A box3d physics backend for flutter_scene. It implements the PhysicsSimulation contract from package:scene (rigid bodies, colliders, joints, queries, and collision events) against the box3d engine, through the engine-agnostic box3d Dart package.

Status: experimental. The API may change between releases.

Wrap a Box3dPhysicsWorld in flutter_scene's PhysicsWorld component on the scene root, then attach RigidBody and Collider components to the nodes you want simulated (the body must be added before the collider). The scene advances physics on a fixed timestep and interpolates transforms for you.

import 'package:flutter_scene/physics.dart';
import 'package:flutter_scene/scene.dart';
import 'package:flutter_scene_box3d/flutter_scene_box3d.dart';
import 'package:vector_math/vector_math.dart';

await Box3dPhysicsWorld.ensureInitialized();

final scene = Scene();
final world = PhysicsWorld(Box3dPhysicsWorld(gravity: Vector3(0, -9.81, 0)));
scene.root.addComponent(world);

// A static floor.
final floor = Node(localTransform: Matrix4.translation(Vector3(0, -0.5, 0)));
floor.addComponent(RigidBody(type: BodyType.fixed));
floor.addComponent(Collider(shape: BoxShape(halfExtents: Vector3(10, 0.5, 10))));
scene.add(floor);

// A falling dynamic box.
final box = Node(localTransform: Matrix4.translation(Vector3(0, 5, 0)));
box.addComponent(RigidBody(type: BodyType.dynamic_));
box.addComponent(Collider(shape: BoxShape(halfExtents: Vector3.all(0.5))));
scene.add(box);

world.collisions.listen((event) {
  // CollisionBegan / CollisionEnded / TriggerEntered / TriggerExited
});

Each frame, advance and render the scene:

scene.update(deltaSeconds); // steps physics + interpolates
scene.render(camera, canvas, viewport: Offset.zero & size);

Scene queries run through world.raycast, world.raycastAll, world.overlapSphere, world.overlapBox, and world.shapeCast.

Sphere, box, capsule, cylinder, convex hull, triangle mesh, height field, and compound. A collider's localPose is baked into the shape geometry; a non-identity pose on a cylinder or height field is not supported yet.

A triangle mesh collider collides from its front face only, the side its corners wind counter-clockwise around, which is also the side it renders from.

Fixed, spherical, revolute, and prismatic joints are supported through the flutter_scene joint components. box3d has no 6-DOF generic joint, so GenericJoint throws UnsupportedError.

The kinematic character controller and an explicit mass/inertia override are not wired up yet (box3d derives mass from collider density). See the TODO notes in the source.

MIT (see LICENSE).