<!DOCTYPE html>
<html>
<head lang="en">
<meta charset="UTF-8">
<title></title>
</head>
<body>
<canvas id="canvas" style="display:block;border:1px solid #ccc;margin:20px auto"></canvas>
</body>
<script>
var ball={x:512,y:100,r:20,g:2,vx:-4,vy:0,color:"#005588"};//x,y表示坐标 半径r 加速度g 速度vx 速度vy也就是y方向的速度
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;
if(ball.y>=768-ball.r){
ball.y=768-ball.r;
ball.vy=-ball.vy*0.5;
}
}
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>
</html>
