微信小程序绘制雷达图

initRadarChart: function (averageList, referenceList) {
            averageList = [averageList[0], averageList[2], averageList[4], averageList[1], averageList[3]]
            const self = this
            const query = this.createSelectorQuery()
            query
                .select('.radarCanvas')
                .fields({
                    id: true,
                    node: true,
                    size: true
                })
                .exec(async function (res) {
                    console.log('res', res)
                    const canvas = res[0].node
                    // Canvas 绘制上下文
                    const context = canvas.getContext('2d')

                    // 初始化画布大小
                    var mW = 750 // 宽高
                    var mH = 750 // 宽高
                    canvas.width = 750
                    canvas.height = 750

                    let length = 5 // 多少边
                    var x = mW / 2 //中心点
                    var y = mH / 2 //中心点
                    var center = {
                        x: x,
                        y: y
                    }

                    var radarMin = Math.min(x, y) * 1.5
                    var halfMin = radarMin / 2
                    var imgCenter = {
                        x: center.x - halfMin,
                        y: center.y - halfMin
                    } // radarMin = radarMin * 1.5;

                    var radius = halfMin * 0.909 //半径(减去的值用于给绘制的文本留空间)

                    var angle = (Math.PI * 2) / length

                    var data = [
                        {
                            name: '实际值',
                            value: averageList,
                            color: 'rgba(167, 245, 231, 1)'
                        }
                    ]
                    var step = 1
                    var MaxStep = 1 // 50
                    const image = canvas.createImage()
                    // 等待图片加载
                    await new Promise(resolve => {
                        image.onload = resolve
                        image.src = 'https://storesong-file-uat.watsonsestore.com.cn/booking/87be86eb75ca4b5091bc579a1fba05c6.png' // 要加载的图片 url
                    })

                    context.fillStyle = '#fff'
                    context.fillRect(0, 0, mW, mH)
                    // // context.drawImage(res.path, imgCenter.x, imgCenter.y, radarMin, radarMin) // context.save();
                    context.drawImage(image, imgCenter.x, imgCenter.y, radarMin, radarMin) // context.save();

                    var MaxValue = 100

                    data.forEach(function (val) {
                        context.beginPath()
                        context.strokeStyle = val.color
                        var currentRad = (radius * val.value[0]) / MaxValue
                        context.moveTo(center.x, center.y - currentRad)
                        var currentAngle = -Math.PI / 2

                        for (var i = 0; i < length; i++) {
                            currentRad = (radius * val.value[i]) / MaxValue
                            context.lineTo(center.x + currentRad * Math.cos(currentAngle), center.y + currentRad * Math.sin(currentAngle))
                            currentAngle += angle
                        }

                        currentRad = (radius * val.value[0]) / MaxValue
                        context.lineTo(center.x, center.y - currentRad)
                        context.stroke()

                        if (val.color) {
                            context.fillStyle = val.color
                            context.globalAlpha = 0.5
                            context.fill()
                        }

                        context.closePath()
                    })
                    context.save() // 保存以上透明设置

                    context.globalAlpha = 1 // 将画布重新设置不透明

                    // 雷达图导出图片
                    setTimeout(() => {
                        wx.canvasToTempFilePath({
                            canvas: canvas,
                            success(res) {
                                // console.log("res", res)
                                wx.getFileSystemManager().readFile({
                                    filePath: res.tempFilePath, //图片路径
                                    encoding: 'base64', //编码格式
                                    success: res => {
                                        // console.log('data:image/png;base64,' + res.data);
                                        //成功的回调
                                        self.setData({
                                            radarUrl: 'data:image/png;base64,' + res.data
                                        })
                                    }
                                })
                            }
                        })
                    }, 500)
                })
        }