threejs-interaction

name	threejs-interaction
allowed-tools	Read, Glob
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

Iron Law

Always call raycaster.setFromCamera() with normalized device coordinates in range [-1, 1] — raw pixel coordinates produce silent miss-hits on all objects.

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);
}

Other Control Types

Control	Import	Best For
FlyControls	controls/FlyControls.js	Free-flying, space/flight sims
FirstPersonControls	controls/FirstPersonControls.js	FPS with look constraints
PointerLockControls	controls/PointerLockControls.js	Immersive FPS (browser pointer lock)
TrackballControls	controls/TrackballControls.js	Unconstrained rotation (rolls past poles)
MapControls	controls/MapControls.js	Top-down map view

Full code examples → references/advanced-controls.md

TransformControls

Gizmo for moving/rotating/scaling objects.

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

const transformControls = new TransformControls(camera, renderer.domElement);
scene.add(transformControls);

// Attach to object
transformControls.attach(selectedMesh);

// Switch modes
transformControls.setMode("translate"); // 'translate', 'rotate', 'scale'

// Change space
transformControls.setSpace("local"); // 'local', 'world'

// Size
transformControls.setSize(1);

// Events
transformControls.addEventListener("dragging-changed", (event) => {
  // Disable orbit controls while dragging
  orbitControls.enabled = !event.value;
});

transformControls.addEventListener("change", () => {
  renderer.render(scene, camera);
});

// Keyboard shortcuts
window.addEventListener("keydown", (event) => {
  switch (event.key) {
    case "g":
      transformControls.setMode("translate");
      break;
    case "r":
      transformControls.setMode("rotate");
      break;
    case "s":
      transformControls.setMode("scale");
      break;
    case "Escape":
      transformControls.detach();
      break;
  }
});

DragControls

Drag objects directly.

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

const draggableObjects = [mesh1, mesh2, mesh3];
const dragControls = new DragControls(
  draggableObjects,
  camera,
  renderer.domElement,
);

dragControls.addEventListener("dragstart", (event) => {
  orbitControls.enabled = false;
  event.object.material.emissive.set(0xaaaaaa);
});

dragControls.addEventListener("drag", (event) => {
  // Constrain to ground plane
  event.object.position.y = 0;
});

dragControls.addEventListener("dragend", (event) => {
  orbitControls.enabled = true;
  event.object.material.emissive.set(0x000000);
});

Selection System

Click to Select

const raycaster = new THREE.Raycaster();
const mouse = new THREE.Vector2();
let selectedObject = null;

function onMouseDown(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(selectableObjects);

  // Deselect previous
  if (selectedObject) {
    selectedObject.material.emissive.set(0x000000);
  }

  // Select new
  if (intersects.length > 0) {
    selectedObject = intersects[0].object;
    selectedObject.material.emissive.set(0x444444);
  } else {
    selectedObject = null;
  }
}

Hover Effects

const raycaster = new THREE.Raycaster();
const mouse = new THREE.Vector2();
let hoveredObject = null;

function onMouseMove(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(hoverableObjects);

  // Reset previous hover
  if (hoveredObject) {
    hoveredObject.material.color.set(hoveredObject.userData.originalColor);
    document.body.style.cursor = "default";
  }

  // Apply new hover
  if (intersects.length > 0) {
    hoveredObject = intersects[0].object;
    if (!hoveredObject.userData.originalColor) {
      hoveredObject.userData.originalColor =
        hoveredObject.material.color.getHex();
    }
    hoveredObject.material.color.set(0xff6600);
    document.body.style.cursor = "pointer";
  } else {
    hoveredObject = null;
  }
}

window.addEventListener("mousemove", onMouseMove);

Keyboard Input

const keys = {};

document.addEventListener("keydown", (event) => {
  keys[event.code] = true;
});

document.addEventListener("keyup", (event) => {
  keys[event.code] = false;
});

function update() {
  const speed = 0.1;

  if (keys["KeyW"]) player.position.z -= speed;
  if (keys["KeyS"]) player.position.z += speed;
  if (keys["KeyA"]) player.position.x -= speed;
  if (keys["KeyD"]) player.position.x += speed;
  if (keys["Space"]) player.position.y += speed;
  if (keys["ShiftLeft"]) player.position.y -= speed;
}

References

• references/advanced-controls.md — FlyControls, FirstPersonControls, PointerLockControls, TrackballControls, MapControls; box selection; world↔screen coordinate conversion; InteractionManager class; performance tips

See Also

• threejs-fundamentals - Camera and scene setup
• threejs-animation - Animating interactions
• threejs-shaders - Visual feedback effects