const ctx = wx.createCanvasContext('output-canvas');

let windowWidth = 100;

let windowHeight = 460;

ctx.drawImage(this.data.baseCloth, 0, 0, windowWidth, windowHeight);

ctx.draw(false,

    wx.canvasToTempFilePath({

        canvasId: 'output-canvas',

        success(res) {

            wx.navigateTo({

            url: '/pages/diy/preview/preview?file=' + res.tempFilePath,

            })

        }

    })

);

代码如上，canvas里是有内容的 图片是画上去了的

但是一输出就一个空白的图片，为什么？