# Spectral Terminal Emulator Architecture

## Design Philosophy

Spectral is designed to be the fastest terminal emulator while solving the font rendering problems that plague other GPU-accelerated terminals (especially Ghostty's "too thin" font issue on non-macOS platforms).

## Key Differentiators

1. **MSDF Font Rendering**: Multi-channel signed distance fields for GPU-native font rasterization with configurable per-pixel thickening across all platforms
2. **Compute Shader Glyph Generation**: Glyph rasterization happens on GPU, not CPU — eliminating the biggest bottleneck in existing terminals
3. **SIMD-Optimized Parser**: VT100/ANSI escape sequence parsing with SIMD byte scanning for CSI/OSC/DCS sequences
4. **Unified wgpu Backend**: Single Rust codebase renders via Metal on macOS, Vulkan on Linux, DirectX 12 on Windows
5. **Cross-Platform Font Thickening**: `font-thicken` and `font-thicken-strength` work identically on macOS, Linux, and Windows via MSDF threshold adjustment

## Crate Structure

```
spectral/
├── spectral-core/     # Terminal grid, cell model, VT parser, damage tracking
├── spectral-pty/      # PTY abstraction (Unix/Windows)
├── spectral-font/     # Font discovery, MSDF atlas, metrics
└── spectral-render/   # wgpu renderer, compute shaders, frame pacing
```

## Renderer Architecture

```
PTY bytes → SIMD VT Parser → Terminal Grid → Damage Tracker
                                            ↓
                                    Renderable Content Iterator
                                            ↓
                              Font Shaper (HarfBuzz/swash)
                                            ↓
                              Glyph Cache (HashMap<GlyphKey, AtlasSlot>)
                                            ↓
                              MSDF Compute Pass (missing glyphs)
                                            ↓
                              Texture Atlas Update
                                            ↓
                              GPU Render Pass (Instanced Quads)
                                            ↓
                              wgpu Surface Present
```

## Performance Targets

| Benchmark | Target |
|-----------|--------|
| ASCII cat /dev/urandom | >150 MB/s (faster than Kitty's 121) |
| Key-to-screen latency | <8ms (120Hz refresh, no batching) |
| Startup time | <100ms cold |
| Memory (100k scrollback lines) | <50MB |
| Font atlas (complete Unicode BMP) | <16MB GPU |