[Feature] 2D rigid body creation and management

[vmarcella]

Overview

Add 2D rigid bodies that can be added to the physics world with configurable
mass, velocity, and body type (static, dynamic, kinematic).

Current State

Requires PhysicsWorld2D to be implemented. No rigid body support exists.

Scope

Goals:

• Create static rigid bodies (immovable, infinite mass)
• Create dynamic rigid bodies (affected by forces/gravity)
• Create kinematic rigid bodies (user-controlled movement)
• Set position, rotation, velocity
• Apply forces and impulses

Non-Goals:

• Collision shapes
• Collision response
• Joints/constraints

Proposed API

pub enum RigidBodyType {
 Static,
 Dynamic,
 Kinematic,
}

pub struct RigidBody2D {
 // handle to physics world body
}

pub struct RigidBody2DBuilder {
 body_type: RigidBodyType,
 position: [f32; 2],
 rotation: f32,
 mass: f32,
}

impl RigidBody2DBuilder {
 pub fn new(body_type: RigidBodyType) -> Self;
 pub fn with_position(self, x: f32, y: f32) -> Self;
 pub fn with_rotation(self, radians: f32) -> Self;
 pub fn with_mass(self, mass: f32) -> Self;
 pub fn build(self, world: &mut PhysicsWorld2D) -> RigidBody2D;
}

impl RigidBody2D {
 pub fn position(&self) -> [f32; 2];
 pub fn rotation(&self) -> f32;
 pub fn set_position(&mut self, x: f32, y: f32);
 pub fn set_velocity(&mut self, vx: f32, vy: f32);
 pub fn apply_force(&mut self, fx: f32, fy: f32);
 pub fn apply_impulse(&mut self, ix: f32, iy: f32);
}

Acceptance Criteria

• Static bodies remain fixed regardless of forces
• Dynamic bodies respond to gravity and forces
• Kinematic bodies can be moved programmatically
• Position and rotation can be queried after stepping
• Forces and impulses affect dynamic bodies correctly

Affected Crates

lambda-rs, lambda-rs-platform

Notes

• Bodies without shapes won't collide but can still move
• Handle system prevents dangling references