Javascript 如何使用html2canvas前后拍摄画布

我使用这个开源代码，尝试拍摄T恤的正面和背面。 正如图中所示，应该有我添加的所有内容 我尝试使用以下代码：

我的想法是从前面给T恤拍照，然后把它翻过来，从后面给它拍照

        $("#tshirtFacing").attr("src", assets_folder + "img/crew_front.png");

        a = JSON.stringify(canvas);
        canvas.clear();
        try {
            var json = JSON.parse(b);
            canvas.loadFromJSON(b);
        } catch (e) {}

        canvas.renderAll();
        setTimeout(function() {
            canvas.calcOffset();
        }, 200);

        html2canvas(document.querySelector("#shirtDiv"), {
            useCORS: true,
            width: 530,
            height: 630,
            windowWidth: 530,
            windowHeight: 630,
            x: 195,
            y: 0,
            scrollY: -410
        }).then(canvas => {
            var data = canvas.toDataURL('image/png');
            var image = new Image();
            image.src = data;
            document.querySelector("#image_get").append(canvas);

        });

        $("#tshirtFacing").attr("src", assets_folder + "img/crew_back.png");
        b = JSON.stringify(canvas);
        canvas.clear();
        try {
            var json = JSON.parse(a);
            canvas.loadFromJSON(a);
        } catch (e) {}

        canvas.renderAll();
        setTimeout(function() {
            canvas.calcOffset();
        }, 200);

        html2canvas(document.querySelector("#shirtDiv"), {
            useCORS: true,
            width: 530,
            height: 630,
            windowWidth: 530,
            windowHeight: 630,
            x: 195,
            y: 0,
            scrollY: -410
        }).then(canvas => {
            var data = canvas.toDataURL('image/png');
            var image = new Image();
            image.src = data;
            document.querySelector("#image_get").append(canvas);

        });

这段代码工作正常，但我只看到文本。我添加的图像不会显示在最终照片中