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import { System, SystemNames } from ".";
import {
Acceleration,
BoundingBox,
ComponentNames,
Forces,
Gravity,
Velocity,
Mass,
Jump,
} from "../components";
import { PhysicsConstants } from "../config";
import type { Entity } from "../entities";
import type { Force2D } from "../interfaces";
export class Physics extends System {
constructor() {
super(SystemNames.Physics);
}
public update(
dt: number,
entityMap: Map<number, Entity>,
componentEntities: Map<string, Set<number>>
): void {
componentEntities.get(ComponentNames.Forces)?.forEach((entityId) => {
const entity = entityMap.get(entityId);
const mass = entity.getComponent<Mass>(ComponentNames.Mass).mass;
const forces = entity.getComponent<Forces>(ComponentNames.Forces).forces;
const velocity = entity.getComponent<Velocity>(ComponentNames.Velocity);
const inertia = entity.getComponent<Moment>(
ComponentNames.Moment
).inertia;
// F_g = mg, applied only until terminal velocity is reached
if (entity.hasComponent(ComponentNames.Gravity)) {
const gravity = entity.getComponent<Gravity>(ComponentNames.Gravity);
if (velocity.dCartesian.dy <= gravity.terminalVelocity) {
forces.push({
fCartesian: {
fy: mass * PhysicsConstants.GRAVITY,
},
});
}
}
// ma = Σ(F), Iα = Σ(T)
const sumOfForces = forces.reduce(
(accum: Force2D, { fCartesian, torque }: Force2D) => ({
fCartesian: {
fx: accum.fCartesian.fx + (fCartesian?.fx ?? 0),
fy: accum.fCartesian.fy + (fCartesian?.fy ?? 0),
},
torque: accum.torque + (torque ?? 0),
}),
{ fCartesian: { fx: 0, fy: 0 }, torque: 0 }
);
// integrate accelerations
const [ddy, ddx] = [
sumOfForces.fCartesian.fy,
sumOfForces.fCartesian.fx,
].map((x) => x / mass);
velocity.dCartesian.dx += ddx * dt;
velocity.dCartesian.dy += ddy * dt;
velocity.dTheta += (sumOfForces.torque * dt) / inertia;
// clear the forces
entity.getComponent<Forces>(ComponentNames.Forces).forces = [];
// maybe we fell off the floor
if (ddy > 0 && entity.hasComponent(ComponentNames.Jump)) {
entity.getComponent<Jump>(ComponentNames.Jump).canJump = false;
}
});
componentEntities.get(ComponentNames.Velocity)?.forEach((entityId) => {
const entity = entityMap.get(entityId);
const velocity = entity.getComponent<Velocity>(ComponentNames.Velocity);
const boundingBox = entity.getComponent<BoundingBox>(
ComponentNames.BoundingBox
);
// integrate velocity
boundingBox.center.x += velocity.dCartesian.dx * dt;
boundingBox.center.y += velocity.dCartesian.dy * dt;
boundingBox.rotation += velocity.dTheta * dt;
boundingBox.rotation =
(boundingBox.rotation < 0
? 360 + boundingBox.rotation
: boundingBox.rotation) % 360;
});
}
}
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