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.gravity = 40;
		this.groundFriction = 6;
		this.airFriction = 2;

		this.absVelocity = new Vec2();
		this.velocity = new Vec2();

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

	collideTop(bounds, absVelocity) {
		if (this.onGround || bounds === this.oldGroundBounds)
			return;

		this.onGround = true;
		this.groundBounds = bounds;
		this.groundVelocity = absVelocity;

		this.velocity.x -= absVelocity.x;
		this.velocity.y = 0;
		this.entity.bounds.bottom = bounds.top;
	}

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

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

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

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

	update(dt) {

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

		if (this.entity.has("collider")) {

			let jumping =
				this.groundVelocity &&
				this.velocity.y < this.groundVelocity.y;

			// Check if we're still on the same ground
			if (this.onGround) {
				let stillOnGround =
					(this.entity.bounds.intersects(this.groundBounds)) &&
					(this.entity.bounds.intersectSide(this.groundBounds) === "top") &&
					!jumping;

				if (stillOnGround) {
					this.entity.bounds.bottom = this.groundBounds.top;
				} else {
					this.velocity.x += this.groundVelocity.x;
					this.velocity.y += this.groundVelocity.y;

					this.onGround = false;
					this.oldGroundBounds = this.groundBounds;
					this.groundBounds = null;
					this.groundVelocity = null;
				}
			}

			// Collide with new stuff
			if (!jumping) {
				let collider = this.entity.t.collider;
				collider.entities.forEach(e => {
					let vel;
					if (e.has("physics"))
						vel = e.t.physics.absVelocity;
					else
						vel = zeroVector;

					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.oldGroundBounds = null;
		}

		// Track the last time we were on the ground
		if (this.onGround)
			this.timeLastOnGround = this.entity.time;

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

	postUpdate(dt) {
		this.jumped = false;

		// Update absVelocity
		if (this.onGround) {
			this.absVelocity.x = this.velocity.x + this.groundVelocity.x;
			this.absVelocity.y = this.velocity.y + this.groundVelocity.y;
		} else {
			this.absVelocity.x = this.velocity.x;
			this.absVelocity.y = this.velocity.y;
		}

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