Gamedev Canvas Workshop - lesson 3

Bounce off the walls.

by Zecheng Hu

HTML

<canvas id="myCanvas" width="480" height="320"></canvas>

CSS

canvas { background: #eee; }

JavaScript

var canvas = document.getElementById("myCanvas");
var ctx = canvas.getContext("2d");
var ballRadius = 8;
var x = canvas.width/3;
var y = canvas.height-30;
var dx = 3;
var dy = -3;
var randomColor = 'rgb(' + (Math.floor(Math.random() * 256)) + ',' + (Math.floor(Math.random() * 256)) + ',' + (Math.floor(Math.random() * 256)) + ')';

function drawBall() {
    ctx.beginPath();
    ctx.arc(x, y, ballRadius, 0, Math.PI*2);
    randomColor = 'rgb(' + (Math.floor(Math.random() * 256)) + ',' + (Math.floor(Math.random() * 256)) + ',' + (Math.floor(Math.random() * 256)) + ')';
    ctx.fillStyle = randomColor;
    
    ctx.fill();
    ctx.closePath();
}

function draw() {
    ctx.clearRect(0, 0, canvas.width, canvas.height);
    drawBall();
    
    if(x + dx > canvas.width-ballRadius || x + dx < ballRadius ) {
        dx = -dx;
     
    }

    if(y + dy > canvas.height-ballRadius || y + dy < ballRadius ) {
        dy = -dy;
    }
    
    
    x += dx;
    y += dy;
}

setInterval(draw, 5);