A body's motion type is STATIC (floors, shelves), DYNAMIC (moved by gravity, forces and collisions) or ANIMATED (moved only by you, like a lift, and never pushed back). PhysicsAggregate creates a body and a shape sized from the mesh's bounding box; mass: 0 makes it static. This fragment runs in First Render's room (scene, floor) after enableHavok:
const book = BABYLON.MeshBuilder.CreateBox('book1',
{ width: 312 / 4000 + 0.02, height: 0.3, depth: 0.22 }, scene); // placeBooks' size
book.position.set(0, 1, 0); // 1 m above the floor
new BABYLON.PhysicsAggregate(floor, BABYLON.PhysicsShapeType.BOX, { mass: 0 }, scene);
const { body } = new BABYLON.PhysicsAggregate(book, BABYLON.PhysicsShapeType.BOX,
{ mass: 0.62, friction: 0.6, restitution: 0.3 }, scene); // a 0.62 kg hardcover
for (let frame = 1; frame <= 60; frame++) {
scene.render(); // one fixed 1/60 s physics step each
if ([12, 24, 60].includes(frame)) {
console.log(frame, book.position.y.toFixed(3), body.getLinearVelocity().y.toFixed(2));
}
}Output
12 0.800 -1.96 24 0.208 -3.92 60 0.150 0.00
The book falls 0.2 m in 12 frames (gt²/2 = 0.196 m), reaches the floor after frame 24 at 3.9 m/s and settles at 0.150 m, half its height; resting bodies then sleep until touched. Then the pre-step trap: setting book.position.y = 2 after the loop changed nothing (the next frame printed 0.150 again), because the body's pose overwrites the node each step. With body.disablePreStep = false for one frame, the book teleported to 1.998. Keep the pre-step on for bodies you move by hand, or drive an animated body with setTargetTransform(), which moves it by velocity so that it still pushes what it meets.
<!doctype html>
<style>
body { margin: 0; background: #f7f3ec; font: 13px system-ui, sans-serif; color: #333; }
canvas { width: 100%; max-width: 600px; height: 250px; display: block; touch-action: none; outline: none; }
#plot { display: block; width: 100%; max-width: 600px; height: 140px; background: #fff; } #info { max-width: 600px; padding: 4px 8px; font-family: monospace; }
</style>
<canvas id="view"></canvas>
<canvas id="plot" width="600" height="140"></canvas><div id="info"></div>
<script src="https://cdn.jsdelivr.net/npm/babylonjs@9.28.0/babylon.js"></script>
<script>
// ---- BookNest's bookstore: the helpers the book keeps in bookstore.js ----
const ROOM = { width: 8, depth: 6, height: 3, wall: 0.15 };
const BOOKS = [
{ id: 1, title: 'The Quiet Harbor', author: 'Mara Ellison', color: '#1f5f8b', pages: 312, price: 14.99, rating: 4.6, inStock: true },
{ id: 2, title: 'Patterns of the Deep Web', author: 'Tomas Reyes', color: '#5b3f99', pages: 428, price: 32.5, rating: 4.4, inStock: true },
{ id: 3, title: 'Salt and Saffron', author: 'Priya Nair', color: '#e09a10', pages: 256, price: 24, rating: 4.8, inStock: false },
{ id: 4, title: 'Small Steps to Big Summits', author: 'Dana Whitfield', color: '#3f7d3a', pages: 198, price: 18.5, rating: 4.3, inStock: true },
{ id: 5, title: "The Clockmaker's Paradox", author: 'Julian Voss', color: '#b5452f', pages: 344, price: 16.75, rating: 4.7, inStock: true },
{ id: 6, title: 'Gardens in Glass', author: 'Lena Hart', color: '#2a9d8f', pages: 176, price: 21.3, rating: 4.5, inStock: true },
];
function createScene(engine) {
const scene = new BABYLON.Scene(engine);
scene.clearColor = BABYLON.Color4.FromHexString('#cfd8dcff');
const sky = new BABYLON.HemisphericLight('sky', new BABYLON.Vector3(0.3, 1, -0.4), scene);
sky.groundColor = new BABYLON.Color3(0.35, 0.32, 0.3);
return scene;
}
function paint(scene, name, hex) { // a matte color
const material = new BABYLON.StandardMaterial(name, scene);
material.diffuseColor = BABYLON.Color3.FromHexString(hex);
material.specularColor = BABYLON.Color3.Black();
return material;
}
function createRoom(scene) { // floor and three walls, front open
const room = new BABYLON.TransformNode('room', scene);
const floor = BABYLON.MeshBuilder.CreateGround('floor', { width: ROOM.width, height: ROOM.depth }, scene);
floor.material = paint(scene, 'oak', '#b08d6a');
floor.parent = room;
const plaster = paint(scene, 'plaster', '#fff3e0');
for (const [name, width, x, z] of [['backWall', 8, 0, 3], ['leftWall', 6, -4, 0], ['rightWall', 6, 4, 0]]) {
const wall = BABYLON.MeshBuilder.CreateBox(name, { width, height: ROOM.height, depth: ROOM.wall }, scene);
wall.position.set(x, ROOM.height / 2, z);
wall.rotation.y = x ? Math.PI / 2 : 0;
wall.material = plaster;
wall.parent = room;
}
return room;
}
function createBookcase(scene, name, x) { // 8 boxes merged into 1 mesh
const [w, h, d, t] = [3, 2.2, 0.35, 0.04];
const parts = [[t, h, d, -w / 2, h / 2, 0], [t, h, d, w / 2, h / 2, 0], [w, h, t, 0, h / 2, d / 2 - t / 2]];
for (let i = 0; i < 5; i++) parts.push([w, t, d, 0, 0.1 + i * 0.5, 0]);
const bookcase = BABYLON.Mesh.MergeMeshes(parts.map(([width, height, depth, px, py, pz]) => {
const part = BABYLON.MeshBuilder.CreateBox('part', { width, height, depth }, scene);
part.position.set(px, py, pz);
return part;
}), true);
bookcase.name = name;
bookcase.material = paint(scene, 'walnut', '#6d4c33');
bookcase.position.set(x, 0, ROOM.depth / 2 - ROOM.wall / 2 - d / 2); // against the back wall
return bookcase;
}
function drawCover(scene, book) { // cover art painted on a canvas
const tex = new BABYLON.DynamicTexture('cover' + book.id, { width: 256, height: 384 }, scene);
const c = tex.getContext();
c.fillStyle = book.color; c.fillRect(0, 0, 256, 384);
c.fillStyle = 'rgba(0,0,0,0.4)'; c.fillRect(0, 0, 18, 384); // the dark left edge
c.strokeStyle = '#fff8e1'; c.lineWidth = 3; c.strokeRect(34, 24, 202, 336);
c.fillStyle = '#fff8e1'; c.textAlign = 'center'; c.font = 'bold 30px Georgia';
const lines = [''];
for (const word of book.title.split(' ')) {
const test = (lines[lines.length - 1] + ' ' + word).trim();
if (c.measureText(test).width > 180) lines.push(word); else lines[lines.length - 1] = test;
}
lines.forEach((line, i) => c.fillText(line, 135, 110 + i * 38));
c.font = '20px Georgia'; c.fillText(book.author, 135, 330);
tex.update();
return tex;
}
function placeBooks(scene, bookcase, shelf = 2) { // six books, spines out, covers on +x
const strip = new BABYLON.Vector4(0, 0, 0.07, 1);
const faceUV = [strip, strip, new BABYLON.Vector4(0, 0, 1, 1), strip, strip, strip];
let x = -0.35; // left end of the row, local to the bookcase
return BOOKS.map((record) => {
const width = record.pages / 4000 + 0.02; // spine thickness from page count
const book = BABYLON.MeshBuilder.CreateBox(`book${record.id}`, { width, height: 0.3, depth: 0.22, faceUV, wrap: true }, scene);
book.parent = bookcase;
book.position.set(x + width / 2, 0.12 + shelf * 0.5 + 0.15, -0.02);
x += width + 0.012;
book.material = new BABYLON.StandardMaterial(record.title, scene);
book.material.diffuseTexture = drawCover(scene, record);
book.material.specularColor = new BABYLON.Color3(0.15, 0.15, 0.15);
book.metadata = record; // the record, for picking
return book;
});
}
// The book cuts the storefront with CSG2 (Manifold WebAssembly); this sandbox cannot download
// the .wasm, so the older pure-JavaScript BABYLON.CSG makes the same cuts here.
function createFrontWall(scene) {
const box = (width, height, depth, x, y) => {
const mesh = BABYLON.MeshBuilder.CreateBox('cut', { width, height, depth }, scene);
mesh.position.set(x, y, -ROOM.depth / 2);
return mesh;
};
const solid = box(ROOM.width, ROOM.height, ROOM.wall, 0, ROOM.height / 2);
const windowHole = box(3.2, 1.6, 1, -1.4, 1.6), doorHole = box(1.1, 2.2, 1, 2.3, 1.1);
const wall = BABYLON.CSG.FromMesh(solid).subtract(BABYLON.CSG.FromMesh(windowHole))
.subtract(BABYLON.CSG.FromMesh(doorHole)).toMesh('frontWall', scene.getMaterialByName('plaster'), scene);
[solid, windowHole, doorHole].forEach((mesh) => mesh.dispose());
return wall;
}
// ---- end of the bookstore helpers ----
/*
With Havok (whose .wasm this sandboxed preview cannot download) the book would be:
new BABYLON.PhysicsAggregate(floor, BABYLON.PhysicsShapeType.BOX, { mass: 0 }, scene);
const { body } = new BABYLON.PhysicsAggregate(book, BABYLON.PhysicsShapeType.BOX,
{ mass: 0.62, friction: 0.6, restitution: 0.3 }, scene);
Here a few lines of explicit integration play the same body: gravity, one fixed step per
frame, a bounce with restitution 0.3, then sleep when it comes to rest.
*/
const canvas = document.getElementById('view');
const engine = new BABYLON.Engine(canvas, true, {}, true);
const scene = createScene(engine);
const floor = BABYLON.MeshBuilder.CreateGround('floor', { width: 4, height: 3 }, scene);
floor.material = paint(scene, 'oak', '#b08d6a');
const camera = new BABYLON.ArcRotateCamera('cam', -Math.PI / 2 - 0.4, 1.3, 2.6, new BABYLON.Vector3(0, 0.55, 0), scene);
camera.attachControl(canvas, true);
const book = BABYLON.MeshBuilder.CreateBox('book1', { width: 312 / 4000 + 0.02, height: 0.3, depth: 0.22 }, scene);
book.material = paint(scene, 'cover', BOOKS[0].color);
const body = { mass: 0.62, restitution: 0.3, velocity: 0, sleeping: false, halfHeight: 0.15 };
const STEP = 1 / 60, G = -9.81;
function stepBody() { // one fixed physics step
if (body.sleeping) return;
body.velocity += G * STEP;
book.position.y += body.velocity * STEP;
if (book.position.y < body.halfHeight) { // contact with the static floor
book.position.y = body.halfHeight;
body.velocity = -body.velocity * body.restitution;
if (Math.abs(body.velocity) < 0.3) { body.velocity = 0; body.sleeping = true; } // at rest: sleep
}
}
const ctx = document.getElementById('plot').getContext('2d');
const info = document.getElementById('info');
let frame = 0, log = [];
function drop() {
book.position.set(0, 1, 0); // 1 m above the floor
Object.assign(body, { velocity: 0, sleeping: false });
frame = 0; log = [];
ctx.clearRect(0, 0, 600, 140);
ctx.strokeStyle = '#ddd'; ctx.strokeRect(40, 10, 540, 110);
ctx.fillStyle = '#333'; ctx.font = '11px sans-serif';
ctx.fillText('1 m', 12, 16); ctx.fillText('0', 26, 122); ctx.fillText('frame 90', 535, 134);
}
scene.onBeforeRenderObservable.add(() => {
if (frame >= 90) return;
frame++;
stepBody();
const x = 40 + frame / 90 * 540, y = 120 - book.position.y * 110;
ctx.fillStyle = '#1f5f8b';
ctx.fillRect(x - 1.5, y - 1.5, 3, 3);
if ([12, 24, 60].includes(frame)) log.push(`frame ${frame}: y ${book.position.y.toFixed(3)}, v ${body.velocity.toFixed(2)}`);
info.textContent = log.join(' ') + (body.sleeping ? ' (sleeping)' : '');
if (frame === 90) setTimeout(drop, 1200);
});
drop();
engine.runRenderLoop(() => scene.render());
addEventListener('resize', () => engine.resize());
</script>