First working implementation

Author: dpoettler

ExtendedChars.cpp

@@ -0,0 +1,20 @@
+#pragma once
+#include <Arduino.h>
+
+// Structure for individual Unicode characters
+struct UnicodeChar {
+    uint16_t code;
+    const char* description;
+};
+
+class ExtendedChars {
+public:
+    static String extendChars(const String &str);
+
+    // Supported character sets
+    static const UnicodeChar ADDITIONAL_CHARS[];
+    static const uint8_t ADDITIONAL_CHARS_COUNT;
+
+private:
+    ExtendedChars() = delete;
+};

ExtendedChars.h

@@ -4,15 +4,16 @@
     "authors": [
       {
         "name": "David Pöttler",
-        "email": "david.e.poettler@gmail.com"
+        "email": "david.e.poettler@gmail.com",
+        "maintainer": true
       }
     ],
     "description": "ExtendedChars is an extension library for the Adafruit GFX library adding support for UTF8 characters.",
     "keywords": ["display", "UTF8", "Adafruit", "GFX"],
     "license": "GPL-3.0",
     "repository": {
       "type": "git",
-      "url": "https://github.com/dpoettler/ExtendedChars"
+      "url": "https://github.com/dpoettler/ExtendedChars.git"
     },
     "frameworks": "arduino",
     "platforms": "*",

include/ExtendedChars.h

@@ -0,0 +1,52 @@
+#include "ExtendedChars.h"
+
+// Define the static members
+const UnicodeChar ExtendedChars::ADDITIONAL_CHARS[] = {
+    {0x00C4, "Ä"},  // Upper Ä umlaut
+    {0x00D6, "Ö"},  // Upper Ö umlaut
+    {0x00DC, "Ü"},  // Upper Ü umlaut
+    {0x00E4, "ä"},  // Lower ä umlaut
+    {0x00F6, "ö"},  // Lower ö umlaut
+    {0x00FC, "ü"},  // Lower ü umlaut
+    {0x00DF, "ß"},  // Sharp ß
+};
+
+const uint8_t ExtendedChars::ADDITIONAL_CHARS_COUNT = sizeof(ADDITIONAL_CHARS) / sizeof(ADDITIONAL_CHARS[0]);
+
+namespace {
+    bool isInSupportedChars(uint16_t unicode) {
+        for (uint8_t i = 0; i < ExtendedChars::ADDITIONAL_CHARS_COUNT; i++) {
+            if (unicode == ExtendedChars::ADDITIONAL_CHARS[i].code) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    uint16_t extractUnicode(char firstByte, char secondByte) {
+        return ((firstByte & 0x1F) << 6) | (secondByte & 0x3F);
+    }
+}
+
+String ExtendedChars::extendChars(const String &str) {
+    String result;
+    result.reserve(str.length());
+
+    for (size_t i = 0; i < str.length(); i++) {
+        if ((str[i] & 0x80) == 0) {
+            result += str[i];
+        }
+        else if ((str[i] & 0xE0) == 0xC0) {
+            uint16_t unicode = extractUnicode(str[i], str[i + 1]);
+            if (isInSupportedChars(unicode)) {
+                result += (char)unicode;
+            }
+            i++;
+        }
+        else if ((str[i] & 0xF0) == 0xE0) {
+            result += str.substring(i, i + 3);
+            i += 2;
+        }
+    }
+    return result;
+}