Phase 1: road network and heat

Roads are a jittered 7x7 grid with ~a quarter of the edges thinned out, kept
connected. The loops are the point: "take a different road" is not a decision
without alternative routes.

Every metre driven adds heat to that segment; all roads shed it slowly. Crossing
a threshold escalates Clear -> Patrol -> Barricade -> Turret, each of which puts
real obstructions on the tarmac. Hysteresis stops a road on a boundary from
rebuilding its barricade every few seconds.

Level changes are deferred while the car is on the segment. Building a barricade
around the player would spawn a static collider inside the chassis, and the
player is meant to discover escalation by returning to a road, not by watching
it assemble behind them.

Checkpoint positions are seeded from the segment id, so a stretch of road always
fortifies in the same place — recognising it is part of learning the map.

Scenery now avoids the tarmac and the car spawns at a junction.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/physics/physics.test.ts

@@ -10,7 +10,9 @@ const IDLE: DriverInput = { throttle: 0, steer: 0, handbrake: false, respawn: fa
 
 /** Rapier runs headless, so vehicle tuning is checkable without a browser. */
 async function run(input: Partial<DriverInput>, seconds: number) {
-  const physics = await createPhysics(generateWorld(1, 0));
+  const world = generateWorld(1, 0);
+  const physics = await createPhysics(world);
+  const start = physics.chassis.translation();
   const state = createDriveState();
   const handling = deriveHandling(freshCondition());
   const cmd = { ...IDLE, ...input };
@@ -21,8 +23,10 @@ async function run(input: Partial<DriverInput>, seconds: number) {
     physics.step(STEP);
     maxYawRate = Math.max(maxYawRate, Math.abs(physics.chassis.angvel().y));
   }
+  const now = physics.chassis.translation();
   return {
-    pos: physics.chassis.translation(),
+    // Displacement from the spawn point, which is a road junction, not the origin.
+    pos: { x: now.x - start.x, y: now.y, z: now.z - start.z },
     speed: physics.vehicle.currentVehicleSpeed(),
     maxYawRate,
     grounded: [0, 1, 2, 3].every((i) => physics.vehicle.wheelIsInContact(i)),

src/physics/physics.ts

@@ -13,6 +13,18 @@ export interface PhysicsWorld {
   drainImpactForce(): number;
   step(dt: number): void;
   respawn(): void;
+  /** Static box, added and removed at runtime as road heat rises and falls. */
+  addStaticBox(box: StaticBox): RAPIER.RigidBody;
+  removeBody(body: RAPIER.RigidBody): void;
+}
+
+export interface StaticBox {
+  x: number;
+  z: number;
+  yaw: number;
+  width: number;
+  height: number;
+  depth: number;
 }
 
 /** Contacts weaker than this are just kerb-scrubbing, not damage. */
@@ -55,7 +67,7 @@ export async function createPhysics(model: WorldModel): Promise<PhysicsWorld> {
   // --- Car chassis ---
   const chassis = world.createRigidBody(
     RAPIER.RigidBodyDesc.dynamic()
-      .setTranslation(CAR.spawn.x, CAR.spawn.y, CAR.spawn.z)
+      .setTranslation(model.spawn.x, CAR.spawn.y, model.spawn.z)
       .setLinearDamping(0.1)
       .setAngularDamping(0.4)
       // The mass comes from here, not from collider density, so the centre of mass
@@ -127,8 +139,25 @@ export async function createPhysics(model: WorldModel): Promise<PhysicsWorld> {
       return v;
     },
 
+    addStaticBox(box) {
+      const body = world.createRigidBody(
+        RAPIER.RigidBodyDesc.fixed()
+          .setTranslation(box.x, box.height / 2, box.z)
+          .setRotation({ x: 0, y: Math.sin(box.yaw / 2), z: 0, w: Math.cos(box.yaw / 2) }),
+      );
+      world.createCollider(
+        RAPIER.ColliderDesc.cuboid(box.width / 2, box.height / 2, box.depth / 2).setFriction(0.8),
+        body,
+      );
+      return body;
+    },
+
+    removeBody(body) {
+      world.removeRigidBody(body);
+    },
+
     respawn() {
-      chassis.setTranslation({ x: CAR.spawn.x, y: CAR.spawn.y, z: CAR.spawn.z }, true);
+      chassis.setTranslation({ x: model.spawn.x, y: CAR.spawn.y, z: model.spawn.z }, true);
       chassis.setRotation({ x: 0, y: 0, z: 0, w: 1 }, true);
       chassis.setLinvel({ x: 0, y: 0, z: 0 }, true);
       chassis.setAngvel({ x: 0, y: 0, z: 0 }, true);