code: public void setShear(double proportionX, double proportionY) {
  		xx = 1;
  		xy = proportionX;
  		xd = 0;
  		yx = proportionY;
  		yy = 1;
  		yd = 0;
  	}
docs: Set transformation to a shear.
  
  @param proportionX
  The proportion of shearing in x direction.
  @param proportionY
  The proportion of shearing in y direction.