code: function resizeCanvas() {
    // When zoomed out to less than 100%, for some very strange reason,
    // some browsers report devicePixelRatio as less than 1
    // and only part of the canvas is cleared then.
    var ratio =  Math.max(window.devicePixelRatio || 1, 1);
  
    // This part causes the canvas to be cleared
    canvas.width = canvas.offsetWidth * ratio;
    canvas.height = canvas.offsetHeight * ratio;
    canvas.getContext("2d").scale(ratio, ratio);
  
    // This library does not listen for canvas changes, so after the canvas is automatically
    // cleared by the browser, SignaturePad#isEmpty might still return false, even though the
    // canvas looks empty, because the internal data of this library wasn't cleared. To make sure
    // that the state of this library is consistent with visual state of the canvas, you
    // have to clear it manually.
    signaturePad.clear();
  }
docs: Adjust canvas coordinate space taking into account pixel ratio, to make it look crisp on mobile devices. This also causes canvas to be cleared.