go-chart go后端生成图表base64

const imgStrPrefix = "data:image/png;base64,"

func imgToStr(imgContent bytes.Buffer) string {
        return imgStrPrefix + base64.StdEncoding.EncodeToString(imgContent.Bytes())
}

func loadTTF(filename string) (ttf *truetype.Font, err error) {
        ttfContent, err := ioutil.ReadFile(app.Cfg.Templatesdir + filename)
        if err != nil {
                return ttf, err
        }
        ttf, err = truetype.Parse(ttfContent)
        return
}

func ToBarChart(title string, data interface{}, xkey string, ykey string, ymin float64, ymax float64, isReverse bool) template.HTML {
        values := make([]chart.Value, 0)
        items, isSucc := data.([]map[string]interface{})
        if !isSucc {
                logger.Errorf("传入数据不符合格式")
                return ""
        }
        if isReverse {
                for i := len(items) - 1; i >= 0; i-- {
                        cValueTmp := chart.Value{
                                Value: items[i][ykey].(float64),
                                Label: items[i][xkey].(string),
                        }
                        values = append(values, cValueTmp)
                }
        } else {
                for _, item := range items {
                        cValueTmp := chart.Value{
                                Value: item[ykey].(float64),
                                Label: item[xkey].(string),
                        }
                        values = append(values, cValueTmp)
                }
        }

        ttf, err := loadTTF("MSYH.TTF")
        if err != nil {
                logger.Warnf("加载字体失败：%v", err)
        }
        yrange := chart.ContinuousRange{
                Min: ymin,
                Max: ymax,
        }
        graph := chart.BarChart{
                Font:  ttf,
                Title: title,
                TitleStyle: chart.Style{
                        Show:                true,
                        TextHorizontalAlign: chart.TextHorizontalAlignCenter,
                },
                XAxis: chart.Style{
                        Show:        true,
                        StrokeWidth: 1,
                },
                YAxis: chart.YAxis{
                        Name: "数量",
                        Style: chart.Style{
                                Show:        true,
                                StrokeWidth: 1,
                        },
                        Range: &yrange,
                        ValueFormatter: func(v interface{}) string {
                                if vf, isFloat := v.(float64); isFloat {
                                        vi := int64(vf)
                                        return fmt.Sprintf("%d", vi)
                                }
                                return ""
                        },
                },
                Canvas: chart.Style{
                        Show: true,
                        Padding: chart.Box{
                                Top:   4,
                                IsSet: true,
                        },
                        FillColor: drawing.Color{120, 9, 9, 9},
                },
                Background: chart.Style{
                        Padding: chart.Box{
                                Top: 40,
                        },
                },
                Height:   512,
                BarWidth: 60,

                Bars: values,
        }

        //buffer := bytes.NewBuffer([]byte{})
        var buffer bytes.Buffer
        //f,err := os.Create("chart.png")
        err = graph.Render(chart.PNG, &buffer)
        if err != nil {
                logger.Errorf("图表渲染错误:%v", err)
        }
        base64str := imgToStr(buffer)
        return template.HTML(fmt.Sprintf("<img src='%s' />", base64str))
}