PhotonLab: High-Performance FDTD Solver in Rust & WebAssembly

PhotonLab is an engineering-grade electromagnetic field simulator designed to run directly in modern web browsers. Unlike traditional physics engines that rely on server-side computation, PhotonLab executes the Finite-Difference Time-Domain (FDTD) method entirely on the client side using WebAssembly and WebGL2.

This project demonstrates how low-level systems programming (Rust) can be bridged with web technologies to visualize complex wave dynamics (refraction, interference, diffraction) at 60 FPS on standard hardware.

🚀 Live Demo on Vercel

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🏗 System Architecture

The simulation pipeline is designed to minimize JavaScript overhead and maximize memory throughput.

1. The Physics Core (Rust + Wasm)

At the heart of the engine is a customized Yee Lattice implementation written in Rust.

• Memory Layout: Uses flat 1D arrays for 2D fields (Ez, Hx, Hy) to ensure cache locality and enable potential SIMD optimizations.
• Boundaries: Implements CPML (Convolutional Perfectly Matched Layer) to mathematically simulate infinite open space, absorbing outgoing waves without artificial reflections.
• Stability: Automatically enforces the Courant–Friedrichs–Lewy (CFL) condition to prevent numerical divergence.

2. Zero-Copy Rendering (WebGL2)

Visualizing 262,144 cells (512×512 grid) every 16ms requires bypassing the standard DOM.

• Direct Memory Access: Instead of copying data from Wasm to JS arrays (which causes GC pauses), the render engine passes a raw pointer from the Wasm linear memory directly to WebGL.
• Texture Float: The electromagnetic field data is uploaded as an R32F (32-bit floating point) texture.
• Shading: A custom fragment shader applies a "Viridis" or "Diverging" colormap and performs bilinear interpolation on the GPU.

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🧪 Simulation Capabilities

This is not just a visualizer; it is a quantitative tool.

Main Interface	Double Slit	Parabolic Reflector

Signal Monitor	Lens Focusing

• Wave Sources: Plane Wave (Interference studies), Gaussian Pulse (Broadband analysis), Point Source.
• Material System: Modeling of dielectrics (Glass, Water), PEC (Perfect Electric Conductors), and custom refractive indices.
• Preset Scenarios: Double Slit, Parabolic Reflector, Lens Focusing, and Empty Canvas for custom experiments.
• Real-time Telemetry:
  • Oscilloscope: Probe specific grid points to analyze signal amplitude vs. time.
  • Energy Monitor: Tracks global system energy (ε|E|² + μ|H|²) to detect numerical instability (NaN/Infinity).

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🚀 Quick Start

Prerequisites: Rust (cargo, wasm-pack) and Node.js.

# 1. Build the Physics Engine
cd rust-core
wasm-pack build --target web

# 2. Launch the Interface
cd ../web
npm install
npm run dev

Open http://localhost:5173 in your browser.

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📁 Project Structure

PhotonLab/
├── rust-core/              # Wasm physics engine
│   ├── src/
│   │   ├── fdtd.rs         # Yee algorithm core
│   │   ├── cpml.rs         # CPML boundary layer
│   │   ├── materials.rs    # Material definitions
│   │   ├── scenarios.rs    # Preset experiments
│   │   └── sources.rs      # Wave source types
│   └── pkg/                # Compiled wasm output
└── web/                    # React frontend
    ├── src/
    │   ├── components/     # UI components
    │   ├── shaders/        # WebGL shaders
    │   └── hooks/          # useSimulation hook
    └── scripts/
        └── capture.js      # Automated screenshot bot

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📸 Automated Screenshots

Generate documentation screenshots with Puppeteer:

cd web
npm run capture

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📚 Technical References

• Computational Electrodynamics: The Finite-Difference Time-Domain Method, Taflove & Hagness.
• Theory and Computation of Electromagnetic Fields, Jin.

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Built for the open-source scientific community.