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;
+    }
+};
+
+}

Userland/Libraries/LibVT/Terminal.cpp

@@ -998,6 +998,9 @@ void Terminal::on_input(u8 byte)
 
 void Terminal::emit_code_point(u32 code_point)
 {
+    auto working_set = m_working_sets[m_active_working_set_index];
+    code_point = m_character_set_translator.translate_code_point(working_set, code_point);
+
     auto new_column = cursor_column() + 1;
     if (new_column < columns()) {
         put_character_at(cursor_row(), cursor_column(), code_point);
@@ -1099,7 +1102,13 @@ void Terminal::execute_escape_sequence(Intermediates intermediates, bool ignore,
             DECPNM();
             return;
         }
-    } else if (intermediates[0] == '#') {
+        unimplemented_escape_sequence(intermediates, last_byte);
+        return;
+    }
+
+    char intermediate = intermediates[0];
+    switch (intermediate) {
+    case '#':
         switch (last_byte) {
         case '8':
             // Confidence Test - Fill screen with E's
@@ -1110,7 +1119,39 @@ void Terminal::execute_escape_sequence(Intermediates intermediates, bool ignore,
             }
             return;
         }
+        break;
+    case '(':
+    case ')':
+    case '*':
+    case '+':
+        // Determine G0..G3 index
+        size_t working_set_index = intermediate - '(';
+
+        CharacterSet new_set;
+        switch (last_byte) {
+        case 'B':
+            new_set = CharacterSet::Iso_8859_1;
+            break;
+        case '0':
+            new_set = CharacterSet::VT100;
+            break;
+        case 'U':
+            new_set = CharacterSet::Null;
+            break;
+        case 'K':
+            new_set = CharacterSet::UserDefined;
+            break;
+        default:
+            unimplemented_escape_sequence(intermediates, last_byte);
+            return;
+        }
+
+        dbgln_if(TERMINAL_DEBUG, "Setting G{} working set to character set {}", working_set_index, to_underlying(new_set));
+        VERIFY(working_set_index <= 3);
+        m_working_sets[working_set_index] = new_set;
+        return;
     }
+
     unimplemented_escape_sequence(intermediates, last_byte);
 }
 

Userland/Libraries/LibVT/Terminal.h

@@ -12,6 +12,7 @@
 #include <AK/String.h>
 #include <AK/Vector.h>
 #include <Kernel/API/KeyCode.h>
+#include <LibVT/CharacterSet.h>
 #include <LibVT/EscapeSequenceParser.h>
 #include <LibVT/Position.h>
 
@@ -443,6 +444,10 @@ protected:
     Optional<u16> m_column_before_carriage_return;
     bool m_controls_are_logically_generated { false };
     CursorKeysMode m_cursor_keys_mode { Cursor };
+
+    CharacterSetTranslator m_character_set_translator {};
+    size_t m_active_working_set_index { 0 };
+    CharacterSet m_working_sets[4] { Iso_8859_1 };
 };
 
 }