Make an invisible {@link canvas}.
@param {number} width The width of the canvas
@param {number} height The height of the canvas
@returns {external:canvas} A canvas DOM element
@private
function makeCanvas(width, height) {
  var c = document.createElement("canvas");
  c.width = width;
  c.height = height;
  // when retina support is enabled, context.getImageData() reads from the wrong pixel causing NinePatch to break
  if (platform.isEjecta()) {
    c.retinaResolutionEnabled = false;
  }
  return c;
}