微信小程序canvas生成图片为空白问题

项目中用canvas生成图片时都为空白，原因为 wx.canvasToTempFilePath必须写在wx.draw()的回调中才能实现

createImg ( imgPath) {//生成图片const ctx = wx.createCanvasContext('canvasId')ctx.drawImage(imgPath, 0, 0, w, 280)ctx.draw(false,function() {wx.canvasToTempFilePath({ //写在 draw的回调里面才能生成图片x: 0,y: 0,width: 375,height: 280,destWidth: 375, destHeight: 280, canvasId: 'canvasId',success: function (res) {console.log(res.tempFilePath);}})})}

官方wx.canvasToTempFilePath说明：https://developers./miniprogram/dev/api/canvas/wx.canvasToTempFilePath.html