Project 2: ANSI Escape Sequence Renderer

Parse ANSI escape sequences and render a terminal buffer.

Quick Reference

Attribute Value
Difficulty Advanced
Time Estimate 1 week
Language C (Alternatives: Rust)
Prerequisites Project 1, parsing basics
Key Topics ANSI codes, screen buffers

1. Learning Objectives

By completing this project, you will:

  1. Parse ANSI escape sequences accurately.
  2. Maintain a 2D screen buffer with attributes.
  3. Implement cursor movement and color changes.
  4. Render buffer consistently without flicker.
  5. Handle unknown sequences safely.

2. Theoretical Foundation

2.1 Core Concepts

  • Escape Sequences: CSI sequences (ESC [) control cursor, color, erase, and modes.
  • Screen Buffer: A terminal is a 2D grid of cells with chars + attributes.
  • Attributes: Each cell has foreground, background, and style flags.

2.2 Why This Matters

tmux reconstructs screen state from raw program output. Without accurate ANSI parsing, panes cannot be rendered correctly.

2.3 Common Misconceptions

  • “ANSI is just colors”: It drives cursor, erase, and mode changes too.

3. Project Specification

3.1 What You Will Build

A renderer that ingests a byte stream with ANSI codes and outputs the final screen state (for debugging or testing).

3.2 Functional Requirements

  1. Parse cursor movement (H, f, A/B/C/D).
  2. Parse clear screen/line (J, K).
  3. Parse basic colors (30-37, 40-47) and reset (0).
  4. Maintain a fixed-size buffer (e.g., 80x24).
  5. Render to a debug format (plain grid + attributes).

3.5 Real World Outcome

You can pipe program output into your renderer and see the resolved screen snapshot instead of raw escape codes.

4. Solution Architecture

Input stream -> Parser -> Screen buffer -> Renderer

4.2 Key Components

Component Responsibility Key Decisions
Parser Decode CSI sequences minimal subset
Buffer Store cells fixed size
Renderer Output state debug format

5. Implementation Guide

5.3 The Core Question You Are Answering

“How does a terminal reconstruct screen state from a byte stream?”

5.10 Implementation Phases

Phase 1: Parser

  • detect ESC sequences

Phase 2: Buffer

  • apply cursor + write ops

Phase 3: Renderer

  • dump buffer as text

6. Testing Strategy

  • Feed known ANSI strings and compare buffer state.

7. Common Pitfalls and Debugging

  • Missing reset handling leaves attributes stuck.
  • Cursor out of bounds corrupts buffer.

12. Submission / Completion Criteria

Minimum Viable Completion:

  • Cursor movement and clear screen supported

Full Completion:

  • Colors and attributes handled