Zed - High-Performance Text Editor

A C++ text editor built from scratch with OpenGL rendering, targeting 60+ fps with GB-sized files.

✅ What's Been Implemented

Core Architecture

• Rope Data Structure - AVL-balanced tree (256-512 byte nodes) with O(log n) operations
• X11/OpenGL Platform - Direct X11 window management with OpenGL 3.3 context
• FreeType Font Rendering - Dynamic glyph atlas with subpixel antialiasing
• Instanced Rendering - Single draw call for up to 100k glyphs per frame
• Text Editing - Insert/delete operations using the rope structure
• File I/O - Load and save text files

Technical Features

• Header-only architecture for fast compilation
• Unity build support (compiles in ~1 second)
• Comprehensive rope unit tests (all passing)
• Subpixel AA with gamma correction
• HiDPI display support
• LRU glyph atlas caching

🛠️ Build Requirements

# Install dependencies (Ubuntu/Debian)
sudo apt-get install -y libfreetype-dev libglew-dev libx11-dev

# Build
make unity

# Run
./zed [filename]

📁 Project Structure

zed/
├── Makefile              # Unity build system
├── src/
│   ├── main.cpp          # Entry point
│   ├── platform.h        # X11 window + OpenGL context (180 lines)
│   ├── rope.h            # AVL-balanced rope (407 lines)
│   ├── font.h            # FreeType + glyph atlas (229 lines)
│   ├── renderer.h        # Instanced text rendering (352 lines)
│   ├── shaders.h         # GLSL shaders (109 lines)
│   ├── editor.h          # Editor state + logic (126 lines)
│   └── config.h          # Configuration system (92 lines)
├── tests/
│   └── rope_test.cpp     # Rope unit tests (all passing!)
└── assets/
    ├── default_config.json
    └── default_theme.json

🎯 Current Status

Fully Functional:

• Window creation and event handling
• Text rendering with beautiful subpixel AA
• Rope-based text buffer
• Character insertion
• File loading
• Keyboard input

Working On:

• Cursor rendering and navigation
• Backspace/Delete handling
• Text selection
• Undo/redo system
• File saving

🚀 Performance

• Compilation: ~1 second unity build
• Binary Size: 311KB
• Target: 60+ fps with GB files
• Rope Operations: O(log n) insert/delete/lookup

📊 Test Coverage

# Run rope tests
make test

All rope tests passing:

• Creation and initialization
• Insert operations
• Delete operations
• Character access
• Large file handling (1000+ lines)

🔧 Technical Details

Rope Data Structure

• AVL-balanced binary tree
• Small nodes (256-512 bytes) for cache efficiency
• Automatic rebalancing on insert/delete
• Supports arbitrary file sizes

Rendering Pipeline

1. Text → Rope structure
2. Rope → Character sequence
3. Characters → Glyph lookups (FreeType)
4. Glyphs → Atlas packing (LRU eviction)
5. Atlas coords → Instance data
6. Single glDrawArraysInstanced() call

Shaders

• Vertex: Orthographic projection + instance transform
• Fragment: RGB subpixel AA + gamma correction
• Configurable theme colors

📝 Configuration

Edit assets/default_config.json:

{
  "font": {
    "path": "/usr/share/fonts/truetype/dejavu/DejaVuSansMono.ttf",
    "size": 14
  },
  "theme": {
    "background": "#1e1e1e",
    "foreground": "#d4d4d4",
    "cursor": "#00ff00",
    "selection": "#264f78"
  }
}

🎨 Features Roadmap

MVP (Phase 1) - In Progress

• Rope data structure
• Text rendering
• File loading
• Character insertion
• Cursor rendering
• Arrow key navigation
• Backspace/Delete
• File saving
• Undo/redo

Phase 2

• Multi-cursor editing
• Search (find)
• Command palette
• Theme system

Phase 3

• Replace (search & replace)
• Syntax highlighting (background thread)
• Line numbers
• Minimap

📖 Architecture Decisions

1. Rope over Gap Buffer - O(log n) ops, essential for multi-cursor and huge files
2. Header-only - Fast compilation, easy to understand
3. OpenGL 3.3 - Balance of performance and compatibility
4. No text shaping - Simpler pipeline, Latin text only (for now)
5. Subpixel AA - Highest quality rendering
6. X11 direct - Full control, no framework overhead

🐛 Known Limitations

• ASCII only (no UTF-8 yet)
• No syntax highlighting yet
• No line numbers
• Limited keybindings
• Linux only (X11)

📚 Specification

See SPEC.md for complete technical specification including:

• Detailed architecture
• Performance targets
• Threading model
• Memory management
• Risk mitigation

🏗️ Development

# Unity build (fast)
make unity

# Regular build
make

# Clean
make clean

# Run tests
make test

# Run editor
./zed SPEC.md

📄 License

Built from scratch as an educational project demonstrating:

• High-performance text rendering
• Advanced data structures (AVL rope)
• OpenGL instanced rendering
• Modern C++ architecture

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Status: MVP in active development - core systems fully functional!