smartgame/js/traits/TPhysics.js

import {Trait} from "../Entity.js";
import Vec2 from "../Vec2.js";

let zeroVector = new Vec2(0, 0);

export default class TPhysics extends Trait {
	constructor(entity) {
		super(entity, "physics");

		this.velocity = new Vec2();
		this.gravity = 40;
		this.groundFriction = 6;
		this.airFriction = 2;

		this.timeLastOnGround = 0;
		this.onGround = false;
		this.groundBounds = null;
		this.groundVelocity = null;
	}

	collideTop(bounds, velocity) {
		if (!this.groundBounds || bounds.top < this.groundBounds.top) {
			this.groundBounds = bounds;
			this.groundVelocity = velocity;
		}
	}

	collideWall(bounds, velocity) {
		let side = this.entity.bounds.intersectSide(bounds);

		if (side === "top")
			return this.collideTop(bounds, velocity);
	}

	collidePlatform(bounds, velocity) {
		let side = this.entity.bounds.intersectSide(bounds);

		if (side === "top")
			return this.collideTop(bounds, velocity);
	}

	update(dt) {

		// Collide
		if (this.entity.has("collider")) {
			let collider = this.entity.t.collider;
			this.groundBounds = null;
			this.groundVelocity = null;

			collider.entities.forEach(e => {
				let vel = zeroVector;
				if (e.has("physics"))
					vel = e.t.physics.velocity;

				if (e.has("wall"))
					this.collideWall(e.bounds, vel);
				else if (e.has("platform"))
					this.collidePlatform(e.bounds, vel);
			});
			collider.structures.forEach((s, i) => {
				let bounds = collider.structureBounds[i];
				if (s.attrs.wall)
					this.collideWall(bounds, zeroVector);
				else if (s.attrs.platform)
					this.collidePlatform(bounds, zeroVector);
			});
		}

		this.onGround =
			(this.groundVelocity && this.velocity.y >= this.groundVelocity.y);

		if (this.onGround) {
			this.timeLastOnGround = this.entity.time;
			this.velocity.y = this.groundVelocity.y;
		}

		if (!this.onGround)
			this.velocity.y += this.gravity * dt;

		// Apply friction
		var fric = this.onGround ? this.groundFriction : this.airFriction;
		var xRatio = 1 / (1 + (dt * fric));
		this.velocity.x *= xRatio;
	}

	postUpdate(dt) {

		// Move
		this.entity.bounds.pos.x += this.velocity.x * dt;
		this.entity.bounds.pos.y += this.velocity.y * dt;

		if (this.onGround)
			this.entity.bounds.bottom = this.groundBounds.top;
	}
}