<button id=
"btn"
>变换</button>
<button id=
"con"
>暂停</button>
<canvas id=
"canvas"
width=
"400"
height=
"290"
style=
"border:1px solid black"
>当前浏览器不支持canvas,请更换浏览器后再试</canvas>
<script>
btn.onclick =
function
(){history.go();}
con.onclick =
function
(){
if
(this.innerHTML == '暂停'){
this.innerHTML = '恢复';
clearInterval(oTimer);
}
else
{
this.innerHTML = '暂停';
oTimer = setInterval(fnInterval,50);
}
}
var
canvas = document.getElementById('canvas');
var
H=290,W=400;
var
ball = {};
var
IMG;
var
URL = 'http:
function
initial(){
if
(canvas.getContext){
var
cxt = canvas.getContext('2d');
var
tempR = Math.
floor
(Math.random()*30+20);
var
tempX = Math.
floor
(Math.random()*(W-tempR) + tempR);
var
tempY = Math.
floor
(Math.random()*(H-tempR) + tempR)
ball = {
x:tempX,
y:tempY,
r:tempR,
stepX:Math.
floor
(Math.random() * 21 -10),
stepY:Math.
floor
(Math.random() * 21 -10)
};
IMG = document.createElement('img');
IMG.src=URL;
IMG.onload =
function
(){
cxt.drawImage(IMG,0,0);
}
}
}
function
update(){
ball.x += ball.stepX;
ball.y += ball.stepY;
bumpTest(ball);
}
function
bumpTest(ele){
if
(ele.x <= ele.r){
ele.x = ele.r;
ele.stepX = -ele.stepX;
}
if
(ele.x >= W - ele.r){
ele.x = W - ele.r;
ele.stepX = -ele.stepX;
}
if
(ele.y <= ele.r){
ele.y = ele.r;
ele.stepY = -ele.stepY;
}
if
(ele.y >= H - ele.r){
ele.y = H - ele.r;
ele.stepY = -ele.stepY;
}
}
function
render(){
canvas.height = H;
if
(canvas.getContext){
var
cxt = canvas.getContext('2d');
cxt.save();
cxt.beginPath();
cxt.fillStyle = '#000';
cxt.fillRect(0,0,W,H);
cxt.beginPath();
cxt.arc(ball.x,ball.y,ball.r,0,2*Math.PI);
cxt.fillStyle = '#000';
cxt.fill();
cxt.clip();
cxt.drawImage(IMG,0,0);
cxt.restore();
}
}
initial();
clearInterval(oTimer);
function
fnInterval(){
update();
render();
}
var
oTimer = setInterval(fnInterval,50);
</script>