效果

代码

style.css

body{
  margin: 0;
  padding: 0;
  overflow: hidden;
  background: #2d9b95;
background: -moz-radial-gradient(center, ellipse cover, #2d9b95 0%, #0e1329 100%);
background: -webkit-gradient(radial, center center, 0px, center center, 100%, color-stop(0%,#2d9b95), color-stop(100%,#0e1329));
background: -webkit-radial-gradient(center, ellipse cover, #2d9b95 0%,#0e1329 100%);
background: -o-radial-gradient(center, ellipse cover, #2d9b95 0%,#0e1329 100%);
background: -ms-radial-gradient(center, ellipse cover, #2d9b95 0%,#0e1329 100%);
background: radial-gradient(ellipse at center, #2d9b95 0%,#0e1329 100%);
filter: progid:DXImageTransform.Microsoft.gradient( startColorstr='#2d9b95', endColorstr='#0e1329',GradientType=1 );
}

index.js

window.requestAnimFrame = (function(){
  return  window.requestAnimationFrame || 
    window.webkitRequestAnimationFrame || 
    window.mozRequestAnimationFrame    || 
    window.oRequestAnimationFrame      || 
    window.msRequestAnimationFrame     ||  
    function( callback ){
    window.setTimeout(callback, 1000 / 60);
  };
})();

var canvas = document.getElementsByTagName("canvas")[0];
var ctx = canvas.getContext("2d");
var w = $(document).width();
var h = $(document).height();
canvas.width = w;
canvas.height = h;

var mols = [];

function init(){
  for(var i=0;i<18;i++){
    var mol = new generate_mol("C8H10N4O2");
    mols.push(mol);
    var mol = new generate_mol("C6H6O");
    mols.push(mol);
    var mol = new generate_mol("C6H6");
    mols.push(mol);
  }
}

function draw(){
  canvas.width = canvas.width;
  for(var i=0;i<mols.length;i++){
    var m = mols[i];
    m.x += m.vx;
    if(m.x >= w-100 || m.x <= 0){
      m.vx = -m.vx;
    }
    m.y += m.vy;
    if(m.y >= h-100 || m.y <= 0){
      m.vy = -m.vy;
    }
    
    m.r += 0.005;
    m.draw();
  }
}

function generate_mol(mol){
  this.x = Math.random()*w;
  this.y = Math.random()*h;
  this.vx = Math.random()*-2;
  this.vy = Math.random()*2;
  this.vr = 0.1;
  this.r = Math.random()*Math.PI;
  this.draw = function(){
    if(mol == "C6H6O"){
      //Phenol
      ctx.save();
      ctx.translate(this.x+20,this.y+80);
      ctx.rotate(this.r);
      ctx.translate(-this.x+20,-this.y-80);
      ctx.beginPath();
      ctx.moveTo(this.x,this.y + 5);
      ctx.lineTo(this.x,this.y + 30);
      ctx.lineTo(this.x - 26,this.y + 45);
      ctx.lineTo(this.x - 26,this.y + 75);
      ctx.lineTo(this.x,this.y + 90);
      ctx.lineTo(this.x + 26,this.y + 75);
      ctx.lineTo(this.x + 26,this.y + 45);
      ctx.lineTo(this.x,this.y + 30);
      ctx.moveTo(this.x - 20,this.y + 47);
      ctx.lineTo(this.x - 20,this.y + 73);
      ctx.moveTo(this.x,this.y + 83);
      ctx.lineTo(this.x + 22,this.y + 70);
      ctx.moveTo(this.x,this.y + 36);
      ctx.lineTo(this.x + 22,this.y + 49);
      ctx.strokeStyle = "rgba(255,255,255,0.2)";
      ctx.lineWidth = 3;
      ctx.stroke();
      ctx.fillStyle = "rgba(255,255,255,0.2)";
      ctx.font = "15px Arial";
      ctx.fillText("OH", this.x - 5, this.y);
      ctx.closePath();
      ctx.restore();
    }
    else if(mol == "C8H10N4O2"){
      //Caffeine
      ctx.save();
      ctx.translate(this.x+20,this.y+80);
      ctx.rotate(this.r);
      ctx.translate(-this.x+20,-this.y-80);
      ctx.beginPath();
      ctx.moveTo(this.x,this.y + 5);
      ctx.lineTo(this.x,this.y + 22);
      ctx.moveTo(this.x-9,this.y + 35);
      ctx.lineTo(this.x - 26,this.y + 45);
      ctx.lineTo(this.x - 26,this.y + 75);
      ctx.lineTo(this.x,this.y + 90);
      ctx.lineTo(this.x + 18,this.y + 80);
      ctx.moveTo(this.x + 26,this.y + 68);
      ctx.lineTo(this.x + 26,this.y + 45);
      ctx.lineTo(this.x + 9,this.y + 35);
      ctx.moveTo(this.x - 20,this.y + 47);
      ctx.lineTo(this.x - 20,this.y + 73);
      ctx.moveTo(this.x + 23,this.y + 42);
      ctx.lineTo(this.x + 36,this.y + 32);
      ctx.moveTo(this.x + 26,this.y + 46);
      ctx.lineTo(this.x + 39,this.y + 36);
      ctx.moveTo(this.x + 34,this.y + 81);
      ctx.lineTo(this.x + 48,this.y + 90);
      ctx.moveTo(this.x - 2,this.y + 88);
      ctx.lineTo(this.x - 2,this.y + 110);
      ctx.moveTo(this.x + 3,this.y + 88);
      ctx.lineTo(this.x + 3,this.y + 110);
      ctx.moveTo(this.x - 26,this.y + 45);
      ctx.lineTo(this.x - 46,this.y + 38);
      ctx.moveTo(this.x - 60,this.y + 44);
      ctx.lineTo(this.x - 74,this.y + 58);
      ctx.lineTo(this.x - 61,this.y + 77);
      ctx.moveTo(this.x - 58,this.y + 49);
      ctx.lineTo(this.x - 68,this.y + 59);
      ctx.moveTo(this.x - 46,this.y + 82);
      ctx.lineTo(this.x - 26,this.y + 73);
      ctx.moveTo(this.x - 60,this.y + 86);
      ctx.lineTo(this.x - 70,this.y + 100);
      ctx.strokeStyle = "rgba(255,255,255,0.2)";
      ctx.lineWidth = 3;
      ctx.stroke();
      ctx.fillStyle = "rgba(255,255,255,0.2)";
      ctx.font = "15px Arial";
      ctx.fillText("CH", this.x - 5, this.y);
      ctx.fillText("3", this.x + 18, this.y+6);
      ctx.fillText("N", this.x - 5, this.y+37);
      ctx.fillText("O", this.x + 38, this.y+35);
      ctx.fillText("N", this.x + 21, this.y+81);
      ctx.fillText("CH", this.x + 50, this.y+99);
      ctx.fillText("3", this.x + 72, this.y+105);
      ctx.fillText("O", this.x - 5, this.y+124);
      ctx.fillText("N", this.x - 59, this.y+42);
      ctx.fillText("N", this.x - 59, this.y+84);
      ctx.fillText("H  C", this.x - 98, this.y+114);
      ctx.fillText("3", this.x - 87, this.y+119);
      ctx.closePath();
      ctx.restore();
    }
    else if(mol == "C6H6"){
      //Benzene
      ctx.save();
      ctx.translate(this.x+20,this.y+80);
      ctx.rotate(this.r);
      ctx.translate(-this.x+20,-this.y-80);
      ctx.beginPath();
      ctx.moveTo(this.x,this.y + 30);
      ctx.lineTo(this.x - 26,this.y + 45);
      ctx.lineTo(this.x - 26,this.y + 75);
      ctx.lineTo(this.x,this.y + 90);
      ctx.lineTo(this.x + 26,this.y + 75);
      ctx.lineTo(this.x + 26,this.y + 45);
      ctx.lineTo(this.x,this.y + 30);
      ctx.moveTo(this.x - 20,this.y + 47);
      ctx.lineTo(this.x - 20,this.y + 73);
      ctx.moveTo(this.x,this.y + 83);
      ctx.lineTo(this.x + 22,this.y + 70);
      ctx.moveTo(this.x,this.y + 36);
      ctx.lineTo(this.x + 22,this.y + 49);
      ctx.strokeStyle = "rgba(255,255,255,0.2)";
      ctx.lineWidth = 3;
      ctx.stroke();
      ctx.closePath();
      ctx.restore();
    }
  }
}

init();

function animloop() {
  draw();
  requestAnimFrame(animloop);
}

animloop();

html以及全部源文件我都已上传到“我的资源”中，需要的朋友可以下载哦！