Create an Animated Physics Game with JavaScript

Bybomber bot

JavaScript has become one of the most popular programming languages for game development in recent years, especially for browser-based games. By leveraging web technologies like HTML5 canvas and JavaScript physics libraries, developers can create engaging, dynamic games with realistic physics simulations.

In this article, we‘ll explore the process of building an animated physics game using vanilla JavaScript. Whether you‘re an experienced JavaScript developer looking to get into game development or a beginner eager to learn, this guide will walk you through the key concepts and techniques you need to create your own physics-based masterpiece.

Tools & Technologies

To create a physics game with JavaScript, you‘ll need a basic understanding of web technologies like HTML and CSS. The game itself will be rendered on an HTML5 canvas element, which provides a drawing surface for graphics.

JavaScript will be used to program the game logic, handle user input, and animate the game objects. While you can certainly write all the physics code from scratch, it‘s often easier to utilize existing physics libraries. Some popular open-source options include:

  • Matter.js – A 2D rigid body physics engine
  • Box2D – A 2D physics engine originally written in C++, with JavaScript ports available
  • Planck.js – A JavaScript rewrite of Box2D
  • P2.js – A 2D physics library that uses shape-based collision detection

These libraries handle complex calculations for things like gravity, friction, collisions, constraints, and more. They provide APIs to create and manipulate physical bodies in your game world.

In addition to a physics library, you may want to use a game framework or engine to simplify common game development tasks. Some lightweight, JavaScript-friendly options are:

  • Phaser – A fast, free, open-source framework for Canvas and WebGL powered games
  • Playground.js – A framework for quick game prototyping and development
  • Crafty – A flexible, lightweight framework for 2D games

However, for the sake of learning, this guide will focus on building a game from scratch using vanilla JavaScript.

Game Development Process

The game development process typically involves the following steps:

  1. Conceptualization – Come up with a game concept or idea. Determine the basic gameplay, objectives, and mechanics.

  2. Design – Flesh out the details of your game concept. Create sketches, sprites, and other artwork. Map out levels and stages. Write out the game rules and logic.

  3. Development – Write code to bring your game design to life. Create the game world, characters, and objects. Program the game rules, physics, and interactivity.

  4. Testing – Play through your game at various stages to identify bugs and areas for improvement. Have others test the game and provide feedback.

  5. Launch – Once the game is polished and ready, release it on the web, mobile app stores, or other platforms for players to enjoy.

  6. Maintenance – After launch, continue to gather player feedback, fix bugs, and release updates to keep your game fresh and compatible with new devices/platforms.

Of course, the process is often iterative and stages may overlap. Prototyping, for example, is a crucial step that involves creating a basic playable version to test your core game mechanic. You may go through several prototypes before settling on a final design.

Building a Simple Physics Game

Now let‘s walk through the process of actually building a simple physics-based game with JavaScript. Our example game will have a player-controlled character that can jump and collide with platforms.

HTML Setup

First, create an HTML file with a canvas element to serve as the game container:

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Physics Game</title>
<style>
body {
margin: 0;
overflow: hidden;
}
canvas {
background: black;
}
</style>
</head>
<body>
<canvas id="gameCanvas"></canvas>

<script src="physics.js"></script>
<script src="game.js"></script>
</body>
</html>

The physics.js file will contain our physics simulation code, while game.js will hold the game-specific logic.

Physics & Game Objects

In our physics.js file, we‘ll define a simple vector class to represent positions and velocities:

class Vector {
constructor(x = 0, y = 0) {
this.x = x;
this.y = y;
}

add(v) {
return new Vector(this.x + v.x, this.y + v.y);
}

subtr(v) {
return new Vector(this.x – v.x, this.y – v.y);
}

mag() {
return Math.sqrt(this.x2 + this.y2);
}

mult(n) {
return new Vector(this.xn, this.yn);
}

normal() {
return new Vector(-this.y, this.x).unit();
}

unit() {
if(this.mag() === 0) {
return new Vector(0,0);
} else {
return new Vector(this.x/this.mag(), this.y/this.mag());
}
}
}

Next, we‘ll create a basic rigid body class to represent the physical objects in our game:

class Body {
constructor(x, y, w, h) {
this.pos = new Vector(x, y);
this.vel = new Vector();
this.width = w;
this.height = h;
this.mass = w*h;
}

applyForce(f) {
let a = f.mult(1/this.mass);
this.vel = this.vel.add(a);
}

update() {
// Update velocity based on gravity
this.applyForce(new Vector(0, 0.2));

// Update position based on velocity
this.pos = this.pos.add(this.vel);

}

draw(ctx) {
ctx.fillStyle = "white";
ctx.fillRect(this.pos.x, this.pos.y, this.width, this.height);
}
}

In our game.js file, we can create some bodies to represent the player character and platforms:

const canvas = document.getElementById("gameCanvas");
const ctx = canvas.getContext("2d");
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;

let player;
let platforms = [];

function reset() {
player = new Body(50, 50, 20, 40);

platforms = [
new Body(0, canvas.height-10, canvas.width, 10),
new Body(canvas.width/2, canvas.height/2, 100, 10),
];
}

function update() {
player.update();

for(let i = 0; i < platforms.length; i++) {
platforms[i].draw(ctx);
}

player.draw(ctx);

requestAnimationFrame(update);
}

reset();
requestAnimationFrame(update);

Player Controls

To let the player control the character, we‘ll add event listeners for keyboard input:

const JUMP_SPEED = -5;
const MOVE_SPEED = 0.5;

let keyState = {};

window.addEventListener(‘keydown‘, (e) => {
keyState[e.code] = true;
});

window.addEventListener(‘keyup‘, (e) => {
keyState[e.code] = false;
});

function controls() {
if(keyState[‘ArrowLeft‘]) {
player.vel.x -= MOVE_SPEED;
}

if(keyState[‘ArrowRight‘]) {
player.vel.x += MOVE_SPEED;
}

if(keyState[‘Space‘] && isOnGround()) {
player.vel.y = JUMP_SPEED;
}

player.vel.x *= 0.9; // Friction
}

function isOnGround() {
for(let i = 0; i < platforms.length; i++) {
let p = platforms[i];
if(player.pos.y + player.height >= p.pos.y &&
player.pos.y + player.height <= p.pos.y + p.height &&
player.pos.x + player.width >= p.pos.x &&
player.pos.x <= p.pos.x + p.width) {
return true;
}
}
return false;
}

Don‘t forget to call the controls() function from the update() loop.

Collision Detection

To prevent the player from falling through platforms, we need to add collision detection and response:

function collide(b1, b2) {
return b1.pos.x + b1.width >= b2.pos.x &&
b1.pos.x <= b2.pos.x + b2.width &&
b1.pos.y + b1.height >= b2.pos.y &&
b1.pos.y <= b2.pos.y + b2.height;
}

function resolveCollision(b1, b2) {
const w = 0.5 (b1.width + b2.width);
const h = 0.5 (b1.height + b2.height);
const dx = (b1.pos.x + b1.width/2) – (b2.pos.x + b2.width/2);
const dy = (b1.pos.y + b1.height/2) – (b2.pos.y + b2.height/2);

const wy = w dy;
const hx = h dx;

if(wy > hx) {
if(wy > -hx) {
// Bottom
b1.pos.y = b2.pos.y + b2.height;
b1.vel.y = 0;
} else {
// Left
b1.pos.x = b2.pos.x – b1.width;
b1.vel.x = 0;
}
} else {
if(wy > -hx) {
// Right
b1.pos.x = b2.pos.x + b2.width;
b1.vel.x = 0;
} else {
// Top
b1.pos.y = b2.pos.y – b1.height;
b1.vel.y = 0;
}
}
}

function checkCollisions() {
for(let i = 0; i < platforms.length; i++) {
if(collide(player, platforms[i])) {
resolveCollision(player, platforms[i]);
}
}
}

Add a call to checkCollisions() in the update() function.

Graphics & Sound

To make the game more visually appealing, you can load sprite images for the player character and platforms. Use the drawImage() method to render them on the canvas.

You can also add sound effects using the Web Audio API. Load audio files and play them at the appropriate times, such as when the player jumps or lands on a platform.

Advanced Techniques

Once you have the basics down, you can explore more advanced physics game development techniques:

  • Soft body physics – Simulate deformable bodies like cloth, ropes, and jelly
  • Particle systems – Create visual effects like explosions, fire, and smoke
  • Destructible terrain – Let the player destroy or modify the game environment
  • Procedural generation – Automatically generate levels, landscapes, and other game content
  • Scripting – Allow players to create their own game modes and behaviors using scripting languages

Popular Libraries & Engines

In addition to the ones mentioned earlier, here are a few more notable physics libraries and game engines for JavaScript:

  • Cannon.js – A lightweight and simple 3D physics engine
  • Ammo.js – A direct port of the Bullet physics engine to JavaScript, using Emscripten
  • Three.js – A powerful 3D graphics library that pairs well with physics engines
  • Babylon.js – A complete 3D game engine with a built-in physics engine

Each has its own strengths and weaknesses, so research and experiment to find the right tools for your game development needs.

Learning Resources

To dive deeper into JavaScript game development, check out these resources:

With a solid understanding of JavaScript and a curious mind, you can start creating amazing physics games in no time. So dive in, have fun, and happy coding!

Conclusion

Building a physics game with JavaScript is a fun and rewarding experience that exercises your creativity and problem-solving skills.

By working with HTML5 canvas, physics engines, and JavaScript game frameworks, you can craft performant, engaging games that run right in the browser.

Start simple, experiment often, and don‘t be afraid to make mistakes. Seek out online tutorials, code samples, and communities to learn from.

Remember, game development is an iterative process. Prototype, playtest, and polish until you have something you‘re proud to share with the world.

We covered a lot of ground in this article, but there‘s so much more to explore. From here, you can dive into multiplayer networking, 3D graphics, VR/AR integration, and other cutting-edge web game technologies.

The most important thing is to enjoy the journey and express your creativity through code. So what are you waiting for? Go make something awesome!

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