子域离屏canvas画不到主域上

// src/myOpenDataContext/index.js let sharedCanvas = wx.getSharedCanvas(); let context = sharedCanvas.getContext("2d");   context.fillStyle = "#fff"; context.fillRect(0, 0, 100, 100);   context.fillText("获取的数据", 0, 0);

//game.js   let openDataContext = wx.getOpenDataContext(); let sharedCanvas = openDataContext.canvas;     let canvas = wx.createCanvas(); let context = canvas.getContext("2d"); context.drawImage(sharedCanvas, 0, 0);   // new Main();

我想让开放域上的离屏canvas在主域上显示，但是完全没效果，全部是黑色，这是为什么