Chapter 4 Demos: Fireworks

Based on Fireworks by dtrooper. (http://jsfiddle.net/dtrooper/AceJJ/)

by dledle2

CSS

body {
    background-color: #TDH777;
    margin: 0px;
    overflow: hidden;
}

JavaScript

var SCREEN_WIDTH = window.innerWidth,
    SCREEN_HEIGHT = window.innerHeight,
    mousePos = {
        x: 200,
        y: 200
    },

    // create canvas
    canvas = document.createElement('canvas'),
    context = canvas.getContext('2d'),
    particles = [],
    rockets = [],
    MAX_PARTICLES = 400,
    colorCode = 0;

// init
$(document).ready(function() {
    document.body.appendChild(canvas);
    canvas.width = SCREEN_WIDTH;
    canvas.height = SCREEN_HEIGHT;
    setInterval(launch, 800);
    setInterval(loop, 1000 / 50);
});

// update mouse position
$(document).mousemove(function(e) {
    e.preventDefault();
    mousePos = {
        x: e.clientX,
        y: e.clientY
    };
});

// launch more rockets!!!
$(document).mousedown(function(e) {
    for (var i = 0; i < 5; i++) {
        launchFrom(Math.random() * SCREEN_WIDTH * 2 / 3 + SCREEN_WIDTH / 6);
    }
});

function launch() {
    launchFrom(mousePos.x);
}

function launchFrom(x) {
    if (rockets.length < 10) {
        var rocket = new Rocket(x);
        rocket.explosionColor = Math.floor(Math.random() * 360 / 10) * 10;
        rocket.vel.y = Math.random() * -3 - 4;
        rocket.vel.x = Math.random() * 6 - 3;
        rocket.size = 8;
        rocket.shrink = 0.999;
        rocket.gravity = 0.01;
        rockets.push(rocket);
    }
}

function loop() {
    // update screen size
    if (SCREEN_WIDTH != window.innerWidth) {
        canvas.width = SCREEN_WIDTH = window.innerWidth;
    }
    if (SCREEN_HEIGHT != window.innerHeight) {
        canvas.height = SCREEN_HEIGHT = window.innerHeight;
    }

    // clear canvas
    context.fillStyle = "rgba(0, 0, 0, 0.05)";
    context.fillRect(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT);

    var existingRockets = [];

    for (var i = 0; i < rockets.length; i++) {
        // update and render
        rockets[i].update();
        rockets[i].render(context);

        // calculate distance with Pythagoras
        var distance = Math.sqrt(Math.pow(mousePos.x -...