threejs-fundamentals

import * as THREE from "three";
 
// Create scene, camera, renderer
const scene = new THREE.Scene();
const camera = new THREE.PerspectiveCamera(
  75,
  window.innerWidth / window.innerHeight,
  0.1,
  1000,
);
const renderer = new THREE.WebGLRenderer({ antialias: true });
 
renderer.setSize(window.innerWidth, window.innerHeight);
renderer.setPixelRatio(Math.min(window.devicePixelRatio, 2));
document.body.appendChild(renderer.domElement);
 
// Add a mesh
const geometry = new THREE.BoxGeometry(1, 1, 1);
const material = new THREE.MeshStandardMaterial({ color: 0x00ff00 });
const cube = new THREE.Mesh(geometry, material);
scene.add(cube);
 
// Add light
scene.add(new THREE.AmbientLight(0xffffff, 0.5));
const dirLight = new THREE.DirectionalLight(0xffffff, 1);
dirLight.position.set(5, 5, 5);
scene.add(dirLight);
 
camera.position.z = 5;
 
// Animation loop
function animate() {
  requestAnimationFrame(animate);
  cube.rotation.x += 0.01;
  cube.rotation.y += 0.01;
  renderer.render(scene, camera);
}
animate();
 
// Handle resize
window.addEventListener("resize", () => {
  camera.aspect = window.innerWidth / window.innerHeight;
  camera.updateProjectionMatrix();
  renderer.setSize(window.innerWidth, window.innerHeight);
});

const scene = new THREE.Scene();
scene.background = new THREE.Color(0x000000); // Solid color
scene.background = texture; // Skybox texture
scene.background = cubeTexture; // Cubemap
scene.environment = envMap; // Environment map for PBR
scene.fog = new THREE.Fog(0xffffff, 1, 100); // Linear fog
scene.fog = new THREE.FogExp2(0xffffff, 0.02); // Exponential fog

// PerspectiveCamera(fov, aspect, near, far)
const camera = new THREE.PerspectiveCamera(
  75, // Field of view (degrees)
  window.innerWidth / window.innerHeight, // Aspect ratio
  0.1, // Near clipping plane
  1000, // Far clipping plane
);
 
camera.position.set(0, 5, 10);
camera.lookAt(0, 0, 0);
camera.updateProjectionMatrix(); // Call after changing fov, aspect, near, far

// OrthographicCamera(left, right, top, bottom, near, far)
const aspect = window.innerWidth / window.innerHeight;
const frustumSize = 10;
const camera = new THREE.OrthographicCamera(
  (frustumSize * aspect) / -2,
  (frustumSize * aspect) / 2,
  frustumSize / 2,
  frustumSize / -2,
  0.1,
  1000,
);

const cameras = [];
for (let i = 0; i < 4; i++) {
  const subcamera = new THREE.PerspectiveCamera(40, 1, 0.1, 100);
  subcamera.viewport = new THREE.Vector4(
    Math.floor(i % 2) * 0.5,
    Math.floor(i / 2) * 0.5,
    0.5,
    0.5,
  );
  cameras.push(subcamera);
}
const arrayCamera = new THREE.ArrayCamera(cameras);

const cubeRenderTarget = new THREE.WebGLCubeRenderTarget(256);
const cubeCamera = new THREE.CubeCamera(0.1, 1000, cubeRenderTarget);
scene.add(cubeCamera);
 
// Use for reflections
material.envMap = cubeRenderTarget.texture;
 
// Update each frame (expensive!)
cubeCamera.position.copy(reflectiveMesh.position);
cubeCamera.update(renderer, scene);

const renderer = new THREE.WebGLRenderer({
  canvas: document.querySelector("#canvas"), // Optional existing canvas
  antialias: true, // Smooth edges
  alpha: true, // Transparent background
  powerPreference: "high-performance", // GPU hint
  preserveDrawingBuffer: true, // For screenshots
});
 
renderer.setSize(width, height);
renderer.setPixelRatio(Math.min(window.devicePixelRatio, 2));
 
// Tone mapping
renderer.toneMapping = THREE.ACESFilmicToneMapping;
renderer.toneMappingExposure = 1.0;
 
// Color space (Three.js r152+)
renderer.outputColorSpace = THREE.SRGBColorSpace;
 
// Shadows
renderer.shadowMap.enabled = true;
renderer.shadowMap.type = THREE.PCFSoftShadowMap;
 
// Clear color
renderer.setClearColor(0x000000, 1);
 
// Render
renderer.render(scene, camera);

const obj = new THREE.Object3D();
 
// Transform
obj.position.set(x, y, z);
obj.rotation.set(x, y, z); // Euler angles (radians)
obj.quaternion.set(x, y, z, w); // Quaternion rotation
obj.scale.set(x, y, z);
 
// Local vs World transforms
obj.getWorldPosition(targetVector);
obj.getWorldQuaternion(targetQuaternion);
obj.getWorldDirection(targetVector);
 
// Hierarchy
obj.add(child);
obj.remove(child);
obj.parent;
obj.children;
 
// Visibility
obj.visible = false;
 
// Layers (for selective rendering/raycasting)
obj.layers.set(1);
obj.layers.enable(2);
obj.layers.disable(0);
 
// Traverse hierarchy
obj.traverse((child) => {
  if (child.isMesh) child.material.color.set(0xff0000);
});
 
// Matrix updates
obj.matrixAutoUpdate = true; // Default: auto-update matrices
obj.updateMatrix(); // Manual matrix update
obj.updateMatrixWorld(true); // Update world matrix recursively

const group = new THREE.Group();
group.add(mesh1);
group.add(mesh2);
scene.add(group);
 
// Transform entire group
group.position.x = 5;
group.rotation.y = Math.PI / 4;

const mesh = new THREE.Mesh(geometry, material);
 
// Multiple materials (one per geometry group)
const mesh = new THREE.Mesh(geometry, [material1, material2]);
 
// Useful properties
mesh.geometry;
mesh.material;
mesh.castShadow = true;
mesh.receiveShadow = true;
 
// Frustum culling
mesh.frustumCulled = true; // Default: skip if outside camera view
 
// Render order
mesh.renderOrder = 10; // Higher = rendered later

// Axes helper
const axesHelper = new THREE.AxesHelper(5);
scene.add(axesHelper); // Red=X, Green=Y, Blue=Z

const v = new THREE.Vector3(x, y, z);
v.set(x, y, z);
v.copy(otherVector);
v.clone();
 
// Operations (modify in place)
v.add(v2);
v.sub(v2);
v.multiply(v2);
v.multiplyScalar(2);
v.divideScalar(2);
v.normalize();
v.negate();
v.clamp(min, max);
v.lerp(target, alpha);
 
// Calculations (return new value)
v.length();
v.lengthSq(); // Faster than length()
v.distanceTo(v2);
v.dot(v2);
v.cross(v2); // Modifies v
v.angleTo(v2);
 
// Transform
v.applyMatrix4(matrix);
v.applyQuaternion(q);
v.project(camera); // World to NDC
v.unproject(camera); // NDC to world

const m = new THREE.Matrix4();
m.identity();
m.copy(other);
m.clone();
 
// Build transforms
m.makeTranslation(x, y, z);
m.makeRotationX(theta);
m.makeRotationY(theta);
m.makeRotationZ(theta);
m.makeRotationFromQuaternion(q);
m.makeScale(x, y, z);
 
// Compose/decompose
m.compose(position, quaternion, scale);
m.decompose(position, quaternion, scale);
 
// Operations
m.multiply(m2); // m = m * m2
m.premultiply(m2); // m = m2 * m
m.invert();
m.transpose();
 
// Camera matrices
m.makePerspective(left, right, top, bottom, near, far);
m.makeOrthographic(left, right, top, bottom, near, far);
m.lookAt(eye, target, up);

const q = new THREE.Quaternion();
q.setFromEuler(euler);
q.setFromAxisAngle(axis, angle);
q.setFromRotationMatrix(matrix);
 
q.multiply(q2);
q.slerp(target, t); // Spherical interpolation
q.normalize();
q.invert();

const euler = new THREE.Euler(x, y, z, "XYZ"); // Order matters!
euler.setFromQuaternion(q);
euler.setFromRotationMatrix(m);
 
// Rotation orders: 'XYZ', 'YXZ', 'ZXY', 'XZY', 'YZX', 'ZYX'

const color = new THREE.Color(0xff0000);
const color = new THREE.Color("red");
const color = new THREE.Color("rgb(255, 0, 0)");
const color = new THREE.Color("#ff0000");
 
color.setHex(0x00ff00);
color.setRGB(r, g, b); // 0-1 range
color.setHSL(h, s, l); // 0-1 range
 
color.lerp(otherColor, alpha);
color.multiply(otherColor);
color.multiplyScalar(2);

THREE.MathUtils.clamp(value, min, max);
THREE.MathUtils.lerp(start, end, alpha);
THREE.MathUtils.mapLinear(value, inMin, inMax, outMin, outMax);
THREE.MathUtils.degToRad(degrees);
THREE.MathUtils.radToDeg(radians);
THREE.MathUtils.randFloat(min, max);
THREE.MathUtils.randInt(min, max);
THREE.MathUtils.smoothstep(x, min, max);
THREE.MathUtils.smootherstep(x, min, max);

function dispose() {
  // Dispose geometries
  mesh.geometry.dispose();
 
  // Dispose materials
  if (Array.isArray(mesh.material)) {
    mesh.material.forEach((m) => m.dispose());
  } else {
    mesh.material.dispose();
  }
 
  // Dispose textures
  texture.dispose();
 
  // Remove from scene
  scene.remove(mesh);
 
  // Dispose renderer
  renderer.dispose();
}

const clock = new THREE.Clock();
 
function animate() {
  const delta = clock.getDelta(); // Time since last frame (seconds)
  const elapsed = clock.getElapsedTime(); // Total time (seconds)
 
  mesh.rotation.y += delta * 0.5; // Consistent speed regardless of framerate
 
  requestAnimationFrame(animate);
  renderer.render(scene, camera);
}

function onWindowResize() {
  const width = window.innerWidth;
  const height = window.innerHeight;
 
  camera.aspect = width / height;
  camera.updateProjectionMatrix();
 
  renderer.setSize(width, height);
  renderer.setPixelRatio(Math.min(window.devicePixelRatio, 2));
}
window.addEventListener("resize", onWindowResize);

const manager = new THREE.LoadingManager();
 
manager.onStart = (url, loaded, total) => console.log("Started loading");
manager.onLoad = () => console.log("All loaded");
manager.onProgress = (url, loaded, total) => console.log(`${loaded}/${total}`);
manager.onError = (url) => console.error(`Error loading ${url}`);
 
const textureLoader = new THREE.TextureLoader(manager);
const gltfLoader = new GLTFLoader(manager);

// Merge static geometries
import { mergeGeometries } from "three/examples/jsm/utils/BufferGeometryUtils.js";
const merged = mergeGeometries([geo1, geo2, geo3]);
 
// LOD
const lod = new THREE.LOD();
lod.addLevel(highDetailMesh, 0);
lod.addLevel(medDetailMesh, 50);
lod.addLevel(lowDetailMesh, 100);
scene.add(lod);