<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
</head>
<body>
<canvas id="canvas" style="border: 1px solid #aaa;display: block;margin: 50px auto;" >
当前浏览器不支持Canvas，请更换浏览器后再试
</canvas>
<script type="text/javascript">
var ball={x:512,y:100,r:20,g:2,vx:-4,vy:0,color:"red"}
window.onload=function(){
var canvas=document.getElementById("canvas");
canvas.width=1024;
canvas.height=768;
var context=canvas.getContext("2d");
setInterval(
function(){
render(context);
update()
},
50
)
}
function update(){
ball.x+=ball.vx;
ball.y+=ball.vy;
ball.vy+=ball.g;
}
function render(cxt){
cxt.clearRect(0,0,cxt.canvas.width,cxt.canvas.height);
cxt.fillStyle=ball.color;
cxt.beginPath();
cxt.arc(ball.x,ball.y,ball.r,0,2*Math.PI);
cxt.closePath();
cxt.fill();
}
</script>
</body>
</html>
怎么让小球一直重复掉落