如何使用Html5裏的cavas畫一面國旗

    var canvas = document.getElementById("canvas");//創建一個cavas畫板
    var context = canvas.getContext('2d');//設置畫板屬性
    var width=canvas.width;
    var height=width*2/3;
    context.fillStyle="red";
    context.fillRect(0,0,width,height);
    var maxR = 0.15, minR = 0.05;
    var maxX = 0.55, maxY = 0.35;//大五星的位置
    var minX = [0.80, 0.90, 0.90, 0.80,0.65,0.50,0.40];//各個小五角星的x座標
    var minY = [0.20, 0.30, 0.45, 0.55,0.60,0.60,0.50];//各個小五角星的y座標
    var ox = height * maxX, oy = height * maxY;
html代碼

<canvas id="canvas" width="600" height="400"></canvas>   

js代碼

create5star(context,ox,oy,height * maxR,"#ff0",0);//繪製大五角星
    for (var idx = 0; idx < 7; idx++) {
        var  sx = minX[idx] * height, sy = minY[idx] * height;
        var  theta = Math.atan((oy - sy)/(ox - sx));
        create5star(context,sx, sy, height * minR, "#ff0",-Math.PI/2+theta);    // 畫小五角星
    }
    //繪製五角星
    function create5star(context,sx,sy,radius,color,rotato){
        context.save();
        context.fillStyle=color;
        context.translate(sx,sy);//移動座標原點
        context.rotate(Math.PI+rotato);//旋轉
        context.beginPath();//創建路徑
        var x = Math.sin(0);
        var y= Math.cos(0);
        var dig = Math.PI/5 *4;
        for(var i = 0;i< 5;i++){//畫五角星的五條邊
            var x = Math.sin(i*dig);
            var y = Math.cos(i*dig);
            context.lineTo(x*radius,y*radius);
        }
        context.closePath();
        context.stroke();
        context.fill();
        context.restore();
    }