The Borrowser 🦀🌐

A web browser engine written from scratch in Rust.

Borrowser is a learning-focused project that builds a real browser stack—HTML parsing, CSS cascade, layout, rendering, networking, and desktop UI—from the ground up.
The goal: deeply understand every part of a browser engine, while keeping code clean, modular, and production-quality.

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🙋 Why “Borrowser”?

Think Borrow Checker + Browser → Borrowser.
A full browser engine built with Rust’s safety and clarity, nothing borrowed from Chromium 😉.

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Next steps

1. HTML Replaced Elements & Form Controls (Phase 1: <img>, <a>, <input type=text>)

2. Border Support (borders + border-radius basics)

   • inputs/buttons look awful without borders; also helps with debugging layout boxes.

3. CSS Color Support (to reduce “everything looks wrong” quickly)

4. CSS Unit Support (em/rem/% etc.)

5. Inline Formatting Polishing (baseline/vertical-align, better line-height behavior, etc.)

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✨ Current Capabilities

Borrowser currently supports:

Browser Shell

• Native desktop window (via winit)
• Custom tab strip with navigation (Back / Forward / Refresh / New Tab)
• Independent per-tab session state and navigation history
• URL bar with proper navigation handling

Networking

• Streaming HTML over HTTP
• Parallel streaming of external CSS files

HTML & CSS

• HTML tokenizer + DOM tree builder
• CSS parser: selectors, specificity, inline styles
• Cascade + computed styles (inheritance + defaults)
• Incremental DOM/CSS updates via multi-threaded runtimes

Layout & Rendering

• Styled tree construction
• Block layout engine (CSS box model, margins, padding)
• Inline layout engine with:
  • whitespace collapsing
  • word-wrapping
  • line boxes + fragments
• Painting backgrounds + text via egui + wgpu
• Scrollable viewport with proper page background selection

Architecture

• Fully session-aware message bus (CoreCommand / CoreEvent)
• Separate runtimes for:
  • Networking
  • HTML parsing
  • CSS parsing
• Thread-safe, highly modular design

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🧩 Documentation

Borrowser is built to be understood, not black magic.

• 📘 Architecture Overview
  Deep dive into every subsystem: DOM, CSS cascade, layout, runtimes, rendering pipeline, message bus, and threading model.

• 🗺️ Project Roadmap
  The long-term vision, planned features, and sequencing of future work.

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🚀 Running Borrowser

Requirements:

• Latest stable Rust
• A GPU that supports wgpu (almost all modern machines)

Run in release mode for a smooth experience:

cargo run --release