add start of box2d physics

server/game/room/world/physics.js

@@ -0,0 +1,48 @@
+'use strict';
+
+// This file is very similar, but not identical to its client counterpart
+// so most changes done to it should be mirrored there to keep consistent
+// physics between client and server.
+
+const Box2D = require('box2d-html5');
+
+const b2Vec2 = Box2D.b2Vec2;
+
+class Physics {
+	constructor() {
+		this.world = new Box2D.b2World(new b2Vec2(0, 0), false);
+	}
+
+	createBody(body) {
+		let bodyDef = new Box2D.b2BodyDef();
+		bodyDef.userData = body;
+		bodyDef.position = new b2Vec2(body.x || 0, body.y || 0);
+		bodyDef.fixedRotation = false;
+		bodyDef.active = true;
+		bodyDef.linearVelocity = new b2Vec2(body.xvel || 0, body.yvel || 0);
+		bodyDef.angularVelocity = body.rvel || 0;
+		bodyDef.type = body.type == 'static' ?
+			Box2D.b2Body.b2_staticBody : Box2D.b2Body.b2_dynamicBody;
+		let b2body = this.world.CreateBody(bodyDef);
+
+		let fixtureDef = new Box2D.b2FixtureDef();
+		fixtureDef.density = 10;
+		fixtureDef.friction = 1;
+		fixtureDef.restitution = 0;
+
+		for (var poly of body.structure) {
+			poly.map(vertex => new b2Vec2(vertex[0], vertex[1]));
+			fixtureDef.shape = new Box2D.b2PolygonShape();
+			fixtureDef.shape.SetAsArray(poly, poly.length);
+			b2body.CreateFixture(fixtureDef);
+		}
+
+		body.b2body = b2body;
+	}
+
+	step() {
+		this.world.Step(1, 5, 1 / 60);
+	}
+}
+
+module.exports = Physics;