code: public void setFlipX(double x0, double x1) {
  		xx = -1;
  		xy = 0;
  		xd = x0 + x1;
  		yx = 0;
  		yy = 1;
  		yd = 0;
  	}
docs: Sets the transformation to be a flip around the X axis. Flips the X
  coordinates so that the x0 becomes x1 and vice verse.
  
  @param x0
  The X coordinate to flip.
  @param x1
  The X coordinate to flip to.