@Override public void perspective(float fov,float aspect,float zNear,float zFar){
  float ymax=zNear * (float)Math.tan(fov / 2);
  float ymin=-ymax;
  float xmin=ymin * aspect;
  float xmax=ymax * aspect;
  frustum(xmin,xmax,ymin,ymax,zNear,zFar);
}

@ Override public void perspective ( float fov , float aspect , float zNear , float zFar ) { float ymax = zNear * ( float ) Math . tan ( fov / 2 ) ; float ymin = - ymax ; float xmin = ymin * aspect ; float xmax = ymax * aspect ; frustum ( xmin , xmax , ymin , ymax , zNear , zFar ) ; }
similar to gluperspective ( ) . implementation based on mesa ' s glu . c
