Why I Built a Zero-Underline Vietnamese IME for Linux in Rust

Anyone who has used Linux in Vietnam knows the long-standing frustration of typing Vietnamese on desktop environments—especially with the widespread adoption of Wayland (GNOME, KDE Plasma, Hyprland, Sway).

Traditional Input Method Engines (IMEs) rely on a pre-edit buffer. While this works reasonably well on macOS or Windows, on Linux it often produces:

1. Flickering Underlines: Every keystroke shows an underlined temporary word that interrupts code auto-completion in VS Code, Neovim, and terminal emulators.
2. Clipboard Race Conditions: Many input methods simulate backspaces and paste transformed characters via the system clipboard, colliding with your actual clipboard history or password managers.
3. Broken English Words: When typing common English words containing Vietnamese key combinations (e.g., test, search, code), words often get mangled into unnatural accent marks unless manually disabled.

To fix these problems at the root, I built Viet+ (VietC): a modern, zero-latency, zero-underline Vietnamese IME written 100% in Rust.

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⚡ The Architecture: Direct Virtual Keystroke Injection

Instead of hijacking the desktop text field with a pre-edit overlay, Viet+ operates directly at the device input layer:

[Hardware Keyboard]
       │
       ▼
 [Viet+ Engine (Rust)] ───► [Finite State Machine & Telex/VNI Rules]
       │
       ▼ (Direct Unicode via /dev/uinput or wtype)
[Target Application: Terminal, Browser, IDE]

1. Zero Underline (No Pre-Edit Buffer)

Viet+ processes keystrokes in-flight. Characters appear directly in your active application as real Unicode text. No ghost underlines, no flickering text frames, and no disruption to IDE autocomplete dropdowns.

2. Intelligent English Auto-Restoration

A common nuisance when typing bilingual technical documents is accidentally turning English words into accented Vietnamese (e.g. typing as becoming á, or format becoming fórmat).

Viet+ embeds an intelligent trie-based dictionary check. If you type an English word pattern, the engine automatically rolls back the diacritics and restores clean English text without requiring you to constantly hit Ctrl + Space or switch modes.

Nguyeenx DDawng Khoa   ➔   Nguyễn Đăng Khoa
Khoong cos gif quis    ➔   Không có gì quí
search for the test    ➔   search for the test  (Auto-Restored!)

3. Wayland & X11 First-Class Support

Viet+ is designed for modern Wayland compositors:

• Wayland: Native virtual keyboard protocol integration via wtype and wl-clipboard.
• X11: Seamless fallback using xdotool and X11 key injection.
• Hyprland / Sway / GNOME / KDE: Tested across leading tiling and desktop window managers.

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🦀 Why Rust?

Input methods require predictable microsecond latency. Every key press must be intercepted, checked against grammar state machines, and re-emitted before the user's next keystroke lands.

By using Rust:

• Zero Garbage Collection: Predictable sub-millisecond response times.
• Safe Memory Concurrency: Safe IPC communication between background daemons and system trays.
• 100% Test Coverage: Viet+ includes 151 unit tests validating complex Telex, VNI, tone placement rules, and edge-case word combinations.

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🚀 1-Command Installation

You can install Viet+ on Arch Linux, Fedora, Ubuntu, Debian, or openSUSE with a single command:

curl -fsSL https://raw.githubusercontent.com/vndangkhoa/vietc/main/install.sh | bash

Once installed, start the background daemon:

vietc &

Toggle between Vietnamese and English modes effortlessly using Ctrl + Space (customizable).

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🔗 Check it Out on GitHub

Viet+ is 100% open-source under the MIT license. If you're running Linux and want a smooth, native typing experience without UI clutter:

⭐ GitHub Repository: https://github.com/vndangkhoa/vietc

Feedback, issues, and PRs are warmly welcome!