JavaScript Asteroids
In this one video I make Asteroids using pure JavaScript. I structured everything so you will completely understand every line of code.
If you want to make games you have to know how to make Asteroids! It requires you to understand moving in a 3D space, collision detection, inertia, velocity, rotating shapes using math instead of rotating the canvas, reacting immediately to user input, animating polygons, creating and destroying objects, trigonometry, and numerous other related topics!
Unlike most everyone I take the time to edit my videos. That means I cover the same amount in 1/3rd of the time. I provide all the heavily commented code below. For best results print it out and pause your way through the video while taking notes. The Asteroids game is available here to play.
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Code from Video
I added the homework solutions to the code below
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ASTEROIDS.HTML <!doctype html> <html lang="en"> <head> <meta charset="utf-8"> <meta name="viewport" content="width = device-width, initial-scale = 1"> <title>JavaScript Asteroids</title> <link rel="stylesheet" type="text/css" href="style.css"> <script src="asteroids.js"></script> </head> <body> <div id='container'> <canvas id='my-canvas' ></canvas> </div> </body> </html> STYLE.CSS body{ background: #000; } #container { max-width: 1400px; margin: auto; } #my-canvas { background: #000; } ASTEROIDS.JS let canvas; let ctx; let canvasWidth = 1400; let canvasHeight = 1000; let keys = []; let ship; let bullets = []; let asteroids = []; let score = 0; let lives = 3; // HOMEWORK SOLUTION - Contributed by luckyboysunday let highScore; let localStorageName = "HighScore"; document.addEventListener('DOMContentLoaded', SetupCanvas); function SetupCanvas(){ canvas = document.getElementById("my-canvas"); ctx = canvas.getContext("2d"); canvas.width = canvasWidth; canvas.height = canvasHeight; ctx.fillStyle = "black"; ctx.fillRect(0, 0, canvas.width, canvas.height); ship = new Ship(); for(let i = 0; i < 8; i++){ asteroids.push(new Asteroid()); } // Store all possible keycodes in an array so that // multiple keys can work at the same time // document.body.addEventListener("keydown", function(e) { // keys[e.keyCode] = true; // }); // document.body.addEventListener("keyup", function(e) { // keys[e.keyCode] = false; // if (e.keyCode === 32){ // bullets.push(new Bullet(ship.angle)); // } // }); document.body.addEventListener("keydown", HandleKeyDown); document.body.addEventListener("keyup", HandleKeyUp); // HOMEWORK SOLUTION - Contributed by luckyboysunday // Retrieves locally stored high scores if (localStorage.getItem(localStorageName) == null) { highScore = 0; } else { highScore = localStorage.getItem(localStorageName); } Render(); } // HOMEWORK SOLUTION // Move event handling functions so that we can turn off // event handling if game over is reached function HandleKeyDown(e){ keys[e.keyCode] = true; } function HandleKeyUp(e){ keys[e.keyCode] = false; if (e.keyCode === 32){ bullets.push(new Bullet(ship.angle)); } } class Ship { constructor() { this.visible = true; this.x = canvasWidth / 2; this.y = canvasHeight / 2; this.movingForward = false; this.speed = 0.1; this.velX = 0; this.velY = 0; this.rotateSpeed = 0.001; this.radius = 15; this.angle = 0; this.strokeColor = 'white'; // Used to know where to fire the bullet from this.noseX = canvasWidth / 2 + 15; this.noseY = canvasHeight / 2; } Rotate(dir) { this.angle += this.rotateSpeed * dir; } Update() { // Get current direction ship is facing let radians = this.angle / Math.PI * 180; // If moving forward calculate changing values of x & y // If you want to find the new point x use the // formula oldX + cos(radians) * distance // Forumla for y oldY + sin(radians) * distance if (this.movingForward) { this.velX += Math.cos(radians) * this.speed; this.velY += Math.sin(radians) * this.speed; } // If ship goes off board place it on the opposite // side if (this.x < this.radius) { this.x = canvas.width; } if (this.x > canvas.width) { this.x = this.radius; } if (this.y < this.radius) { this.y = canvas.height; } if (this.y > canvas.height) { this.y = this.radius; } // Slow ship speed when not holding key this.velX *= 0.99; this.velY *= 0.99; // Change value of x & y while accounting for // air friction this.x -= this.velX; this.y -= this.velY; } Draw() { ctx.strokeStyle = this.strokeColor; ctx.beginPath(); // Angle between vertices of the ship let vertAngle = ((Math.PI * 2) / 3); let radians = this.angle / Math.PI * 180; // Where to fire bullet from this.noseX = this.x - this.radius * Math.cos(radians); this.noseY = this.y - this.radius * Math.sin(radians); for (let i = 0; i < 3; i++) { ctx.lineTo(this.x - this.radius * Math.cos(vertAngle * i + radians), this.y - this.radius * Math.sin(vertAngle * i + radians)); } ctx.closePath(); ctx.stroke(); } } class Bullet{ constructor(angle) { this.visible = true; this.x = ship.noseX; this.y = ship.noseY; this.angle = angle; this.height = 4; this.width = 4; this.speed = 5; this.velX = 0; this.velY = 0; } Update(){ let radians = this.angle / Math.PI * 180; this.x -= Math.cos(radians) * this.speed; this.y -= Math.sin(radians) * this.speed; } Draw(){ ctx.fillStyle = 'white'; ctx.fillRect(this.x,this.y,this.width,this.height); } } class Asteroid{ constructor(x,y,radius,level,collisionRadius) { this.visible = true; this.x = x || Math.floor(Math.random() * canvasWidth); this.y = y || Math.floor(Math.random() * canvasHeight); this.speed = 3; this.radius = radius || 50; this.angle = Math.floor(Math.random() * 359); this.strokeColor = 'white'; this.collisionRadius = collisionRadius || 46; // Used to decide if this asteroid can be broken into smaller pieces this.level = level || 1; } Update(){ let radians = this.angle / Math.PI * 180; this.x += Math.cos(radians) * this.speed; this.y += Math.sin(radians) * this.speed; if (this.x < this.radius) { this.x = canvas.width; } if (this.x > canvas.width) { this.x = this.radius; } if (this.y < this.radius) { this.y = canvas.height; } if (this.y > canvas.height) { this.y = this.radius; } } Draw(){ ctx.beginPath(); let vertAngle = ((Math.PI * 2) / 6); var radians = this.angle / Math.PI * 180; for(let i = 0; i < 6; i++){ ctx.lineTo(this.x - this.radius * Math.cos(vertAngle * i + radians), this.y - this.radius * Math.sin(vertAngle * i + radians)); } ctx.closePath(); ctx.stroke(); } } function CircleCollision(p1x, p1y, r1, p2x, p2y, r2){ let radiusSum; let xDiff; let yDiff; radiusSum = r1 + r2; xDiff = p1x - p2x; yDiff = p1y - p2y; if (radiusSum > Math.sqrt((xDiff * xDiff) + (yDiff * yDiff))) { return true; } else { return false; } } // Handles drawing life ships on screen function DrawLifeShips(){ let startX = 1350; let startY = 10; let points = [[9, 9], [-9, 9]]; ctx.strokeStyle = 'white'; // Stroke color of ships // Cycle through all live ships remaining for(let i = 0; i < lives; i++){ // Start drawing ship ctx.beginPath(); // Move to origin point ctx.moveTo(startX, startY); // Cycle through all other points for(let j = 0; j < points.length; j++){ ctx.lineTo(startX + points[j][0], startY + points[j][1]); } // Draw from last point to 1st origin point ctx.closePath(); // Stroke the ship shape white ctx.stroke(); // Move next shape 30 pixels to the left startX -= 30; } } function Render() { // Check if the ship is moving forward ship.movingForward = (keys[87]); if (keys[68]) { // d key rotate right ship.Rotate(1); } if (keys[65]) { // a key rotate left ship.Rotate(-1); } ctx.clearRect(0, 0, canvasWidth, canvasHeight); // Display score ctx.fillStyle = 'white'; ctx.font = '21px Arial'; ctx.fillText("SCORE : " + score.toString(), 20, 35); // If no lives signal game over if(lives <= 0){ // HOMEWORK SOLUTION // If Game over remove event listeners to stop getting keyboard input document.body.removeEventListener("keydown", HandleKeyDown); document.body.removeEventListener("keyup", HandleKeyUp); ship.visible = false; ctx.fillStyle = 'white'; ctx.font = '50px Arial'; ctx.fillText("GAME OVER", canvasWidth / 2 - 150, canvasHeight / 2); } // HOME WORK SOLUTION : Creates a new level and increases asteroid speed if(asteroids.length === 0){ ship.x = canvasWidth / 2; ship.y = canvasHeight / 2; ship.velX = 0; ship.velY = 0; for(let i = 0; i < 8; i++){ let asteroid = new Asteroid(); asteroid.speed += .5; asteroids.push(asteroid); } } // Draw life ships DrawLifeShips(); // Check for collision of ship with asteroid if (asteroids.length !== 0) { for(let k = 0; k < asteroids.length; k++){ if(CircleCollision(ship.x, ship.y, 11, asteroids[k].x, asteroids[k].y, asteroids[k].collisionRadius)){ ship.x = canvasWidth / 2; ship.y = canvasHeight / 2; ship.velX = 0; ship.velY = 0; lives -= 1; } } } // Check for collision with bullet and asteroid if (asteroids.length !== 0 && bullets.length != 0){ loop1: for(let l = 0; l < asteroids.length; l++){ for(let m = 0; m < bullets.length; m++){ if(CircleCollision(bullets[m].x, bullets[m].y, 3, asteroids[l].x, asteroids[l].y, asteroids[l].collisionRadius)){ // Check if asteroid can be broken into smaller pieces if(asteroids[l].level === 1){ asteroids.push(new Asteroid(asteroids[l].x - 5, asteroids[l].y - 5, 25, 2, 22)); asteroids.push(new Asteroid(asteroids[l].x + 5, asteroids[l].y + 5, 25, 2, 22)); } else if(asteroids[l].level === 2){ asteroids.push(new Asteroid(asteroids[l].x - 5, asteroids[l].y - 5, 15, 3, 12)); asteroids.push(new Asteroid(asteroids[l].x + 5, asteroids[l].y + 5, 15, 3, 12)); } asteroids.splice(l,1); bullets.splice(m,1); score += 20; // Used to break out of loops because splicing arrays // you are looping through will break otherwise break loop1; } } } } if(ship.visible){ ship.Update(); ship.Draw(); } if (bullets.length !== 0) { for(let i = 0; i < bullets.length; i++){ bullets[i].Update(); bullets[i].Draw(); } } if (asteroids.length !== 0) { for(let j = 0; j < asteroids.length; j++){ asteroids[j].Update(); // Pass j so we can track which asteroid points // to store asteroids[j].Draw(j); } } // HOMEWORK SOLUTION // Updates the high score using local storage highScore = Math.max(score, highScore); localStorage.setItem(localStorageName, highScore); ctx.font = '21px Arial'; ctx.fillText("HIGH SCORE : " + highScore.toString(), 20, 70); requestAnimationFrame(Render); } |
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