Building an Arc Reactor with Three.js

Introduction#

Ever wanted to bring Tony Stark's arc reactor to life in the browser? In this post, we will walk through building an interactive 3D arc reactor using Three.js and React Three Fiber. The result is a glowing, animated reactor that responds to user interaction.

"The arc reactor, a clean energy source — and an incredible WebGL demo."

Setting Up the Scene#

First, let's scaffold our React Three Fiber scene. We need a canvas, proper lighting, and post-processing for the glow effect.

Building the Core Geometry#

The reactor core consists of concentric rings with emissive materials. Each ring rotates at a different speed to create depth.

Custom Glow Shader#

For the signature pulsing glow, we write a custom fragment shader:

uniform float uTime;
uniform vec3 uColor;
varying vec2 vUv;

void main() {
  float dist = length(vUv - 0.5);
  float glow = 0.05 / dist;
  glow *= smoothstep(0.5, 0.2, dist);
  glow *= 0.8 + 0.2 * sin(uTime * 2.0);

  gl_FragColor = vec4(uColor * glow, glow);
}

Integrating the Shader#

We attach the shader material using shaderMaterial from drei:

Performance Considerations#

When building 3D web experiences, performance matters:

Key Optimizations#

• Use useMemo for static geometries to avoid re-creation
• Limit draw calls by merging geometries where possible
• Use frameloop="demand" for scenes that only need to re-render on interaction
• Profile with the Three.js inspector extension

Conclusion#

Building 3D experiences on the web is more accessible than ever with React Three Fiber. The arc reactor project demonstrates how combining simple geometries with emissive materials and post-processing can produce stunning visual results.

The full source code is available on GitHub — feel free to fork it and add your own Stark-inspired touches.