threejs-fundamentals

# Three.js Fundamentals ## Quick Start ```javascript 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); }); ``` ## Core Classes ### Scene Container for all 3D objects, lights, and cameras. ```javascript 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 ``` ### Cameras **PerspectiveCamera** - Most common, simulates human eye. ```javascript // 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** - No perspective distortion, good for 2D/isometric. ```javascript // 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, ); ``` **ArrayCamera** - Multiple viewports with sub-cameras. ```javascript 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); ``` **CubeCamera** - Renders environment maps for reflections. ```javascript 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); ``` ### WebGLRenderer ```javascript 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); ``` ### Object3D Base class for all 3D objects. Mesh, Group, Light, Camera all extend Object3D. ```javascript 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 ``` ### Group Empty container for organizing objects. ```javascript 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; ``` ### Mesh Combines geometry and material. ```javascript 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 ``` ## Coordinate System Three.js uses a **right-handed coordinate system**: - **+X** points right - **+Y** points up - **+Z** points toward viewer (out of screen) ```javascript // Axes helper const axesHelper = new THREE.AxesHelper(5); scene.add(axesHelper); // Red=X, Green=Y, Blue=Z ``` ## Math Utilities ### Vector3 ```javascript 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 ``` ### Matrix4 ```javascript 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); ``` ### Quaternion ```javascript 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(); ``` ### Euler ```javascript 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' ``` ### Color ```javascript 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); ``` ### MathUtils ```javascript 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); ``` ## Common Patterns ### Proper Cleanup ```javascript 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(); } ``` ### Clock for Animation ```javascript 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); } ``` ### Responsive Canvas ```javascript 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); ```