RoadHazard

RoadHazard

Oil slicks, smoke clouds and bomb craters left lying on the road.

What it does

• An oil slick spins a car out, once per car per slick. The side the car enters on decides which way.
• A smoke cloud blinds an AI driver while it is inside, and for blindSeconds after.
• A crater jolts a car and damages it on the way in.

Each hazard is a pooled entity that lives life seconds and shrinks away over the last fade. Lay one with dropHazard. A bomb that bursts on the road turns into a crater from a pool named crater, if the scene has one. Whoever laid a hazard is safe from it for its first 1.5 seconds, so the player does not spin on the oil they just dropped.

Use it in a scene

{
  "OilBlueprint": {
    "tags": ["hazard"],
    "components": {
      "Pool": { "name": "oil", "size": 14 },
      "MeshPrimitive": {
        "primitive": "cylinder",
        "diameter": 5.4,
        "height": 0.03,
        "material": {
          "diffuseColor": [0.02, 0.02, 0.025],
          "specularColor": [0.8, 0.8, 0.85]
        }
      },
      "RoadHazard": { "kind": "oil", "radius": 2.7, "life": 16 }
    }
  },
  "CraterBlueprint": {
    "tags": ["hazard"],
    "components": {
      "Pool": { "name": "crater", "size": 10 },
      "MeshPrimitive": {
        "primitive": "cylinder",
        "diameter": 4.6,
        "height": 0.03,
        "material": { "diffuseColor": [0.09, 0.07, 0.06] }
      },
      "RoadHazard": {
        "kind": "crater",
        "radius": 2.2,
        "life": 30,
        "fade": 2,
        "spin": 3,
        "damage": 12
      }
    }
  }
}

Lay one from code with the helper in RoadHazard.defs:

export function dropHazard(world: World, pool: string, x: number, z: number, owner: string, yaw = 0): Entity | null {
  const e = world.acquire(pool, { x, y: 0.02, z });
  if (!e) return null;
  const h = e.get(RoadHazardComponent);
  if (h) h.owner = owner;
  const mp = e.get(MeshPrimitiveComponent);
  if (mp) mp.rotation[1] = yaw;
  return e;
}

dropHazard(world, 'oil', x, z, owner) lays a slick from the oil pool at (x, z). It returns null if the pool is not up yet.

Which way oil spins

A car that clips the left edge of a slick should spin the other way from one that clips the right edge. oilSpin works that out with one dot product:

export function oilSpin(carX: number, carZ: number, heading: number, hx: number, hz: number, strength: number): number {
  const rx = Math.cos(heading), rz = -Math.sin(heading);
  const side = (hx - carX) * rx + (hz - carZ) * rz;
  return (side >= 0 ? 1 : -1) * strength;
}

(rx, rz) points straight across the car, so the sign of side says which half of the slick the car came in on. Every spin is the same size: spin rad/s, with no grip for slipSeconds. Each slick keeps a set of the cars it has spun, so a car that sits in the oil for 30 frames spins once, not 30 times. A crater uses the same sum at 0.4 of its spin for 0.3 seconds, which reads as a jolt.

How a hazard fades

  const g = grow > 0 ? Math.min(1, age / grow) : 1;
  const left = life - age;
  const f = fade > 0 ? Math.min(1, left / fade) : 1;
  return Math.max(0.001, (0.35 + 0.65 * g) * f);

A new slick starts at 35% size and spreads to full in a quarter second. Take the defaults, a 14 s life and a 1.5 s fade. At 13 seconds the slick has 1 second left, so it is at two thirds of full size. Its 2.6 m reach shrinks to 1.7 m, plus 0.6 m of slack for the car's body. A dying slick looks smaller and is a smaller trap.

Settings

Events

RoadFX draws the smoke cloud off roadHazard.laid. A director reads owner on roadHazard.entered to credit a kill to whoever laid the slick.

Needs

• MeshPrimitive draws the hazard and gives each car's position.
• CarDrive marks which entities are cars, and gives their heading.
• CarCollision takes the spin, skips ghost cars, and scales crater damage by damageTaken.
• AutoRunnerDriver takes the blind from smoke.
• Health takes crater damage.