LibVT: Implement G0..G3 and VT100 translation table

Userland/Libraries/LibVT/CharacterSet.h

@@ -0,0 +1,59 @@
+/*
+ * Copyright (c) 2021, The SerenityOS Developers.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+namespace VT {
+
+enum CharacterSet {
+    Iso_8859_1,
+    Null,
+    UserDefined,
+    VT100,
+};
+
+class CharacterSetTranslator {
+public:
+    u32 translate_code_point(CharacterSet active_set, u32 code_point)
+    {
+        // Only translate 0x7F and lower
+        if (code_point > 127)
+            return code_point;
+
+        // FIXME: implement other character sets
+        if (active_set != CharacterSet::VT100)
+            return code_point;
+
+        // VT100 translation table - https://en.wikipedia.org/wiki/Box-drawing_character#Unix,_CP/M,_BBS
+        switch (code_point) {
+        case 0x6A:
+            return 0x2518;
+        case 0x6B:
+            return 0x2510;
+        case 0x6C:
+            return 0x250C;
+        case 0x6D:
+            return 0x2514;
+        case 0x6E:
+            return 0x253C;
+        case 0x71:
+            return 0x2500;
+        case 0x74:
+            return 0x251C;
+        case 0x75:
+            return 0x2524;
+        case 0x76:
+            return 0x2534;
+        case 0x77:
+            return 0x252C;
+        case 0x78:
+            return 0x2502;
+        }
+        return code_point;
+    }
+};
+
+}