MSX Text Encoding

VS Code extension that adds support for MSX legacy text encodings. Open, edit, and save files using the original MSX character sets.

Supported Character Sets

Features

Open files with MSX encoding

Use MSX Encoding: Open File with MSX Encoding from the Command Palette or the explorer context menu. The file is opened via a virtual filesystem (msxenc://) that transparently decodes MSX bytes to Unicode and encodes back on save.

Convert files

• MSX Encoding: Convert MSX → UTF-8 — Reads an MSX-encoded file and converts it to UTF-8 in place.
• MSX Encoding: Convert UTF-8 → MSX Encoding — Converts a UTF-8 file to MSX encoding in place.

Status bar

When editing a file opened with MSX encoding, the status bar shows the active charset. Click it to switch to a different charset.

Character Map

A 16×16 grid showing all 256 characters of the selected MSX charset. Use MSX Encoding: Show MSX Character Map or Ctrl+Shift+M (Cmd+Shift+M on macOS).

• Choose any of the 8 supported MSX charsets.
• Click cells to accumulate characters in a text field.
• Insert button sends the text to your cursor in the active editor.
• Hover over cells to see hex values and Unicode codepoints.
• Graphic characters (0x00-0x1F) are highlighted with a blue tint.

Escape mechanism (0x01)

MSX uses byte 0x01 as an escape prefix for graphic characters in the 0x00-0x1F VRAM range. The byte following the escape has a +0x40 offset added:

• Decoding: 0x01 + byte → graphic character at position byte - 0x40 (e.g., 0x01 0x54 → position 0x14 = ├)
• Encoding: graphic characters that map to 0x00-0x1F → 0x01 + (byte + 0x40)
• Without the escape prefix, bytes 0x00-0x1F are treated as standard control codes (TAB, LF, CR, etc.)

Arabic charset (simplified)

The Arabic charset uses a simplified mapping: each byte decodes to the abstract Unicode letter (e.g., ب BEH) regardless of the contextual form (initial, medial, final, isolated). The Arabic Shaping Algorithm is not implemented — Unicode rendering handles visual presentation.

Configuration

Development

npm install        # Install dependencies
npm run compile    # Build the extension
npm run watch      # Build in watch mode

Press F5 to launch the Extension Development Host for testing.

Packaging

To generate a .vsix file for distribution:

npm run package

This creates msx-text-encoding-<version>.vsix. Install it in VS Code with:

code --install-extension msx-text-encoding-0.1.0.vsix

Or via the Command Palette: Extensions: Install from VSIX...

References

Character mappings are based on the openMSX emulator's authoritative MSXVID*.TXT mapping files from Unicode 13.0+ (Symbols for Legacy Computing block).