Try one real physics body with Rapier

1. STEP 1

   Use one exact package

   Keep your working game separate. Download the original example source into a new folder, then install the pinned dependency with Node 24. The source ZIP contains Forge code and notices; the upstream library is installed separately.

   npm install --ignore-scripts --no-audit --no-fund
   npm run build
   npm run check
   python3 -m http.server 8080

   Check: npm run build verifies the exact module hash; npm run check passes six real WASM cases.

2. STEP 2

   Let physics own the fall

   Open physics.mjs. Rapier owns a dynamic body and its cuboid collider; the ground is fixed. Units are metres and seconds. No visual animation decides whether the body is touching the floor.

   const world = new RAPIER.World({x:0, y:-9.81, z:0});
   world.timestep = 1/60;
   world.createCollider(RAPIER.ColliderDesc.cuboid(5,.1,5)
     .setTranslation(0,-.1,0));

   Check: After Start the height falls from 3 m and settles near 0.35 m; floor contact becomes visible in the text state.

3. STEP 3

   Use one fixed clock

   Reuse your existing simulation loop. This example uses Forge’s bounded fixedStep helper: each update advances1/60 second, with at most0.1 second catch-up per rendered frame. The browser’s drawing rate does not own gravity. Pause and Step one tick make the distinction visible.

   fixedStep(clock, elapsedSeconds, () => probe.step());
   // Rendering reads probe.snapshot(); it does not step physics.

   Check: While paused the measured state stays still. One tick adds exactly one step. An explicit upward impulse lifts the body; it returns to the floor.

4. STEP 4

   Stop and release the world

   Dispose world releases the event queue and physics world once. Restart releases the previous world before creating a fresh one. Connect only this proven loop to your existing project; character movement, vehicle handling, camera, multiplayer and target-device tests are separate work.

   probe.dispose(); // idempotent; future step/impulse is rejected
   probe = createPhysicsProbe(RAPIER);

   Check: Dispose stops all steps; a new Start begins from 3 m with zero contacts. Failed library loading gives a useful error while this guide remains readable.

Download original example source Open the standalone example