Please enable JavaScript to view the comments powered by Disqus.

Part 3: Phaser Multiplayer Game Tutorial: Storing game data in server, physics and collision

Implement game mechanics


Repository available here:

This is a continuation of a multiplayer game tutorial series with Phaser.js. We’ve implemented an authoritative server with the help of p2 physics in the server. We have some basic player movements, but our game is very boring at the moment.

In this part 3 tutorial, we’ll add some mechanics into our game. We’ll give the bigger player the ability to eat a smaller player to become a bigger circle.

New Client Side Script: colide.js

//we call this function when the main player colides with some other bodies.
function player_coll (body, bodyB, shapeA, shapeB, equation) {
	//the id of the collided body that player made contact with 
	var key =; 
	//the type of the body the player made contact with 
	var type = body.sprite.type; 
	if (type == "player_body") {
		//send the player collision
		socket.emit('player_collision', {id: key}); 

We created a colide.js script that will deal with collisions in the client side. Make sure to reference in index.html before main.js as

In the script, we added player_coll function, which is called on player collision. The parameter “body” is the phaser body that the main player collides with.

We first check to see if the colided body is actually a enemy player or not (Since we are adding other physics material later). If this body type (body.sprite.type) is a enemy player body, then we tell the server we made a collision. body.sprite.type will be more clear in main.js on the next section.

Client Side: main.js

var socket; 
socket = io.connect();

canvas_width = window.innerWidth * window.devicePixelRatio;
canvas_height = window.innerHeight * window.devicePixelRatio;

game = new Phaser.Game(canvas_width,canvas_height, Phaser.CANVAS, 'gameDiv');

//the enemy player list 
var enemies = [];

var gameProperties = { 
	gameWidth: 4000,
	gameHeight: 4000,
	game_elemnt: "gameDiv",
	in_game: false,

var main = function(game){

function onsocketConnected () {
	console.log("connected to server"); 
	gameProperties.in_game = true;
	// send the server our initial position and tell it we are connected
	socket.emit('new_player', {x: 0, y: 0, angle: 0});

// When the server notifies us of client disconnection, we find the disconnected
// enemy and remove from our game
function onRemovePlayer (data) {
	var removePlayer = findplayerbyid(;
	// Player not found
	if (!removePlayer) {
		console.log('Player not found: ',
	enemies.splice(enemies.indexOf(removePlayer), 1);

function createPlayer (data) {
	player =, 0);
	player.radius = data.size;

	// set a fill and line style
	player.lineStyle(2, 0xffd900, 1);
	player.drawCircle(0, 0, player.radius * 2);
	player.body_size = player.radius; 
	//set the initial size;
	player.initial_size = player.radius;

	// draw a shape
	game.physics.p2.enableBody(player, true);
	player.body.addCircle(player.body_size, 0 , 0);[0].sensor = true;
	//enable collision and when it makes a contact with another body, call player_coll
	player.body.onBeginContact.add(player_coll, this); 
	//We need this line to make camera follow player, Phaser.Camera.FOLLOW_LOCKON, 0.5, 0.5);

// this is the enemy class. 
var remote_player = function (id, startx, starty, startSize, start_angle) {
	this.x = startx;
	this.y = starty;
	//this is the unique socket id. We use it as a unique name for enemy = id;
	this.angle = start_angle;
	this.player = , this.y);
	//intialize the size with the server value
	this.player.radius = startSize

	// set a fill and line style
	this.player.lineStyle(2, 0xffd900, 1);
	this.player.drawCircle(0, 0, this.player.radius * 2);
	//we set the initial size;
	this.initial_size = startSize;
	//we set the body size to the current player radius
	this.player.body_size = this.player.radius; 
	this.player.type = "player_body"; =;

	// draw a shape
	game.physics.p2.enableBody(this.player, true);
	this.player.body.addCircle(this.player.body_size, 0 , 0);[0].sensor = true;

//Server will tell us when a new enemy player connects to the server.
//We create a new enemy in our game.
function onNewPlayer (data) {
	//enemy object 
	//the new parameter, data.size is used as initial circle size
	var new_enemy = new remote_player(, data.x, data.y, data.size, data.angle); 

//Server tells us there is a new enemy movement. We find the moved enemy
//and sync the enemy movement with the server
function onEnemyMove (data) {
	console.log("moving enemy");
	var movePlayer = findplayerbyid (; 
	if (!movePlayer) {
	var newPointer = {
		x: data.x,
		y: data.y, 
		worldX: data.x,
		worldY: data.y, 
	//check if the server enemy size is not equivalent to the client
	if (data.size != movePlayer.player.body_size) {
		movePlayer.player.body_size = data.size; 
		var new_scale = movePlayer.player.body_size / movePlayer.initial_size; 
		movePlayer.player.body.addCircle(movePlayer.player.body_size, 0 , 0);[0].sensor = true;
	var distance = distanceToPointer(movePlayer.player, newPointer);
	speed = distance/0.05;
	movePlayer.rotation = movetoPointer(movePlayer.player, speed, newPointer);

//we're receiving the calculated position from the server and changing the player position
function onInputRecieved (data) {
	//we're forming a new pointer with the new position
	var newPointer = {
		x: data.x,
		y: data.y, 
		worldX: data.x,
		worldY: data.y, 
	var distance = distanceToPointer(player, newPointer);
	//we're receiving player position every 50ms. We're interpolating 
	//between the current position and the new position so that player
	//does jerk. 
	speed = distance/0.05;
	//move to the new position. 
	player.rotation = movetoPointer(player, speed, newPointer);


//new function: This function is called when the player eats another player
function onGained (data) {
	//get the new body size from the server
	player.body_size = data.new_size;
	//get the new scale 
	var new_scale = data.new_size/player.initial_size;
	//set the new scale
	//create new circle body with the raidus of our player size
	player.body.addCircle(player.body_size, 0 , 0);[0].sensor = true;

//destroy our player when the server tells us he's dead
function onKilled (data) {

//This is where we use the socket id. 
//Search through enemies list to find the right enemy of the id.
function findplayerbyid (id) {
	for (var i = 0; i < enemies.length; i++) {
		if (enemies[i].id == id) {
			return enemies[i]; 

main.prototype = {
	preload: function() {
		game.stage.disableVisibilityChange = true;
		game.scale.scaleMode = Phaser.ScaleManager.RESIZE;, 0, gameProperties.gameWidth, gameProperties.gameHeight, false, false, false, false);
		game.physics.p2.setBoundsToWorld(false, false, false, false, false)
		game.physics.p2.gravity.y = 0;
		game.physics.p2.applyGravity = false; 
		game.physics.p2.enableBody(game.physics.p2.walls, false); 
		// physics start system

	create: function () {
		game.stage.backgroundColor = 0xE1A193;;
		console.log("client started");
		socket.on("connect", onsocketConnected); 
		//listen for main player creation
		socket.on("create_player", createPlayer);
		//listen to new enemy connections
		socket.on("new_enemyPlayer", onNewPlayer);
		//listen to enemy movement 
		socket.on("enemy_move", onEnemyMove);
		//when received remove_player, remove the player passed; 
		socket.on('remove_player', onRemovePlayer); 
		//when the player receives the new input
		socket.on('input_recieved', onInputRecieved);
		//when the player gets killed
		socket.on('killed', onKilled);
		//when the player gains in size
		socket.on('gained', onGained);
	update: function () {
		// emit the player input
		//move the player when the player is made 
		if (gameProperties.in_game) {
			//we're making a new mouse pointer and sending this input to 
			//the server.
			var pointer = game.input.mousePointer;
			//Send a new position data to the server 
			socket.emit('input_fired', {
				pointer_x: pointer.x, 
				pointer_y: pointer.y, 
				pointer_worldx: pointer.worldX, 
				pointer_worldy: pointer.worldY, 

var gameBootstrapper = {
    init: function(gameContainerElementId){
		game.state.add('main', main);


Two functions we added in our client side is onGained and onKilled. For this demo, we generate a random circle size in the server side to use it as an initial size. This will be more clear when we jump to the server side.

We get the initial circle size from the server and use it to initialize our player object in onCreatePlayer. In the last tutorial, we called onCreatePlayer when we connected to the server. We changed it so that we create a player when the server actually tells us to.

Next thing that we change is onEnemyMove function. We need to make sure we update all our enemies’ sizes when they change. You can see what we added to update the enemy’s size in onEnemyMove function.

We added player.body.onBeginContact.add(player_coll, this) to call a player_coll function when the player colides with other enemies. Make sure to add this.player.type = "player_body"; in remote_player function. This is to know what the player colided with during collision.

Moving on to Server side.

Server: App.js:

var express = require('express');
//require p2 physics library in the server.
var p2 = require('p2'); 

var app = express();
var serv = require('http').Server(app);
//get the functions required to move players in the server.
var physicsPlayer = require('./server/physics/playermovement.js');

app.get('/',function(req, res) {
	res.sendFile(__dirname + '/client/index.html');
app.use('/client',express.static(__dirname + '/client'));

serv.listen(process.env.PORT || 2000);
console.log("Server started.");

var player_lst = [];

//needed for physics update 
var startTime = (new Date).getTime();
var lastTime;
var timeStep= 1/70; 

//the physics world in the server. This is where all the physics happens. 
//we set gravity to 0 since we are just following mouse pointers.
var world = new p2.World({
  gravity : [0,0]

//a player class in the server
var Player = function (startX, startY, startAngle) {
  this.x = startX
  this.y = startY
  this.angle = startAngle
  this.speed = 500;
  //We need to intilaize with true.
  this.sendData = true;
  this.size = getRndInteger(40, 100); 
  this.dead = false;

//We call physics handler 60fps. The physics is calculated here. 
setInterval(physics_hanlder, 1000/60);

//Steps the physics world. 
function physics_hanlder() {
	var currentTime = (new Date).getTime();
	timeElapsed = currentTime - startTime;
	var dt = lastTime ? (timeElapsed - lastTime) / 1000 : 0;
    dt = Math.min(1 / 10, dt);

// when a new player connects, we make a new instance of the player object,
// and send a new player message to the client. 
function onNewplayer (data) {
	//new player instance
	var newPlayer = new Player(data.x, data.y, data.angle);
	//create an instance of player body 
	playerBody = new p2.Body ({
		mass: 0,
		position: [0,0],
		fixedRotation: true
	//add the playerbody into the player object 
	newPlayer.playerBody = playerBody;
	console.log("created new player with id " +; =; 	
	this.emit('create_player', {size: newPlayer.size});
	//information to be sent to all clients except sender
	var current_info = {
		x: newPlayer.x,
		y: newPlayer.y,
		angle: newPlayer.angle,
		size: newPlayer.size
	//send to the new player about everyone who is already connected. 	
	for (i = 0; i < player_lst.length; i++) {
		existingPlayer = player_lst[i];
		var player_info = {
			x: existingPlayer.x,
			y: existingPlayer.y, 
			angle: existingPlayer.angle,	
			size: existingPlayer.size
		console.log("pushing player");
		//send message to the sender-client only
		this.emit("new_enemyPlayer", player_info);
	//send message to every connected client except the sender
	this.broadcast.emit('new_enemyPlayer', current_info);


//instead of listening to player positions, we listen to user inputs 
function onInputFired (data) {
	var movePlayer = find_playerid(,; 
	if (!movePlayer || movePlayer.dead) {
		console.log('no player'); 

	//when sendData is true, we send the data back to client. 
	if (!movePlayer.sendData) {
	//every 50ms, we send the data. 
	setTimeout(function() {movePlayer.sendData = true}, 50);
	//we set sendData to false when we send the data. 
	movePlayer.sendData = false;
	//Make a new pointer with the new inputs from the client. 
	//contains player positions in server
	var serverPointer = {
		x: data.pointer_x,
		y: data.pointer_y,
		worldX: data.pointer_worldx, 		
		worldY: data.pointer_worldy
	//moving the player to the new inputs from the player
	if (physicsPlayer.distanceToPointer(movePlayer, serverPointer) <= 30) {
		movePlayer.playerBody.angle = physicsPlayer.movetoPointer(movePlayer, 0, serverPointer, 1000);
	} else {
		movePlayer.playerBody.angle = physicsPlayer.movetoPointer(movePlayer, movePlayer.speed, serverPointer);	
	movePlayer.x = movePlayer.playerBody.position[0]; 
	movePlayer.y = movePlayer.playerBody.position[1];
	//new player position to be sent back to client. 
	var info = {
		x: movePlayer.playerBody.position[0],
		y: movePlayer.playerBody.position[1],
		angle: movePlayer.playerBody.angle

	//send to sender (not to every clients). 
	this.emit('input_recieved', info);
	//data to be sent back to everyone except sender 
	var moveplayerData = {
		x: movePlayer.playerBody.position[0],
		y: movePlayer.playerBody.position[1],
		angle: movePlayer.playerBody.angle,
		size: movePlayer.size
	//send to everyone except sender 
	this.broadcast.emit('enemy_move', moveplayerData);

function onPlayerCollision (data) {
	var movePlayer = find_playerid(; 
	var enemyPlayer = find_playerid(; 
	if (movePlayer.dead || enemyPlayer.dead)
	if (!movePlayer || !enemyPlayer)

	if (movePlayer.size == enemyPlayer)
	//the main player size is less than the enemy size
	else if (movePlayer.size < enemyPlayer.size) {
		var gained_size = movePlayer.size / 2;
		enemyPlayer.size += gained_size; 
		//provide the new size the enemy will become
		this.broadcast.emit('remove_player', {id:});"gained", {new_size: enemyPlayer.size}); 
	} else {
		var gained_size = enemyPlayer.size / 2;
		movePlayer.size += gained_size;
		this.emit('remove_player', {id:}); 
		this.emit("gained", {new_size: movePlayer.size});"killed"); 
		//send to everyone except sender.
		this.broadcast.emit('remove_player', {id:});
	console.log("someone ate someone!!!");

function playerKilled (player) {
	player.dead = true; 

function getRndInteger(min, max) {
    return Math.floor(Math.random() * (max - min + 1) ) + min;

//call when a client disconnects and tell the clients except sender to remove the disconnected player
function onClientdisconnect() {

	var removePlayer = find_playerid(; 
	if (removePlayer) {
		player_lst.splice(player_lst.indexOf(removePlayer), 1);
	console.log("removing player " +;
	//send message to every connected client except the sender
	this.broadcast.emit('remove_player', {id:});

// find player by the the unique socket id 
function find_playerid(id) {

	for (var i = 0; i < player_lst.length; i++) {

		if (player_lst[i].id == id) {
			return player_lst[i]; 
	return false; 

 // io connection 
var io = require('')(serv,{});

io.sockets.on('connection', function(socket){
	console.log("socket connected"); 
	// listen for disconnection; 
	socket.on('disconnect', onClientdisconnect); 
	// listen for new player
	socket.on("new_player", onNewplayer);
	//we dont need this anymore
	socket.on("move_player", onMovePlayer);
	//listen for new player inputs. 
	socket.on("input_fired", onInputFired);
	//listen for player collision
	socket.on("player_collision", onPlayerCollision);


In the server side, app.js, we added onPlayerCollision function, which is called when the player in the client makes a collision with another enemy.

Next thing we added is getRndInteger function to generate a random player size in the beginning for a demo purpose. This is to make sure bigger player eats a smaller player. We use this random integer in the Player function (class) as this.size = getRndInteger(40, 100);.

Last thing we need is “dead” property in the Player function. We need this to keep track of player’s state.

Now type in "node app" in the command, open two clients and eat each other!!!!

And that’s it for this part of the tutorial!. We added some simple game mechanics like In the next tutorial, we’ll generate “food”, and keep track of its quantity throughout the game.

<< Part 2 Part 4 >>