var can1;

var can2;

var ctx1;

var ctx2;

var canWidth;

var canHeight;

var lastTime;

var deltaTime;

var bgPic=new Image();

document.body.onload=game;

function game()

{

init();

lastTime=Date.now();

deltaTime=0;

gameloop();

}

function init()

{

//获得canvas context

can1=document.getElementById("canvas1");//fishes,dust,UI,circle

ctx1=can1.getContext('2d');

can2=document.getElementById("canvas2");//background,one,fruits

ctx2=can2.getContext('2d');

bgPic.src="./src/background.jpg";

canWidth=can1.width;

canHeight=can1.height;

}

function gameloop()

{

window.requestAnimationFrame(gameloop);//setInterval,setTimeout,frame per second

console.log("loop");

var now=Date.now();

deltaTime=now-lastTime;

lastTime=now;

drawBackground();

}