Can't draw rectangle on existing <canvas> that renders PDF with pdfjs

Kiran

Task

<canvas id="pdfCanvas">Create an existing canvas in your web canvas The fabric canvas new fabric.Canvas("pdfCanvas");has mouse.down, mouse.up, mouse.move methods that make the drawn rectangle rendered on top of the canvas PDF "pdfCanvas" using PDF.js browsers now display the rendered PDF now in Draw rectangle on pdf, it hides rendered canvas but does draw objects

question

Here's a fiddle to see the problem: - run the above https://jsfiddle.net/hiitskiran/wgz8qore/2/ - you can see the fabric rectangle is hidden behind the rendered pdf - click on the pdf canvas area to see the fabric object

Alessandro

What I see from your fiddle is that you don't await the result of the method that is page.renderasync , then unfortunately if you do page.render, the fabric.canvas instance will clear your previously populated canvas and we can't do anything for that This. So I try another approach: first, I wait for the pdf.js page.rendermethod, then I call the .toDataURL that I did before filling the canvas, I can put a copy of the old content, then I put the new fabric.canvas you previously filled with the canvas background and Finish drawing the rectangle.

var url = 'http://www.africau.edu/images/default/sample.pdf';
var canvas = document.getElementById('pdfcanvas');
var context = canvas.getContext('2d');
PDFJS.disableWorker = true;
PDFJS.getDocument(url).then(function(pdf) {
  pdf.getPage(1).then(function(page) {
    var scale = 1.5;
    var viewport = page.getViewport(scale);
    canvas.height = viewport.height;
    canvas.width = viewport.width;
    page.render({
      canvasContext: context,
      viewport: viewport
    }).then(function() {

      var bg = canvas.toDataURL("image/png");
      var fcanvas = new fabric.Canvas("pdfcanvas", {
        selection: false
      });
   fcanvas.setBackgroundImage(bg,fcanvas.renderAll.bind(fcanvas));
      fcanvas.setWidth(300);
      fcanvas.setHeight(300);
      var rect = new fabric.Rect({
        left: 100,
        top: 100,
        width: 50,
        height: 50,
        fill: '#FF454F',
        opacity: 0.5,
        transparentCorners: true,
        borderColor: "gray",
        cornerColor: "gray",
        cornerSize: 5
      });
      fcanvas.add(rect);
      fcanvas.renderAll();
    });
  });
});
<script src="https://rawgit.com/kangax/fabric.js/master/dist/fabric.js"></script>
<script src="https://seikichi.github.io/tmp/PDFJS.0.8.715/pdf.min.js"></script>
<canvas id="pdfcanvas" style="border:1px solid black"></canvas>

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