Imported from Lemioni/maturita-app (.agent/skills/skills/threejs-skills/SKILL.md). Install upstream with npx skills add Lemioni/maturita-app --skill threejs-skills. Copyright stays with the author.

Three.js Skills

Systematically create high-quality 3D scenes and interactive experiences using Three.js best practices.

When to Use

• Requests 3D visualizations or graphics ("create a 3D model", "show in 3D")
• Wants interactive 3D experiences ("rotating cube", "explorable scene")
• Needs WebGL or canvas-based rendering
• Asks for animations, particles, or visual effects
• Mentions Three.js, WebGL, or 3D rendering
• Wants to visualize data in 3D space

Core Setup Pattern

1. Essential Three.js Imports

Always use the correct CDN version (r128):

import * as THREE from "https://cdnjs.cloudflare.com/ajax/libs/three.js/r128/three.min.js";

CRITICAL: Do NOT use example imports like THREE.OrbitControls - they won't work on the CDN.

2. Scene Initialization

Every Three.js artifact needs these core components:

// Scene - contains all 3D objects
const scene = new THREE.Scene();

// Camera - defines viewing perspective
const camera = new THREE.PerspectiveCamera(
  75, // Field of view
  window.innerWidth / window.innerHeight, // Aspect ratio
  0.1, // Near clipping plane
  1000, // Far clipping plane
);
camera.position.z = 5;

// Renderer - draws the scene
const renderer = new THREE.WebGLRenderer({ antialias: true });
renderer.setSize(window.innerWidth, window.innerHeight);
document.body.appendChild(renderer.domElement);

3. Animation Loop

Use requestAnimationFrame for smooth rendering:

function animate() {
  requestAnimationFrame(animate);

  // Update object transformations here
  mesh.rotation.x += 0.01;
  mesh.rotation.y += 0.01;

  renderer.render(scene, camera);
}
animate();

Systematic Development Process

1. Define the Scene

Start by identifying:

• What objects need to be rendered
• Camera position and field of view
• Lighting setup required
• Interaction model (static, rotating, user-controlled)

2. Build Geometry

Choose appropriate geometry types:

Basic Shapes:

• BoxGeometry - cubes, rectangular prisms
• SphereGeometry - spheres, planets
• CylinderGeometry - cylinders, tubes
• PlaneGeometry - flat surfaces, ground planes
• TorusGeometry - donuts, rings

IMPORTANT: Do NOT use CapsuleGeometry (introduced in r142, not available in r128)

Alternatives for capsules:

• Combine CylinderGeometry + 2 SphereGeometry
• Use SphereGeometry with adjusted parameters
• Create custom geometry with vertices

3. Apply Materials

Choose materials based on visual needs:

Common Materials:

• MeshBasicMaterial - unlit, flat colors (no lighting needed)
• MeshStandardMaterial - physically-based, realistic (needs lighting)
• MeshPhongMaterial - shiny surfaces with specular highlights
• MeshLambertMaterial - matte surfaces, diffuse reflection

const material = new THREE.MeshStandardMaterial({
  color: 0x00ff00,
  metalness: 0.5,
  roughness: 0.5,
});

4. Add Lighting

If using lit materials (Standard, Phong, Lambert), add lights:

// Ambient light - general illumination
const ambientLight = new THREE.AmbientLight(0xffffff, 0.5);
scene.add(ambientLight);

// Directional light - like sunlight
const directionalLight = new THREE.DirectionalLight(0xffffff, 0.8);
directionalLight.position.set(5, 5, 5);
scene.add(directionalLight);

Skip lighting if using MeshBasicMaterial - it's unlit by design.

5. Handle Responsiveness

Always add window resize handling:

window.addEventListener("resize", () => {
  camera.aspect = window.innerWidth / window.innerHeight;
  camera.updateProjectionMatrix();
  renderer.setSize(window.innerWidth, window.innerHeight);
});

Common Patterns

Rotating Object

function animate() {
  requestAnimationFrame(animate);
  mesh.rotation.x += 0.01;
  mesh.rotation.y += 0.01;
  renderer.render(scene, camera);
}

Custom Camera Controls (OrbitControls Alternative)

Since THREE.OrbitControls isn't available on CDN, implement custom controls:

let isDragging = false;
let previousMousePosition = { x: 0, y: 0 };

renderer.domElement.addEventListener("mousedown", () => {
  isDragging = true;
});

renderer.domElement.addEventListener("mouseup", () => {
  isDragging = false;
});

renderer.domElement.addEventListener("mousemove", (event) => {
  if (isDragging) {
    const deltaX = event.clientX - previousMousePosition.x;
    const deltaY = event.clientY - previousMousePosition.y;

    // Rotate camera around scene
    const rotationSpeed = 0.005;
    camera.position.x += deltaX * rotationSpeed;
    camera.position.y -= deltaY * rotationSpeed;
    camera.lookAt(scene.position);
  }

  previousMousePosition = { x: event.clientX, y: event.clientY };
});

// Zoom with mouse wheel
renderer.domElement.addEventListener("wheel", (event) => {
  event.preventDefault();
  camera.position.z += event.deltaY * 0.01;
  camera.position.z = Math.max(2, Math.min(20, camera.position.z)); // Clamp
});

Raycasting for Object Selection

Detect mouse clicks and hovers on 3D objects:

const raycaster = new THREE.Raycaster();
const mouse = new THREE.Vector2();
const clickableObjects = []; // Array of meshes that can be clicked

// Update mouse position
window.addEventListener("mousemove", (event) => {
  mouse.x = (event.clientX / window.innerWidth) * 2 - 1;
  mouse.y = -(event.clientY / window.innerHeight) * 2 + 1;
});

// Detect clicks
window.addEventListener("click", () => {
  raycaster.setFromCamera(mouse, camera);
  const intersects = raycaster.intersectObjects(clickableObjects);

  if (intersects.length > 0) {
    const clickedObject = intersects[0].object;
    // Handle click - change color, scale, etc.
    clickedObject.material.color.set(0xff0000);
  }
});

// Hover effect in animation loop
function animate() {
  requestAnimationFrame(animate);

  raycaster.setFromCamera(mouse, camera);
  const intersects = raycaster.intersectObjects(clickableObjects);

  // Reset all objects
  clickableObjects.forEach((obj) => {
    obj.scale.set(1, 1, 1);
  });

  // Highlight hovered object
  if (intersects.length > 0) {
    intersects[0].object.scale.set(1.2, 1.2, 1.2);
    document.body.style.cursor = "pointer";
  } else {
    document.body.style.cursor = "default";
  }

  renderer.render(scene, camera);
}

Particle System

const particlesGeometry = new THREE.BufferGeometry();
const particlesCount = 1000;
const posArray = new Float32Array(particlesCount * 3);

for (let i = 0; i < particlesCount * 3; i++) {
  posArray[i] = (Math.random() - 0.5) * 10;
}

particlesGeometry.setAttribute(
  "position",
  new THREE.BufferAttribute(posArray, 3),
);

const particlesMaterial = new THREE.PointsMaterial({
  size: 0.02,
  color: 0xffffff,
});

const particlesMesh = new THREE.Points(particlesGeometry, particlesMaterial);
scene.add(particlesMesh);

User Interaction (Mouse Movement)

let mouseX = 0;
let mouseY = 0;

document.addEventListener("mousemove", (event) => {
  mouseX = (event.clientX / window.innerWidth) * 2 - 1;
  mouseY = -(event.clientY / window.innerHeight) * 2 + 1;
});

function animate() {
  requestAnimationFrame(animate);
  camera.position.x = mouseX * 2;
  camera.position.y = mouseY * 2;
  camera.lookAt(scene.position);
  renderer.render(scene, camera);
}

Loading Textures

const textureLoader = new THREE.TextureLoader();
const texture = textureLoader.load("texture-url.jpg");

const material = new THREE.MeshStandardMaterial({
  map: texture,
});

Best Practices

Performance

• Reuse geometries and materials when creating multiple similar objects
• Use BufferGeometry for custom shapes (more efficient)
• Limit particle counts to maintain 60fps (start with 1000-5000)
• Dispose of resources when removing objects:

  geometry.dispose();
  material.dispose();
  texture.dispose();

Visual Quality

• Always set antialias: true on renderer for smooth edges
• Use appropriate camera FOV (45-75 degrees typical)
• Position lights thoughtfully - avoid overlapping multiple bright lights
• Add ambient + directional lighting for realistic scenes

Code Organization

• Initialize scene, camera, renderer at the top
• Group related objects (e.g., all particles in one group)
• Keep animation logic in the animate function
• Separate object creation into functions for complex scenes

Common Pitfalls to Avoid

• ❌ Using THREE.OrbitControls - not available on CDN
• ❌ Using THREE.CapsuleGeometry - requires r142+
• ❌ Forgetting to add objects to scene with scene.add()
• ❌ Using lit materials without adding lights
• ❌ Not handling window resize
• ❌ Forgetting to call renderer.render() in animation loop

Example Workflow

User: "Create an interactive 3D sphere that responds to mouse movement"

1. Setup: Import Three.js (r128), create scene/camera/renderer
2. Geometry: Create SphereGeometry(1, 32, 32) for smooth sphere
3. Material: Use MeshStandardMaterial for realistic look
4. Lighting: Add ambient + directional lights
5. Interaction: Track mouse position, update camera
6. Animation: Rotate sphere, render continuously
7. Responsive: Add window resize handler
8. Result: Smooth, interactive 3D sphere ✓

Troubleshooting

Black screen / Nothing renders:

• Check if objects added to scene
• Verify camera position isn't inside objects
• Ensure renderer.render() is called
• Add lights if using lit materials

Poor performance:

• Reduce particle count
• Lower geometry detail (segments)
• Reuse materials/geometries
• Check browser console for errors

Objects not visible:

• Check object position vs camera position
• Verify material has visible color/properties
• Ensure camera far plane includes objects
• Add lighting if needed

Advanced Techniques

Visual Polish for Portfolio-Grade Rendering

Shadows:

// Enable shadows on renderer
renderer.shadowMap.enabled = true;
renderer.shadowMap.type = THREE.PCFSoftShadowMap; // Soft shadows

// Light that casts shadows
const directionalLight = new THREE.DirectionalLight(0xffffff, 1);
directionalLight.position.set(5, 10, 5);
directionalLight.castShadow = true;

// Configure shadow quality
directionalLight.shadow.mapSize.width = 2048;
directionalLight.shadow.mapSize.height = 2048;
directionalLight.shadow.camera.near = 0.5;
directionalLight.shadow.camera.far = 50;

scene.add(directionalLight);

// Objects cast and receive shadows
mesh.castShadow = true;
mesh.receiveShadow = true;

// Ground plane receives shadows
const groundGeometry = new THREE.PlaneGeometry(20, 20);
const groundMaterial = new THREE.MeshStandardMaterial({ color: 0x808080 });
const ground = new THREE.Mesh(groundGeometry, groundMaterial);
ground.rotation.x = -Math.PI / 2;
ground.receiveShadow = true;
scene.add(ground);

Environment Maps & Reflections:

// Create environment map from cubemap
const loader = new THREE.CubeTextureLoader();
const envMap = loader.load([
  "px.jpg",
  "nx.jpg", // positive x, negative x
  "py.jpg",
  "ny.jpg", // positive y, negative y
  "pz.jpg",
  "nz.jpg", // positive z, negative z
]);

scene.environment = envMap; // Affects all PBR materials
scene.background = envMap; // Optional: use as skybox

// Or apply to specific materials
const material = new THREE.MeshStandardMaterial({
  metalness: 1.0,
  roughness: 0.1,
  envMap: envMap,
});

Tone Mapping & Output Encoding:

// Improve color accuracy and HDR rendering
renderer.toneMapping = THREE.ACESFilmicToneMapping;
renderer.toneMappingExposure = 1.0;
renderer.outputEncoding = THREE.sRGBEncoding;

// Makes colors more vibrant and realistic

Fog for Depth:

// Linear fog
scene.fog = new THREE.Fog(0xcccccc, 10, 50); // color, near, far

// Or exponential fog (more realistic)
scene.fog = new THREE.FogExp2(0xcccccc, 0.02); // color, density

Custom Geometry from Vertices

const geometry = new THREE.BufferGeometry();
const vertices = new Float32Array([-1, -1, 0, 1, -1, 0, 1, 1, 0]);
geometry.setAttribute("position", new THREE.BufferAttribute(vertices, 3));

Post-Processing Effects

While advanced post-processing may not be available in r128 CDN, basic effects can be achieved with shaders and render targets.

Group Objects

const group = new THREE.Group();
group.add(mesh1);
group.add(mesh2);
group.rotation.y = Math.PI / 4;
scene.add(group);

Summary

Three.js artifacts require systematic setup:

1. Import correct CDN version (r128)
2. Initialize scene, camera, renderer
3. Create geometry + material = mesh
4. Add lighting if using lit materials
5. Implement animation loop
6. Handle window resize
7. Avoid r128 incompatible features

Follow these patterns for reliable, performant 3D experiences.

Modern Three.js & Production Practices

While this skill focuses on CDN-based Three.js (r128) for artifact compatibility, here's what you'd do in production environments:

Modular Imports with Build Tools

// In production with npm/vite/webpack:
import * as THREE from "three";
import { OrbitControls } from "three/examples/jsm/controls/OrbitControls";
import { GLTFLoader } from "three/examples/jsm/loaders/GLTFLoader";
import { EffectComposer } from "three/examples/jsm/postprocessing/EffectComposer";

Benefits:

• Tree-shaking (smaller bundle sizes)
• Access to full example library (OrbitControls, loaders, etc.)
• Latest Three.js features (r150+)
• TypeScript support

Animation Libraries (GSAP Integration)

// Smooth timeline-based animations
import gsap from "gsap";

// Instead of manual animation loops:
gsap.to(mesh.position, {
  x: 5,
  duration: 2,
  ease: "power2.inOut",
});

// Complex sequences:
const timeline = gsap.timeline();
timeline
  .to(mesh.rotation, { y: Math.PI * 2, duration: 2 })
  .to(mesh.scale, { x: 2, y: 2, z: 2, duration: 1 }, "-=1");

Why GSAP:

• Professional easing functions
• Timeline control (pause, reverse, scrub)
• Better than manual lerping for complex animations

Scroll-Based Interactions

// Sync 3D animations with page scroll
let scrollY = window.scrollY;

window.addEventListener("scroll", () => {
  scrollY = window.scrollY;
});

function animate() {
  requestAnimationFrame(animate);

  // Rotate based on scroll position
  mesh.rotation.y = scrollY * 0.001;

  // Move camera through scene
  camera.position.y = -(scrollY / window.innerHeight) * 10;

  renderer.render(scene, camera);
}

Advanced scroll libraries:

• ScrollTrigger (GSAP plugin)
• Locomotive Scroll
• Lenis smooth scroll

Performance Optimization in Production

// Level of Detail (LOD)
const lod = new THREE.LOD();
lod.addLevel(highDetailMesh, 0); // Close up
lod.addLevel(mediumDetailMesh, 10); // Medium distance
lod.addLevel(lowDetailMesh, 50); // Far away
scene.add(lod);

// Instanced meshes for many identical objects
const geometry = new THREE.BoxGeometry();
const material = new THREE.MeshStandardMaterial();
const instancedMesh = new THREE.InstancedMesh(geometry, material, 1000);

// Set transforms for each instance
const matrix = new THREE.Matrix4();
for (let i = 0; i < 1000; i++) {
  matrix.setPosition(
    Math.random() * 100,
    Math.random() * 100,
    Math.random() * 100,
  );
  instancedMesh.setMatrixAt(i, matrix);
}

Modern Loading Patterns

// In production, load 3D models:
import { GLTFLoader } from "three/examples/jsm/loaders/GLTFLoader";

const loader = new GLTFLoader();
loader.load("model.gltf", (gltf) => {
  scene.add(gltf.scene);

  // Traverse and setup materials
  gltf.scene.traverse((child) => {
    if (child.isMesh) {
      child.castShadow = true;
      child.receiveShadow = true;
    }
  });
});

When to Use What

CDN Approach (Current Skill):

• Quick prototypes and demos
• Educational content
• Artifacts and embedded experiences
• No build step required

Production Build Approach:

• Client projects and portfolios
• Complex applications
• Need latest features (r150+)
• Performance-critical applications
• Team collaboration with version control

Recommended Production Stack

Three.js (latest) + Vite/Webpack
├── GSAP (animations)
├── React Three Fiber (optional - React integration)
├── Drei (helper components)
├── Leva (debug GUI)
└── Post-processing effects

This skill provides CDN-compatible foundations. In production, you'd layer on these modern tools for professional results.