Extract XCUI text editing core and window seam headers

engine/include/XCEngine/UI/Text/UITextEditing.h

@@ -0,0 +1,29 @@
+#pragma once
+
+#include <cstddef>
+#include <cstdint>
+#include <string>
+#include <vector>
+
+namespace XCEngine {
+namespace UI {
+namespace Text {
+
+std::size_t CountUtf8Codepoints(const std::string& text);
+std::size_t AdvanceUtf8Offset(const std::string& text, std::size_t offset);
+std::size_t RetreatUtf8Offset(const std::string& text, std::size_t offset);
+void AppendUtf8Codepoint(std::string& text, std::uint32_t codepoint);
+
+std::vector<std::string> SplitLines(const std::string& text);
+std::size_t CountTextLines(const std::string& text);
+std::size_t CountUtf8CodepointsInRange(
+    const std::string& text,
+    std::size_t beginOffset,
+    std::size_t endOffset);
+std::size_t FindLineStartOffset(const std::string& text, std::size_t caret);
+std::size_t FindLineEndOffset(const std::string& text, std::size_t caret);
+std::size_t MoveCaretVertically(const std::string& text, std::size_t caret, int lineDelta);
+
+} // namespace Text
+} // namespace UI
+} // namespace XCEngine