<canvas id="canvas"></canvas>
<div id="start">Drag me!</div>
<div id="end">No, drag me!</div>
body {
  height: 100vh;
  margin: 0;
  overflow: hidden;
  background: #333;
}

div {
  position: absolute;
  display: flex;
  justify-content: center;
  align-items: center;
  font-size: 20px;
  background: ivory;
  font-family: 'Segoe UI', sans-serif;
  border-radius: 5px;
  cursor: grab;
  user-select: none;
  box-shadow: 0 0 2px 1px rgba(0,0,0,0.5);
  
}

#start {
  width: 100px;
  height: 75px;
  left: 50px;
  top: 50px;
}

#end {
  width: 150px;
  height: 110px;
  bottom: 100px;
  right: 100px;
}

canvas {
  position: absolute;
  width: 100%;
  height: 100%;
  box-sizing: border-box;
  pointer-events: none;
}
var canvas = document.getElementById("canvas"),
    ctx = canvas.getContext("2d"),
    $1 = $('#start'),
    $2 = $('#end');


var drawThatShit = function() {
  canvas.width = window.innerWidth;
  canvas.height = window.innerHeight;

  var ramp = ctx.createLinearGradient(0, 0, canvas.width / 1.5, 0);
  ramp.addColorStop("0", "blue");
  ramp.addColorStop("0.8" ,"magenta");
  ramp.addColorStop("1", "red");
  
  ctx.setLineDash([20, 10]);
  ctx.strokeStyle = ramp;
  ctx.lineWidth = 5;
  
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  
  var $1_left = $1.offset().left,
      $1_top =  $1.offset().top,
      $2_left = $2.offset().left,
      $2_top =  $2.offset().top;
  
  ctx.beginPath();
  ctx.moveTo($1_left + $1.width() / 2, $1_top + $1.height() / 2);
  ctx.quadraticCurveTo($1.width() * 2, $1.height() * 2, $2_left, $2_top + $2.height() / 2);
  ctx.stroke();
}

drawThatShit();


$( window ).resize(function() {
  drawThatShit();
});

$(document).ready(function() {
    var $dragging = null;
    $('body').on("mousedown", "div", function(e) {
        $(this).attr('unselectable', 'on').addClass('draggable');
        var el_w = $('.draggable').outerWidth(),
            el_h = $('.draggable').outerHeight();
        $('body').on("mousemove", function(e) {
            if ($dragging) {
                drawThatShit();
                $dragging.offset({
                    top: e.pageY - el_h / 2,
                    left: e.pageX - el_w / 2
                });
            }
        });
        $dragging = $(e.target);
    }).on("mouseup", ".draggable", function(e) {
        $dragging = null;
        $(this).removeAttr('unselectable').removeClass('draggable');
    });
});

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

  1. https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js