Project 7: VT100 State Machine

A complete VT100/VT220/xterm-compatible terminal state machine that handles cursor movement, screen manipulation, modes, and all standard escape sequences.

Quick Reference

Attribute Value
Primary Language C
Alternative Languages Rust, Zig
Difficulty Level 3: Advanced (The Engineer)
Time Estimate 3-4 weeks
Knowledge Area State Machines / Terminal Emulation
Tooling VT100 Emulator Core
Prerequisites Projects 2, 5, 6

What You Will Build

A complete VT100/VT220/xterm-compatible terminal state machine that handles cursor movement, screen manipulation, modes, and all standard escape sequences.

Why It Matters

This project builds core skills that appear repeatedly in real-world systems and tooling.

Core Challenges

  • Full escape sequence coverage → CSI, OSC, DCS, ESC, C0/C1
  • Screen buffer management → Primary and alternate screens
  • Cursor state → Position, visibility, saved positions
  • Mode flags → Origin mode, wrap mode, cursor mode
  • Tab stops → Programmable tab positions

Key Concepts

Real-World Outcome

$ ./vt100_terminal

# Full-screen applications work!
$ vim file.txt     # ✓ Cursor movement, insert/command modes
$ htop             # ✓ Colors, cursor positioning, updates
$ tmux             # ✓ Alternate screen, mouse (partial)
$ less file.txt    # ✓ Scrolling, searching
$ man ls           # ✓ Bold, underlining

# Window title changes work
$ echo -e "\x1b]0;My Custom Title\x07"
# (Window title changes to "My Custom Title")

Implementation Guide

  1. Reproduce the simplest happy-path scenario.
  2. Build the smallest working version of the core feature.
  3. Add input validation and error handling.
  4. Add instrumentation/logging to confirm behavior.
  5. Refactor into clean modules with tests.

Milestones

  • Milestone 1: Minimal working program that runs end-to-end.
  • Milestone 2: Correct outputs for typical inputs.
  • Milestone 3: Robust handling of edge cases.
  • Milestone 4: Clean structure and documented usage.

Validation Checklist

  • Output matches the real-world outcome example
  • Handles invalid inputs safely
  • Provides clear errors and exit codes
  • Repeatable results across runs

References

  • Main guide: TERMINAL_EMULATOR_DEEP_DIVE_PROJECTS.md
  • “Language Implementation Patterns” by Terence Parr