docs: function _wrapByCanvas(img) {
      if (img.tagName === 'CANVAS') { return img; }
      var canv = document.createElement('canvas');
      canv.width = img.width;
      canv.height = img.height;
      canv.getContext('2d').drawImage(img, 0, 0, img.width, img.height);
      return canv;
  }