Physics

Physics in XR Blocks is powered by the Rapier physics engine.

Getting started

To use physics in your scene, import the RAPIER physics engine, then pass the RAPIER component into the physics options:

import * as xb from 'xrblocks';
import RAPIER from '@dimforge/rapier3d-simd-compat';

const options = new xb.Options();
options.physics.RAPIER = RAPIER;
xb.init(options);

See /samples/Ballpit and /samples/Drone for examples of using physics.

TypeScript Setup

The Rapier physics library comes in several different variants such as @dimforge/rapier3d and @dimforge/rapier3d-simd-compat.

XR Blocks supports the different 3D variants of RAPIER by using a virtual import rapier3d for types instead of directly importing from one of the specific packages. When using TypeScript, you will need to link the virtual import to your installed version of Rapier. For example, when using @dimforge/rapier3d-simd-compat:

tsconfig.json

{
  "compilerOptions": {
    "paths": {
      "rapier3d": ["./node_modules/@dimforge/rapier3d-simd-compat/rapier"]
    }
  }
  //...
}

Physics

The Physics controller will initialize RAPIER, create a RAPIER world, and call world.step for every physics step. Is is accessible from xb.core.physics and has the following properties:

1. RAPIER - the global RAPIER object.
2. blendedWorld - the global RAPIER.world object.
3. fps - the fixed physics update rate.
4. options - physics options.

Adding physics to objects

In the Script.initPhysics method, you can create rigid bodies corresponding to your object. Then in the Script.physicsStep method, copy the translation and rotation of the rigid body to your object.

For example:

export class Ball extends xb.Script {
  //...

  initPhysics(physics) {
    const RAPIER = physics.RAPIER;
    const desc = RAPIER.RigidBodyDesc.dynamic().setTranslation(
      ...this.position
    );
    const shape = RAPIER.ColliderDesc.ball(this.radius);
    this.body = world.createRigidBody(desc);
    this.collider = world.createCollider(shape, this.body);
  }

  physicsStep() {
    this.position.copy(this.body.translation());
    this.quaternion.copy(this.body.rotation());
  }
}

Physics Options

By default, we uses the following options in PhysicsOptions in the initial xb.init call:

{
  fps: 45,
  gravity: {x: 0.0, y: -9.81, z: 0.0},
  // Have `Physics` automatically call world.step.
  worldStep: true,
  // Use an event queue when calling world.step.
  useEventQueue: false
};