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countdown.html
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countdown.html
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<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html;charset=UTF-8" />
<style>
#cas {
display: block;
border: 1px solid;
margin: auto;
}
</style>
<title>秒表</title>
</head>
<body>
<canvas id="cas" width="500" height="500">浏览器不支持canvas</canvas>
<div style="width:100px;margin:10px auto">
<input
type="text"
name=""
id="time"
style="width:40px;"
value="50"
/><button id="startBtn">开始</button>
</div>
<script>
window.requestNextAnimationFrame = function() {
return (
window.requestAnimationFrame ||
window.webkitRequestAnimationFrame ||
window.mozRequestAnimationFrame ||
window.msRequestAnimationFrame ||
function(callback, element) {
var self = this,
start,
finish;
window.setTimeout(function() {
start = +new Date();
callback(start);
finish = +new Date();
self.timeout = 1000 / 60 - (finish - start);
}, self.timeout);
}
);
};
function StopWatch(canvasDOM, centerX, centerY, radius, angle) {
this.canvasDOM = canvasDOM;
this.context = canvasDOM.getContext("2d");
this.x = centerX;
this.y = centerY;
this.radius = radius;
this.angle = angle;
}
StopWatch.prototype = {
startTime: 0,
running: false,
elapsed: 0,
drawCircle: function(x, y, r, fillStyle, strokeStyle) {
this.context.save();
this.context.beginPath();
this.context.arc(x, y, r, 0, 2 * Math.PI);
this.context.fillStyle = fillStyle;
this.context.strokeStyle = strokeStyle;
this.context.fill();
this.context.stroke();
this.context.restore();
},
drawNum: function(x, y, r) {
this.context.beginPath();
this.context.textAlign = "center";
this.context.textBaseline = "middle";
var angle = 0;
for (var i = 0; i < 12; i++) {
var newRadius = r - 8;
this.context.moveTo(
x + r * Math.cos(angle),
y + r * Math.sin(angle)
);
this.context.lineTo(
x + newRadius * Math.cos(angle),
y + newRadius * Math.sin(angle)
);
const text = i * 5 + 15 >= 60 ? i * 5 - 45 : i * 5 + 15;
this.context.fillText(
text,
x + (r + 40) * Math.cos(angle),
y + (r + 40) * Math.sin(angle)
);
angle += Math.PI / 30;
for (var j = 0; j < 4; j++) {
newRadius = r - 3;
this.context.moveTo(
x + r * Math.cos(angle),
y + r * Math.sin(angle)
);
this.context.lineTo(
x + newRadius * Math.cos(angle),
y + newRadius * Math.sin(angle)
);
angle += Math.PI / 30;
}
}
this.context.stroke();
},
drawPoint: function(x, y, r, angle) {
this.context.beginPath();
this.context.moveTo(x, y);
this.context.lineTo(x + r * Math.cos(angle), y + r * Math.sin(angle));
this.context.stroke();
this.drawCircle(x, y, 10, "#ccc");
this.drawCircle(
x + r * Math.cos(angle),
y + r * Math.sin(angle),
5,
"#ccc"
);
},
drawWatch: function() {
this.context.clearRect(
0,
0,
this.canvasDOM.width,
this.canvasDOM.height
);
this.drawCircle(this.x, this.y, this.radius, "#ccc");
this.drawCircle(this.x, this.y, this.radius - 20, "#FFF");
this.drawNum(this.x, this.y, this.radius - 20);
this.drawPoint(this.x, this.y, this.radius - 10, this.angle);
},
start: function() {
this.startTime = +new Date();
this.running = true;
},
stop: function() {
this.elapsed = +new Date() - this.startTime;
this.running = false;
},
isRunning: function() {
return this.running;
},
getElapsedTime: function() {
if (this.running) {
return +new Date() - this.startTime;
} else {
return this.elapsed;
}
}
};
const canvas = document.getElementById("cas");
const sw = new StopWatch(
canvas,
canvas.width / 2,
canvas.height / 2,
150,
-0.5 * Math.PI
);
sw.drawWatch();
document.getElementById("startBtn").onclick = function() {
var time;
try {
time = parseInt(document.getElementById("time").value);
} catch (err) {
alert("格式错误");
return;
}
sw.angle = (Math.PI * time) / 30 - 0.5 * Math.PI;
sw.running = true;
sw.drawWatch();
sw.elapsed = 0;
sw.start();
animate();
function animate() {
if (sw.isRunning() && sw.getElapsedTime() <= time * 1000) {
var t = sw.getElapsedTime();
sw.angle =
(Math.PI * time) / 30 - (Math.PI * t) / 30000 - 0.5 * Math.PI;
sw.drawWatch();
requestAnimationFrame(animate);
}
}
};
</script>
</body>
</html>