基于canvas的超酷跟随鼠标粒子动画

var canvas = document.querySelector('canvas');
canvas.height = window.innerHeight;
canvas.width = window.innerWidth;
c = canvas.getContext('2d');
 
window.addEventListener('resize', function () {
    canvas.height = window.innerHeight;
    canvas.width = window.innerWidth;
 
    initCanvas();
});
 
var mouse = {
    x: undefined,
    y: undefined };
 
window.addEventListener('mousemove',
function (event) {
    mouse.x = event.x;
    mouse.y = event.y;
    drawCircles();
});
 
window.addEventListener("touchmove",
function (event) {
    let touch = event.touches[0];
    mouse.x = touch.clientX;
    mouse.y = touch.clientY;
    drawCircles();
});
 
 
function Circle(x, y, radius, vx, vy, rgb, opacity, birth, life) {
    this.x = x;
    this.y = y;
    this.radius = radius;
    this.minRadius = radius;
    this.vx = vx;
    this.vy = vy;
    this.birth = birth;
    this.life = life;
    this.opacity = opacity;
 
    this.draw = function () {
        c.beginPath();
        c.arc(this.x, this.y, this.radius, Math.PI * 2, false);
        c.fillStyle = 'rgba(' + rgb + ',' + this.opacity + ')';
        c.fill();
    };
 
    this.update = function () {
        if (this.x + this.radius > innerWidth || this.x - this.radius < 0) {
            this.vx = -this.vx;
        }
 
        if (this.y + this.radius > innerHeight || this.y - this.radius < 0) {
            this.vy = -this.vy;
        }
 
        this.x += this.vx;
        this.y += this.vy;
 
        this.opacity = 1 - (frame - this.birth) * 1 / this.life;
 
        if (frame > this.birth + this.life) {
            for (let i = 0; i < circleArray.length; i++) {
                if (this.birth == circleArray[i].birth && this.life == circleArray[i].life) {
                    circleArray.splice(i, 1);
                    break;
                }
            }
        } else {
            this.draw();
        }
    };
 
}
 
var circleArray = [];
 
function initCanvas() {
    circleArray = [];
}
 
var colorArray = [
'355,85,80',
'9,80,100',
'343,81,45'];
 
 
function drawCircles() {
    for (let i = 0; i < 6; i++) {
        let radius = Math.floor(Math.random() * 4) + 2;
        let vx = Math.random() * 2 - 1;
        let vy = Math.random() * 2 - 1;
        let spawnFrame = frame;
        let rgb = colorArray[Math.floor(Math.random() * colorArray.length)];
        let life = 100;
        circleArray.push(new Circle(mouse.x, mouse.y, radius, vx, vy, rgb, 1, spawnFrame, life));
 
    }
}
 
var frame = 0;
function animate() {
    requestAnimationFrame(animate);
    frame += 1;
    c.clearRect(0, 0, innerWidth, innerHeight);
    for (let i = 0; i < circleArray.length; i++) {
        circleArray[i].update();
    }
 
}
 
initCanvas();
animate();
 
// This is just for demo purposes :
for (let i = 1; i < 110; i++) {
    (function (index) {
        setTimeout(function () {
            mouse.x = 100 + i * 10;
            mouse.y = 100;
            drawCircles();
        }, i * 10);
    })(i);
}