Implement C++ solution to truncate UTF8 strings

src/openrct2-ui/windows/TextInput.cpp

@@ -105,11 +105,7 @@ public:
 
     void SetText(std::string_view text, size_t maxLength)
     {
-        char* tmp = new char[maxLength];
-        safe_strcpy(tmp, std::string(text).c_str(), maxLength);
-        _buffer = tmp;
-        delete[] tmp;
-        _buffer.resize(maxLength);
+        _buffer = String::UTF8Truncate(text, maxLength);
         _maxInputLength = maxLength;
         gTextInput = context_start_text_input(_buffer.data(), maxLength);
     }

src/openrct2/core/String.cpp

@@ -807,6 +807,22 @@ namespace String
         return res;
 #endif
     }
+
+    std::string_view UTF8Truncate(std::string_view v, size_t size)
+    {
+        auto trunc = v.substr(0, size);
+        for (size_t i = 0; i < trunc.size();)
+        {
+            auto length = UTF8GetCodePointSize(trunc.substr(i, trunc.size()));
+            if (!length.has_value())
+            {
+                return trunc.substr(0, i);
+            }
+            i += *length;
+        }
+
+        return trunc;
+    }
 } // namespace String
 
 char32_t CodepointView::iterator::GetNextCodepoint(const char* ch, const char** next)

src/openrct2/core/String.hpp

@@ -147,6 +147,37 @@ namespace String
         }
         return result;
     }
+
+    /**
+     * Returns codepoint size or no value if not valid
+     */
+    constexpr std::optional<int> UTF8GetCodePointSize(std::string_view v)
+    {
+        if (v.size() >= 1 && !(v[0] & 0x80))
+        {
+            return { 1 };
+        }
+        else if (v.size() >= 2 && ((v[0] & 0xE0) == 0xC0))
+        {
+            return { 2 };
+        }
+        else if (v.size() >= 3 && ((v[0] & 0xF0) == 0xE0))
+        {
+            return { 3 };
+        }
+        else if (v.size() >= 4 && ((v[0] & 0xF8) == 0xF0))
+        {
+            return { 4 };
+        }
+        return {};
+    }
+
+    /**
+     * Truncates a string to at most `size` bytes,
+     * making sure not to cut in the middle of a sequence.
+     */
+    std::string_view UTF8Truncate(std::string_view v, size_t size);
+
 } // namespace String
 
 class CodepointView