function centerGraphic(rect, boundingRect) {
  // Set rect to center, keep width / height ratio.
  var aspect = boundingRect.width / boundingRect.height;
  var width = rect.height * aspect;
  var height;

  if (width <= rect.width) {
    height = rect.height;
  } else {
    width = rect.width;
    height = width / aspect;
  }

  var cx = rect.x + rect.width / 2;
  var cy = rect.y + rect.height / 2;
  return {
    x: cx - width / 2,
    y: cy - height / 2,
    width: width,
    height: height
  };
}
Get position of centered element in bounding box.

@param  rect         element local bounding box
@param  boundingRect constraint bounding box
@return element position containing x, y, width, and height