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06-演示-随机颜色绘制绘制圆.html
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06-演示-随机颜色绘制绘制圆.html
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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
</head>
<body>
<canvas id="cv"></canvas>
<script>
var cv = document.getElementById('cv');
cv.height = 400;
cv.width = 600;
cv.style.border = '1px solid red';
var context = cv.getContext('2d');
var toRadian = function (angle) {
return angle / 180 * Math.PI;
};
// 动画绘制圆
var startAngle = -90,
x = cv.width / 2,
y = cv.height / 2,
r = 100,
step = 3,
timerId = null;
// 设置颜色（目的：观察有没有重复绘制）
context.fillStyle = 'rgba(255, 0, 0, .5)';
// 获取随机数从 0-255
function getRandom() {
return Math.floor( Math.random() * 256 );
}
// 获取随机颜色
function getColor() {
return [getRandom(), getRandom(), getRandom()];
}
timerId = setInterval(function () {
// 判断是否达到目标值：
if (startAngle >= 270) {
clearInterval(timerId);
return;
}
// 方式一：开启新路径（每次只绘制3度）
// context.beginPath();
context.clearRect(0, 0, cv.width, cv.height);
context.fillStyle = 'rgb(' + getColor().join(',') + ')'
context.moveTo(x, y);
context.arc(x, y, r, toRadian(startAngle), toRadian(startAngle + step))
context.fill();
startAngle += step;
}, 50);
</script>
</body>
</html>