39.canvas画个饼图

css

*{
     margin: 0;
     padding: 0;
     margin-top: 10vh;
}
body{
     text-align: center;
}
canvas{
    margin: 0 auto;
    border: 1px solid #CCCCCC;
}

js

<script type="text/javascript">
            window.addEventListener('load',function(){
                var canvas = document.createElement('canvas')
                document.body.appendChild(canvas)
                canvas.id = 'myCanvas'
                canvas.width = 400;
                canvas.height= 400;
                var myCanvas = document.getElementById('myCanvas')
                
                //检测浏览器是否支持canvas属性
                if(!myCanvas||!myCanvas.getContext){
                    return
                }
                
                var ctx = myCanvas.getContext('2d')
                drawScreen()
                function drawScreen(){
                    var deg = Math.PI/180
                    var obj = {
                        x:200,
                        y:200,
                        r:80,
                        sDeg:[30,111,190,233,280,345],
                        eDeg:[111,190,233,280,345,30],
                        style:['#f00','#0f0','#00f','#789','#abcdef']
                    }
                    for (var i = 0; i < obj.sDeg.length; i++) { 
                        drawPie(ctx,obj.x, obj.y, obj.r, obj.sDeg[i] * deg, obj.eDeg[i] * deg); 
                        ctx.fill(); 
                        ctx.fillStyle = obj.style[i]; 
                    }
                }
                function drawPie(ctx,x,y,r,sDeg,eDeg){
                    //保存初始状态
                    ctx.save()
                    
                    //位移到目标点
                    ctx.translate(x,y)
                    ctx.beginPath()
                    
                    //画出圆弧
                    ctx.arc(0,0,r,sDeg,eDeg)
                    
                    //再次保存以备旋转
                    ctx.save()
                    //旋转至起始角度
                    ctx.rotate(eDeg)
                    //移动到终点,连接终点与圆心
                    ctx.moveTo(r,0)
                    ctx.lineTo(0,0)
                    //还原
                    ctx.restore()
                    //旋转至起点位置
                    ctx.rotate(sDeg)
                    //从圆心连接到起点位置
                    ctx.lineTo(r,0)
                    ctx.closePath()
                    //还原到最初的状态
                    ctx.restore()
                    
                }
            },false)
            
        </script>