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physics.md

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Physics Module

Import:

import 'package:gamengine/physics.dart';

What It Contains

  • Components: RigidBody, CircleCollider, RectangleCollider, GravitySource
  • Systems: PhysicsSystem, CollisionSystem
  • Debug: PhysicsDebugSettings, PhysicsVectorsOverlay
  • Event: CollisionEvent

Basic Setup

final physics = PhysicsSystem(world: world, gravitationalConstant: 1.0);
final collisions = CollisionSystem(world: world, eventBus: engine.events);

engine.addSystem(physics, 500);
engine.addSystem(collisions, 490);

// Optional (debug): add a render pass and a settings component to enable
// physics vectors overlay.
final renderSystem = engine.systems.whereType<RenderSystem>().first;
renderSystem.addPass(PhysicsVectorsOverlay());

engine.addEntity(
  Entity()..add(PhysicsDebugSettings(enabled: true)),
);

Entity Setup

final ship = Entity()
  ..add(Transform())
  ..add(RigidBody(mass: 1.2))
  ..add(CircleCollider(radius: 14));

// Optional (debug): override debug visibility per entity.
// - enabled: null  => follow global PhysicsDebugSettings.enabled
// - enabled: true  => force show debug for this entity
// - enabled: false => force hide debug for this entity
ship.add(PhysicsDebugOverride(enabled: false));

final planet = Entity()
  ..add(Transform())
  ..add(GravitySource(mass: 420000, minDistance: 60))
  ..add(CircleCollider(radius: 90));

Collision Filtering

Colliders now support bitmask-based filtering:

  • collisionLayer: which layer the collider belongs to
  • collisionMask: which layers it is allowed to collide with

Both colliders must allow the pair for collision resolution to happen.

const playerLayer = 1 << 0;
const enemyLayer = 1 << 1;
const pickupLayer = 1 << 2;

final player = Entity()
  ..add(Transform())
  ..add(RigidBody())
  ..add(
    CircleCollider(
      radius: 14,
      collisionLayer: playerLayer,
      collisionMask: enemyLayer,
    ),
  );

final pickup = Entity()
  ..add(Transform())
  ..add(
    CircleCollider(
      radius: 8,
      collisionLayer: pickupLayer,
      collisionMask: 0,
    ),
  );

In this example, the player can collide with enemies, and the pickup collides with nothing.

Collision Consumption

for (final event in engine.events.read<CollisionEvent>()) {
  // react to impacts (particles, damage, sound)
}