[JavaScript知识库]前端：运用canvas标签绘制烟花，提前祝大家新年快乐

1. 运行效果

2. 参考代码

js代码
firework.js

var SCREEN_WIDTH = window.innerWidth,
    SCREEN_HEIGHT = window.innerHeight,
    mousePos = {
        x: 400,
        y: 300
    },


    // 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 - rockets[i].pos.x, 2) + Math.pow(mousePos.y -
            rockets[i].pos.y, 2
        )); // random chance of 1% if rockets is above the middle 
        var randomChance = rockets[i].pos.y < SCREEN_HEIGHT * 2 / 3 ? Math.random() * 100 <= 1 : false;
        /* Explosion rules - 80% of screen - going down - close
               to the mouse - 1% chance of random explosion */
        if (rockets[i].pos.y < SCREEN_HEIGHT / 5 || rockets[i].vel.y >= 0 ||
            distance < 50 || randomChance) {
            rockets[i].explode();
        } else {
            existingRockets.push(rockets[i]);
        }
    }
    rockets = existingRockets;
    var existingParticles = [];
    for (var i = 0; i < particles.length; i++) {
        particles[i].update(); // render and save particles that can be rendered 
        if (particles[i].exists()) {
            particles[i].render(context);
            existingParticles.push(particles[i]);
        }
    } // update array with existing particles - old particles should be garbage collected particles = existingParticles;
    while (particles.length > MAX_PARTICLES) {
        particles.shift();
    }
}

function Particle(pos) {
    this.pos = {
        x: pos ? pos.x : 0,
        y: pos ? pos.y : 0
    };

    this.vel = {
        x: 0,
        y: 0
    };

    this.shrink = .97;
    this.size = 2;

    this.resistance = 1;
    this.gravity = 0;

    this.flick = false;

    this.alpha = 1;
    this.fade = 0;
    this.color = 0;
}

Particle.prototype.update = function () {
    // apply resistance
    this.vel.x *= this.resistance;
    this.vel.y *= this.resistance;

    // gravity down
    this.vel.y += this.gravity;

    // update position based on speed
    this.pos.x += this.vel.x;
    this.pos.y += this.vel.y;

    // shrink
    this.size *= this.shrink;

    // fade out
    this.alpha -= this.fade;
};

Particle.prototype.render = function (c) {
    if (!this.exists()) {
        return;
    }

    c.save();

    c.globalCompositeOperation = 'lighter';

    var x = this.pos.x,
        y = this.pos.y,
        r = this.size / 2;

    var gradient = c.createRadialGradient(x, y, 0.1, x, y, r);
    gradient.addColorStop(0.1, "rgba(255,255,255," + this.alpha + ")");
    gradient.addColorStop(0.8, "hsla(" + this.color + ", 100%, 50%, " + this.alpha + ")");
    gradient.addColorStop(1, "hsla(" + this.color + ", 100%, 50%, 0.1)");

    c.fillStyle = gradient;

    c.beginPath();
    c.arc(this.pos.x, this.pos.y, this.flick ? Math.random() * this.size : this.size, 0, Math.PI * 2, true);

    c.closePath();
    c.fill();

    c.restore();
};

Particle.prototype.exists = function () {
    return this.alpha >= 0.1 && this.size >= 1;
};

function Rocket(x) {
    Particle.apply(this, [{
        x: x,
        y: SCREEN_HEIGHT
    }]);

    this.explosionColor = 0;
}

Rocket.prototype = new Particle();
Rocket.prototype.constructor = Rocket;

Rocket.prototype.explode = function () {
    var count = Math.random() * 10 + 80;

    for (var i = 0; i < count; i++) {
        var particle = new Particle(this.pos);
        var angle = Math.random() * Math.PI *2; // emulate 3D effect by using cosine and put more particles in the middle var
        speed = Math.cos(Math.random() * Math.PI / 2) * 15;
        particle.vel.x = Math.cos(angle) * speed;
        particle.vel.y = Math.sin(angle) * speed;
        particle.size = 10;
        particle.gravity = 0.2;
        particle.resistance = 0.92;
        particle.shrink = Math.random() * 0.05 + 0.93;
        particle.flick = true;
        particle.color = this.explosionColor;
        particles.push(particle);
    }
};
Rocket.prototype.render = function (c) {
    if (!this.exists()) {
        return;
    }
    c.save();
    c.globalCompositeOperation = 'lighter';
    var x = this.pos.x,
        y = this.pos.y,
        r = this.size / 2;
    var gradient = c.createRadialGradient(x, y, 0.1, x, y, r);
    gradient.addColorStop(0.1, "rgba(255, 255, 255 ," + this.alpha + ")");
    gradient.addColorStop(1, "rgba(0, 0, 0, " + this.alpha + ")");
    c.fillStyle = gradient;
    c.beginPath();
    c.arc(this.pos.x, this.pos.y, this.flick ? Math.random() * this.size / 2 + this.size / 2 : this.size, 0,
        Math.PI * 2, true);
    c.closePath();
    c.fill();
    c.restore();
}; //# sourceURL=pen.js

html代码

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>烟花</title>
    <style type="text/css">
        * {
            margin: 0;
            padding: 0;
        }
    </style>
    <script src="https://blog-static.cnblogs.com/files/liuze-2/jquery.js"></script>
    <script src="./firework.js"></script>
</head>
<body>
</body>
</html>