Extract XCUI text editing core and window seam headers

engine/src/UI/Text/UITextEditing.cpp

@@ -0,0 +1,179 @@
+#include <XCEngine/UI/Text/UITextEditing.h>
+
+#include <algorithm>
+
+namespace XCEngine {
+namespace UI {
+namespace Text {
+
+namespace {
+
+bool IsUtf8ContinuationByte(unsigned char value) {
+    return (value & 0xC0u) == 0x80u;
+}
+
+} // namespace
+
+std::size_t CountUtf8Codepoints(const std::string& text) {
+    std::size_t count = 0u;
+    for (unsigned char ch : text) {
+        if (!IsUtf8ContinuationByte(ch)) {
+            ++count;
+        }
+    }
+    return count;
+}
+
+std::size_t AdvanceUtf8Offset(const std::string& text, std::size_t offset) {
+    if (offset >= text.size()) {
+        return text.size();
+    }
+
+    ++offset;
+    while (offset < text.size() && IsUtf8ContinuationByte(static_cast<unsigned char>(text[offset]))) {
+        ++offset;
+    }
+    return offset;
+}
+
+std::size_t RetreatUtf8Offset(const std::string& text, std::size_t offset) {
+    if (offset == 0u || text.empty()) {
+        return 0u;
+    }
+
+    offset = (std::min)(offset, text.size());
+    do {
+        --offset;
+    } while (offset > 0u && IsUtf8ContinuationByte(static_cast<unsigned char>(text[offset])));
+    return offset;
+}
+
+void AppendUtf8Codepoint(std::string& text, std::uint32_t codepoint) {
+    if (codepoint <= 0x7Fu) {
+        text.push_back(static_cast<char>(codepoint));
+        return;
+    }
+
+    if (codepoint <= 0x7FFu) {
+        text.push_back(static_cast<char>(0xC0u | ((codepoint >> 6u) & 0x1Fu)));
+        text.push_back(static_cast<char>(0x80u | (codepoint & 0x3Fu)));
+        return;
+    }
+
+    if (codepoint >= 0xD800u && codepoint <= 0xDFFFu) {
+        return;
+    }
+
+    if (codepoint <= 0xFFFFu) {
+        text.push_back(static_cast<char>(0xE0u | ((codepoint >> 12u) & 0x0Fu)));
+        text.push_back(static_cast<char>(0x80u | ((codepoint >> 6u) & 0x3Fu)));
+        text.push_back(static_cast<char>(0x80u | (codepoint & 0x3Fu)));
+        return;
+    }
+
+    if (codepoint <= 0x10FFFFu) {
+        text.push_back(static_cast<char>(0xF0u | ((codepoint >> 18u) & 0x07u)));
+        text.push_back(static_cast<char>(0x80u | ((codepoint >> 12u) & 0x3Fu)));
+        text.push_back(static_cast<char>(0x80u | ((codepoint >> 6u) & 0x3Fu)));
+        text.push_back(static_cast<char>(0x80u | (codepoint & 0x3Fu)));
+    }
+}
+
+std::vector<std::string> SplitLines(const std::string& text) {
+    std::vector<std::string> lines = {};
+    std::size_t lineStart = 0u;
+    for (std::size_t index = 0u; index < text.size(); ++index) {
+        if (text[index] != '\n') {
+            continue;
+        }
+
+        lines.push_back(text.substr(lineStart, index - lineStart));
+        lineStart = index + 1u;
+    }
+
+    lines.push_back(text.substr(lineStart));
+    return lines;
+}
+
+std::size_t CountTextLines(const std::string& text) {
+    return SplitLines(text).size();
+}
+
+std::size_t CountUtf8CodepointsInRange(
+    const std::string& text,
+    std::size_t beginOffset,
+    std::size_t endOffset) {
+    beginOffset = (std::min)(beginOffset, text.size());
+    endOffset = (std::min)(endOffset, text.size());
+    if (endOffset <= beginOffset) {
+        return 0u;
+    }
+
+    std::size_t count = 0u;
+    std::size_t offset = beginOffset;
+    while (offset < endOffset) {
+        ++count;
+        offset = AdvanceUtf8Offset(text, offset);
+    }
+    return count;
+}
+
+std::size_t FindLineStartOffset(const std::string& text, std::size_t caret) {
+    caret = (std::min)(caret, text.size());
+    while (caret > 0u && text[caret - 1u] != '\n') {
+        --caret;
+    }
+    return caret;
+}
+
+std::size_t FindLineEndOffset(const std::string& text, std::size_t caret) {
+    caret = (std::min)(caret, text.size());
+    while (caret < text.size() && text[caret] != '\n') {
+        ++caret;
+    }
+    return caret;
+}
+
+std::size_t MoveCaretVertically(const std::string& text, std::size_t caret, int lineDelta) {
+    if (lineDelta == 0 || text.empty()) {
+        return (std::min)(caret, text.size());
+    }
+
+    const std::size_t currentLineStart = FindLineStartOffset(text, caret);
+    const std::size_t currentLineEnd = FindLineEndOffset(text, caret);
+    const std::size_t column = CountUtf8CodepointsInRange(text, currentLineStart, caret);
+
+    if (lineDelta < 0) {
+        if (currentLineStart == 0u) {
+            return caret;
+        }
+
+        const std::size_t previousLineEnd = currentLineStart - 1u;
+        const std::size_t previousLineStart = FindLineStartOffset(text, previousLineEnd);
+        const std::size_t previousLineLength =
+            CountUtf8CodepointsInRange(text, previousLineStart, previousLineEnd);
+        std::size_t offset = previousLineStart;
+        for (std::size_t step = 0u; step < (std::min)(column, previousLineLength); ++step) {
+            offset = AdvanceUtf8Offset(text, offset);
+        }
+        return offset;
+    }
+
+    if (currentLineEnd >= text.size()) {
+        return caret;
+    }
+
+    const std::size_t nextLineStart = currentLineEnd + 1u;
+    const std::size_t nextLineEnd = FindLineEndOffset(text, nextLineStart);
+    const std::size_t nextLineLength =
+        CountUtf8CodepointsInRange(text, nextLineStart, nextLineEnd);
+    std::size_t offset = nextLineStart;
+    for (std::size_t step = 0u; step < (std::min)(column, nextLineLength); ++step) {
+        offset = AdvanceUtf8Offset(text, offset);
+    }
+    return offset;
+}
+
+} // namespace Text
+} // namespace UI
+} // namespace XCEngine