<!DOCTYPE html>
<body>
  <canvas id="canvas" width="300" height="300"></canvas>
</body>
<script>
  /*
  The expected behavior of filter-generated shadows is tested against
  a drawing using only rectangles that draws the shadows manually.
  */
  var canvas = document.getElementById('canvas');
  var ctx = canvas.getContext('2d');
  ctx.fillStyle = 'red';
  ctx.fillRect(20, 20, 50, 50);
  ctx.fillStyle = 'black';
  ctx.fillRect(10, 10, 50, 50);
</script>
