code: public Surface preConcatenate (AffineTransform xf) {
      AffineTransform txf = tx();
      Transforms.multiply(xf.m00, xf.m01, xf.m10, xf.m11, xf.tx, xf.ty, txf, txf);
      return this;
    }
docs: Pre-concatenates {@code xf} onto this surface's transform.