js+canvas实现粒子特效（跟随鼠标动）

如何利用元素js+canvas实现粒子动态特效，并且跟随鼠标变化。下面web建站小编给大家详细介绍一下具体实现代码！

具体实现代码如下：

class Particle {
  constructor(opts) {
    this.x = 0
    this.y = 0
    this.r = 0
    this.vx = 0
    this.vy = 0
    this.fillStyle = '#000'
    this.strokeStyle = 'rgba(0, 0, 0, 0)'
    this.theta = randomNum([0, Math.PI])
  
    Object.assign(this, opts)
    return this
  }
  render(ctx) {
    let {
      x,
      y,
      r,
      vx,
      vy,
      fillStyle,
      strokeStyle
    } = this
  
    ctx.save()
    ctx.translate(x, y)
    ctx.fillStyle = fillStyle
    ctx.beginPath()
    ctx.arc(0, 0, r, 0, 2 * Math.PI)
    ctx.fill()
    ctx.restore()
  
    return this
  }
}

function randomNum(arr, int) {
  const max = Math.max(...arr)
  const min = Math.min(...arr)
  const num = Math.random() * (max - min) + min
  
  return int ? Math.round(num) : num
}

let colors = ['pink', 'blue', 'lightpink', 'lightblue', 'lightskyblue', '#FF33FF', '#FF99FF'];
function randomColor(colors) {
  return colors[randomNum([0, colors.length - 1], true)]
}

const canvas = document.querySelector('#canvas')
const ctx = canvas.getContext('2d')

let W = canvas.width = window.innerWidth
let H = canvas.height = window.innerHeight

let mouse = {
  x: W / 2,
  y: H / 2
}

canvas.addEventListener('mousemove', function(e) {
  mouse.x = e.clientX
  mouse.y = e.clientY
})

canvas.addEventListener('mouseout', function() {
  mouse = {
    x: W / 2,
    y: H / 2
  }
})

let particles = [],
  particleNum = 0
let force, theta

function createParticle() {
  for (let i = 0; i < particleNum; i++) {
    particles.push(new Particle({
      x: mouse.x,
      y: mouse.y,
      r: randomNum([5, 40]),
      vx: Math.sin(theta) * force,
      vy: Math.cos(theta) * force,
      fillStyle: randomColor(colors),
      wander: randomNum([0.5, 2]),
      drag: randomNum([0.9, 0.99])
    }))
  }
}

function move(p, i) {
  p.x += p.vx
  p.y += p.vy
  p.vx *= p.drag
  p.vy *= p.drag
  p.theta += randomNum([-0.5, 0.5]) * p.wander
  p.vx += Math.sin(p.theta) * 0.1
  p.vy += Math.cos(p.theta) * 0.1
  p.r *= 0.96
  if (p.r <= 0.5) {
    particles.splice(i, 1)
  }
} 

function draw(p, i) {
  p.render(ctx)
};

(function updating() {
  window.requestAnimationFrame(updating)
  ctx.clearRect(0, 0, W, H)
  ctx.globalCompositeOperation = 'lighter'
  
  particleNum = randomNum([1, 4])
  force = randomNum([2, 8])
  theta = randomNum([0, 2 * Math.PI])
  createParticle()
  
  particles.forEach(move)
  particles.forEach(draw)
})()

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