var canvas = document.getElementById('myCanvas'),width = canvas.width,height = canvas.height,ctx = canvas.getContext('2d');
var step,startAngle,endAngle,add=Math.PI*2/100;
ctx.shadowOffsetX = 0; // 设置水平位移
ctx.shadowOffsetY = 0; // 设置垂直位移
ctx.shadowBlur = 10; // 设置模糊度
ctx.lineWidth = 1.0;
counterClockwise = false;
var x;
var y;
var radius;
var animation_interval = 20,n = 100;
var varName;
function drawCircle(X,Y,Radius){
step=1;
startAngle=0;
ctx.strokeStyle ='#FFF';//圆圈颜色
ctx.shadowColor = '#000'; // 设置阴影颜色
//圆心位置
x=X;
y=Y;
radius = Radius;
varName= setInterval(animation, animation_interval);
}
function actiondo(){
var draw=function(){drawCircle(400,500,80);};
draw();
draw=function(){drawCircle(400,500,50);};
draw();
}
var animation = function () {
if (step <= n) {
endAngle = startAngle + add ;
drawArc(startAngle, endAngle);
startAngle = endAngle;
step++;
} else {
clearInterval(varName);
}
};
function drawArc(s, e) {
ctx.beginPath();
ctx.arc(x, y, radius, s, e, counterClockwise);
ctx.lineWidth = 1.0;
ctx.stroke();
}