canvas元素在单击后变为不可见

Question

我正在尝试在画布上编写撤消/重做功能。我正在使用fabric-js绘制对象。撤消？重做工作正常，但问题是在调用撤消/重做功能后，如果我点击画布元素变为不可见。我试过canvas.renderAll（）我仍然遇到问题。

撤消::

的步骤

1. 在元素绘制之前我将canvas.toDataURl()保存在变量数组中。

   2.单击撤消按钮时，我使用清除布料方法清除画布，然后使用Previous`toDataUrl（）将变量Array绘制到画布上。

代码::

     function undoDrawOnCanvas() {
        console.log('inside undodrawn');
        // If we have some restore points
        if (restorePoints.length > 0) {
            // Create a new Image object

            var oImg = new Image();
            // When the image object is fully loaded in the memory...
            oImg.onload = function() {

                //Saving point for Redo
                c_redo=document.getElementById("design_text").toDataURL("image/png");

                canvas.clear();

                // Get the canvas context
                var canvasContext = document.getElementById("design_text").getContext("2d");
                // and draw the image (restore point) on the canvas. That would overwrite anything
                // already drawn on the canvas, which will basically restore it to a previous point.
                canvasContext.drawImage(oImg, 0, 0);
            }
            // The source of the image, is the last restoration point
            oImg.src = restorePoints.pop();

        }
    }