Hopalong Visoxide

This project was vibe coded with Claude Opus 4.6 in opencode.

A real-time Barry Martin's Hopalong Orbits visualizer built with Rust, using eframe/egui for the UI and wgpu for GPU-accelerated particle rendering.

This is a native desktop port of the Hopalong Orbits Visualizer (originally by Iacopo Sassarini, updated by Sam Leatherdale), rewritten from TypeScript/Three.js to Rust.

Watch the demo video on YouTube

What is it?

The Hopalong attractor is a mathematical fractal discovered by Barry Martin. This visualizer generates orbit patterns from the attractor equations and renders them as ~196,000 glowing particles flying toward the camera, creating a mesmerizing tunnel effect. New orbit patterns are generated every 3 seconds with smooth fly-through transitions between them.

Features

• GPU-accelerated rendering via wgpu (Vulkan/Metal/DX12 backends)
• Instanced billboard particles with galaxy sprite texturing and additive blending
• Exponential fog for depth perception
• Smooth orbit transitions - old patterns fly past as new ones emerge from behind
• Real-time settings panel (Tab to toggle) with sliders for:
  • Speed, rotation speed, camera FOV
  • Points per subset, subset count, level count
• Keyboard shortcuts for speed, rotation, mouse lock, camera centre, reset
• FPS counter (toggleable in settings)

Building

Requires Rust 2024 edition (1.85+).

cargo build --release

Running

cargo run --release

Controls

Key	Action
Tab	Toggle settings panel
Arrow Up/Down	Increase/decrease speed
Arrow Left/Right	Increase/decrease rotation
L	Toggle mouse lock
C	Centre camera + toggle lock
R	Reset all settings to defaults
Q	Quit

Mouse movement controls camera position when unlocked.

Architecture

src/
  main.rs              Entry point (eframe::run_native)
  app.rs               eframe::App impl, egui UI, input handling
  sim.rs               Hopalong attractor math, camera state, particle management
  renderer.rs          wgpu pipeline, instanced billboards, CallbackTrait impl
  shaders/
    particle.wgsl      Billboard vertex + fragment shader with fog
assets/
  galaxy.png           Particle sprite texture

How it works

1. Orbit generation (sim.rs): Computes 2D points using Barry Martin's Hopalong equations with three formula variants (sqrt, fourth-root, logarithmic). Points are normalized to a fixed coordinate range.

2. Particle sets: The 2D orbit is replicated across multiple depth levels and color subsets (default: 7x7 = 49 sets of 4,000 points each). Each set has its own Z position, rotation, and baked copy of orbit data.

3. Animation loop: Every frame, particle sets advance toward the camera. When a set passes the camera, it wraps to the back. Every 3 seconds, a new orbit is generated - sets pick up the new pattern only when they individually wrap, creating a gradual transition.

4. Rendering (renderer.rs): Each particle is an instanced camera-facing quad textured with a galaxy sprite. Additive blending makes overlapping particles glow brighter. Exponential fog fades distant particles to black.

Dependencies

Crate	Purpose
eframe	Window + event loop + wgpu init
egui / egui-wgpu	UI widgets + custom render callback
wgpu	GPU rendering
bytemuck	Safe struct-to-byte-buffer casting
glam	Math (Mat4, Vec3, perspective projection)
rand	Random orbit parameters
image	Load galaxy.png sprite

License

MIT