echart 颜色渐变

option = {
    tooltip : {
        trigger: 'axis'
    },
    legend: {
        data:['邮件营销','联盟广告','直接访问','搜索引擎']
    },
    toolbox: {
        show : true,
        feature : {
            mark : {show: true},
            dataView : {show: true, readOnly: false},
            magicType : {show: true, type: ['line', 'bar', 'stack', 'tiled']},
            restore : {show: true},
            saveAsImage : {show: true}
        }
    },
    calculable : true,
    xAxis : [
        {
            type : 'category',
            boundaryGap : false,
            data : ['周一','周二','周三','周四','周五','周六','周日']
        }
    ],
    yAxis : [
        {
            type : 'value'
        }
    ],
    series : [
        {
            name:'邮件营销',
            type:'bar',
            stack: '总量',
            symbol: 'none',
            itemStyle: {
                normal: {
                     // 区域图，纵向渐变填充
                     color : (function (){
                            var zrColor = require('zrender/tool/color');
                            return zrColor.getLinearGradient(
                                0,150, 0,300,
                                [[0, '#46aaff'],[1, '#ff0000']]
                            )
                     })()
                }
            },
            data:[
                120, 132, 301, 134, 230, 210
            ]
        }
    ]
};