echarts饼图轮播

要实现echarts饼图轮播，可以使用echarts提供的graphic组件和动画效果。具体步骤如下：

1. 在option中设置graphic组件，用于绘制饼图和轮播按钮。
2. 在series中设置data数据，用于绘制饼图。
3. 使用setInterval函数和echarts提供的dispatchAction方法，实现轮播效果。

以下是一个简单的示例代码：

option = {
    graphic: {
        type: 'group',
        left: 'center',
        top: 'middle',
        children: [
            {
                type: 'pie',
                id: 'pie',
                z: 10,
                label: {
                    show: false
                },
                labelLine: {
                    show: false
                },
                emphasis: {
                    scale: true
                },
                data: []
            },
            {
                type: 'circle',
                shape: {
                    cx: 0,
                    cy: 0,
                    r: 30
                },
                style: {
                    fill: '#fff',
                    stroke: '#999',
                    lineWidth: 2
                },
                onclick: function () {
                    // 点击按钮时触发轮播
                    var pie = myChart.getOption().graphic.children[0];
                    var currentIndex = pie.currentIndex || 0;
                    var dataLength = option.series[0].data.length;
                    myChart.dispatchAction({
                        type: 'downplay',
                        seriesIndex: 0,
                        dataIndex: currentIndex
                    });
                    currentIndex = (currentIndex + 1) % dataLength;
                    myChart.dispatchAction({
                        type: 'highlight',
                        seriesIndex: 0,
                        dataIndex: currentIndex
                    });
                    myChart.dispatchAction({
                        type: 'showTip',
                        seriesIndex: 0,
                        dataIndex: currentIndex
                    });
                    pie.currentIndex = currentIndex;
                }
            }
        ]
    },
    series: [
        {
            type: 'pie',
            radius: ['40%', '70%'],
            avoidLabelOverlap: false,
            label: {
                show: false,
                position: 'center'
            },
            emphasis: {
                label: {
                    show: true,
                    fontSize: '30',
                    fontWeight: 'bold'
                }
            },
            labelLine: {
                show: false
            },
            data: [
                {value: 335, name: '直接访问'},
                {value: 310, name: '邮件营销'},
                {value: 234, name: '联盟广告'},
                {value: 135, name: '视频广告'},
                {value: 1548, name: '搜索引擎'}
            ]
        }
    ]
};

// 使用setInterval函数实现轮播
setInterval(function () {
    var pie = myChart.getOption().graphic.children[0];
    var currentIndex = pie.currentIndex || 0;
    var dataLength = option.series[0].data.length;
    myChart.dispatchAction({
        type: 'downplay',
        seriesIndex: 0,
        dataIndex: currentIndex
    });
    currentIndex = (currentIndex + 1) % dataLength;
    myChart.dispatchAction({
        type: 'highlight',
        seriesIndex: 0,
        dataIndex: currentIndex
    });
    myChart.dispatchAction({
        type: 'showTip',
        seriesIndex: 0,
        dataIndex: currentIndex
    });
    pie.currentIndex = currentIndex;
}, 2000);

// 渲染图表
var myChart = echarts.init(document.getElementById('main'));
myChart.setOption(option);