canvas-饼状图

function d2a(n){
    return n*Math.PI/180;
}
function rnd(m,n){
    return parseInt(m+Math.random()*(n-m));
}
document.addEventListener('DOMContentLoaded',function(){
    var oC = document.getElementById('c1');
    var gd = oC.getContext('2d');
    var cx = 200;
    var cy = 200;
    var r = 100;
    var arr = [98,80,65,34,12];
    var sum = 0;
    //求和
    for(var i = 0;i<arr.length;i++){
        sum+=arr[i];
    }
    //算比例
    var aDeg = [];
    for(var i = 0;i<arr.length;i++) {
        aDeg[i] = arr[i]/sum*360;    
}
    //画每一部分
    console.log(aDeg);
    var d = 0;
    for(var i = 0;i<aDeg.length;i++){
        drawPie(d,d+aDeg[i]);
        d+=aDeg[i];
    }
    function drawPie(start,end){
        gd.beginPath();
        gd.fillStyle ='rgb('+rnd(0,256)+','+rnd(0,256)+','+rnd(0,256)+')';
        gd.moveTo(cx,cy);
        gd.arc(cx,cy,r,d2a(start),d2a(end),false);
        gd.closePath();
        gd.fill();
    }
},false);