;
 
-  String GetTitle() override;
-  void SetTitle(String title) override;
+  std::string GetTitle() override;
+  void SetTitle(std::string title) override;
 
   WindowVisibilityType GetVisibility() override;
   void SetVisibility(WindowVisibilityType visibility) override;
diff --git a/include/cru/ui/Base.h b/include/cru/ui/Base.h
index b4b2f18e..3f270b39 100644
--- a/include/cru/ui/Base.h
+++ b/include/cru/ui/Base.h
@@ -1,7 +1,9 @@
 #pragma once
-#include "cru/base/Base.h"
-#include "cru/platform/graphics/Base.h"
-#include "cru/platform/gui/Base.h"
+#include <cru/base/Base.h>
+#include <cru/platform/Color.h>
+#include <cru/platform/GraphicsBase.h>
+#include <cru/platform/Matrix.h>
+#include <cru/platform/gui/Input.h>
 
 #ifdef CRU_IS_DLL
 #ifdef CRU_UI_EXPORT_API
@@ -25,8 +27,7 @@ using cru::platform::Size;
 using cru::platform::TextRange;
 using cru::platform::Thickness;
 using cru::platform::gui::MouseButton;
-
-namespace mouse_buttons = cru::platform::gui::mouse_buttons;
+using cru::platform::gui::MouseButtons;
 
 namespace colors = cru::platform::colors;
 
diff --git a/include/cru/ui/ThemeManager.h b/include/cru/ui/ThemeManager.h
index 72ade899..10d90060 100644
--- a/include/cru/ui/ThemeManager.h
+++ b/include/cru/ui/ThemeManager.h
@@ -27,7 +27,7 @@ class CRU_UI_API ThemeManager : public Object {
       std::unique_ptr<ThemeResourceDictionary> theme_resource_dictionary);
 
   template <typename T>
-  T GetResource(const String& key) {
+  T GetResource(std::string_view key) {
     for (const auto& resource_dictionary : theme_resource_dictionary_list_) {
       try {
         return resource_dictionary->GetResource<T>(key);
@@ -35,18 +35,19 @@ class CRU_UI_API ThemeManager : public Object {
       }
     }
     throw ThemeResourceKeyNotExistException(
-        std::format("Theme resource key {} not exist.", key.ToUtf8()));
+        std::format("Theme resource key {} not exist.", key));
   }
 
-  String GetResourceString(const String& key);
+  std::string GetResourceString(std::string_view key);
 
   std::shared_ptr<platform::graphics::IBrush> GetResourceBrush(
-      const String& key);
+      std::string_view key);
 
-  std::shared_ptr<platform::graphics::IFont> GetResourceFont(const String& key);
+  std::shared_ptr<platform::graphics::IFont> GetResourceFont(
+      std::string_view key);
 
   std::shared_ptr<style::StyleRuleSet> GetResourceStyleRuleSet(
-      const String& key);
+      std::string_view key);
 
   IEvent<std::nullptr_t>* ThemeResourceChangeEvent() {
     return &theme_resource_change_event_;
diff --git a/include/cru/ui/ThemeResourceDictionary.h b/include/cru/ui/ThemeResourceDictionary.h
index 0cbda01b..90cbe520 100644
--- a/include/cru/ui/ThemeResourceDictionary.h
+++ b/include/cru/ui/ThemeResourceDictionary.h
@@ -44,11 +44,11 @@ class CRU_UI_API ThemeResourceDictionary : public Object {
 
  public:
   template <typename T>
-  T GetResource(const String& key) {
-    auto find_result = resource_map_.find(key);
+  T GetResource(std::string_view key) {
+    auto find_result = resource_map_.find(std::string(key));
     if (find_result == resource_map_.cend()) {
       throw ThemeResourceKeyNotExistException(
-          std::format("Theme resource key {} not exist.", key.ToUtf8()));
+          std::format("Theme resource key {} not exist.", key));
     }
 
     auto& cache = find_result->second.cache;
@@ -73,12 +73,12 @@ class CRU_UI_API ThemeResourceDictionary : public Object {
     CRU_DEFAULT_COPY(ResourceEntry)
     CRU_DEFAULT_MOVE(ResourceEntry)
 
-    String name;
+    std::string name;
     xml::XmlElementNode* xml_node;
     std::unordered_map<std::type_index, std::any> cache;
   };
 
   std::unique_ptr<xml::XmlElementNode> xml_root_;
-  std::unordered_map<String, ResourceEntry> resource_map_;
+  std::unordered_map<std::string, ResourceEntry> resource_map_;
 };
 }  // namespace cru::ui
diff --git a/include/cru/ui/components/Input.h b/include/cru/ui/components/Input.h
index e808afd7..0f077983 100644
--- a/include/cru/ui/components/Input.h
+++ b/include/cru/ui/components/Input.h
@@ -5,17 +5,17 @@
 namespace cru::ui::components {
 struct CRU_UI_API InputValidateResult {
   bool valid;
-  String message;
+  std::string message;
 };
 
 struct CRU_UI_API IInputValidator : public virtual Interface {
-  virtual InputValidateResult Validate(StringView text) const = 0;
+  virtual InputValidateResult Validate(std::string_view text) const = 0;
 };
 
 struct CRU_UI_API InputChangeEventArgs {
-  String text;
+  std::string text;
   bool valid;
-  String message;
+  std::string message;
 };
 
 class CRU_UI_API Input : public Component {
@@ -26,8 +26,8 @@ class CRU_UI_API Input : public Component {
  public:
   controls::Control* GetRootControl() override;
 
-  String GetText() const;
-  void SetText(String text);
+  std::string GetText() const;
+  void SetText(std::string text);
 
   IInputValidator* GetValidator() const;
   void SetValidator(IInputValidator* validator);
@@ -48,7 +48,7 @@ class CRU_UI_API Input : public Component {
 class CRU_UI_API FloatInputValidator : public Object,
                                        public virtual IInputValidator {
  public:
-  InputValidateResult Validate(StringView text) const override;
+  InputValidateResult Validate(std::string_view text) const override;
 
   std::optional<float> min;
   std::optional<float> max;
diff --git a/include/cru/ui/components/Menu.h b/include/cru/ui/components/Menu.h
index 913f5c92..554a8898 100644
--- a/include/cru/ui/components/Menu.h
+++ b/include/cru/ui/components/Menu.h
@@ -14,7 +14,7 @@ namespace cru::ui::components {
 class CRU_UI_API MenuItem : public Component {
  public:
   MenuItem();
-  explicit MenuItem(String text);
+  explicit MenuItem(std::string text);
 
   CRU_DELETE_COPY(MenuItem)
   CRU_DELETE_MOVE(MenuItem)
@@ -24,7 +24,7 @@ class CRU_UI_API MenuItem : public Component {
  public:
   controls::Control* GetRootControl() override { return &container_; }
 
-  void SetText(String text);
+  void SetText(std::string text);
 
   void SetOnClick(std::function<void()> on_click) {
     on_click_ = std::move(on_click);
@@ -55,10 +55,10 @@ class CRU_UI_API Menu : public Component {
   Component* RemoveItemAt(Index index);
   void ClearItems();
 
-  void AddTextItem(String text, std::function<void()> on_click) {
+  void AddTextItem(std::string text, std::function<void()> on_click) {
     AddTextItemAt(std::move(text), GetItemCount(), std::move(on_click));
   }
-  void AddTextItemAt(String text, Index index, std::function<void()> on_click);
+  void AddTextItemAt(std::string text, Index index, std::function<void()> on_click);
 
   void SetOnItemClick(std::function<void(Index)> on_item_click) {
     on_item_click_ = std::move(on_item_click);
diff --git a/include/cru/ui/components/PopupButton.h b/include/cru/ui/components/PopupButton.h
index c8ef9c50..5fa69044 100644
--- a/include/cru/ui/components/PopupButton.h
+++ b/include/cru/ui/components/PopupButton.h
@@ -18,14 +18,14 @@ class CRU_UI_API PopupMenuTextButton : public Component {
 
   ui::controls::Button* GetButton() { return &button_; }
 
-  String GetButtonText() { return button_text_.GetText(); }
-  void SetButtonText(String text) { button_text_.SetText(std::move(text)); }
+  std::string GetButtonText() { return button_text_.GetText(); }
+  void SetButtonText(std::string text) { button_text_.SetText(std::move(text)); }
 
   void SetButtonTextColor(const Color& color) {
     button_text_.SetTextColor(color);
   }
 
-  void SetMenuItems(std::vector<String> items);
+  void SetMenuItems(std::vector<std::string> items);
 
   IEvent<Index>* MenuItemSelectedEvent() { return &menu_item_selected_event_; }
 
@@ -47,7 +47,7 @@ class CRU_UI_API PopupMenuIconButton : public Component {
 
   ui::controls::IconButton* GetButton() { return &button_; }
 
-  void SetMenuItems(std::vector<String> items);
+  void SetMenuItems(std::vector<std::string> items);
 
   IEvent<Index>* MenuItemSelectedEvent() { return &menu_item_selected_event_; }
 
diff --git a/include/cru/ui/components/Select.h b/include/cru/ui/components/Select.h
index d5ff0b43..9efe9a04 100644
--- a/include/cru/ui/components/Select.h
+++ b/include/cru/ui/components/Select.h
@@ -13,8 +13,8 @@ class CRU_UI_API Select : public Component {
  public:
   ui::controls::Control* GetRootControl() override { return &button_; }
 
-  std::vector<String> GetItems() const { return items_; }
-  void SetItems(std::vector<String> items);
+  std::vector<std::string> GetItems() const { return items_; }
+  void SetItems(std::vector<std::string> items);
 
   Index GetSelectedIndex() const { return selected_index_; }
   void SetSelectedIndex(Index index);
@@ -23,7 +23,7 @@ class CRU_UI_API Select : public Component {
 
  private:
   Index selected_index_;
-  std::vector<String> items_;
+  std::vector<std::string> items_;
 
   ui::controls::Button button_;
   ui::controls::TextBlock button_text_;
diff --git a/include/cru/ui/controls/IconButton.h b/include/cru/ui/controls/IconButton.h
index 632450e2..9dbb3a3d 100644
--- a/include/cru/ui/controls/IconButton.h
+++ b/include/cru/ui/controls/IconButton.h
@@ -21,7 +21,7 @@ class CRU_UI_API IconButton : public NoChildControl,
 
  public:
   IconButton();
-  IconButton(StringView icon_svg_path_data_string, const Rect& view_port);
+  IconButton(std::string_view icon_svg_path_data_string, const Rect& view_port);
   ~IconButton() override;
 
   String GetControlType() const final { return kControlType.ToString(); }
@@ -84,10 +84,10 @@ class CRU_UI_API IconButton : public NoChildControl,
   }
 
   void SetIconFillColor(const Color& color);
-  void SetIconWithSvgPathDataString(StringView icon_svg_path_data_string,
+  void SetIconWithSvgPathDataString(std::string_view icon_svg_path_data_string,
                                     const Rect& view_port);
   void SetIconWithSvgPathDataStringResourceKey(
-      StringView icon_svg_path_data_string_resource_key, const Rect& view_port);
+      std::string_view icon_svg_path_data_string_resource_key, const Rect& view_port);
 
   std::shared_ptr<platform::graphics::IBrush> GetContentBrush() const override {
     return GetIconFillBrush();
diff --git a/include/cru/ui/controls/TextBlock.h b/include/cru/ui/controls/TextBlock.h
index 52e227eb..66330b23 100644
--- a/include/cru/ui/controls/TextBlock.h
+++ b/include/cru/ui/controls/TextBlock.h
@@ -16,8 +16,8 @@ class CRU_UI_API TextBlock : public NoChildControl,
  public:
   static constexpr StringView kControlType = u"TextBlock";
 
-  static std::unique_ptr<TextBlock> Create(String text,
-    bool selectable = false) {
+  static std::unique_ptr<TextBlock> Create(std::string text,
+                                           bool selectable = false) {
     auto c = std::make_unique<TextBlock>();
     c->SetText(std::move(text));
     c->SetSelectable(selectable);
@@ -36,8 +36,8 @@ class CRU_UI_API TextBlock : public NoChildControl,
 
   render::RenderObject* GetRenderObject() const override;
 
-  String GetText() const;
-  void SetText(String text);
+  std::string GetText() const;
+  void SetText(std::string text);
 
   bool IsSelectable() const;
   void SetSelectable(bool value);
diff --git a/include/cru/ui/controls/TextBox.h b/include/cru/ui/controls/TextBox.h
index 9388d3fd..13f5d356 100644
--- a/include/cru/ui/controls/TextBox.h
+++ b/include/cru/ui/controls/TextBox.h
@@ -37,9 +37,9 @@ class CRU_UI_API TextBox : public NoChildControl,
 
   void ApplyBorderStyle(const style::ApplyBorderStyleInfo& style) override;
 
-  String GetText() const { return service_->GetText(); }
-  StringView GetTextView() const { return service_->GetTextView(); }
-  void SetText(String text) { service_->SetText(std::move(text)); }
+  std::string GetText() const { return service_->GetText(); }
+  std::string_view GetTextView() const { return service_->GetTextView(); }
+  void SetText(std::string text) { service_->SetText(std::move(text)); }
 
   IEvent<std::nullptr_t>* TextChangeEvent() {
     return service_->TextChangeEvent();
diff --git a/include/cru/ui/controls/TextHostControlService.h b/include/cru/ui/controls/TextHostControlService.h
index 95f7a067..a945e427 100644
--- a/include/cru/ui/controls/TextHostControlService.h
+++ b/include/cru/ui/controls/TextHostControlService.h
@@ -48,10 +48,10 @@ class TextControlMovePattern : public Object {
   static std::vector<TextControlMovePattern> kDefaultPatterns;
 
   using MoveFunction =
-      std::function<Index(TextHostControlService* service, StringView text,
-                          Index current_position)>;
+      std::function<Index(TextHostControlService* service,
+                          std::string_view text, Index current_position)>;
 
-  TextControlMovePattern(String name, helper::ShortcutKeyBind key_bind,
+  TextControlMovePattern(std::string name, helper::ShortcutKeyBind key_bind,
                          MoveFunction move_function)
       : name_(std::move(name)),
         key_bind_(key_bind),
@@ -63,15 +63,15 @@ class TextControlMovePattern : public Object {
   ~TextControlMovePattern() override = default;
 
  public:
-  String GetName() const { return name_; }
+  std::string GetName() const { return name_; }
   helper::ShortcutKeyBind GetKeyBind() const { return key_bind_; }
-  Index Move(TextHostControlService* service, StringView text,
+  Index Move(TextHostControlService* service, std::string_view text,
              Index current_position) const {
     return move_function_(service, text, current_position);
   }
 
  private:
-  String name_;
+  std::string name_;
   helper::ShortcutKeyBind key_bind_;
   MoveFunction move_function_;
 };
@@ -101,11 +101,11 @@ class CRU_UI_API TextHostControlService : public Object {
   // If text contains line feed characters, it will be converted to space.
   void SetMultiLine(bool multi_line);
 
-  String GetText() { return this->text_; }
-  StringView GetTextView() { return this->text_; }
-  void SetText(String text, bool stop_composition = false);
+  std::string GetText() { return this->text_; }
+  std::string_view GetTextView() { return this->text_; }
+  void SetText(std::string text, bool stop_composition = false);
 
-  void InsertText(Index position, StringView text,
+  void InsertText(Index position, std::string_view text,
                   bool stop_composition = false);
   void DeleteChar(Index position, bool stop_composition = false);
 
@@ -126,7 +126,7 @@ class CRU_UI_API TextHostControlService : public Object {
   Index GetCaretPosition() { return selection_.GetEnd(); }
   TextRange GetSelection() { return selection_; }
 
-  StringView GetSelectedText();
+  std::string_view GetSelectedText();
 
   void SetSelection(Index caret_position);
   void SetSelection(TextRange selection, bool scroll_to_caret = true);
@@ -139,7 +139,7 @@ class CRU_UI_API TextHostControlService : public Object {
   void DeleteSelectedText();
   // If some text is selected, then they are deleted first. Then insert text
   // into caret position.
-  void ReplaceSelectedText(StringView text);
+  void ReplaceSelectedText(std::string_view text);
 
   void ScrollToCaret();
 
@@ -199,7 +199,7 @@ class CRU_UI_API TextHostControlService : public Object {
   EventRevokerListGuard event_guard_;
   EventRevokerListGuard input_method_context_event_guard_;
 
-  String text_;
+  std::string text_;
   TextRange selection_;
 
   bool enable_ = false;
diff --git a/include/cru/ui/events/KeyEventArgs.h b/include/cru/ui/events/KeyEventArgs.h
index 0ece9126..bf6c8c0f 100644
--- a/include/cru/ui/events/KeyEventArgs.h
+++ b/include/cru/ui/events/KeyEventArgs.h
@@ -1,7 +1,7 @@
 #pragma once
 #include "UiEventArgs.h"
 
-#include "cru/platform/gui/Keyboard.h"
+#include "cru/platform/gui/Input.h"
 
 namespace cru::ui::events {
 class CRU_UI_API KeyEventArgs : public UiEventArgs {
@@ -26,4 +26,4 @@ class CRU_UI_API KeyEventArgs : public UiEventArgs {
   platform::gui::KeyModifier key_modifier_;
 };
 
-}  // namespace cru::ui::event
+}  // namespace cru::ui::events
diff --git a/include/cru/ui/events/MouseButtonEventArgs.h b/include/cru/ui/events/MouseButtonEventArgs.h
index 13b3b0a4..57a84cfb 100644
--- a/include/cru/ui/events/MouseButtonEventArgs.h
+++ b/include/cru/ui/events/MouseButtonEventArgs.h
@@ -1,20 +1,21 @@
 #pragma once
 #include "MouseEventArgs.h"
 
-#include "cru/platform/gui/Keyboard.h"
+#include "cru/platform/gui/Input.h"
 
 namespace cru::ui::events {
 
 class CRU_UI_API MouseButtonEventArgs : public MouseEventArgs {
  public:
   MouseButtonEventArgs(Object* sender, Object* original_sender,
-                       const Point& point, const MouseButton button,
+                       const Point& point,
+                       const platform::gui::MouseButton button,
                        platform::gui::KeyModifier key_modifier)
       : MouseEventArgs(sender, original_sender, point),
         button_(button),
         key_modifier_(key_modifier) {}
   MouseButtonEventArgs(Object* sender, Object* original_sender,
-                       const MouseButton button,
+                       const platform::gui::MouseButton button,
                        platform::gui::KeyModifier key_modifier)
       : MouseEventArgs(sender, original_sender),
         button_(button),
@@ -25,11 +26,11 @@ class CRU_UI_API MouseButtonEventArgs : public MouseEventArgs {
   MouseButtonEventArgs& operator=(MouseButtonEventArgs&& other) = default;
   ~MouseButtonEventArgs() override = default;
 
-  MouseButton GetButton() const { return button_; }
+  platform::gui::MouseButton GetButton() const { return button_; }
   platform::gui::KeyModifier GetKeyModifier() const { return key_modifier_; }
 
  private:
-  MouseButton button_;
+  platform::gui::MouseButton button_;
   platform::gui::KeyModifier key_modifier_;
 };
-}  // namespace cru::ui::event
+}  // namespace cru::ui::events
diff --git a/include/cru/ui/events/MouseWheelEventArgs.h b/include/cru/ui/events/MouseWheelEventArgs.h
index 85791491..9ed63924 100644
--- a/include/cru/ui/events/MouseWheelEventArgs.h
+++ b/include/cru/ui/events/MouseWheelEventArgs.h
@@ -1,7 +1,7 @@
 #pragma once
 #include "MouseEventArgs.h"
 
-#include "cru/platform/gui/Keyboard.h"
+#include <cru/platform/gui/Input.h>
 
 namespace cru::ui::events {
 class CRU_UI_API MouseWheelEventArgs : public MouseEventArgs {
@@ -26,4 +26,4 @@ class CRU_UI_API MouseWheelEventArgs : public MouseEventArgs {
   float delta_;
   platform::gui::KeyModifier key_modifier_;
 };
-}  // namespace cru::ui::event
+}  // namespace cru::ui::events
diff --git a/include/cru/ui/helper/ClickDetector.h b/include/cru/ui/helper/ClickDetector.h
index ec63b92a..b83f0e20 100644
--- a/include/cru/ui/helper/ClickDetector.h
+++ b/include/cru/ui/helper/ClickDetector.h
@@ -79,7 +79,7 @@ class ClickDetector : public Object {
   ClickState state_ = ClickState::None;
 
   bool enable_ = true;
-  MouseButton trigger_button_ = mouse_buttons::left | mouse_buttons::right;
+  MouseButton trigger_button_ = MouseButtons::Left | MouseButtons::Right;
 
   Event<ClickEventArgs> event_;
   Event<ClickState> state_change_event_;
diff --git a/include/cru/ui/helper/ShortcutHub.h b/include/cru/ui/helper/ShortcutHub.h
index 19d8c8c9..a5973ab5 100644
--- a/include/cru/ui/helper/ShortcutHub.h
+++ b/include/cru/ui/helper/ShortcutHub.h
@@ -4,7 +4,7 @@
 #include "../events/KeyEventArgs.h"
 #include "cru/base/Base.h"
 #include "cru/base/Event.h"
-#include "cru/platform/gui/Keyboard.h"
+#include <cru/platform/gui/Input.h>
 
 #include <cstddef>
 #include <functional>
@@ -18,7 +18,7 @@ class ShortcutKeyBind {
  public:
   ShortcutKeyBind(
       platform::gui::KeyCode key,
-      platform::gui::KeyModifier modifier = platform::gui::KeyModifiers::none)
+      platform::gui::KeyModifier modifier = platform::gui::KeyModifiers::None)
       : key_(key), modifier_(modifier) {}
 
   CRU_DEFAULT_COPY(ShortcutKeyBind)
@@ -46,10 +46,10 @@ class ShortcutKeyBind {
     return !this->operator==(other);
   }
 
-  String ToString() const {
-    String result = u"(";
+  std::string ToString() const {
+    std::string result = "(";
     result += platform::gui::ToString(modifier_);
-    result += u")";
+    result += ")";
     result += platform::gui::ToString(key_);
     return result;
   }
@@ -59,7 +59,7 @@ class ShortcutKeyBind {
   platform::gui::KeyModifier modifier_;
 };
 
-inline String ToString(const ShortcutKeyBind& key_bind) {
+inline std::string ToString(const ShortcutKeyBind& key_bind) {
   return key_bind.ToString();
 }
 }  // namespace cru::ui::helper
@@ -79,7 +79,7 @@ struct hash<cru::ui::helper::ShortcutKeyBind> {
 namespace cru::ui::helper {
 struct Shortcut {
   // Just for debug.
-  String name;
+  std::string name;
   ShortcutKeyBind key_bind;
   // Return true if it consumes the shortcut. Or return false if it does not
   // handle the shortcut.
@@ -88,7 +88,7 @@ struct Shortcut {
 
 struct ShortcutInfo {
   int id;
-  String name;
+  std::string name;
   ShortcutKeyBind key_bind;
   std::function<bool()> handler;
 };
@@ -103,7 +103,7 @@ class CRU_UI_API ShortcutHub : public Object {
 
   ~ShortcutHub() override = default;
 
-  int RegisterShortcut(String name, ShortcutKeyBind bind,
+  int RegisterShortcut(std::string name, ShortcutKeyBind bind,
                        std::function<bool()> handler) {
     return RegisterShortcut({std::move(name), bind, std::move(handler)});
   }
diff --git a/include/cru/ui/mapper/Mapper.h b/include/cru/ui/mapper/Mapper.h
index f7467120..709288f5 100644
--- a/include/cru/ui/mapper/Mapper.h
+++ b/include/cru/ui/mapper/Mapper.h
@@ -41,14 +41,14 @@ class CRU_UI_API MapperBase : public Object {
   virtual bool XmlElementIsOfThisType(xml::XmlElementNode* node);
 
  protected:
-  void SetAllowedTags(std::vector<String> allowed_tags) {
+  void SetAllowedTags(std::vector<std::string> allowed_tags) {
     allowed_tags_ = std::move(allowed_tags);
   }
 
  private:
   std::type_index type_index_;
 
-  std::vector<String> allowed_tags_;
+  std::vector<std::string> allowed_tags_;
 };
 
 template <typename T>
diff --git a/include/cru/ui/mapper/StringMapper.h b/include/cru/ui/mapper/StringMapper.h
index bfb7314b..01f58c77 100644
--- a/include/cru/ui/mapper/StringMapper.h
+++ b/include/cru/ui/mapper/StringMapper.h
@@ -1,6 +1,8 @@
 #pragma once
 #include "Mapper.h"
 
+#include <cru/base/String.h>
+
 namespace cru::ui::mapper {
 class CRU_UI_API StringMapper : public BasicMapper<String> {
  public:
diff --git a/include/cru/ui/render/RenderObject.h b/include/cru/ui/render/RenderObject.h
index 80fa2e10..eba3b6c4 100644
--- a/include/cru/ui/render/RenderObject.h
+++ b/include/cru/ui/render/RenderObject.h
@@ -4,6 +4,8 @@
 #include "MeasureRequirement.h"
 #include "cru/base/String.h"
 
+#include <cru/platform/graphics/Painter.h>
+
 namespace cru::ui::render {
 struct BoxConstraint {
   static const BoxConstraint kNotLimit;
diff --git a/include/cru/ui/render/ScrollBar.h b/include/cru/ui/render/ScrollBar.h
index 45f80389..fbe14244 100644
--- a/include/cru/ui/render/ScrollBar.h
+++ b/include/cru/ui/render/ScrollBar.h
@@ -39,7 +39,7 @@ enum class ScrollBarAreaKind {
 enum class ScrollBarBrushUsageKind { Arrow, ArrowBackground, Slot, Thumb };
 enum class ScrollBarBrushStateKind { Normal, Hover, Press, Disable };
 
-String CRU_UI_API GenerateScrollBarThemeColorKey(ScrollBarBrushUsageKind usage,
+std::string CRU_UI_API GenerateScrollBarThemeColorKey(ScrollBarBrushUsageKind usage,
                                                  ScrollBarBrushStateKind state);
 
 class CRU_UI_API ScrollBar : public Object {
diff --git a/include/cru/ui/render/TextRenderObject.h b/include/cru/ui/render/TextRenderObject.h
index 72958f6f..b8d1882d 100644
--- a/include/cru/ui/render/TextRenderObject.h
+++ b/include/cru/ui/render/TextRenderObject.h
@@ -35,8 +35,8 @@ class CRU_UI_API TextRenderObject : public RenderObject {
   TextRenderObject& operator=(TextRenderObject&& other) = delete;
   ~TextRenderObject() override;
 
-  String GetText() const;
-  void SetText(String new_text);
+  std::string GetText() const;
+  void SetText(std::string new_text);
 
   std::shared_ptr<platform::graphics::IBrush> GetBrush() { return brush_; }
   void SetBrush(std::shared_ptr<platform::graphics::IBrush> new_brush);
diff --git a/include/cru/ui/style/ApplyBorderStyleInfo.h b/include/cru/ui/style/ApplyBorderStyleInfo.h
index 2a3a7db1..857f73f8 100644
--- a/include/cru/ui/style/ApplyBorderStyleInfo.h
+++ b/include/cru/ui/style/ApplyBorderStyleInfo.h
@@ -1,6 +1,8 @@
 #pragma once
 #include "../Base.h"
 
+#include <cru/platform/graphics/Brush.h>
+
 #include <optional>
 
 namespace cru::ui::style {