/threejs-interaction

name: threejs-interaction
description: Three.js interaction - raycasting, controls, mouse/touch input, object selection. Use when handling user input, implementing click detection, adding camera controls, or creating interactive 3D experiences.

Three.js Interaction

Quick Start

import * as THREE from "three";
import { OrbitControls } from "three/addons/controls/OrbitControls.js";

// Camera controls
const controls = new OrbitControls(camera, renderer.domElement);
controls.enableDamping = true;

// Raycasting for click detection
const raycaster = new THREE.Raycaster();
const mouse = new THREE.Vector2();

function onClick(event) {
  mouse.x = (event.clientX / window.innerWidth) * 2 - 1;
  mouse.y = -(event.clientY / window.innerHeight) * 2 + 1;

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

  if (intersects.length > 0) {
    console.log("Clicked:", intersects[0].object);
  }
}

window.addEventListener("click", onClick);

Raycaster

Basic Raycasting

const raycaster = new THREE.Raycaster();

// From camera (mouse picking)
raycaster.setFromCamera(mousePosition, camera);

// From any origin and direction
raycaster.set(origin, direction); // origin: Vector3, direction: normalized Vector3

// Get intersections
const intersects = raycaster.intersectObjects(objects, recursive);

// intersects array contains:
// {
//   distance: number,          // Distance from ray origin
//   point: Vector3,            // Intersection point in world coords
//   face: Face3,               // Intersected face
//   faceIndex: number,         // Face index
//   object: Object3D,          // Intersected object
//   uv: Vector2,               // UV coordinates at intersection
//   uv1: Vector2,              // Second UV channel
//   normal: Vector3,           // Interpolated face normal
//   instanceId: number         // For InstancedMesh
// }

Mouse Position Conversion

const mouse = new THREE.Vector2();

function updateMouse(event) {
  // For full window
  mouse.x = (event.clientX / window.innerWidth) * 2 - 1;
  mouse.y = -(event.clientY / window.innerHeight) * 2 + 1;
}

// For specific canvas element
function updateMouseCanvas(event, canvas) {
  const rect = canvas.getBoundingClientRect();
  mouse.x = ((event.clientX - rect.left) / rect.width) * 2 - 1;
  mouse.y = -((event.clientY - rect.top) / rect.height) * 2 + 1;
}

Touch Support

function onTouchStart(event) {
  event.preventDefault();

  if (event.touches.length === 1) {
    const touch = event.touches[0];
    mouse.x = (touch.clientX / window.innerWidth) * 2 - 1;
    mouse.y = -(touch.clientY / window.innerHeight) * 2 + 1;

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

    if (intersects.length > 0) {
      handleSelection(intersects[0]);
    }
  }
}

renderer.domElement.addEventListener("touchstart", onTouchStart);

Raycaster Options

const raycaster = new THREE.Raycaster();

// Near/far clipping (default: 0, Infinity)
raycaster.near = 0;
raycaster.far = 100;

// Line/Points precision
raycaster.params.Line.threshold = 0.1;
raycaster.params.Points.threshold = 0.1;

// Layers (only intersect objects on specific layers)
raycaster.layers.set(1);

Efficient Raycasting

// Only check specific objects
const clickables = [mesh1, mesh2, mesh3];
const intersects = raycaster.intersectObjects(clickables, false);

// Use layers for filtering
mesh1.layers.set(1); // Clickable layer
raycaster.layers.set(1);

// Throttle raycast for hover effects
let lastRaycast = 0;
function onMouseMove(event) {
  const now = Date.now();
  if (now - lastRaycast < 50) return; // 20fps max
  lastRaycast = now;

  // Raycast here
}

Camera Controls

OrbitControls

import { OrbitControls } from "three/addons/controls/OrbitControls.js";

const controls = new OrbitControls(camera, renderer.domElement);

// Damping (smooth movement)
controls.enableDamping = true;
controls.dampingFactor = 0.05;

// Rotation limits
controls.minPolarAngle = 0; // Top
controls.maxPolarAngle = Math.PI / 2; // Horizon
controls.minAzimuthAngle = -Math.PI / 4; // Left
controls.maxAzimuthAngle = Math.PI / 4; // Right

// Zoom limits
controls.minDistance = 2;
controls.maxDistance = 50;

// Enable/disable features
controls.enableRotate = true;
controls.enableZoom = true;
controls.enablePan = true;

// Auto-rotate
controls.autoRotate = true;
controls.autoRotateSpeed = 2.0;

// Target (orbit point)
controls.target.set(0, 1, 0);

// Update in animation loop
function animate() {
  controls.update(); // Required for damping and auto-rotate
  renderer.render(scene, camera);
}

FlyControls

import { FlyControls } from "three/addons/controls/FlyControls.js";

const controls = new FlyControls(camera, renderer.domElement);
controls.movementSpeed = 10;
controls.rollSpeed = Math.PI / 24;
controls.dragToLook = true;

// Update with delta
function animate() {
  controls.update(clock.getDelta());
  renderer.render(scene, camera);
}

FirstPersonControls

import { FirstPersonControls } from "three/addons/controls/FirstPersonControls.js";

const controls = new FirstPersonControls(camera, renderer.domElement);
controls.movementSpeed = 10;
controls.lookSpeed = 0.1;
controls.lookVertical = true;
controls.constrainVertical = true;
controls.verticalMin = Math.PI / 4;
controls.verticalMax = (Math.PI * 3) / 4;

function animate() {
  controls.update(clock.getDelta());
}

PointerLockControls

import { PointerLockControls } from "three/addons/controls/PointerLockControls.js";

const controls = new PointerLockControls(camera, document.body);

// Lock pointer on click
document.addEventListener("click", () => {
  controls.lock();
});

controls.addEventListener("lock", () => {
  console.log("Pointe